5. Alcohol and cotton oil as alternative fuels for internal combustion engines

5.1. The fuel properties of alcohol and basic principles of engine conversion
5.2. Conversion design of a L195 diesel engine to ethanol/diesel fuel
5.3. Studies on burning gasoline/ethanol blended fuel in gasoline engines
5.4. Studies on using vegetable oil for diesel engine
5.5. Field test system for evaluating a tractor

This study was launched with the circumstances that the research on refining a alcohol from sweet sorghum had made such enormous strides that the source of raw material for alcohol production was expanded and the technology for alcohol production improved, moreover, the resource of cotton oil was abundant in the northeast regions of China, which promised increased output and reduced the price of alcohol. The goals of the study were to better understand the fuel properties of alcohol and basic principles of conversion in order to provide the representative cross section of converting diesel engine and gasoline engine to blended fuel. In addition, the long period performance of diesel engine burning cotton/diesel blend oil was carried out. Finally, a microcomputer based system for evaluating tractor performance was presented.

5.1. The fuel properties of alcohol and basic principles of engine conversion

5.1.1. Introduction to alcohols

The alcohols are fuels of the family of the OXYGENATES. As is known to all, the alcohol molecule has one or more oxygen, which contributes to the combustion. The alcohols are named accordingly to the basic molecules of hydrocarbon which derives from them: Methanol (CH₃ OH); Ethanol (C₂H₅OH); Propanol (C₃H₇OH); Butanol (C₄H₉OH). Theoretically, any of the organic molecules of the alcohol family can be used as a fuel. The list is somehow more extensive, however, only two of the alcohols are technically and economically suitable as fuels for internal combustion engines. These alcohols are those of the simplest molecular structure, i.e., Methanol and Ethanol.

It is not the purpose of this paper to discuss the production of the alcohols, however, it can be said that:

A. Methanol is produced by a variety of process, the most common are as follows: Distillation of wood; Distillation of coal; Natural gas and petroleum gas.

B. Ethanol is produced mainly from biomass transformation, or bioconversion. It can also be produced by synthesis from petroleum or mineral coal.

Economic reasons dictate, however, the process which can produce the alcohol at the minimum cost. Each country around the world has found the best compromise in the production of an alternative fuel to replace petrol. Of special significance, especially for countries with large areas of land like former USSR, USA, CHINA and BRAZIL, is the methods of production of ethanol from bio-mass conversion. In this process, it can be said that solar energy is stored in the plants by the photosynthesis process. Ethanol from a bio-conversion is therefore "solar energy in a liquid state".

Ethyl alcohol, or ethanol has been used in Germany and France as early as 1894 by the then incipient industry of internal combustion engines. Brazil has utilized ethanol as a fuel since 1925. By that time, the production of ethanol was 70 times bigger than the production and consumption of petrol. There have been times when the push for alternatives to petrol were more vigorous, mainly dictated by strategic and economic reasons. It is interesting to note that in Brazil, there was an intense use of ethanol in the year 1930, 1940, 1950, 1958, and 1973. Unfortunately, petroleum has always been considered abundant, almost limitless in availability. It was cheap and versatile, so the industry has always been very keen in the intensive use of this apparently miraculous fuel. All the development effort was toward the use of petrol and so the engines were developed for this fuel.

In those countries with large territorial areas, ethanol has been the alternative fuel choice to replace petrol. The reason is the fact that alcohol is a renewable source of energy. Currently, ethanol is produced from sugar beets and from molasses. A typical yield is 72.5 liters of ethanol per tonne of sugar cane. Modern crops yield 60 tonnes of sugar cane per hector of land. An area of 1km² of sugar cane crop can yield 6000 tonnes per year in a tropical country like Brazil. Other crops can be used for the production of ethanol. In China, for instance, it has been demonstrated that sweet sorghum ("Shennong No.2 sweet sorghum) can yield 267.4 liters of ethanol per Mu. It has also been shown that 1 tonne of corn can produce nearly 300 liters of alcohol.

5.1.2. Conversion of gasoline (OTTO-Cycle) engines to alcohol

a. Fuel properties of alcohols

The fuel properties of alcohols are shown in Table 5.1

Table 5.1. Fuel properties of alcohols

Item		Isoctane	Methanol	Ethanol
1. Formula		C8H18	CH3OH	C2H5OH
2. Molecular weight		114.224	32.042	46.07
3. Carbon/Hydrogen (W)		5.25	3.0	4.0
4.% Carbon (W)		84.0	37.5	52.17
5.% Hydrogen (W)		16.0	12.5	13.4
6. % Oxygen (W)		0	50.0	34.78
7. Boiling point @ 1 atm °C		99.239	64.5	78.40
8. Freezing point @ 1 atm °C		-107.378	-97.778	-80.00
9. Density @ 15.5 °C lb/gal		5.795	6.637	6.63
10. Viscosity @ 20°C/1 atm, Centipoise		0.503	0.596	1.20
11. Specific heat @ 25°C/1 atm BTU/lb		0.5	0.6	0.6
12. Heat of vaporization,® boiling point/1 atm, BTU/lb		116.69	473.0	361.0
13. Heat of vaporization, @ 25°C/1 atm, BTU/lb		132.0	503.3
14. Heat of combustion @ 25°C, BTU/lb
	a). Higher heating value	20555	9776	12780
	b).Lower heating value	19065	8593	11550
15. Stoichiometric, Ib air/lb fuel		15.13	6.463	9.0
16. Research octane number		100	106	105
17. Flash point temp. °C		-42.778	11.112	12.778
18. Auto-ignition temp. °C		257.23	463.889	422.778
19. Flammability limits
	a).Lower	1.4	6.7	4.3
	b).Higher	7.6	36.0	19.0
20. Latent heat of vaporization @ 20°C, KJ/Kg		349	1177	921.36
21. Cetane number		-	5	8

b. Combustion characteristics

There are some important differences in the combustion characteristics of alcohols and hydrocarbons. Alcohols have higher flame speeds and extended flammability limits. Also, alcohols produce a great number of product moles per mole of fuel burnt, therefore, higher pressure are achieved.

The alcohols mix in all proportions with water due to the polar nature of OH group. Low volatility is indicated by high boiling point and high flash point. Alcohols burn with no luminous flame and produce almost no soot, especially methanol. The tendency to soot increases with molecular weight. Therefore, methanol produces less soot than ethanol.

Combustion of alcohol in presence of air can be initiated by an intensive source of localized energy, such as a flame or a spark and also, the mixture can be ignited by application of energy by means of heat and pressure, such as happens in the compression stroke of a piston engine. The energy of the mixture reaches a level sufficient for ignition to take place after a brief period of delay called ignition delay, or induction time, between the sudden heating of the mixture and the onset of ignition (formation of a flame front which propagates at high speed throughout the whole mixture). The high latent heat of vaporization of alcohols cools the air entering the combustion chamber of the engine, thereby increasing the air density and mass flow. This leads to increased volumetric efficiency and reduced compression temperatures. Together with the low level of combustion temperature, these effects also improve the thermal efficiency by 10%.

The higher flame speed, giving earlier energy release in the power stroke, results in a power increase of 11% at normal conditions and up to 20% at the higher levels of a compression ratio (14:1). Blending ethanol with gasoline at 0.1x%, the power rises to about 0.1%. Power continues to rise steadily as the mixture is enriched to an equivalence ratio of about 1:4. Because of the low proportion of carbon in alcohols, soot formation does not occur and therefore alcohols burn with low luminosity and therefore low radiation. In conjunction with lower flame temperature, about 10% less heat is lost to the engine coolant. The lower flame temperature of alcohols results in much lower NOx (Nitrogen Oxides) emissions. The wider flammability limits of alcohols permit smooth engine operation even at very lean mixtures. But aldehyde emissions are noticeably higher. For ethanol, emissions are acetaldehydes and for methanol, emissions are of formaldehydes. Increasing compression ratio from 9 to 14, aldehyde emissions can be reduced by 50%, to level compared to that for gasoline. An addition of 10% water reduces aldehyde emissions by 40% and NOx by 50%. Addition of 10% water in the alcohol can be tolerated without loss of thermal efficiency.

The oxygen contents of alcohols depresses the heating value of the fuel in comparison with hydrocarbon fuels. The heat of combustion per unit volume of alcohol is approximately half that of isooctane. However, the stoichiometric fuel-air mass ratios are such big that the quantity of energy content based on unit mass of stoichiometric mixture become comparable with that of hydrocarbons.

Methanol is not miscible with hydrocarbons and separation ensues readily in the presence of small quantities of water, particularly with reduction in temperature. Anhydrous ethanol, on the other hand, is completely miscible in all proportions with gasoline, although separation may be effected by water addition or by cooling. If water is already present, the water tolerance is higher for ethanol than for methanol, and can be improved by the addition of higher alcohols, such as butanol. Also benzene or Acetone can be used.

The high heat of vaporization and constant boiling point make cold starting very difficult with neat alcohols. The problem is not as severe as in case of alcohols blended with gasoline. Ethanol has a constant boiling point of 80 ° C (78.8° C). Gasoline which has a high vapor pressure (therefore highly volatile) can be used for cold start.

c. Corrosiveness of alcohols

Dry methanol is very corrosive to some aluminum alloys, but additional water at 1% almost completely inhibits corrosion. It must be noted that methanol with additional water at more than 2% becomes corrosive again. The same happens with less than 1% water. Nitride and neoprene rubbers, generally satisfactory as elastomers in contact with methanol and polyacetal plastics, are very resistant. Silicon rubber as well as vinyl can be used for gasket material. Ethanol always contains acetic acid and is particularly corrosive to aluminum alloys. Also certain alloys containing lead are attacked with general result of the lead being leached out, leaving a porous surface. The Same phenomenon exists with alloys of zinc, such as ZAMAC (Al+ Zn). The zinc is leached out as a white zinc oxide, which clogs the small orifices and jets.

Carburettors are normally made of zamac alloy. Experience has shown that if the carburettor is protected with a coat of Nickel the corrosion problem is overcome. The process recommended is electrolysis Nickel plating. In this process, the carburettor parts are immersed in a bath of hot Nickel, which due to its very low viscosity, covers evenly all the surfaces without clogging the orifices. The floats on the carburettor float-bowl are generally made of porous plastics which are attacked by the ethanol and the end result is swelling and cracking. It is found that nylon floats arc more durable. A float can be made with thin sheet of BRASS (0.005 inches) or 0.125mm thickness, molded and welded with pure Tin (Sn). Alloys of Tin and Lead (Sn+ Pb) shall be avoid as welding material. All bronze parts shall be brass or stainless steel. Steel fuel lines shall be replaced by nylon tube (NYLON 11). Fuel filters used for gasoline are not recommended for the many alcohols. The internal element collapses after the glue that bonds it together is softened by the alcohol. Special filters are necessary. Also due to the higher flows, filters have to be bigger. The filter body must be made of Nylon or Teflon.

d. Drive ability and Performance

Engine Performance and durability on alcohol depends almost entirely upon mixture preparation. It is essential that, at low engine speed and power output, the fuel and air be intimately mixed so that the alcohol is fully vaporized, and even more important for durability that drops of liquid alcohol are not allowed to contact cylinder bores in any quantity, especially while the cylinder bores have wall temperatures below 70 °C.

Substantial amount of heat additional to that required when gasoline is used as a fuel must be used to condition the air/fuel mixture under part loaded conditions. Existing gasoline inlet manifold and hot-spot systems cannot provide the necessary amount of heat since the demand is 6 times greater than that for gasoline, and the extra heat must be taken either from the cooling system of the engine, or from the exhaust gases. There are advantages and disadvantages. Exhaust gas systems warm up more rapidly, but require relatively bulky ducts to carry the necessary volumes of air with minimal pressure drops. Water-heated systems can prove inadequate during warm-up at low ambient temperature, and cylinder wall wetting is then inevitable over long periods .Whichever system is used, means must be provided to reduce the extra heat input at high power output, since residual heat and high turbulence make high heat input unnecessary and volumetric efficiency will be unfavorably affected if the same proportion of heat is added at high power as at low power. High temperatures in the combustion chamber due to too much heat being introduced can cause formation of hot-spots, such as the tips of spark-plugs .Since alcohols .especially methanol, can be readily ignited by hot surfaces, pre-ignition can occur. It must be emphasized here that pre-ignition and knocking in alcohol engine is a much more dangerous condition than gasoline engines. Rapid and catastrophic failure of the engine can occur, since the piston crown collapses in a short time after pre-ignition occurs. Times as short as 10 to 15 seconds have been recorded. Spark-plug coolers, other than for gasoline engines, must be used (two ranges cooler). Type recommended is BOSCHW5DC with gaps of 0.3 mm to 0.5 mm. With correct preparation and fast warm-up, lubricating oils are not usually a problem. Bore wear is caused by the "washing" action of liquid fuel in contact with the cylinder liner. The wear problem is believed to be caused by formic acid attack, when methanol is used, or acetic acid attack when ethanol is used. Highly alkaline oils have been supplied, with Total Base Number (TBN) of around 30. However, deposits from these oils can cause even more damage by clogging oil passages and there have been engine failures. If, however, the mixture preparation is adequate, oils with TBN=9 can be successfully used. It has been demonstrated that a counter-flow heat exchanger installed in an alcohol engine for the purpose to recover heat from the exhaust, and to warm-up the inlet air, is the proper solution for the mixture preparation in order to be adequate. Means to control the amount of heat introduced into the engine at high loads have been devised and successfully tested. One such system utilizes an S.U. constant-depression carburettor associated with a water-jacked elbow and an air inlet with a split-plate which automatically divests hot air and cold air depending upon the position of the carburettor piston.

e. Engine response to alcohol

Some properties of alcohols can be turned into advantages by designing the engine to adequately take advantage of such properties. The mass caloric value, or the energy available per unit of mass of the fuel in a liquid state, is the most important characteristic of a fuel. There are some figures: Gasoline =43961 KJ/kg, Ethanol= 26795 KJ/kg, Hydrated ethanol (5% water) =25120 KJ/kg, Hydrated methanol (5% water) =19678 KJ/kg. Another important property is the heat of combustion, or the energy available per unit of volume of a mixture chemically correct (stoichiometric) of a fuel and air: Gasoline=3600 KJ/kg, Ethanol=3412 KJ/kg, Methanol=3181 KJ/kg. The engine power is proportional to the heat of combustion (or the energy content of the gases inside of the cylinder). Note, there is not much difference between various liquid fuels.

The fuel consumption is inversely proportional to the caloric value. This characteristic alone would lead to a consumption 64% bigger than gasoline (75% for hydrated ethanol):

Ethanol (anhydrous): petrol/ethanol=43961/26795=1.64

therefore, 64% increase;

Hydrated ethanol: 43961/25120=1.75

therefore, 75% increase

Methanol: 43961/19678=2.23

therefore, 123% increase.

Other properties, however, are favorable to the increase of power and reduction of fuel consumption. Such properties are as follows: 1).Number of molecules or products is more than that of reactants; 2).Extended limits of flammability; 3).High octane number; 4).High latent heat of vaporization; 5).Constant boiling temperature; 6).High density.

The increase of the number of molecules during combustion implies in a higher pressure inside the cylinder, regardless of the effects of combustion itself. This variation is bigger for ethanol than for gasoline, 1063 against 1055. The extended limits of flammability permit ethanol engines to run at extremely weak mixtures, therefore limiting fuel consumption. High octane number of ethanol and methanol permits the use of very high compression ratio, therefore increasing thermal efficiency. High latent heat of vaporization of alcohol, 904 KJ/kg for ethanol, compared to 418.7 KJ/kg for gasoline leads to: 1).Higher volumetric efficiency; 2).Lower compression work; 3). Less losses of heat to the cooling system; 4).Higher heat recirculation by admission of an air heating. For a chemically correct mixture, therefore, the combined effects of the previously discussed characteristics are as follows:

Here, the first, second, third, fourth, and fifth are heat of combustion, number of molecules, total efficiency, total cylinder charge, and indicated efficiency, respectively.

It can be seen that an alcohol (ethanol) engine can have 18% more power than with gasoline, for the same displacement similarly:

On, in other words, an alcohol engine with optimized combustion, should have only a 17% increase in fuel consumption, not 64% as the heating values of both fuels would suggest.

The overall thermal efficiency of an engine can be expressed as inversely proportional to the specific fuel consumption and the caloric value:

h. =63200000/ (SFC* HV)

Therefore, h.=63200000/ (220* 10500) =27.35 for gasoline; and

h.=63200000/(260*6400)=38.16, for ethanol.

Note that the SFC data is obtained in actual laboratory test of an alcohol engine with optimized combustion. The overall efficiency of an optimized ethanol engine is 38% against only 27% of a gasoline engine of same displacement.

5.1.3. Conversion of diesel engines

When diesel engines are converted to alcohols, some properties of gasoline, diesel and alcohol should be concerned. Table 5.2 shows the properties of the fuels .There are several methods for converting a diesel engine to alcohol to be discussed.

Table 5.2. Some properties of fuels

	Gasoline	Diesel	Methanol	Ethanol
1. Cetane number	-	50	5	8
2. Octane number	96	-	112	107
3. Auto-ignition tempt. ° C	371	315	446	390
4. Latent heat of vaporization (KJ/Kg)	349	220	1177	914
5. Lower heating value (KJ/Kg)	4400	42600	19945	26700

a. Cetane number and cetane improving additive

For a fuel to burn in a diesel engine, it must have a high cetane number or ability to self-ignite at high temperatures and pressures. There exists a significant difference among gasoline, diesel and alcohol in terms of cetane number and auto ignition. A high cetane number leads to a short ignition delay period, whereas a low cetane number results in a long ignition delay period. From table 5.2, it can be seen that alcohols have lower cetane number than that of diesel, which is not desired when diesel engines are converted to alcohol. Fortunately, some additives, an example of which is nitrate glycol, can increase the cetane number of alcohols. This means that ignition delay period will become short, which will reduce tendency to cause a diesel knock. However, too short ignition delay period will cause a lower rate of heat release which is not wanted.

b. Alcohol-diesel emulsions

Because alcohols have limited solubility in diesel, stable emulsion must be formed that will allow it to be injected before separation occurs. Hydroshear emulsification unit can be used to produce emulsions of diesel-alcohol. However, the emulsion can only remain stable for 45 seconds. And, 12% alcohol (energy basis) is the maximum percentage. In addition, this kind of method has several problems which are as follows: 1).Specific fuel consumption at low speed increases; 2).High cost; 3).Instability. Therefore, other methods are developed.

c. Fumigation

Fumigation is a process of introducing alcohol into the diesel engine (up to 50%) by means of a carburettor in the inlet manifold. At the same time, the diesel pump operates at a reduced flow. In this process, diesel fuel is used for generating a pilot flame. And, alcohol is used as a fumigated fuel. Two points should be noted in using this method. At low loads, quantity of alcohol must be reduced to prevent misfire .On the other hand, at high loads, quantity of alcohol must also be reduced to prevent pre-ignition.

d. Dual injection

In dual injection system, a small amount of diesel is injected as a pilot fuel for ignition source. And a large amount of alcohol is injected as main fuel. It must be noted that the pilot fuel must be injected prior to injection of alcohol. Some ideal results can be achieved when this method is used. Thermal efficiency is better. At the same time, NOx emission is lower. Moreover, CO emissions and HC emissions are the same. However, the system requires two fuel pumps, thus, leading to a high cost. Meanwhile, alcohol needs additives for lubricity.

e. Heated surfaces

Alcohol can ignite with hot surfaces. For this reason, glow-plugs can be utilized as a source of ignition for alcohol. In this system, specific fuel consumption depends on glow-plug positions and temperatures. It must be noted that the temperature of glow-plugs must vary with load. However, the glow-plug becomes inefficient at a high load. In addition, the specific fuel consumption is higher than that of diesel.

f. Spark-ignition

When a spark plug is used, diesel engine can be converted to Otto cycle engine. In this case, compression ratio should be reduced, from 16: 1 to 10.5: 1. There are two types about this kind of conversion. They are as follows:

Type 1: The original fuel injection system is maintained. Alcohol needs additive for lubricity (Nitride glycol). Besides, both distributor and sparkplug need to be installed, thus leading to a high cost of conversion. It is critical to adjust an ideal injection and spark-time for this kind of conversion.

Type 2: Original fuel injection is eliminated. But, a carburettor, a spark-plug and a distributor need to be installed, which increases the cost of conversion. In this conversion, spark timing is critical.

Both the type 1 and type 2 conversion have a lower thermal efficiency than that of diesel.

g. Neat methanol for diesel cycle

Fig.5.1 shows the basic principle of this conversion in this system, methanol is introduced to the combustion chamber through two separated accesses. One methanol is passed through inlet manifold over an exhaust-heated aluminum bed (h=70%) heated to 400 ° C. Another methanol with 2% castor oil as additive is injected to the combustion chamber. In the first access, dimethyl ether is produced from methanol. The DME reacts at a normal diesel engine compression temperature and raises the gas temperature above ignition temperatures of methanol .It acts as a pilot fuel; In the second access, no additive to the methanol is to be converted to DME. 2% castor oil is added in order to improve lubricity. In this system, the thermal efficiency is better than that of diesel. Furthermore, ignition delay period is reduced, which leads to a decrease of rate of the pressure rising. This means that the engine has no diesel"knock" and has a smoother combustion. At the same time, the peak pressure is 18% higher than that of diesel. Fortunately, this can be compensated by retarding the injection timing. The problem of this conversion is that DME conversion becomes poor at high speed and at low loads due to the drops of exhaust gas temperature. Pilot flow (DME) which is critical depends on load and speed, less upon temperature. At a high speed, a fuel pump runs out of the design point.

Fig. 5.1 Basic principle of this conversion.

5.2. Conversion design of a L195 diesel engine to ethanol/diesel fuel

5.2.1 Technical parameters of L195 diesel engine

L195 diesel engine, which is widely utilized as a prime mover for a variety of vehicles, including small tractors, is a very popular engine. Table 5.3 shows the specifications of L195 engine.

5.2.2. Conversion design of L195 diesel engine

a. General design of conversion approach

Alcohol has a low cetane number, high octane number, high auto-ignition temperature, high latent heat of vaporization and low level of heating value. Because of the above reasons, the original diesel fuel system would be maintained when this diesel engine is converted to ethanol/alcohol blend fuel. In this system, the diesel fuel provided a pilot-flame for the alcohol that would be aspirated through the inlet manifold by means of a carburettor specifically manufactured to handle ethanol. In addition, a heat exchanger is needed in order to heat the air which flows to the carburettor. In this way, it is not necessary to change original compression ratio. This system, also known as "Fumigation" system was chosen because the high compression ratio of the engine would provide a good condition for the ignition of diesel even in the presence of a cooled charge of air/ethanol. At the same time, the speed control of engine should be modified in order to maintain a ideal proportion of diesel oil. The configuration of L195 engine after conversion is shown in Fig. 5.2.

Table 5.3. specifications of L195 engine

1. Type of engine	four strokes, compression ignition
2. Displacement (cm)	815
3. Bore/Stroke(mm/mm)	95/115
4. Compression ratio	21
5. Normal speed (RPM)	2000
6. 12 hr. calibrated power (KW)	8.826
7. Specific fuel consumption (k/kwh)	257
8. Type of diesel pump	BFGIAK 85
9. Type of injector	ZS4S1
10. Ignition delay period (°CA)	16-20

b. The calculation and selection of carburettor

A carburettor, namely the MBB/WEBER, was bought from Brazil. It was nickel plated and utilized in Brazil in alcohol fueled vehicles. The carburettor was installed in the converted inlet manifold. The main jet was calibrated to a new value. The original jet size of 195 mm was discarded and a smaller one of 150 mm was installed. The ideal main jet size can be deduced from follow formula:

d_s = (4G_f/u_sV_{f· t}p_f)^1/2

In which,

d_s-Size of main jet, mm
G_f-Optical injection amount of fuel at calibrated conditions Kg/s;
V_{f· t}-Theoretical velocity of fuel to the main jet, m/s
u_s-Volume of flow coefficient
p_f-Density of ethanol, Kg/m³

Fig. 5.2. The configuration of L195 engine after conversion

1. Carburettor
2. Heat exchanger
3. Diesel oil control bolt
4. Accelerator linkage
5. Cold air manifold to heat exchanger
6. Hot air carburettor manifold
7. Sxhaust manifold
8. Inlet manifold
9. Cold air by-pass manifold
10. Air filter

c. Selection of heat exchanger

Heat exchanger is a basic piece of equipment in any modern alcohol converted engine. The high latent heat of vaporization of the alcohol causes the air-fuel charge to cool down to freezing temperatures inside the inlet manifold, impairing combustion. To compensate for the unacceptable drop in temperature, a heat exchanger was installed in the exhaust manifold of the engine to recover the heat rejected and to transfer this heat into the inlet air-stream. This causes the air/fuel charge to increase its temperature and therefore a good proportion of the alcohol is evaporated, making combustion more likely to occur on a greater percentage of the engine cycle.

The heat exchanger was made in New Zealand, where it had been successfully utilized in alcohol converted engines. Details of the heat exchanger are shown in Fig. 5.3.

Fig. 5.3. Heat exchanger

The principle of the heat exchanger is very simple. From Fig.5.3, it can be seen that a series of copper rods traverse the connection surface between cold air manifold of the heat exchanger and exhaust manifold of the engine. In this way, the heat from exhaust air is transferred to the copper rods. Meanwhile, the copper rods pass the heat to cold air inside the heat exchanger.

d. Conversion design of air supply system

The original air supply system was converted to a new one. The new manifold was designed, so that two separate air inlets were provided. One, from the air filter to the inlet manifold, is used for diesel oil. And the other, from the air filter, to the heat exchanger and from the heat exchanger back to the manifold through the carburettor is used for alcohol. The working process of the new air supply system is shown in Fig. 5.2.

e. Conversion design of controlling system

Control of diesel oil and alcohol quantities

In order to limit the maximum diesel flow, a modification on the speed control of the engine was made. A longer lever was installed in the speed control shaft which controls the fuel pump rack. Therefore, an external stop was made so that, by means of a bolt, it can be calibrated to any amount of diesel injection, from zero to 100%. A drawing of the system is shown in Fig. 5.2

Fig. 5.4. Accelerator linkage

In order to control the amount of alcohol introduced to the combustion chamber of the engine, the carburettor throttle was connected to the accelerator pedal, which also controls the speed-governor of the engine, thus the diesel flow. The travel of the speed governor was limited to about 50% and the control linkage was made so that the diesel is accelerated first and then the alcohol. This is to avoid flame-out due to the cooling effect that the full charge of alcohol would cause. The control linkage can be seen in Fig. 5.4.

Cold air control

If the amount of diesel oil injected to the combustion chamber is changed, the cold air supply will also be altered. in order to fulfil the above aim, a control valve for the cold air was installed on the inlet manifold. Fig. 5.5 shows the cold air control system. And its working processes are as follows: When the engine is started, the control valve for the cold air is totally open so that very small quantities of alcohol are admitted into the engine; After started, the cold air valve is closed to enable the air from the filter to circulate through the heat exchanger and then through the carburettor which will, at this stage, be fully operative.

Finally, it should be noted that the above pipes which are manufactured from steel are connected by flanges. Fig. 5.6 shows the conversion piping system.

f. Engine tests and analyses

In order to be able to verify the effectiveness of the conversion, tests were carried out for the determination of power and fuel consumption characteristics. Because a reference value was needed, the engine was tested first in its original 100% diesel configuration.

Fig. 5.5 Cold air control

Test with 100% diesel fuel

The carburettor throttle was disconnected and maintained to be closed. The by-pass cold air manifold was opened and the engine started. It was found that power, specific fuel consumption at 2000 RPM were 8.35 KW, 245.6 g/kw h, respectively.

Tests with 180 proof alcohol/diesel blend fuel

When throttle of the carburettor was connected with the accelerator pedal again, the engine can be started. The engine was originally installed in a small farm tractor, and the original configuration was maintained. A tank for ethanol was installed at the back of the tractor, so that alcohol would be fed to the carburettor by gravity. No pumps could be used since the tractor has no battery. The engine was started by manual cranking helped by a decompression valve. The engine was cold started with the accelerator at mid-point, with the diesel limiting bold back-off and the inlet manifold having the passage totally open. This is necessary so that very small quantities of alcohol are admitted into the engine. From the test results, it is known that the engine starts well, though needs some more number of cranking rotations. After being started, the cold-air valve is closed to enable the air from the filter to circulate through the heat exchanger and then through the carburettor which will, at this stage, be fully operative. During the tests, it was found that at full throttle opening, the amount of alcohol is too much, or the mixture strength too high. Some preignition occurs which would be avoided. It is necessary to open the cold-air by-passing manifold in order to introduce more cold air and so reduce the amount of air that pass through the heat exchanger and carburettor. This reduces the mixture strength at full load, which is what is needed.

Fig. 5.6 The conversion piping system.

After many experiments, it was found that, with 40%-60% cold-air by-pass manifold open, the converted engine shows better performance. The power and specific fuel consumption at 2000 RPM are 8.502 kw, 178.3 g/kw-h (not including alcohol), respectively. The ratio of alcohol to diesel is 2: 1. From the test results, it can be seen that the conversion has been successful. The engine can be started well, its overall performance is ideal. In addition, the power using blended oil is higher than that of diesel oil.

Fig.5.7: the cold-air by-pass manifold

At present, the control is manual, but a suggestion for automatic cold-air control is given for further development. A drawing with the suggested control system using a throttle linked to the carburettor is shown in Fig. 5.7.

Conclusion and discussion

The technique of converting LI 95 diesel engine to alcohol/diesel blended fuel is both simple and economical. When there is no alcohol available, the engine can use diesel oil easily. Therefore, it has a wide adaptability.

The heat exchanger can supply sufficient heat to the alcohol, thus offsetting the low inlet air temperature due to the high latent heat of alcohol.

It is practicable to convert a compression internal engine to alcohol/diesel fuel, because the converted engine can be started well and its power is also higher than that of diesel oil. Unfortunately, the converted engine has not reached calibrated power (8.826kw). This is because of following reason. At this test, although the heat exchanger supplies sufficient heat to alcohol, an asbestos gasket between the cylinder head and the inlet manifold prevents heat from the heated engine to be able to reach the inlet manifold. This is undesirable since the manifold needs all the heat that is available to warm up the very cool air/alcohol charge. Later, a copper gasket was used, the converted engine has shown a ideal performance during more than two years field operation. No erosion of carburettor was founded.

In order to improve the performance of the converted engine, it is necessary to have a better thermal insulation in the heated exchanger and manifold to the carburettor. Also exhaust manifold must be thermally insulated.

In order to guarantee good supply of alcohol to the carburettor, it is necessary to locate the alcohol tank as high as possible.

The laboratory tests are preliminary. The detail tests both in laboratory and in the field will be done in future.

5.3. Studies on burning gasoline/ethanol blended fuel in gasoline engines

The goals of the study were to better understand some of the properties of blended fuel, to investigate the performance of engine in laboratories and of vehicles under road conditions, as well as to study the effect of blended fuel on engine parts in corrosion and wearing.

5.3.1. Performance of blend fuel

A. The starting performance of blended fuel

The starting performance of gasoline depends on its forerunning point and the temperature at which 10% distillate is released. When gasoline is mixed with alcohol, the starting performance of the blend fuel mainly depends on the performance of alcohol vaporization. The latent heat of alcohol is about 216 Kcal/Kg, while that of gasoline is 80 Kcal/kg.Besides, the latent heat of alcohol also increases with the proportion of water in alcohol. This .makes alcohol absorb much more heat than gasoline does during vaporization, thus reducing the admission temperature in engine, and causing difficulty in starting the engine. The specific heat of alcohol is 0.65 Kcal/kg°C at 20°C, which is higher than that of gasoline (0.58 Kcal/Kg°C). It increases too with the proportion of water in alcohol, leading to low temperature at the end of compression stroke and making it difficult for the engine to start. In addition, the low boiling point of alcohol as well as arise in temperature in the engine may cause an air plug, and make the engine difficult to start. This means that the starting performance of blend fuel is poor. Therefore, it is necessary to solve the starting problem when gasoline engine is converted to gasoline/ethanol blended fuel.

B. The octane number of blend fuel

Alcohol has a high octane number, RON being 110, and MON 90. Its antiknock performance is good. If alcohol contains a certain amount of water, it is favorable to improve its antiknock performance, hence the enhancement of the compression ratio of the engine occurs when the blended fuel is burned. Meanwhile, an alcohol blend requires no or reduced additive of antiknock substance, which may reduce air pollution caused by lead (pb). But the effect on increasing of the octane number of blended fuel is not the same when gasoline is mixed with different kinds of alcohol, as is shown in Table 5.4. Data in the Table 5.4 show that the change in octane number of blended fuel is in nonlinear correlation with the proportion of alcohol added. A 5%-20% alcohol blend has a higher mixed octane number. This means that the effect on raising the octane number of blend fuel is more notable. In addition, the lower the octane number of base gasoline is, the more notable the effect on raising the octane number of blended fuel will be.

Table 5.4. Octane number (Motor method)

Ethanol in the mixture (%)	Octane (M)		Mixed octane (M)
	a	b	a	b
0	72.5	60.6	-	-
5	74.8	-	118.5	-
10	76.6	-	113.5	-
15	78.5	73.4	112.5	143.00
20	80.3	76.7	111.5	141.10
25	81.4	-	108.1	-
55	-	87.4	-	109.33
60	-	87.7	-	105.77
70	-	88.6	-	100.60
80	-	89.7	-	96.98
90	-	89.9	-	93.16
100	90.0	91.6	90.0	91.60

a - Data in this column are from literature (2).
b - Data in this column are collected from laboratory.

Based on the foregoing conclusion, selecting 15%-20% of low proof alcohol blend has the advantage of putting the alcohol's high antiknock performance into full play. Meanwhile if a low octane gasoline is used as the base for the blend, without adding any antiknock fluid, not only can the pollution by lead be reduced, but also the cost of fuel is decreased, thus making the use of mixed fuel on gasoline engine more adapTable.

5.3.2. conversion methods and materials of gasoline engine

A Van with 492 QA gasoline engine was used as sample machine. The conversion methods of the engine were designed according to the following requirements. Firstly, the conversion of the engine should meet the needs of the blended fuel with 15%-20% alcohol of 170-180 proof. Moreover, the conversion and operation of the engine should be convenient. And the performance of original engine should not be changed too much. In some circumstances, the engine may be switched over to gasoline alone. Furthermore, during operation, the ratio of alcohol to gasoline should not fluctuate more than 5% After some possible conversion methods were analyzed. the method using two float chambers of one carburettor was adopted. During operation, two fuel supply systems fed alcohol and gasoline to one carburettor through two float chambers, respectively. According to the different ways in which alcohol and gasoline were mixed , there were approaches. In the first approach, the alcohol and gasoline were mixed inside the main metering jet tube of the carburettor; In the second approach, the alcohol from the alcohol float chamber was conducted to a new main metering jet tube opposite to the main metering jet tube of gasoline. In this way, alcohol was injected through the new main discharge nozzle. At the same time, gasoline was injected through the original main discharge nozzle. Therefore, they were mixed inside the inlet manifold from the venturi throat to throttle of the carburettor. Fig.5.8 shows schematic arrangement of fuel supply systems . And Fig.5.9 shows structure of the carburettor (Type 231) used for both the first and the second approaches.

Fig. 5.8 schematic arrangement of fuel supply systems

1 - Alcohol tank
2 - Alcohol filter
3 - Alcohol pump
4 - Gasoline pump
5 - Alcohol float chamber
6 - Carburettor
7 - T-tube
8 - Engine
9 - Gasoline filter
10 - Gasoline tank

Fig. 5.9 Structure of the carburettor

1 - Alcohol inlet (second approach)
2 - Carburettor
3 - Alcohol flood chamber
4 - Alcohol outlet
5 - Alcohol pipe
6 - Alcohol inlet (first approach)

After conversion, several contrast tests between the original engine and the converted engine were carried out in order to investigate the engine characteristics, including velocity performance and load performance, exhaust gases, zero load performance, vehicle's travelling performance, and corrosion and wearing.

5.3.3. Test results and discussions

A. Engine bench test

The velocity and load performance of engines are shown in Fig.5.10, Fig.5.11, Fig. 5.12, and Fig. 5.13.

a. Stability of the ratio of alcohol to gasoline

From the velocity performances of the engine, it can be seen that the absolute value of ratio of alcohol to gasoline fluctuated from 1% to 2% under very wide speed range of the engine for both approaches. In addition, from the load performances of engine, it can be seen that the absolute value of the ratio of alcohol to gasoline varies at the range of 1.2%-2.5% from a small percentage of an open throttle to the complete opening of the throttle for both float chamber methods. Therefore, it shows that the ratio of alcohol to gasoline is basically stable at different velocities and loads.

Fig. 5.10 The velocity performance of the engine velocity in the first approach (2400rpm)

Fig. 5.11 The engine load performance for the first approach

Fig. 5.12 The engine velocity performance for the second approach

Fig.5.13 The engine load performance for the second approach (2000rpm)

b. Power and specific fuel consumption

From the velocity performances of engine, it can be seen that the power of engine operating on blend fuel is about the same as that of the engine running on gasoline alone. Although the caloric value of alcohol is lower than that of gasoline, the air-fuel ratio of alcohol is lower than that of gasoline. So the caloric values of combustible gas in the two cases are about the same. Test showed that the engine using blended fuel, which is made by mixing gasoline with 15%-20% 170 proof or above alcohol, can reach the original power of the engine.

From the load performances of the engine, it can be seen that the engine's specific fuel consumption when using blended fuel is higher than that when operating on gasoline alone. This happens because the caloric value of blended fuel is lower than that of gasoline. However, due to the fact that blend fuel has a higher octane number, the combustion properties are improved when blended fuel is used. Therefore, the effective efficiency of blended fuel is higher than that of gasoline under all RPM and load conditions.

B. Start performance

Table 5.5. Vacuum levels of idle port and main discharge nozzle.

Throttle	100% open of choke		100% close of choke
open (angle)	Idle port nozzle	Main discharge	Idle port nozzle	Main discharge
11°	230	1	240	80
22.5°	215	6	225	105

Note: unit, mm H₂O

In choosing the conversion methods, the start problem of the engine has already been considered when engine is started, the throttle of the carburettor is open at a small percentage. Table 5.5 shows the vacuum levels of idle port and main discharge nozzle for the converted engine. The test results show that the vacuum levels of idle port is much higher than that of main discharge nozzle during the start. Therefore, when engine is started, the fuel supply depends on the idle port. At this time, the main discharge nozzle nearly stops supplying fuel. This means that it is the idling system that affected the start performance of the engine.

The velocity performance of the converted engine at idle condition was tested. Fig.5.14 shows the test results. From Fig. 5.14, it is known that the ratio of alcohol to gasoline fluctuates between 3% and 7.5% at 800-2000 RPM. The engine burns nearly gasoline alone under 800 RPM. Above results indicate that the fuel injected from idle port is nearly gasoline alone at a low speed starting condition. Hence, the alcohol does not have an effect on the star performance of the engine.

Because there is no alcohol in the idling system for the second conversion approach, the alcohol can not affect the starting performance of the engine. In fact the "Hongxing" van using the converted engine had no start problems during more than 50000 km trip through two winters.

Fig.5.14 The velocity performance of the converted engine at idle condition

C. Vehicle's travelling performance

The converted engine through the second approach was installed in the "Hongxing"van. The van was tested in the Shenda Road in order to see both the acceleration of engine and fuel consumption per unit distance at a constant speed. In addition, #70 gasoline alone was used in the same vehicle to contrast with the burning blended fuel. The ignition-delay periods were adjusted to a optical value in above two cases.

The data in acceleration test were shown in Table 5.6. From the Table 5.6, it can be seen that the acceleration time of the vehicle running on blended fuel is 2.94 seconds less than that of operating on gasoline. The acceleration of the former is 0.04 m/s² faster than that of the latter. The fuel consumption per unit acceleration of vehicle on the blended fuel is 174.68 g/ms²and on gasoline is 174.83 g/m· s². The two are nearly the same.

Table 5.6. Acceleration properties

Velocity (km/h)		Time (e)		Acceleration (m/s2)		Fuel consumption (g)
Begin	End	B	G	B	G	B	G	R (%)
		26.4	29.1	0.42	0.38	71.67	63.13	16.3
		27.1	31.7	0.41	0.35	69.21	66.72	17.4
30	70	29.3	30.9	0.88	0.36	70.71	67.00	18.0
		29.4	30.6	0.38	0.36	73.93	63.83	16.7
		24.2	28.8	0.46	0.39	72.56	62.78	16.7
Average		27.28	30.22	0.41	0.37	71.62	64.69	16.6

Note:

B: Blend fuel;
G: Gasoline;
R: Ratio of ethanol to gasoline in the blend fuel

Table 5.7 and Table 5.8 show the fuel consumption at a constant speed of the van. The data in the Table 5.7 and Table 5.8 indicate that the average fuel consumption per 100 km of the vehicle running on blend fuel is 0.62 kg higher than that of running on gasoline alone. The difference is 8.16%. The reason is that the heat value of alcohol is only 2/3 of the gasoline heat value. In addition, the heat consumption ratio of vehicle running on blend fuel is 3.3 kcal/km higher than that of running on gasoline. The difference is only 0.45%. Moreover, the ratio of alcohol to gasoline is ranged within 18.2% to 20% at different speeds, which shows that the ratio is stable.

Table 5.7. Fuel consumption of blend fuel at a constant speed

	Time (s)	Velocity (km/hr)	Fuel consumption (g)		Fuel consumption rate (kg/100 km)		Heat consumption ratio (106 cal/100 km)
			Alcohol	Gasoline	Alcohol	Gasoline
1.	120.5	29.87	15.58	60.40	1.56	6.04	-
2.	121	29.75	16.81	60.94	1.68	6.09	-
3.	120.8	29.81	16.20	60.7	1.62	6.07	73.46
4.	89.2	40.35	14.8	57.7	1.48	5.77	-
5.	90.1	39.96	15.6	60.6	1.56	6.06	-
6.	99.65	40.16	15.7	59.1	1.52	5.91	71.18
7.	72.2	49.86	13.9	57.9	1.39	5.79	-
8.	71.8	50.16	15.6	58.8	1.56	5.88	-
9.	72	50	14, 8	58.4	1.48	5.84	70.2
10.	59.4	60.60	14.8	59.4	1.48	5.94	-
11.	58.9	61.12	15.2	62.2	1.52	6.22	72.84
12.	59.15	60.86	15.0	60.8	1.50	6.08	-
13.	51.5	69.90	14.4	64.2	1.44	6.42	-
14.	51.2	70.31	15.2	66.0	1.52	6.60	-
Average	51.35	70.11	14.8	65.1	1.48	6.51	77.24

Table 5.8. Fuel consumption of gasoline at a constant speed

	Time (s)	Velocity (km/hr)	Fuel consumption (g)	Fuel consumption rate (kg/100 km)	Heat consumption consumption rate (106cal/100km)
1.	120.9	29.78	69.3	6.93	-
2.	119.6	30.1	71.2	7.12	-
3.	120.25	29.94	70.2	7.02	73.71
4.	89.6	40.18	67.6	6.76	-
5.	89.7	40.13	69.4	6.94	-
6.	89.65	40.16	68.5	6.85	71.93
7.	72.1	49.93	66.4	6.64	-
8.	72.3	49.79	65.9	6.59	-
9.	72.2	49.86	66.2	6.62	69.51
10.	59.6	60.4	68.2	6.82	-
11.	59.1	60.91	69.1	6.91	-
12.	59.35	60.66	68.6	6.86	72.03
13.	51.2	70.31	74.8	7.48	-
14.	51.6	69.77	76.4	7.64	-
Average	51.4	70.04	75.6	7.56	79.38

D. The effect of blended fuel on corrosion and wearing down of the engine

During the operation of the engine, the metal particles from the machine elements, due to the wearing down of the engine, entered lubricating oil at a suspension state. According to the theory analysis, the amount of metal particles suspended in the lubricating oil is related to the wearing down level of machine elements. Therefore, the wearing down of the engine can be estimated by measuring the iron content in the oil residue in engine. The machine elements which are easy to wear down are in the cylinder wall and piston ring. In our study, the wearing down of engine operating on blended fuel was estimated by measuring the iron content in oil residue in the engine after a car had traveled a certain mileage. The Fig. was then compared with that in the engine burning gasoline. At the same time, the kinematic viscosity and the acid value of oil residue in the two cases were also tested in order to determine the corrosion of engine.

The test data are shown in Table 5.9/Table 5.10 and Table 5.11. The Table 5.9, Table 5.10 and Table 5.11 show the iron content in residue oil, kinematic viscosity and acid value, respectively. The results indicate that the iron content in the oil residue of a car using blended fuel was lower than that of car using gasoline. Furthermore, the kinematic viscosity and the acid value of oil residue in the two cases were nearly the same, suggesting that alcohol had produced no more adverse effect on diluting and acidifying the oil than gasoline did. Besides, the maximum wearing down amounts of the engine cylinder burning blended fuels were 0.05 mm and 0.07 mm in within the diameter's direction after 25000 km and 51000 km, were travelled. respectively. The average maximum wearing down amount of engine cylinder in the diameter's direction was 0.014 mm which was lower than a typical wearing down amount. For example, the average maximum wearing amount per 10000 km of 492 QA engine burning gasoline is 0.0296 mm which is measured by a vehicle maintenance factory. All above results suggest that the blended fuel with 15%-20% alcohol of 170-180 proof has no apparent effect on corrosion and wearing of the engine.

Table 5.9. Iron content in residue oil

	Distance (km)		Iron center it using blend fuel		Iron content using gasoline
	Blend fuel	Gasoline	Total (ppm)	ppm/1000km	Total (ppm)	ppm/1000km
1.	4400	7700	58	13.18	223	28.96
2.	4400	4300	55	12.50	215	50.00
3.	5000	4700	35	7.00	115	24.47
4.	4600	4100	122	26.52	169	41.20
5.	4600	4600	224	48.70	143	31.09
6.	4300	5300	190	44.19	129	24.34
7.	4500	-	121	26.89
8.	4700	-	125	26.60
Average			116.25	25.70	165.67	33.35

Table 5.10. Kinematic viscosity of lubricating oil

Distance (km)		Kinematic viscosity of (40°C, 10-6m/s) lubricating oil
		Using blend fuel	Using gasoline
1.	4600	95.7	-
2.	4600	109	-
3.	4300	92.39	-
4.	4300	-	102.7
5.	4700	-	89.6
6.	4100	-	90.73
Average	-	99.03	94.34

Table 5.11. Acid value of residue oil

Distance (km)		Acid value (mg KOH/g)
		Using blend fuel	Using gasoline
1.	4600	0.50	-
2.	4600	0.69	-
3.	4300	0.51	-
4.	4300	-	0.41
5.	4700	-	0.69
6.	4100	-	0.60
Average	-	0.57	0.57

E. The effect of blended fuel on the exhaust value

Generally speaking, exhaust gases of engine at idling condition can be measured as sample gases. However, the converted engine supplies nearly no alcohol at a very low speed. Hence, the exhaust gases were measured at 550 RPM. Both HC and CO content were measured. When the engine burns blended fuel, the HC and CO content are 500 PPM and 6.8%, respectively. Whereas, the engine burning gasoline alone exhaust 500 PPM HC and 6.8% CO. The test data indicated that the exhaust value of engine operating on blend fuel are lower than that engine using gasoline alone. Furthermore, exhaust values of the engine operating on blended fuel can meet the regulations of China's Exhaust Standards.

5.3.4. Conclusion

Mixing gasoline with 15%-20% alcohol of 170-180 proof is a suitable choice for popularizing the use of blended fuel in the gasoline engine in China.

Burning a mixture of lead-free low -octane gasoline and low-proof alcohol can not only make the best use of high-octane value of alcohol but also reduce fuel cost.

No appreciable corrosion and unnatural wearing down in the main engine parts were observed.

When a gasoline engine is converted to alcohol/gasoline blended fuel, it is crucial to maintain the stability of ratio between alcohol and gasoline during the operation of the engine.

The conversions of the two approaches are simple. It is easy to control the engine. The cost of the conversion is low. And the engine performance is satisfactory and stable. At the same time, the converted engine can be switched over to gasoline alone when there is no alcohol available.

5.4. Studies on using vegetable oil for diesel engine

5.4.1. Characteristics of fuel

In order to study the possibility of cotton oil being used with diesel. We experimented with a mixture of diesel oil and cotton oil in a model 170F diesel engine for 300 hours.

During the experiment, we measured the performances of the model 170F while using pure diesel oil, 30/70 cotton-diesel oil mixture, 50/50 cotton-diesel oil mixture and pure cotton oil.

Because of the differences in structure and composition between diesel oil and cotton oil, their fuel characteristics differ greatly. Their differences are shown in Table 5.12

Table 5.12. Characteristics of fuel

		Viscosity (cst)	Heat value (kJ/kg)	Specific gravity	Freezing point (°C)	Flash point °C	Moisture content (%)
cotton	oil	76.44	39400	0.923	-3	300	1.12
#0 Diesel	oil	3.0-8.0	44950	0.851	< 0	> 60	-

Table 5.12 indicates that cotton oil has a higher viscosity, lower heat value, greater specific gravity and a higher flash point than diesel oil.

The higher viscosity of cotton oil makes for reduced injection quality, incomplete burning, severe accumulation of carbon and dirty lubricant.

The experiment indicated that the viscosity of cotton fell sharply when temperature rose, the viscosity-temperature characteristics of several oils is shown in Fig. 5.15.

Fig. 5.15 The viscosity-temperature characteristics of several oils

5.4.2. Model 2100 engine test

Model 2100 engine had been fueled with nutsedge tube oil, sunflower oil, cotton oil and diesel fuel blends. With the blend, the power output was similar to that of diesel fuel. But with the straight vegetable oil, the maximum power output dropped by seven percent, and the fuel consumption increased by 14%-16% around the rated power. As a example, the performance curve of model 2100 engine is shown in Fig. 5.16.

5.4.3. The model 170F diesel's performance while using cotton oil, diesel oil and mixture oils.

The experimental model was the 170F diesel engine. That's a single cylinder, horizontal, air-cooled, four-stroke and whirl chamber type combustion chamber. Its rated speed is 2600 rpm, and its rated power is 4 horsepower.

The experimental instruments were a model SCJ-1 hydraulic dynamometer, a model TCY-69 fuel consumption recorder and a temperature dial gauge.

Fig. 5.16. The performance of Model 2100 engine

The diesel run at a rated speed of 2600 rpm and measured the character of the diesel while using several different oils. The load performances of fuels are shown in Fig 5.17. It can be concluded from the experiment that maximum power differs only slightly when the engine used different mixture oils.

5.4.4. A 300-hour-run test

The model 170F diesel ran for 300 hours in order to drive a generator of 2kw.with a lamp as load. The fuel was 30/70 cotton-diesel oil mixture.

The experimental procedure

The model 170F diesel requires to change lubricant every 100 working hours according to its instruction manual. Thus the experiment was divided into 3 parts, of 100 hours each.

The experiment was made by means of the cyclic load method, with 2 hours in each cycle.

The detailed running procedures are as follows:

Start for 2 minutes; low speed without load for 5 minutes; 1 kw load for 50 minutes; 2 kw load for 60 minutes; without load for 3 minutes; and then stop: a total of 2 hours. After a rest, the test was rerun according to the same procedure for another cycle.

Fig. 5.17 The load performances of fuels

The experiment recorded the consumption of fuel. A sample of lubricant every 100 hours was taken and analyzed for the content of iron and copper in the oil. The measurements of piston and cylinder sleeves. the shaft neck of the crank's connection rod and crank pin bearings, and the weight of the piston rings were carried out . The experimental results are shown in Table 5.13, 5.14, 5.15.

Table 5.13. The Experimental Result

	Fuel consumption (kg)		Weightless of rings (g)				Meta1 content (ppm)
Cotton oil	Diesel	1st ring	2nd ring	3rd ring	4th ring	oil ring	Fe	Cu
1st 100hr	20.68	48.26	0.1409	0.0403	0.0249	0.0430	0.0240	29.93	10.24
2nd 100hr	3.40	54.60	0.1024	0.0266	0.0219	0.0242	0.0240	619.9	12.2
3rd 100hr	23.98	55.95	0.6344	0.3324	0.2563	0.1238	0.2170	778.8	32.2

Table 5.14. The Measurement of dimensions

		Shaft neck of crank's connection rod		Connection pin bearings
pre-test	A-A	41.99	41.985	42.03	42.035
	B-B	41.99	41.985	42.04	42.04
The first times	A-A	41.985	41.985	42.035	42.03
	B-B	41.985	41.985	42.03	42.03
The second times	A-A	41.975	41.98	42.04	42.035
	B-B	41.98	41.98	42.04	42.04
The third times	A-A	41.975	41.975	42.045	42.045
	B-B	41.98	41.975	42.04	42.05

Analysis of the experimental result

During 300 hour running, the model 170F diesel was in normal working condition with 30/70 cotton-diesel oil mixture, except for the wear on the radial bush of the valve, caused by a light fit When changing the lubricant, it was discovered that the lubricant degraded, its color turned dark, and its viscosity increased. There was more accumulated carbon at the combustion chamber, piston crown and injector, but the accumulated carbon was loose and can be removed easily. No cementation took place . So it does not affect the normal running.

Table 5.15. The Measurement of Piston and Cylinder Sleeves

		Piston		Cylinder sleeves
Pre-test	A-A	69.87	69.87	70.01	70.00	70.01
	B-B	69.88	69.88	70.00	70.005	70.015
The first times	A-A	69.87	69.865	70.05	70.01	70.005
	B-B	69.87	69.86	70.01	70.005	70.015
The second times	A-A	69.85	69.87	70.055	70.015	70.05
	B-B	69.87	69.865	70.02	70.00	70.015
The third times	A-A	69.86	69.85	70.16	70.025	70.015
	B-B	69.865	69.865	70.10	70.01	70.02

The experimental result shows that the wear down is normal except in the 3rd 100-hour. When disassembled and checked after the 3rd 100-hour running, slight longitudinal gutters were found on the surface of cylinder sleeves and at the piston skirt as well. The analysis shows that the cause does not involve the cotton oil.

The wear down of cylinder sleeves was uneven. The bear on the I-I position was big and became smaller gradually below that position. The biggest ellipsoid was also at that position. The wear condition accords with the wear down rule.

There was slightly wear on the piston skirt, the shaft neck of the crank's connection rod and crank pin bearings, and rings, except the first piston ring. These also accord with the normal wear rule.

The content of iron and copper in the lubricant was measured by means of the ash test. The abnormal content of the 3rd 100-hour is in accordance with previous results.

Conclusion

A diesel engine can be fueled with the mixture of 70% diesel oil and 30% cotton oil.

The model 170F diesel engine can directly use the mixture without changing its structure.

As mentioned above, it can be said that the use of 70% diesel oil and 30% cotton oil has no obvious effect on the life of a diesel engine and the parts are in the normal wear condition.

Because of the high viscosity of cotton oil, it is difficult to start engines below 10 °C. So an additional diesel tank could be used for starting the engine.

5.5. Field test system for evaluating a tractor

Alcohol, as a kind of alternative fuel, can be used for tractors. In the interest of assessing the properties of alcohol when it substitutes for other fuels, like diesel oil, a test system may be used to evaluate a tractor when it uses alcohol or diesel oil as its fuel. When the test is conducted, either a uniform load or an actual load may be provided in accordance with the intended use of the tractor.

5.5.1 Introduction

Presently, tests for evaluating tractor performance are mostly conducted on a concrete test track which can provide controllable uniform conditions and comparable results. Farm tractors, however, always run in the field, which is quite different from a concrete track. With the development of tractor technology, especially in recent years, such improvements as 4-wheel drive, power shift transmission and radial tires have found broad applications. When tested on a track, these tractors do not fully demonstrate their merits. When operated in the field, tractors armed with these improvements demonstrate that the productivity and fuel efficiency are remarkably raised. Therefore, tractor performance tests should be conducted in the field. This paper introduces a loading vehicle that was equipped with a magnetic particle brake (MPB) as the loading device, a TP801 single board microcomputer (SBM) and other devices. The loading vehicle could duplicate an actual load cycle that was obtained in the field and measure parameters of the tested tractor. When tractor performance tests are conducted with MPB and duplication techniques, tractors can be tested in the field without drawing any implement. A new system, which can collect phase shift signals as well as analog signals and impulse signals while it can duplicate two sets of load cycles simultaneously, is also presented in the paper.

5.5.2 SBM based test system

The test system that utilizes MPB as its loading device to simulate load cycle obtained in the field is composed mainly of the following parts.

The loading device is the executive unit to simulate a load cycle. In comparison with eddy current dynamometer and/or electric DC dynamometer, MPB is low in cost, simple in structure (as shown in Fig 5.18) and is more suitable for a mobile test system. When the synchronous drive of the loading vehicle PTO shaft is engaged, the rotation of drive-wheels would make the rotor shaft of MPB rotate proportionally. When excitation current is led into the stator coil of MPB, magnetic flux is generated. This makes magnetic particles magnetize, appear in chain and contact with the surfaces of rotor and stator. The binding forces and frictional forces between magnetic particles and rotor & stator cause the rotor to generate brake torque when rotating. The bigger the excitation current, the larger the brake torque that is produced by MPB, and the heavier the drawbar load which is exerted on the tested tractor by the loading vehicle.

Fig 5.18 Construction of the MPB

A microcomputer system (as shown in Fig 5.19), which contains a SBM, an analog to digital converter (ADC0809), a digital to analog converter (DAC0832), transducers and amplification circuits for signals, plays a dominating role in the process through which the loading vehicle duplicates a load cycle and measures parameters of the tested tractor. The SBM, on the basis of prescribed time or test pass, outputs data to the MPB (through the DAC0832) that was obtained from in-field test and stored in the memory. The MPB produces brake torque to the loading vehicle which in turn supplies a corresponding drawbar load to the tested tractor. While the loading vehicle is duplicating a load cycle, SBM measures such parameters of the tested tractor as drawbar pull, true ground speed, tractive power, slip, fuel consumption, etc. The maximum, minimum and average values of the above parameters can be printed out finally. The curve of drawbar pull can also be plotted out.

The loading vehicle was refitted from a Zetor-6911 two-wheeled tractor. The MPB is mounted on a special frame at the rear axle housing of the loading vehicle (as shown in Fig 5.20) and is connected to the PTO shaft through a universal joint drive shaft. The SBM and other devices are placed in the cab of the vehicle for the purpose of easy operation and observation. The cooling system contains a water tank, a pump, etc. to remove the heat produced by the MPB. The power source of batteries supplies 12V, 24V, 36V DC for the SBM, MPB and other devices.

Fig 5.19 Block diagram of microcomputer system

Fig 5.20 Loading vehicle with the MPB

5.5.3 Research on characteristics of MPB

The MPB employed in the system was produced by Haian Electrical Machinery Factory, Jiangsu province, China. It has a rated current of 0.6 A (current products of this factory have rated currents up to 3 A for more accurate control). Test results for the MPB are as follows:

A. Characteristic of torque-excitation current

The relationship between brake torque M and excitation current I is shown in Fig 5.21, when speed of rotation of the MPB is kept steady. In a whole range of current, the curve appears in two linear regions. The regressive equation is

	-15.703+ 458.206I (0.05<I<0.3)
M =	-|
	- 30.317+ 314.297I (0.30<I<.55)

where M is brake torque in NM and I is excitation current in A.

Fig 5.21 Relationship between torque and excitation current

B. Characteristic of torque-slip speed

Tests show that the effect of I to M is highly remarkable, and that the effect of interaction between I and n is far less than that of n to M. The relationship between torque and speed is shown in Fig 5.22. The regressive equation is

M = -7.122+ 0.015n+ 401.911I

where M is brake torque in MM, I is excitation current in A and n is speed of rotation in r/min.

On the whole, torque has linear relationship with excitation current and speed. Brake torque increases 1.5 MM with every lift of 100 r/min of speed.

C. Transient characteristic of torque

Transient time refers to the period when torque reaches to 80% of the expected value after excitation current has been changed. Test results are given in Table 5.16 and transient curve is shown in Fig 5.23.

Fig.5.22 Relationship between torque and speed

Fig 5.23 Transient characteristic of torque

According to updated test data from the manufacturing factory, the non-response time for torque is 25 ms, ascendant time (to 63% of the expected value) about 250 ms and descendant time (to 37% of the expected value) about 375 ms.

D. Magnetic hysteresis characteristic of torque

When excitation current is increased to 0.54 A and then gradually decreased to zero from 0.54 A, torque is measured 3 seconds after the variation of current, as shown in Fig 5.24. The torque difference due to magnetic hysteresis reduces with time extension. Torque difference nearly disappears after the current has been changed for 7 seconds.

Table 5.16 Transient time of torque

current variation (A)	ascendant time (s)	descendant time (s)
0-0.54	0.92	1.60
0-0.36	0.98	0.9
0-0.18	1.10	0.89

Fig 5.24 Magnetic hysteresis characteristic of torque

The MPB, as the loading device for tractor test, possesses following characteristics:

a. There exists a favorable linear relationship between brake torque and excitation current, and thus it is easy to adjust torque.

b. Large brake power can be obtained with little excitation power.

c. Because torque is nearly irrelevant to speed, it is conveniently controlled.

d. The MPB is simple in structure and carries a low price tag.

5.5.4 Tests for duplicating in-field load cycle

A. Collecting sample load cycle in the field.

Utilizing the loading vehicle, a group of load cycles were gathered when a small four-wheeled tractor was plowing in the field, drawing a single-furrow plow. A set of load cycles, (8 in Fig 5.25), was selected to be the sample load cycle. After being processed, data of the sample load cycle was stored in the memory of the SBM.

Fig 5.25 Duplicating in-field load cycle

B. Simulating and duplicating in-field load cycle with MPB

To evaluate the simulating property of the MPB, tests of duplicating load cycle were conducted when the loading vehicle was stationary. The SBM was timed to output data of the sample load cycle through the DAC0832, offer excitation current for MPB and measure brake torque on the PTO shaft of the loading vehicle. Test results are shown in Fig 5.25. Curves 1 to 3 were duplicated with loading intervals of 360 ms, 240 ms and 180 ms respectively. Curves 4 and 5 were obtained with intervals of 240 ms while the sample load cycle was reduced by 1/4 and 1/2 respectively.

To improve the response property of the MPB, a feedback control program was employed. According to measured torque value, output data was varied at prescribed intervals to speed up the MPB to achieve the desired brake torque value. For feedback control, a table was established in the memory. The programming flowchart is given in Fig 5.26.

C. Tests for duplicating in-field load cycle with the loading vehicle

Tests for duplicating load cycle were conducted in the field with the loading vehicle being drawn by the small four-wheeled tractor. The SBM offered excitation current for the MPB in accordance with test pass and measured drawbar load exerted on the tested tractor by the loading vehicle. Test results are shown in Fig 5.25 (6 and 7).

Fig 5.26 Flowchart of feedback control

D. Results and analysis

The MPB can authentically duplicate the in-field load cycle of implements. Therefore, it is feasible to use the MPB as the loading device for duplicating implement load cycles. There is some difference in test results obtained with the loading vehicle. The reason is that the rolling resistance of the loading vehicle reaches up to 27% of the average value of the sample load cycle. The random variation of the rolling resistance due to the surface conditions of ground directly influenced the simulated drawbar load value. It is supposed to choose a loading vehicle lighter in weight and a MPB larger in brake power. When duplicating a load cycle, the SBM measures parameters such as drawbar pull, drawbar power, ground speed etc. and plots the curve of drawbar pull.

5.5.5 An improved monitor and measurement system

A low-cost versatile monitor and measurement system for tractor and other vehicles (such as rice transplanter) testing was developed utilizing a MCS-51 single chip microcomputer (SCM). Including two DAC0832 chips and current amplifying circuits, the system could simulate two sets of load cycles separately or simultaneously. The system can collect three kinds of signals generated by transducers: analog signals, impulse signals and phase shift signals, while the above-mentioned system could only gather analog and impulse signals. With employment of the SCM, the system is chipper, more compact and flexible in application.

A. System components

The system consists of an SCB-31-5 (II) control board, a commonly-used keyboard & display board, a data acquisition board, a current amplifying board and an electric source board. The SCB-31-5 (II) control board includes on board an 8031 SCM, a 8Kx8bit 2764 EPROM chip, a 8Kx8bit 6264 RAM chip, an ADC0809 A/D converter, a DAC0832 D/A converter, and an 8155 programmable interface chip. The commonly-used keyboard & display board is composed mainly of an 8279 interface chip, an 8-LED digital display and 20 keys. The electric source board supplies + 5VDC. + 12VDC and -12VDC for chips and amplifying circuits.

B. Control board

The 8031, which contains an 8-bit microprocessor, 128 bytes RAM, four 8-bit parallel I/O interface ports, one full duplex serial interface port and two 16-bit timers (counters), is the core part in the SCB-31-5 (II) control board. An assembly language program stored in the 2764 EPROM (address 0000-FFFFH) controls the operation of the system. The ADC0809 (chip select address 6800H) converts analog signals coming from transducers into digital signals that are, then, collected by the 8031. An ADC0809 can accept up to 8 signals. The control board contains one DAC0832 (chip select address 6000H) that converts digital signal output from the 8031 into an analog current signal. After amplified, the current is used to control an MPB for simulating a load cycle. The other DAC0832 (address 2000H) and corresponding interface circuit were built onto the current amplifying board to monitor another MPB for duplicating a second load cycle. Data gathered during test procedure is stored in the 6264 RAM (address 4000-5FFFH) for on-the-spot output. The 8155 chip has 256x8bit RAM (address 7800-78FFH), one 8-bit control port (address 7900H), two 8-bit ports (address 7900H and 7902H), one 6-bit port (address 7903H), and a 14-bit programmable timer/counter (address 7904H and 7905H).

C. Commonly-used keyboard & display board

The 8279 keyboard/display interface chip is employed on this board and is directly connected to the 8031. Without occupying time of CPU, it can automatically complete display and scan. On board there are 8 light-emitting diodes and 20 keys. Fig.5.27 shows that the control board and the commonly-used keyboard & display board were used in a test.

D. Data acquisition board

a. Analog signals

Some transducers, like the BLR force sensor, give out analog signals (voltage or current) to reflect the value of measured parameters. Analog signals generally should be magnified to meet the needs of the A/D converter before they are converted into digital signals, which then can be accepted by the CPU. The amplifying circuit is shown in Fig 5.28. V_in is the analog signal from transducers, V_out is the output signal. If feedback resistance R_fw is adjusted, the magnification factor can be changed. When R₁=1.5K,R₂=1.5K, R_f =4K, and R_fw=4.7K, the relationship between V_out and V_in is shown in Table 5.17.

Fig 5.27 Control board and commonly-used keyboard & display board

Table 5.17 Test data of amplifying circuit

Vin (mV)	0	2.5	5	10	15	20	25	30
Vout (V)	0	0.19	0.36	0.70	1.06	1.43	1.80	2.15
Vin (mV)	35	40	45	50	55	60	65	70
Vout (V)	2.50	2.85	3.23	3.59	3.95	4.30	4.65	5.00

b. Impulse signals

Most transducers for measuring parameters such as speed and rotating speed send out impulse signals in a given time. After having been reformed with a flip-flop circuit, these signals can be counted by a microcomputer, and the corresponding parameters can be calculated. With the inner counters of 8031 and 8155, the system can accept up to 4 parameters.

Fig 5.28 Amplifying circuit

Fig 5.29 Diagram for measuring phase shift signals

c. Phase shift signals

Some transducers output two sine waves. As the measured parameter changes, the phase angle of the two sine waves varies proportionally. The CJQ rotational distance & rotational speed transducer manufactured by Haian Electrical Machinery Factory, Jiangsu province, China, is made on the magneto conversion principle. With the increase of the torque exerted on its shaft, the phase difference enlarges proportionally. The circuit for surveying the phase difference is shown in Fig 5.29. Fig 5.30 depicts the procedure of signal conversion. Two comparison measurers are used in Fig 5.29 to generate square waves S_A and S_B from sine waves output by the transducer. Then, the square waves are reformed. When they pass through the AND. NOT gate (Fig 5.29), Sc (Fig 5.30) is obtained. The time duration t that represents the phase angle is relevant to the torque exerted on the transducer. The SCM counts the time duration t with its timer and then calculates the torque value being measured.

Fig 5.30 Signal conversion

A static surveying test for CJQ-20 transducer was conducted with the system (as shown in Fig 5.27 and Fig 5.31). The linear regressive equation is

N = 2.6174M - 16.1162

where N is the torque being measured in NM and M is the value for t counted by the 8031 SCM. Here, M was adjusted to be 6 when no torque was exerted on the transducer (i.e. N=0).

Fig 5.31 Static measurement test for CJQ-20 transducer

Fig 5.32 Current amplifying board

e. Current amplifying board

This board (shown in Fig 5.32) includes two current amplifying circuits. Because there exists only one DAC0832 (address 6000H) on the control board, which can output one analog signal U₁, another DAC0832 (address 2000H) and the relevant interface circuit were designed, which could output another analog signal U₂ (the left side of Fig 5.33). After U₁ and U₂ are magnified respectively by current amplifying circuits (the right side of Fig 5.33), the excitation current signals (0-2A) for two magnetic particle brakes are obtained.

In Fig 5.33, transistor T₁ forms the middle stage, T₂ and T₃, connected in parallel mode, make up the output stage and supply the excitation current together for the MPB. The emitter resistance R_we and feedback resistance RF are utilized to restrain the current fluctuation. Radiators should be used for T₁ and T₂ to maintain normal temperature.

Fig 5.33 Amplifying circuit for excitation current of the MPB

Conclusions

The MPB is feasible to be employed as the loading device for tractor performance test.

A versatile and inexpensive SCM-based system was developed to duplicate load cycles and measure parameters of a tested tractor.

A feedback control program was used to improve the linear property and hysteresis of the MPB.

The transfer function of the MPB is required.

References

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2. The Brazilian Ethanol Producer's special Committee, Ethanol: The Renewable and Ecological State Solution, Sao paulo, June 1985.

3. Lu Nan, 1992. Technique of Alcohol Production from Sweet Sorghum Stalks, Research and Development of Biomass Energy Technology In China.

5. Harlan W. Van Gerpen, Robert L. May field, Dyna-cart-A Programmable Drawbar Dynamometer for Evaluating Tractor Performance, ASAE Paper No. 821056, 1982.

6. I. W. Grevis-James, D. R. DeVoe, P. D. Bloome, D.G. Batchelder and B. W. Lambert, Microcomputer-Based Data Acquisition for Tractors, TRANSACTIONS of the ASAE-1983.

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