Theoretically, both gasoline and diesel engines are internal combustion engines. Both perform the function of converting chemical energy into mechanical energy using fuel injection system. Small chemical explosions occur in the combustion chambers of both the engines, but the way they take place is different for each engine.
The major difference between the engines is that gasoline engines have a spark plug that produces spark to ignite the air/fuel mixture in the combustion chamber, whereas diesel engines do not have the spark plug and the fuel is ignited by compressed air instead.
Here are a few more differences by ways of their functioning.
Gasoline fuel injection system
- In a gasoline engine, the fuel injection system injects a homogenous mixture of fuel and air into the combustion chamber through the fuel injector
- The mixture is then compressed by the piston which moves up and down in the chamber to pressurize the air and fuel mixture
- The pressurized mixture is then ignited by the spark that is produced by the spark plug
- In gasoline engines, the fuel is not injected with high pressure because the fuel has to mix with air in the fuel valve before getting injected into the chamber. The pressure with which the mixture is injected by the fuel injector into the chamber will be 10 psi to 60 psi
Diesel fuel injection system
- Unlike gasoline engines, diesel engines do not have a spark plug
- In these engines, the air is already present in the combustion chamber and is compressed
- The fuel is injected into the chamber through fuel injectors with very high pressure of about 10,000 psi to 30,000 psi in the form of fine mist
- Since no spark plug is present to produce spark, the heated air will ignite the fuel that is injected into the combustion chamber with high pressure
- In order to withstand high pressure and a temperature of about 400 degrees, fuel injectors of the system are built sturdier compared to that of fuel injectors of the gasoline fuel injection system
- Some of the diesel engine cars have glow plugs
- When the car is idle for a long time or put in cold weather conditions, the temperatures of the cylinders and combustion chambers will be very low. In such situations, the air in the combustion chamber will not get heated enough for ignition
- Glow plugs help in warming up and increasing the temperatures of the cylinders and combustion chambers, creating the ideal condition for ignition
An important aspect of ignition is that in both the engines, the explosions happen at the right time with the right amount of air and fuel. Otherwise, it leads to critical performance issues in cars such as knocking and toxic emissions that lead to decrease in power and durability of the engine.