In this article , we discuss the fuel supply system in diesel engines.
In this article:
1. What Is a Fuel Supply System in a Diesel Engine?
The fuel supply system in a diesel engine is designed to deliver clean, pressurized diesel fuel directly into the combustion chamber. This process occurs under high pressure, and the injection is precisely timed for maximum power, combustion efficiency, and low emissions.
2. Main Components :
✅ Fuel Tank
Holds a reserve of diesel until it’s needed by the engine.
Usually made of metal or composite material.
✅ Fuel Lift Pump
Transfers diesel from the tank toward the injection pump.
Usually a low-pressure, mechanical or electric pump.
✅ Fuel Filter
Removes dirt, sediments, and water from the diesel.
Provides clean fuel to avoid damage to injection components.
✅ Injection Pump
Generates high pressure and controls delivery of the correct amount of diesel to each injector.
Some types include in-line, distributor, or unit injection pumps.
✅ High-Pressure Fuel Lines
Carry pressurized diesel from the injection pump to the injectors.
✅ Fuel Injectors
Atomize the diesel and spray it directly into the combustion chamber.
Controlled by pressure, delivery, and timing signals.
✅ Return Lines
Carry excess or leaked diesel back to the tank, helping regulate pressure and temperature.
Working Principle :
- The fuel lift pump draws diesel from the fuel tank through the filter.
- The cleaned diesel reaches the fuel injection pump.
- The injection pump pressurizes the diesel to a very high pressure (typically 100–1600 bar).
- This high pressure is routed through high-pressure lines toward each fuel injector.
- At the proper moment — typically near top dead center of compression — the injector sprays a fine mist of diesel directly into the combustion chamber.
- The high temperature and pressure in the cylinder cause the diesel to spontaneously ignite without a spark.
- Combustion pushes the piston down, delivering power.
Types of diesel injection systems :
1. Individual Pump System (One-Pump-Per-Cylinder)
Each cylinder has its own high-pressure injection pump, offering precise control but adding complexity.
2. Distributor Pump System:
A single high-pressure pump feeds all cylinders through a distributor, simplifying design while retaining control.
3. Common Rail Direct Injection (CRDI)
A high-pressure rail stores pressurized diesel, and electronically controlled injectors spray it directly into each cylinder — delivering high power, low emissions, and greater efficiency.
4. Unit Injection System
The injector and pump are integrated into a single unit for each cylinder, reducing high-pressure lines and improving injection accuracy.
5. Electronic Control with Sensors (for Precise Timing)
This system uses electronic sensors (such as crankshaft, camshaft, pressure, and temperature sensors) alongside a control unit (ECU) to calculate the exact moment and duration of injection.
This results in more accurate fueling, improved combustion, higher power output, greater fuel efficiency, and reduced emissions — all tailored to the engine’s current operating conditions.
Also Read: Types of diesel injection system in detail.
Summary
The diesel fuel supply system is designed to provide pressurized, atomized, clean diesel directly into the combustion chamber. This guarantees maximum power, high compression, greater fuel efficiency, and reduced emissions, reflecting the robustness and reliability for heavy-duty applications.
Also Read: Fuel injection system in Petrol Engines.
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