PETROL ENGINE
1. Petrol engine works on Otto cycle, in which the heat addition takes place at constant volume.
2. Admitted into the engine cylinder is a well blended mixture of air and petrol or gasoline.
3. Petrol engines are designed for low compression ratios in the range 5:1 to 9:1
4. The admitted charge is ignited with the help of a spark plug which is operated electronically.
5. Otto cycle has higher efficiency than Diesel cycle. But, due to low compression ratio, petrol engines practically have lower efficiency.
6. It is easier to start a petrol engine (even in colder regions) due to lower compression ratio.
7. It is better suited to attain higher speeds in the range of 3000-5000 RPM.
8. Petrol engines are light engines, they can sustain lesser temperatures and pressures.
9. It cannot generate high power. So, it is best suited for lighter vehicles like personal cars and bikes.
10. It is cheaper but its operational cost is more.
DIESEL ENGINE
1. Diesel engine works on Diesel cycle, in which the heat addition takes place at constant pressure.
2. Admitted into the engine cylinder is air alone. Diesel is later sprayed at the end of compression.
3. Diesel engines are designed for higher compression ratios in the range 12:1 to 19:1.
4. The admitted charge gets ignited automatically due to the heat of high compression.
5. Diesel cycle has lower efficiency than Otto cycle. But, due to higher compression ratio, diesel engines practically have higher efficiency.
6. It is difficult to start (especially in colder regions) due to higher compression ratios.
7. It is doesn’t reach higher speeds. Speeds lie in the range 1000-2000 RPM.
8. Diesel engines are heavy engines, they can sustain high temperatures and pressures.
9. It can generate high power. So, it is better suited for heavier vehicles like buses and trucks.
10. It is costlier but operational cost is lower.
