2.1.2 Diesel Engines Explained

Key Concepts

• Compression Ignition
• Fuel Injection
• Turbocharging
• Common Rail Fuel System

Compression Ignition

Diesel engines operate on the principle of compression ignition, where air is compressed in the cylinder to a high temperature, igniting the fuel. This is different from gasoline engines, which use a spark plug to ignite the fuel-air mixture. The high compression ratio in diesel engines (typically 14:1 to 25:1) ensures that the air reaches a temperature high enough to ignite the diesel fuel spontaneously when it is injected into the cylinder.

Example: Think of a diesel engine as a pressure cooker. Just as the pressure cooker uses high pressure to cook food quickly, the diesel engine uses high compression to ignite the fuel without the need for a spark.

Fuel Injection

Fuel injection in diesel engines is a precise process that ensures the fuel is delivered to the combustion chamber at the right time and in the right amount. This is crucial for efficient combustion and optimal engine performance. The fuel injector, which is a high-pressure nozzle, sprays the fuel into the cylinder in a fine mist, allowing it to mix with the compressed air and ignite.

Example: Imagine a fine spray nozzle used to water delicate plants. Just as the nozzle ensures the water is distributed evenly and precisely, the fuel injector ensures the diesel fuel is sprayed into the cylinder in a controlled manner.

Turbocharging

Turbocharging is a technology that increases the power output of a diesel engine by forcing more air into the combustion chamber. A turbocharger uses the exhaust gases from the engine to spin a turbine, which in turn compresses the incoming air, increasing its density. This allows more fuel to be burned, resulting in more power and better fuel efficiency.

Example: Think of a turbocharger as a windmill that captures the energy of the wind to generate electricity. Similarly, the turbocharger captures the energy from the exhaust gases to compress the incoming air, enhancing the engine's performance.

Common Rail Fuel System

The common rail fuel system is an advanced fuel injection technology used in modern diesel engines. It features a high-pressure fuel rail that supplies fuel to each injector. The fuel pressure is maintained at a constant level, allowing for precise control over the injection timing and duration. This results in smoother engine operation, reduced emissions, and improved fuel efficiency.

Example: Consider a common rail fuel system as a water distribution network in a city. Just as the water network ensures a steady supply of water to each household, the common rail system ensures a constant supply of high-pressure fuel to each injector, providing consistent performance.