Sylvie Willis
Fuel injection systems have evolved considerably over the past century, from carburetors to single-point injectors to today's direct fuel injection systems. There are several types of fuel injection systems, which differ in mechanism and working principles. The four main types of fuel injection systems are single-point injection, multi-point injection, sequential injection, and direct injection.
| Characteristics | Values |
|---|---|
| Number of injection points | Single-point, Multi-point, Sequential |
| Air-fuel mixture formation | External, Internal |
| Injection type | Direct, Indirect |
| Injection system | Continuous, Intermittent |
| Injection method | Air-blast, Common-rail |
| Fuel injection system | Carburetor, Fuel injection |
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What You'll Learn
Single-point injection
However, single-point injection is considered somewhat outdated today. It is less efficient than other fuel injection systems, with lower fuel economy. It also results in an ununiform fuel supply to all cylinders, and wets the intake manifold by forming a layer of fuel on it.
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Multi-point injection
In a multi-point injection system, a separate injector nozzle is devoted to each cylinder, positioned just outside its intake port. The fuel vapour is sprayed into the intake port, and the suction created by the piston sucks the atomized fuel with air through the intake valve opening. This ensures that the fuel vapour is almost entirely drawn into the cylinder.
The Bosch Motronic multi-point fuel injection system was the first mass-produced system to use digital electronics, and it played a significant role in the transition from carburettors to fuel injection systems in the 1980s and 1990s.
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Sequential injection
Fuel injection systems have evolved considerably over the past century. Modern injector systems are controlled electronically and are much more accurate, eco-friendly, and efficient than their carburetor predecessors.
One of the most common and effective systems currently in use is Sequential Injection, also known as Sequential Port Fuel Injection (SPFI) or timed injection. Sequential Injection is a type of multiport injection where each injector nozzle is triggered independently, rather than all at once or in groups. This means that the fuel is sprayed immediately before or as the intake valve opens, reducing the amount of time that fuel "hangs around" in the port. This improves efficiency and emissions, and ensures that the fuel is always completely drawn into the cylinder.
In a sequential fuel injection system, the fuel injectors function in coordination with the cylinders they are connected to. Each injector only injects fuel when the intake valve of the cylinder opens and remains idle for the rest of the steps. An ECU (Engine Control Unit) monitors the movement of the cylinders and triggers the injectors only when required. This system is more effective and efficient than other fuel injection systems, and most of today's engines have sequential fuel injection systems.
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Direct injection
The use of direct injection, also known as gasoline direct injection (GDI) or petrol direct injection (PDI), has been credited with boosting fuel efficiency and reducing CO2 emissions. GDI engines first appeared in the 1920s for low-compression truck engines and were later used in some German cars in the 1950s. However, the technology remained rare until an electronic GDI system was introduced in 1996 by Mitsubishi for mass-produced cars. In recent years, GDI has seen rapid adoption by the automotive industry, with its usage increasing significantly in the United States between 2008 and 2016.
While direct injection offers improved fuel efficiency and reduced emissions, it has also been associated with increased carbon buildup on the intake valves and ports. This is due to the fuel not washing over them as it does in port injection systems. Regular cleaning of the fuel injectors and intake system is recommended to mitigate this issue. Additionally, direct injection engines may be more prone to fuel dilution in the oil, which can reduce its effectiveness and lifespan, so it is important to change the oil at recommended intervals.
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Common-rail injection
The common rail system was first prototyped in the 1990s and has since been refined and mass-produced. The first passenger car to use this system was the 1997 Alfa Romeo 156 with a 2.4-L JTD engine. The technology was further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, and the first common-rail-diesel-engine used in a road vehicle was the MN 106-engine by East German VEB IFA Motorenwerke Nordhausen in 1985.
The common rail system is widely used in diesel engines and is also the basis of gasoline direct injection systems used in petrol engines. It is particularly effective in meeting stringent emission control standards, as it provides flexibility in fuel injection timing, quantity, and pressure. The higher the injection pressure, the better the fuel atomizes during injection and mixes with the oxygen in the cylinder, resulting in virtually complete combustion.
Some advanced common rail fuel systems can perform up to five injections per stroke, and the engine's electronic control unit can inject a small amount of diesel before the main injection event to reduce explosiveness and vibration, optimizing injection timing and quantity for variations in fuel quality and cold starting.
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