DIFFERENCE BETWEEN GASOLINE AND DIESEL ENGINES

Both diesel and gasoline engines convert 

chemical energy from fuel into mechanical 

energy through a series of explosions. The 

way these explosions happen is the major difference between these two engines.

In a gasoline engine, the explosion process is:

1. Intake stroke – fuel is mixed with air
2. Compression stroke – piston goes up, mixture of fuel and air is compressed
3. Ignition stroke – fuel/air is ignited through the use of a spark plug
4. Exhaust stroke – piston goes up, pushes exhaust through the exhaust valve

In a diesel engine, the explosion process is:

1. Intake stroke – intake valve opens, air in, piston goes down
2. Compression stroke – piston goes up, air compressed (heated in excess of 540°C)
3. Combustion stroke – fuel is injected (right time), ignition, piston goes down
4. Exhaust – piston goes up, pushes exhaust through the exhaust valve

Diesel engines have no spark plug. They need high compression ratios to generate the high temperatures

 required for fuel auto ignition (the higher the cetane number, the better the ignition).

Compression is much higher with a diesel engine (14:1 to 25:1) than a gasoline engine (8:1 to 12:1). 

Gasoline engines use lower compression ratios to avoid fuel auto ignition (engine knock). Higher 

compression ratios lead to higher thermal efficiencies and better fuel economies.

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