Types of Fuel Injection System

June 11, 2021

Mechanic is cleaning the fuel injector.

Old cars have the carburetor for regulating their speed and acceleration. The carburetor does this by regulating the ratio of fuel and air that goes into the engine. But with the onset of the fuel injection system, contemporary cars are now equipped with a more efficient way of varying speed. 

The fuel injection system was first introduced in the 70s. With its inception, cars were able to gain more power and fuel efficiency. The technology had been developed earlier than that time. Yet, it was only at that time when it was considered a better system for delivering fuel.  

We now reap the benefits of using the fuel injection system when we drive our modern cars. Yet, it would be good to note that fuel injection systems vary from each other. In fact, some fuel injection systems are far better than others. 

Hence, before you buy a car, you should at least learn about the type of fuel injection system it has. You should also learn what effects does a certain type of fuel injection system have on car performance. So, in this post, you will learn about the various types of fuel injection systems. 

Basic Types of Fuel Injection Systems

In this post, you will know the different types of fuel injection systems: Fuel injection systems come in four basic types. 

  • Single-point or Throttle Body Injection (TBI)
  • Port or Multipoint Fuel Injection (MPFI)
  • Sequential Fuel Injection (SPFI)
  • Direct Injection

1) Throttle-Body Injection (TBI)

This type of fuel injection is the simplest and earliest form of the fuel injection system. It was the one that replaced the carburetor with its 1 or 2 injector nozzles along the throttle body. The throttle body, of course, is known as the throat of the engine’s air intake system. 

The single point injection is basically the precursor to the complex multipoint system. It may be a far cry from the contemporary fuel injection systems that we have right now. But it offers far better control than that of the carburetor. Moreover, it is less expensive and requires less service.  

The throttle body injection (TBI) system is one of the pioneering types of fuel injection systems that had become available for cars. The carburetors that it replaced are not highly accurate when it comes to fuel mixing. Hence, with the introduction of TBI, the whole car manufacturing world quickly adapted its use. 

TBIs work like a carburetor. It still enables fuel to be sucked into the cylinders due to the suction power of the engine. However, the control of the TBIs is wrought by an electronic computer found in the vehicle. This computer does the determination of the fuel amount that should go into the engine. Thus, TBIs come with better accuracy in fuel usage. It also prevents the wasting of fuel and increases the efficiency of vehicles. 

2) Multipoint Fuel Injection (MPFI)

The multipoint fuel injection comes with a separate injector nozzle for each cylinder. This separate injector nozzle is found right outside of its intake port. Because of this, the system is often referred to as “Port Injection.”

The good thing about the MPFI is that it shoots the fuel vapor near the intake port. This setup ensures that the fuel vapor will be completely drawn into the cylinder. One great innovation of MPFI over TBI is that it measures fuel better than TBIs. Thus, it provides a more precise air-fuel ratio. It does away with the prospect of the fuel condensing or collecting in along the intake manifold. Thus, it is a remarkable improvement over the TBIs. And it does away with the major issues that hounded the carburetors and the TBI systems. It offers, therefore, better fuel efficiency. 

Since it does away with the issues that hounded TBIs and carburetors systems, the intake manifold can now be made from light-weight material. It can now be wrought in plastic material. Thus, the MPFI allows engineers enough room for flexibility in their engine designs. 

3) Sequential Port Fuel Injection (SPFI)

Sequential fuel injection is like that of the MPBI. Yet, there is one crucial difference between the two systems. This crucial difference, however, spells out which is better between the two. This difference also solved the critical issue that hounds MPBI. 

Sequential fuel Injection is a timed injection of fuel. This means that it triggers the nozzle individually at the most opportune time. This ensures that the fuel will make it to the intake valve. This process is an improvement over the MPBI. It also helps reduce fuel waste. Thus, this system offers the most optimized balance between air and fuel.

The other name for sequential fuel injection is sequential port fuel injection (SPFI). As a timed injection, it has a multi-port injection. Basic MPFI systems also have multiple injectors. Moreover, these injectors spray their fuel all at the same time. This results in fuel hanging around a port for 150 milliseconds when the engine idles. 

You may think that this is just a micro-fraction of a second. Yet, it is a shortcoming that needs to be addressed. Thus, engineers came up with solutions via the SPFI system. Engineers made the SPFI to independently trigger each injector nozzle. They perfectly timed the spraying of fuel before or when the intake valve opens.

4) Direct Injection

The direct injection system varies from other systems. It basically bypasses the intake valves. Instead, it deposits fuel right into the combustion chamber of the cylinder. In a way, this system pushes the fuel injection system to the hilt. It injects fuel directly into where the combustion happens. So, it bypasses the valves. This system is more common among diesel engines. Yet, this system is slowly creeping into the designs of gasoline engines likewise. 

The direct injection system is also referred to as direct-injection gasoline (DIG). It exhibits a more precise fuel metering. It offers engineers another option for precisely influencing the combustion process in the cylinders. So, it also pushes engineers to further scrutinize the air-fuel mixture dynamics. It also drives them to learn about how the internal explosion moves from the ignition point.

Other factors that affect how the internal combustion is wrought inside the engine. These factors include the cylinder’s shape and pistons, the locations of the port and the spark plug, the timing, intensity, and duration of the spark, and how many spark plugs per cylinder. Hence, the direct injection system can be further developed to come up with a lean-burning and low emission engine design. 

How Does Fuel Injection System Work?

Fuel metering is the process by which the necessary amount of fuel is determined and is delivered into the engine. Somewhere in the past, mechanical metering had been used. Yet, in our contemporary time, the method used now is electronic metering. 

There are factors to consider when determining the amount of fuel needed by the engine. One is the amount of air (weight). This refers to the amount of air that goes into the engine to make combustion possible. Moreover, contemporary systems make use of a mass airflow sensor. This sensor sends information to the control unit of the engine. 

The engine control unit also uses the data about the amount of power output needed by the driver (engine load). This data is usually provided by the throttle position sensor (TPS). 

Other sensors also help in providing information to the engine control unit. Sensors like the coolant temperature sensor, the camshaft position sensor, and the oxygen sensor all contribute to providing data on how well the combustion is happening in the engine. 

Fuel is also sent to the fuel tank via fuel lines. This fuel is then pressurized using fuel pumps. The fuel regulator makes the regulation of the fuel pressure. More often, a fuel rail divides the supply of fuel among the required number of cylinders. Then, the fuel injector injects the fuel into the intake air. 

The fuel injection systems depend on the continuous flow of fuel. Vehicles likewise come with an anti-surge vessel. This anti-surge vessel prevents fuel starvation due to lateral G-forces. This anti-surge vessel either comes in a small anti-surge tank or is often integrated with the tank of fuel.