Alcohol can be used as a blend with gasoline as this has the advantage that the existing engines need not be modified and tetra-ethyl lead (TEL) can be eliminated from gasoline, due to the octane-enhancing quality of alcohol. If the engine is to be operated using only pure alco­hol, then some major modifications are required in the engine and fuel system, as listed below:

1. Both alcohols and blends with gasoline are corrosive to many of the engine materials. These materials have to be changed.

2. Adjustment of the carburetor and fuel injection need to be made to compensate for the leaning effect.

3. Change in the fuel pump and circulation system need to be made to avoid vapor lock, as the methanol vaporization rate is very high.

4. Introduction of high energy ignition system with lean mixture.

5. Increase in compression ratio to make better antiknock properties of the fuel.

6. Addition of detergent and volatile primers to reduce engine deposits and assist in cold starting.

7. Use of cooler-running spark plugs to avoid preignition.

General properties of the blends are listed in Table 7.4. The volatil­ity shown by the American Standard Testing Method (ASTM) distillation characteristics of petrol is a compromise between opposing factors to ensure good performance in petrol engines. This requires petrol to have a sufficiently lighter reaction and a 10% distillation temperature in order to start the engine as well as warm up, but the temperature should

not be so low that vapor-locking takes place and stops the engine due to the nonsupply of fuel. As far as volatility is concerned, ethanol-petrol blends are as good as petrol, if not better. Also gum resistance is greater than that of petrol. Aniline points for blends are lower, which indicates more aromatic content than petrol, due to the adding of ethanol to petrol, which helps to improve the octane number marginally. If a small quan­tity of water is introduced into a gasoline-alcohol blend, phase separation takes place, with gasoline-content in the upper phase and alcohol in the lower. This separation produces some undesirable effects. The alco­hol-water mixture tends to pick up sediment and stall the engine on reaching the carburetor [4]. To improve the water tolerance of the blend, benzene and heptanes are added.

Since 1979, gasohol has been sold at 500 filling stations in the mid­western United States, where the corn from which alcohol is commonly made is abundant. This blend yields about the same mileage as unleaded gasoline and even offers an ever renewable source of energy. Moreover, if this blend were to replace gasoline, it could cut as much as 10% of the nation’s oil imports, which totalled $40 billion in 1979. This fuel has a good future in wealthy countries. The blends have some important advantages over pure ethanol, as listed below:

1. The starting difficulty can be removed.

2. There is no abnormal corrosion compared with pure ethanol.

3. Lubrication in a petrol-alcohol blend is more or less the same.

4. Some benzene is added to prevent separation of the layers of petrol and alcohol.

If blends are used, some minor modifications in the engine are required, as listed below:

1. The carburetor jet should be increased to increase the flow 1.56 times that of petrol.

2. The float has to be weighted down to correct levels due to higher spe­cific gravity.

3. The air inlet should be modified to get less air as blends require less air for complete combustion than petrol.

4. Specific arrangement of heating the carburetor and intake manifold should be provided as lower vapor pressure of alcohol makes the starting difficult below 70°C.