Test: Conventional & Alternative Fuels - 3 - Mechanical Engineering MCQ

Advantages of hydrogen as an IC engine fuel:
1. Low emissions
2. Fuel availability
3. Fuel leakage is not a pollutant
4. High energy content per unit volume

It has poor engine volumetric efficiency. Anytime gaseous fuel is used in an engine, the fuel will displace some of the inlet air and poorer volumetric efficiency will result.

A variety of oils can be used to produce biodiesel and these include:

• Virgin oil feedstock
• Pure plant oil or straight vegetable oil
• Animal fats
• Algae

Advantages of LPG:

• Less emission
• It mixes with air at all temperature
• No crankcase dilution
• High octane number hence better antiknock characteristics
• Cost saving of 50%
• Uniform mixture can be supplied to all cylinders in multi-cylinder engines

Each octane number at the higher range of the octane scale will produce greater anti-knock effect compared to the same unit at the lower end of the scale. Because of this non-linear variation, a new scale was derived which expresses the approximate relative engine performance.

For petrol, stoichiometric air-fuel ratio is around 15 : 1.

In the octane number test the performance of unknown gasoline is compared with that of series of reference fuels consisting of mixtures of iso-octane and normal heptane.

Since Iso-octane has a very little tendency to knock and hence it has assigned an octane number of 100.

In case of diesel fuel, its ability to auto-ignite quickly is measured by cetane number.

Cetane number: The cetane rating of a diesel fuel is a measure of its ability to autoignite quickly when it is injected into the compressed and heated air in the engine, ignition delay is affected by several engine design parameter such as compression ratio, injection time, inlet air temperature etc. It is also dependent on hydrocarbon compression of fuel and to some extent on its volatility characteristics. The cetane number is a numerical measure of the influence. The diesel fuel has in determining the ignition delay. Higher the cetane rating of fuel lesser is the property for diesel knock. In India, cetane number lies between 40 to 60.