15-10-2010, 04:43 PM
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This article is presented by:MITHUN SARKAR
DEPARTMENT OF MECHANICAL ENGINEERING
KALYANI GOVERNMENT ENGINEERING COLLEGE
KALYANI, NADIA
INTRODUCTION
In this century, it is believed that crude oil and petroleum products will become very scarce and costly. Day-to-day, fuel economy of engines is getting improved and will continue to improve. However, enormous increase in number of vehicles has started dictating the demand for fuel. With increased use and depletion of fossil fuels, alternative fuel technology will become more common in the coming decades. Because of the high cost of petroleum products, emission problems some developing countries are trying to use alternate fuels for their vehicles.
DIFFICULTIES:
1. Extensive research and development is difficult to justify until the fuels are accepted as viable for large numbers of engines.
2. Most alternate fuels are very costly at present since the quantity used is very less.
3. There is lack of distribution points (service stations) where fuel is available to the public.
LIQUID FUELS:
Liquid fuels are preferred for IC engines because they are easy to store and have reasonably good calorific value. The main alternative is the alcohol
ALCOHOL:
Alcohols are attractive alternate fuels because they can be obtained from both natural and manufactured sources. Methanol and ethanol are two kinds of alcohols that seem most promising.
ADVANTAGES:
1. It is a high octane fuel with anti-knock index numbers of over 100.Engines using high octane fuel can run more efficiently by using higher compression ratios. Alcohols have higher flame speed.
2. It produces less overall emissions compared to gasoline.
3. When alcohols are burned, it forms more moles of exhaust gases, which gives higher pressure and more power in the expansion stroke.
4. It has high latent heat of vaporization which results in a cooler intake process. This raises the volumetric efficiency of the engine and reduces the required work input in the compression stroke.
5. Alcohols have low sulphur content in the fuel.
6. Reduced petroleum imports and transportation.
DISADVANTAGES:
1. Alcohols have low energy content or in other words the calorific value of the fuel is almost half. This means that almost twice as much as gasoline must be burned to give the same energy input to the engine. With equal thermal efficiency and similar engine output usage, twice as much fuel would have to be purchased, and he distance which could be driven with a given fuel tank volume would be cut in half. Automobiles as well as distribution stations would require twice as much storage capacity, twice the number of storage facilities, twice the volume of storage at the service stations, twice as many tank trucks and pipelines, etc. Even with the low energy content of the fuel, engine power for a given displacement would be about the same. This is because of the lower air-fuel ratio needed by alcohol. Alcohol contains oxygen and thus requires less air for stoichiometric combustion. More fuel can be burned with the same amount of air.
2. Combustion of alcohols produces more aldehydes in the exhaust. If as much alcohol fuel was consumed as gasoline. Aldehyde emissions would be a serious problem.
3. Alcohol is much more corrosive than gasoline on copper, brass, aluminum, rubber, and many plastics. This puts some restrictions on the design and manufacturing of engines to be used with this fuel. Fuel lines and tanks, gaskets, and even metal engine parts can deteriorate with long-term alcohol use (resulting in cracked fuel lines, the need for special fuel tank, etc). Methanol is very corrosive on metals.
4. It has poor cold weather starting characteristics due to low vapor pressure and evaporation. Alcohol-fuelled engines generally have difficulty in starting at temperatures below 10 C. Often a small amount of gasoline is added to alcohol fuel, which greatly improves cold-weather starting. However, the need to do this greatly reduces the attractiveness of alcohol.
5. Alcohols have poor ignition characteristics n general.
6. Alcohols have an almost invisible flame, which is considered dangerous when handling fuel. A small amount of gasoline removes this danger.
7. There is the danger of storage tank flammability, due to low vapor pressure. Air can leak into storage tanks and create combustible mixtures.
8. There will be less NOx emissions because of low flame temperatures. However, the resulting lower exhaust temperatures take longer time to heat the catalytic converter to efficient operating temperatures.
9. Many people find the strong odor of alcohol very offensive. Headaches and drizzles have been experienced when refueling an automobile.
10. There is a possibility of vapor lock in fuel delivery systems.
This article is presented by:MITHUN SARKAR
DEPARTMENT OF MECHANICAL ENGINEERING
KALYANI GOVERNMENT ENGINEERING COLLEGE
KALYANI, NADIA
ALCOHOL AS AN ALTERNATIVE FUEL IN I.C ENGINES
INTRODUCTION
In this century, it is believed that crude oil and petroleum products will become very scarce and costly. Day-to-day, fuel economy of engines is getting improved and will continue to improve. However, enormous increase in number of vehicles has started dictating the demand for fuel. With increased use and depletion of fossil fuels, alternative fuel technology will become more common in the coming decades. Because of the high cost of petroleum products, emission problems some developing countries are trying to use alternate fuels for their vehicles.
DIFFICULTIES:
1. Extensive research and development is difficult to justify until the fuels are accepted as viable for large numbers of engines.
2. Most alternate fuels are very costly at present since the quantity used is very less.
3. There is lack of distribution points (service stations) where fuel is available to the public.
LIQUID FUELS:
Liquid fuels are preferred for IC engines because they are easy to store and have reasonably good calorific value. The main alternative is the alcohol
ALCOHOL:
Alcohols are attractive alternate fuels because they can be obtained from both natural and manufactured sources. Methanol and ethanol are two kinds of alcohols that seem most promising.
ADVANTAGES:
1. It is a high octane fuel with anti-knock index numbers of over 100.Engines using high octane fuel can run more efficiently by using higher compression ratios. Alcohols have higher flame speed.
2. It produces less overall emissions compared to gasoline.
3. When alcohols are burned, it forms more moles of exhaust gases, which gives higher pressure and more power in the expansion stroke.
4. It has high latent heat of vaporization which results in a cooler intake process. This raises the volumetric efficiency of the engine and reduces the required work input in the compression stroke.
5. Alcohols have low sulphur content in the fuel.
6. Reduced petroleum imports and transportation.
DISADVANTAGES:
1. Alcohols have low energy content or in other words the calorific value of the fuel is almost half. This means that almost twice as much as gasoline must be burned to give the same energy input to the engine. With equal thermal efficiency and similar engine output usage, twice as much fuel would have to be purchased, and he distance which could be driven with a given fuel tank volume would be cut in half. Automobiles as well as distribution stations would require twice as much storage capacity, twice the number of storage facilities, twice the volume of storage at the service stations, twice as many tank trucks and pipelines, etc. Even with the low energy content of the fuel, engine power for a given displacement would be about the same. This is because of the lower air-fuel ratio needed by alcohol. Alcohol contains oxygen and thus requires less air for stoichiometric combustion. More fuel can be burned with the same amount of air.
2. Combustion of alcohols produces more aldehydes in the exhaust. If as much alcohol fuel was consumed as gasoline. Aldehyde emissions would be a serious problem.
3. Alcohol is much more corrosive than gasoline on copper, brass, aluminum, rubber, and many plastics. This puts some restrictions on the design and manufacturing of engines to be used with this fuel. Fuel lines and tanks, gaskets, and even metal engine parts can deteriorate with long-term alcohol use (resulting in cracked fuel lines, the need for special fuel tank, etc). Methanol is very corrosive on metals.
4. It has poor cold weather starting characteristics due to low vapor pressure and evaporation. Alcohol-fuelled engines generally have difficulty in starting at temperatures below 10 C. Often a small amount of gasoline is added to alcohol fuel, which greatly improves cold-weather starting. However, the need to do this greatly reduces the attractiveness of alcohol.
5. Alcohols have poor ignition characteristics n general.
6. Alcohols have an almost invisible flame, which is considered dangerous when handling fuel. A small amount of gasoline removes this danger.
7. There is the danger of storage tank flammability, due to low vapor pressure. Air can leak into storage tanks and create combustible mixtures.
8. There will be less NOx emissions because of low flame temperatures. However, the resulting lower exhaust temperatures take longer time to heat the catalytic converter to efficient operating temperatures.
9. Many people find the strong odor of alcohol very offensive. Headaches and drizzles have been experienced when refueling an automobile.
10. There is a possibility of vapor lock in fuel delivery systems.
