Fuel Supply System in Diesel Engines - Details of Nozzles and Injectors

A fuel supply system in a diesel engine aims to inject the right amount of pressurized and automated fuel into the engine at the right time. As a result, combustion in a diesel engine occurs when fuel mixes with hot compressed air.

This process involves working with various components, including fuel injection systems, fuel injectors and others. The details are provided below!

A fuel supply system in a diesel engine provides measures, injects and atomises the fuel. Thus, it is also referred to as the "heart" of an engine. Apart from it, the types of injectors directly affect how well an engine performs.

Additionally, fuel injection systems are more expensive since they are produced with remarkable accuracy.

Fuel will flow either due to gravity or through a fuel feed pump, which is available to give energy to an injection pump through a filter. Then, it supplies the cylinder heads' built-in injectors with fuel.

1. Air Injection System

In this system, the air is first compressed using a compressor to very high pressure. After that, fuel is metered and pumped to a nozzle, which is also connected to a source of high-pressure air.

Next, when this nozzle is opened, the air blows the gasoline into the engine and delivers a well-atomised spray. However, since this system is expensive and complicated, this method is no longer used.

2. Solid Injection System

People mostly replace the injection method with this one. This is a direct injection of the atomised, under-pressure fuel into the combustion chamber.

Above all, it requires a pump to supply the gasoline at high pressure (as high as 300 bar abs). Also, it can be further divided into the three following widely employed systems

3. Common Rail System

In this instance, filters allow fuel to pass from the storage tank to a low-pressure pump. The low-pressure pump moves fuel from the high-pressure pump to the common rail.

As a result, high-pressure fuel is gathered in the common rail, and the necessary amount of fuel is then sent to the injectors and cylinders via metering devices. This method is typically used with multi-cylinder and Cummins engines.

4. Individual Pump System

In this case, fuel passes through filters, low-pressure pumps, and the storage tank. This low-pressure pump distributes the fuel to 4 different metering and pressure pumps.

The fuel will be pumped to individual injectors that are available in the cylinder heads using these independent metering and pressure pumps. Also, these are employed in big, slow-moving engines.

5. Distributor System

In distributor systems, fuel will move from a storage tank through filters to the low-pressure pump, then to the metering and pressure pumps. This fuel distributor device distributes and sends the necessary amount of fuel to each injector and cylinder using the fuel metering and pressure pump. Later, it is made use of in small and medium-sized engines.

6. Multipoint Fuel Injection System

At all engine speeds and loads, a multipoint fuel injection system is utilised to provide an air-fuel mixture of the right strength. It helps in providing the necessary quantity to each cylinder of a multi-cylinder engine.

In diesel engines, there are 3 types of nozzles those are:

• Single Hole: These are nozzles with 0.2 mm diameter and are primarily used in combustion chambers. Good mixing of air is challenging in this case. Also, it has the tendency to dribble.
• Multiple Holes: The usual size of multiple hole-type nozzles is 0.35 to 1.5 mm and generally has 4 to 18 holes.
• Pintle: In this case, the spindle is equipped with a projection called a pintle. It prevents weak injection and dribbling, which peeks out from the nozzle's mouth. Moreover, you can also find a conical or cylindrical form of the nozzle to avoid dribbling.

Primarily, there are three types of injectors:

• Air Blast Injectors: These are utilised in systems that inject air. However, methods for injecting air are no longer used since they call for multistage compressors. Therefore, these injectors are no longer in use.
• Mechanically Operated Injectors: The same mechanism that was once used to run IC engine valves now operates them.
• Automatic Fuel Injector: All automotive CI engines use these Automatic Fuel Injectors. They consist of a needle valve that raises the fuel pressure. Apart from it, the gasoline pump is what generates this fuel pressure.

Electronics were first introduced in 1965, and now electronic components account for about 30–40% of the cost of automobiles. In this regard, electronics and computers are used in cars to get maximum power and optimum economy.

Electronic fuel injection systems use a variety of sensors to measure characteristics like temperature, gas pressure, throttle position, air flow rate, etc. Then the Electronic Control Unit (ECU), essentially a computer, receives this data via sensors. Later, this ECU processes the data and controls injectors or other devices to have optimum power, the best economy, and minimal emissions.

Regardless of the type of fuel supply system in a diesel engine, the purpose of a diesel fuel system remains unchanged. It is to precisely and timely inject pressurised and atomised fuel into each engine cylinder. In a diesel engine, combustion happens when this fuel surge and hot compressed air combine.