Engine theory and operation

Engine Theory and Operation

  • Compression ignition engine, or diesel engine, operates on the principle of self-ignition from where it gets its name.
  • Operates based on the Diesel cycle, where air is compressed leading to a rise in temperature, and fuel is subsequently injected, causing the mixture to ignite.
  • The cycle consists of four strokes: intake, compression, power, and exhaust, known as the four-stroke cycle.
  • Intake stroke involves the piston moving from the top to the bottom of the cylinder, creating a vacuum that draws in air.
  • Compression stroke happens after the intake valves close, and the piston compresses the air, resulting in a high temperature.
  • During the power stroke, diesel fuel is injected precisely timed to cause ignition and push the piston down.
  • The exhaust stroke then expels the burnt gases from the cylinder.

Engine Components

  • Diesel engine can be identified in terms of a series of components such as the engine block, cylinder head, pistons, injectors, valves, and crankshaft.
  • Engine block serves as the structure within which the cylinders and other components are housed.
  • Cylinder head contains the valves and forms the top of the combustion chamber.
  • Pistons move up and down within the cylinders, generating power from the ignited fuel-air mixture.
  • Injectors deliver diesel fuel into the cylinder, timed precisely for the power stroke.
  • Valves control the intake of air and the expulsion of exhaust gases from the cylinders.
  • Crankshaft converts the linear motion of the pistons into rotation.

Engine Operation

  • Diesel engine ignites fuel by high compression, where compressing air in the cylinder causes its temperature to rise.
  • Fuel injection occurs when the piston is near the top of the compression stroke, and the high temperature causes the fuel to ignite.
  • Compression ratio is far greater in diesel engines compared to petrol engines due to the need for creating high temperatures, generally ratios are between 14:1 and 25:1.
  • Power stroke involves the high pressure generated by the ignition of the fuel pushing the piston down the cylinder, producing power.
  • The burnt gases are then expelled from the cylinder through the exhaust valve during the exhaust stroke.
  • Diesel engines usually employ a turbocharger to compress the intake air and deliver more oxygen to the cylinders, generate more power and improve engine efficiency.