Diesel Engine vs Petrol Engine

The petrol and diesel fuels are energy dense liquids. Both fuels produce large quantities of heat when burns inside the cylinders. The energy thus produced is the source of power for the engine. The fuel burns inside the cylinder causing the trapped air inside the cylinder to expand forcefully. The expansion of air results in driving down the piston. This force is transferred to the piston rod. The piston rod drives the crankshaft. The crankshaft drives the gearbox, driveshaft and finally wheels.

Diesel engines operate at higher pressures. Diesel engines rotate more forcefully and have higher torque. Petrol engines operate at lower pressures. So they are more lightly constructed. Petrol engines rotate more quickly. This results in higher horsepower.

Petrol engines pre-mix the air and fuel. The mixture is conveyed into the engine cylinder. The mixture is compressed. A spark plug is used to ignite the air-fuel mixture. Diesel engines compress air inside the engine cylinder to higher temperatures. The fuel is sprayed into the compressed air using a fuel injector resulting in combustion.

Diesel engines have longer and narrower engine cylinders. Thus maximum pressure can be created for combustion. One stroke of the piston takes more time, but produces more torque. Petrol engines have shorter and flatter engine cylinders. One stroke of piston takes considerably less time. This causes faster spinning and more horsepower. Turbochargers and direct fuel injection systems are applied to new age diesel engines to generate more horsepower by speeding up the spinning process.

Diesel engines have a wider power band. So fewer gear changes are required resulting in more comfortable drive.