Rajan Wilcox
A diesel fuel injection pump is a device that supplies fuel to the engine. It works with other fuel system parts to send pressurised fuel to the fuel injectors, which release it into the combustion chamber. The pump develops great pressure, typically 15,000 psi or more in newer systems. This high pressure allows for greater responsiveness and easier maintenance of the injection system. Diesel fuel injection pumps can be mechanical or electric, with mechanical pumps using a rotary plunger with pistons to meter out the necessary amount of fuel, while electric pumps are controlled by the engine control module (ECM).
Diesel Fuel Injection Pump Characteristics
| Characteristics | Values |
|---|---|
| Definition | A device that pumps fuel into the cylinders of a diesel engine |
| Function | Supplies the engine with fuel |
| Types | Mechanical or electric |
| Mechanical Pump Mechanism | Uses a rotary plunger with pistons to meter out the required amount of fuel |
| Electric Pump Mechanism | Fuel is pressurized according to required horsepower before being sent to the fuel injectors |
| Fuel Injection Timing | Very slightly before top dead centre of the cylinder's compression stroke |
| Injection Pressure | Can be as high as 620 bar (8992 psi) or 15,000 psi (100 MPa) in newer systems |
| Safety Mechanism | Incorporates a governor to cut fuel supply if the crankshaft rpm endangers the engine |
| Maintenance | Fuel filters should be replaced every 10,000 to 15,000 miles to remove debris |
| Lifespan | Can last between 100,000 to 200,000 miles |
| Historical Development | Earlier diesel pumps used an in-line layout with cam-operated injection cylinders; later designs, such as the Bosch VE pump, vary injection timing with crankshaft speed |
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What You'll Learn
How diesel fuel injection pumps work
A diesel fuel injection pump is the heart of a diesel engine. It supplies the engine with fuel, maintaining a rhythm or timing that keeps the engine running smoothly. The pump also controls the amount of fuel needed to gain the desired power.
The first diesel engines used compressed air to blast fuel into the combustion chamber. The first pumps to use plungers to force metered fuel into the combustion chamber were developed in the 1890s. In 1927, Bosch introduced the mass-produced helix-controlled inline pump. Inline injection pumps look like mini inline engines. They are constructed from separate pump and plunger units connected inline, one per cylinder. They are activated by a cam, which is mechanically connected to the engine. The earliest inline injection pumps delivered 3,000-5,000 psi of injection pressure. Newer systems can reach 15,000 psi or more.
In some fuel systems, fuel injection is coordinated with the generation of high pressure. The start of delivery is when the high-pressure pump starts to deliver fuel to the injector. The difference between the start of delivery and the start of injection is known as injection delay. The end of injection (EOI) is when fuel injection stops.
There are two main types of fuel pumps: mechanical and electric. Mechanical fuel pumps use a rotary plunger with pistons to meter out the amount of fuel needed to power the engine. They send low-pressure fuel to the injectors, which build pressure until the nozzles release the fuel into the combustion chamber. Electric fuel pumps are used in common rail injection and are controlled by the engine control module (ECM). They pressurize the fuel according to the required horsepower before sending it to the fuel injectors, which then open on an electronically timed system.
Modern injection systems reach very high injection pressures and use sophisticated electronic control methods. The performance of diesel engines is heavily influenced by their injection system design.
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Types of diesel fuel injection pumps
A diesel fuel injection pump is an essential component of a diesel engine, responsible for pumping fuel at high pressure directly into the engine's combustion chamber. This process is known as the Direct Injection (DI) method. The pump ensures that the fuel is efficiently delivered from the tank to the combustion chamber without any loss in volume or pressure.
There are several types of diesel fuel injection pumps, each with unique characteristics:
In-line Fuel Injection Pump
The in-line fuel injection pump is one of the mechanically-controlled diesel fuel systems. It matches the number of engine cylinders with an equal number of fuel pressure mechanisms. This pump is commonly used in medium to large trucks and construction machinery. A camshaft drives the fuel pressure and injection quantity control mechanisms within the pump body. Inline pumps are preferred for heavy-duty diesel engines as they can generate high pressure.
Distributor (Rotary) Fuel Injection Pump
The distributor injection pump is another mechanically-controlled diesel fuel pump. Unlike the in-line pump, it has just one fuel pressure mechanism regardless of the number of engine cylinders. The distributor is designed to follow an injection order to distribute pressurised fuel to each cylinder. This pump is controlled electronically by sensors, an electronic control unit, and an actuator.
Common Rail Fuel Injection Pump
The common rail fuel injection pump is an electronically-controlled diesel fuel supply system. It consists of a supply pump, common rail, electronically-controlled injectors, sensors, and a computer that manages all these devices. The engine drives the supply pump, producing high-pressure fuel, which is then distributed to the injectors mounted on each cylinder. This system allows for finer control of injection volumes and higher pressures compared to mechanical systems.
Mechanical and Electric Fuel Pumps
Mechanical fuel pumps use a rotary plunger with pistons to meter out the required amount of fuel to power the engine. They send low-pressure fuel to the injectors, which then build pressure. Electric fuel pumps, on the other hand, are used in common rail injection systems and are controlled by the engine control module (ECM). They pressurise the fuel according to the required horsepower, making the injection system more responsive and easier to maintain.
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History of diesel fuel injection pumps
The history of diesel fuel injection pumps dates back to the end of the 19th century when Rudolf Diesel invented the first commercially successful compression-ignition engine. This early diesel engine offered lower fuel consumption, the ability to use cheaper fuel, and higher power output potential compared to spark ignition engines. However, the fuel injection systems of that time were not designed for high-speed operation, and the weight of the air compressor needed to operate the injection equipment limited their suitability for road vehicles.
In the 1920s, German engineer Robert Bosch developed the in-line injection pump, which is still widely used today. This innovation employed hydraulic systems to pressurize and inject fuel, eliminating the need for a separate air compressor and enabling much higher operating speeds. Bosch's in-line injection pump played a pivotal role in the subsequent adoption of diesel engines for stationary and marine applications over the following decades.
During the 1950s and 1960s, diesel engines gained popularity for use in taxis and vans, but it wasn't until the oil price hikes of the 1970s that they began to attract serious attention in the small passenger car market. VW's introduction of the diesel-powered Golf in 1977 marked a significant milestone, as it was the first diesel car designed to appeal to drivers who would traditionally opt for petrol engines. This vehicle utilized indirect injection and a distributor-type pump, delivering performance comparable to smaller petrol engines.
In the following years, the small diesel engine gained traction in cars, 4WDs, and light commercial vehicles due to its fuel economy, longevity, and environmental advantages. Advancements in technology have led to the evolution of injection pumps, progressing from manually controlled systems to modern electric common rail systems. These improvements have enhanced fuel efficiency, emission control, and engine performance.
Today, diesel engines commonly use fuel transfer pumps, which are driven by the engine to automatically supply fuel to the injection system. Modern injection pumps, often referred to as jerk pumps, utilize the plunger and cam method of fuel injection. These pumps play a critical role in powering the vehicle by igniting the fuel-air mixture, resulting in an explosive force that propels the vehicle forward. The sole function of the fuel injection pump is to supply diesel fuel to the injectors with precision, ensuring efficient combustion and the desired power output.
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Maintaining diesel fuel injection pumps
A diesel fuel injection pump is a device that pumps fuel into the cylinders of a diesel engine. It is an important part of the fuel supply system of the diesel engine, and its working condition directly affects the power, economy, and reliability of the engine.
- Use clean and reliable diesel fuel: The quality of diesel fuel can impact the performance of the fuel injection pump. It is important to select a diesel fuel that meets the brand's requirements and to allow it to deposit for at least 48 hours before use.
- Regularly replace the fuel filter: A clogged fuel filter can block the flow of fuel, leading to engine stalling. It is recommended to replace the fuel filter every 40,000 miles or every 10,000 to 15,000 miles, depending on the source.
- Maintain fuel levels: Driving with a low fuel tank can cause issues with the diesel fuel injection pump. It is recommended to maintain a minimum of ¼ to ¼ tank of fuel or more to prevent air and contaminants from being drawn into the fuel pump.
- Check fuel pressure: Monitoring fuel pressure can help determine if the pump and injectors are functioning properly.
- Inspect the seal of the oil outlet valve: Checking the seal can provide information about the wear of the plunger and the working condition of the oil pump, helping to determine the necessary repair and maintenance methods.
- Maintain accessories: Ensure that the side cover of the pump body, dipstick, filler plug, oil spill valve, oil pool plug, oil level screw, and oil pump fixing bolt are all intact and functioning properly.
- Preventative maintenance: Regularly inspect and maintain the diesel fuel injection pump to prevent issues and guarantee its long-term functionality.
By following these maintenance tips, diesel vehicle owners can help keep their fuel injection pumps functioning properly and extend their service life.
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Diesel fuel injection pumps vs. gasoline engine pumps
A diesel fuel injection pump is a device that pumps fuel into the cylinders of a diesel engine. It works with other fuel system parts to send pressurised fuel to the fuel injectors, which release it into the combustion chamber.
Diesel and gasoline engine pumps have the same purpose: to send fuel from the fuel dispenser to the engine cylinders. They are both lubricated by the fuel itself. However, their designs are different. For instance, gasoline engines inject fuel with a pressure between 10 and 60 pounds per square inch (PSI), while diesel fuel injection systems operate between 10,000 and 30,000 PSI. This is because diesel fuel is denser than gasoline and requires higher pressure to vaporise.
Another difference is in the timing of fuel injection. Diesel injection pumps must be timed precisely to inject the fuel at a particular moment in the compression stroke, while petrol injection pumps deliver the fuel in sync with the engine's intake stroke.
Furthermore, diesel engines do not require spark plugs for fuel ignition, unlike gasoline engines. Instead, the fuel is ignited using extremely compressed air provided by the injection pump.
In terms of durability, diesel injection pumps tend to be more durable and robust due to their design, which can withstand the high pressures involved in diesel engine operation.
Mechanical pumps are being phased out in both diesel and gasoline engines to comply with international emissions directives and increase performance and economy. Advancements in injection pump design, such as the shift to electric common rail systems, have led to improved fuel efficiency, emissions control, and engine performance.
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Frequently asked questions
A diesel fuel injection pump supplies fuel to the engine. It works with other fuel system parts to send pressurised fuel to the fuel injectors, which release it into the combustion chamber.
A fuel pump may be mechanical or electric. Mechanical fuel pumps use a rotary plunger with pistons to determine the amount of fuel needed to power the engine. Electric fuel pumps are used in common rail injection and are controlled by the engine control module (ECM).
The injection pump collects debris, soot or carbon flowing through the fuel supply. It also prevents the engine from being damaged by cutting the fuel supply if the crankshaft rpm endangers the engine.
An injection pump will typically last between 100,000 and 200,000 miles.
Examples of diesel fuel injection pumps include the BOSCH VP30, VP37, and VP44.
