Comparison Of CI And SI Engines

The CI engine has the following advantages over the SI engine.

1. Reliability of the CI engine is much higher than that of the SI engine. This is because in case of the failure of the battery, ignition or carburettor system, the SI engine cannot operate, whereas the CI engine, with a separate fuel injector for each cylinder, has less risk of failure.

2. The distribution of fuel to each cylinder is uniform as each of them has a separate injector, whereas in the SI engine the distribution of fuel mixture is not uniform, owing to the design of the single carburettor and the intake manifold.

3. Since the servicing period of the fuel injection system of CI engine is longer, its maintenance cost is less than that of the SI engine.

4. The expansion ratio of the CI engine is higher than that of the SI engine; therefore, the heat loss to the cylinder walls is less in the CI engine than that of the SI engine. Consequently, the cooling system of the CI engine can be of smaller dimensions.

5. The torque characteristics of the CI engine are more uniform which results in better top gear performance.

6. The CI engine can be switched over from part load to full load soon after starting from cold, whereas the SI engine requires warming up.

7. The fuel (diesel) for the CI engine is cheaper than the fuel (petrol) for SI engine.

8. The fire risk in the CI engine is minimised due to the absence of the ignition system.

9. On part load, the specific fuel consumption of the CI engine is low.