- In a petrol engine, the fuel is mixed with the air before it enters the cylinder, whereas in a diesel engine the fuel is injected (as a fine spray) during the compression stroke
- In a petrol engine, the fuel-air mixture is ignited by spark plugs, (the spark occurring just before the end of the compression stroke, to allow maximum pressure on the descending piston) whereas in a diesel engine it ignites due to the high temperatures caused by compression
- The diesel engine has a higher compression ratio than the petrol engine