5 Types of Fuel Injection System in Diesel Engine

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The fuel system is used to supply fuel from the tank to the engine. This system is specifically designed for maximum engine performance.

In diesel engines, you may already understand that a diesel engine is a self ignition engine. This means that the combustion will occur by it self. The self ignition can arise because there are several factors.

The most dominant, because fuel atomizes in a chamber with high air pressure.

Air pressure in the chamber is higher than the diesel fuel flash point. That's what makes fuel burn spontaneously when atomize.

In the previous article we discussed in detail about the diesel fuel injection system. But there are still less.

How many fuel systems are there in the diesel engine?

We will discuss this in detail.

In general, there are only two types of diesel fuel systems, conventional and common rail. But if we see further, we will find several types.

A. Viewed from the injection method


Injection method means how the fuel is injected into the combustion chamber. There are two types, direct injection and indirect injection

1. Direct injection system

Direct injection system is a method of injecting fuel from a diesel fuel line directly into the combustion chamber (the combustion chamber is located above the piston).

The main feature of this system, the injector will lead directly to the combustion chamber. So that once fuel is injected, the fuel will go straight into the combustion chamber.

Another feature is in the shape of the piston surface, there are basin on the piston surface. The basin serves to spread injected fuel so that combustion can take place more evenly.

Advantages

  • A simpler design
  • Higher power output
  • Better thermal efficiency
  • Lower emissions
  • No glow plug require


Disadvantages

  • Need high compression pressure
  • Need a special injector (multi point injector)


This type is widely applied to weighted vehicles such as 8 wheel (or more) trucks, heavy duty machines.

2. Indirect injection system

Indirect injection (IDI) is a method of ignition by spraying fuel which is carried out in a special room called the pre-combustion chamber.

The main difference is in the injection method, the DI system fuel will be sprayed directly in the combustion chamber. But in the IDI, fuel is sprayed into the pre-combustin chamber, then after it burn, the expansion power will come out to the main combustion chamber to burn the remaining air in the main combustion chamber.

But today the IDI system is not applied by most manufacturers, because the process is longer, this type has many disadvantages compared to the DI system.

Therefore, on the recent IDI vehicles are rarely applied to commercial vehicles whether light or heavy vehicles.

B. Viewed from the injection mechanism


The injection mechanism is how to run fuel from the tank to the injector. There are three types, rotary fuel system, individual fuel system, and common rail system.

The difference is in the high pressure pump used.

1. Rotary fuel system
img by dieselnet.com

Rotary fuel systems use distributor or rotary vane pump.

This type has one shaft with a single plunger. Although there are four injectors, the number of plungers remains single.

How it works ? this plunger located in pump shaft that rotating. And every rotation angle there is a fuel barrel which when the plunger passes through the fuel barrel, the fuel will be injected into one injector.

So, if there are four injectors, there are four fuel barrels that surround the pump shaft.

Advantages
Does not take up much space, making it suitable for vehicles with limited space.
Little moving parts so that the energy produced is more effective.

Disadvantages
Fuel pressure is weak, making it less suitable for high capacity diesel engines.

2. Individual fuel system


Individual fuel system types have pump with individual inline type. That means, the number of plungers is adjusted by the number of injectors.

This is because each plunger will serve one injector, so that if there are four injectors, there are four plungers arranged in line.

How it works ? there is a camshaft where each cam will press one plunger with the right timing. When the plunger is pressed against the cam, the fuel will be sprayed.

It can be said, the number of cam equals the number of injectors, and the cam angle is also adjusted according to the ignition timming.

The main advantages are injection pressure which can reach 18,000 PSI. With that pressure, this pump is suitable to be applied to conventional diesel engines with large capacity.

3. Common rail system


Common rail is an electronic diesel fuel control scheme. That means, in the common rail system you will find a series of ECU-actuator sensors.

This is similar to an EFI system on a petrol engine but there are still differences.

The first difference is in the fuel pump. Common rail system, has two pumps. The first pump is to transferl fuels from fuel tank to the fuel line, and the second is high pressure pump to increase fuel pressure highly.

For a high pressure pump, it is also different from the two types above. The pump used on common rail is continuous, which means the pump will continue to press fuel with a stable pressure.

Meanwhile to control the fuel spraying, each injector will control it through an order from the ECU. In this type, the injector acts like a water tap that can be adjusted open and closed for a certain duration.

For more info about fuel injector, you can read this Understanding fuel injector working