In this article, we discuss the 5 types of fuel injection systems used in diesel engines.
In this article:
1. Individual Pump System (Jerk Pump)
🔹 Diagram
Picture each cylinder with its own small high-pressure pump placed alongside it, directly connected to its respective injector.
🔹 Working Principle:
- The engine’s camshaft drives each plunger upward.
- This upward movement pressurises the diesel in its delivery chamber.
- Once pressure reaches a certain point, delivery valve opens and diesel is forced through the high-pressure pipe into the injector, which then atomises the diesel into the combustion chamber.
🔹 Application:
- Large, heavy-duty diesel engines (ships, heavy trucks).
- Applications where robustness and ease of maintenance are desirable.
🔹 Pros:
- Reliable and simple mechanical components.
- Durable — can handle heavy workloads.
- Each cylinder’s delivery is independent.
🔹 Cons:
- Large number of components — more complex to service.
- Less compact; not lightweight.
- Less flexible control over injection pressure and timing.
2. Distributor Pump System (Distribution or VE, CAV)
🔹 Diagram (concept):
Picture a single rotary pump with a distributor rotor. The rotor internally routes high pressure to each injector in turn.
🔹 Working Principle:
- The drive plate drives a rotating plunger.
- The plunger pressurises the diesel.
- The distributor then directs high pressure to each cylinder’s injector in the correct sequence.
🔹 Application:
- Smaller diesel engines (light trucks, buses).
- Automotive applications where space and simplicity are desirable.
🔹 Pros:
- Compact, lightweight, cost-effective.
- Few moving components.
- Reliable delivery under medium-load conditions.
🔹 Cons:
- Limited pressure delivery (lower than unit or common rail).
- Less flexible for sophisticated injection strategies.
- May struggle under heavy-load or high-demand conditions.
3. Unit Injector System
🔹 Diagram (concept):
Picture each cylinder with its own pump and injector integrated together in a single unit — typically placed directly into the cylinder head.
🔹 Working Principle:
- The engine’s camshaft directly drives the plunger within each injector.
- This generates high pressure directly at the injector.
- The delivery valve then opens, spraying diesel into the combustion chamber.
🔹 Application:
- Large diesel engines (trucks, buses).
- Applications requiring high pressure, simplicity, and robustness.
🔹 Pros:
- Precise delivery; high injection pressure.
- Few components — high robustness.
- Reliable under heavy-load conditions.
🔹 Cons:
- Requires specialized maintenance.
- Higher production and repair costs.
- Limited ability to respond to electronic controls (compared to Common Rail).
4. Unit Pump System
🔹 Diagram (concept):
Picture each cylinder with its own high-pressure pump, connected by a short high-pressure pipe to its respective injector.
🔹 Working Principle:
- The separate pump generates pressure.
- This pressure is routed through delivery lines to each injector.
- Injection occurs when pressure reaches a set point.
🔹 Application:
- Large heavy-duty diesel engines.
- Applications requiring high pressure with flexible delivery.
🔹 Pros:
- Reliable delivery under heavy-load conditions.
- Flexible — separate pump from injector for ease of maintenance.
- Better pressure control than distributor pump.
🔹 Cons:
- Higher complexity.
- Large number of components.
- Requires careful maintenance to avoid pressure drop.
5. Common Rail Injection System
🔹 Diagram (concept):
Picture a high-pressure rail (fuel accumulator) connected to each injector. The rail maintains high pressure at all times.
🔹 Working Principle:
- A high-pressure pump maintains pressure in the rail.
- Each injector is controlled by a solenoid valve.
- The engine control unit (ECU) signals when to release fuel into the cylinder.
🔹 Application:
- Modern diesel engines — from small cars to heavy-duty trucks.
- Applications requiring high power, low emissions, and sophisticated control.
🔹 Pros:
- Precise control of injection pressure, duration, and number of events.
- Flexible delivery for optimizing performance and emissions.
- Higher pressure (typically up to 2000 bar or greater).
🔹 Cons:
- Higher complexity and cost.
- Requires sophisticated electronic controls.
- Maintenance and repairs can be more expensive.
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