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Fuel Injection Pump Working Principle in Diesel Engine

There are two types of injection pumps on conventional diesel engines, inline pump and distributor pump.

We have discussed the difference between the two types of pumps in the previous article, you can access these 3 types of fuel injection pump in diesel engines.

in this article, we will discuss in detail about the inline injection pump.

How does it work ? what are the components? we will discuss it all.

Definition of Inline Injection Pump

Inline injection pump is a high pressure pump on a diesel engine that is used to increase diesel fuel pressure up to 18,000 PSI individually.

That is, each injector will be served by a plunger unit.

It can be said, in a 4 cylinder diesel engine there are 4 injectors and 4 plungers.

The main characteristic of the inline injection pump, lies in the configuration of each plunger. Each plunger is placed in line above a camshaft pump.

That's where the name inline pump is taken. In addition to being called an inline pump, this type is also known as the individual pump because, as explained above, this type uses one plunger for each cylinder.

The main component of the inline injection pump

There are 5 main components in the inline injection pump,

  • Camshaft pump
  • Plunger
  • Fuel barrel
  • Fuel feed
  • Rack and pinion

The camshaft pump is used to drive the plunger in order to press the fuel. While the fuel barrel, is the place to hold fuel that will be pressed to the injector.

This is the configuration, the plunger is located above the camshaft and the fuel barrel is located above the plunger.

Rack and pinion is a mechanism to regulate the amount of fuel in the fuel barrel. This mechanism will regulate the diesel engine RPM.

Fuel feeds are fuel enter-exit door, there are three fuel feeds
inlet feed, used as fuel entrance from the tank to the pump
output feed, used as the fuel exit to the injector in high pressure conditions
return feed, used to drain the remaining fuel that is not pressed into the injector

And how does it work?

1. The outside mechanism of injection pump

Generally, there is a mini pump that is used to transfer fuel from the tank into the injection pump. This pump works mechanically, meaning it is driven by the crankshaft engine.

So, to run the fuel flow we need to crank the engine.

When the crankshaft rotates, the mini pump will send diesel fuel from the tank into the injection pump through the inlet feed. From the inlet feed, the fuel directly fill the fuel barrel and it is ready to be pressed.

2. The injection pump mechanism

The pump camshaft is connected to the engine crankshaft, so that when the engine cranks automatically the pump camshaft rotates.

This rotation will move the plunger, so that the plunger is pressed upwards and as a result the fuel that is already in the fuel barrel is pressed with high pressure and enters the injector.

When the cam has finished pressing the plunger, the plunger returns to the bottom position. This will reopen the fuel barrel chamber, so that the fuel from the inlet feed filling the fuel barrel directly.

3. Engine RPM setting mechanism

To adjust engine RPM on conventional diesel, it is done by adjusting the amount of fuel injected by the injector.

In this case, the control is located in the fuel barrel. How much the amount of fuel in the fuel barrel when it is pressed will affect the engine RPM.

it is the task of rack and pinion. These two components will regulate the amount of fuel in the fuel barrel by regulating fuel disposal through the return feed.

The amount of fule is less (Low RPM)

The amount of fuel is more (high RPM)

So, there is a fuel path inte plunger from the fuel barrel leading to the return feed.

This path is made with a certain slope, so that when the angle of the plunger is rotated, it will affect the amount of fuel contained in the fuel barrel

To be clearer you can see the picture (viewed from side)

a. when low RPM

The amount of pressed fuel is lower, so the angle of plunger can be seen from the picture.

2. when high RPM

The amount of pressed fuel is more, so the angle of plunger can be seen from the picture.

3 Type of Fuel Injection Pump With Definition and Differents

We know that the diesel engine is a self-ignition engine, that means the combustion is occur by itself.

However, combustion in diesel engines does not appear immediately but there are several trigers that cause combustion to occur. At least there must be two things, first high pressure air with a temperature greater than the flash point of the diesel fuel.

second, the fuel is atomize (pulverize) in the high pressure air. If the two trigers are fulfilled, then combustion will occur spontaneously.

To get atomize fuel, a fuel mechanism is needed. The mechanism will force fuel out of the narrow gap with high pressure. To increase the pressure of diesel fuel, we know a component called an injection pump.

Then, how many types of injection pumps are used in diesel engines? we will discuss in detail.

3 Types of Diesel Fuel Pumps

Maybe you only know there are only two types of injection pumps in diesel engines. But if we see further, there is one type that is actually applied to many recent vehicles.

1. Individual inline pump

An individual pump is a pump mechanism with an individual fuel delivery system. That means that each injector will be served by a plunger mechanism.

It can be say, the number of plungers is the same as the number of injectors.

However, all the plungers are placed together in one pump unit in a line position. That is what causes this pump also called the inline injection pump.

The main components of this type of pump, among others;

  • Camshaft with the number of cam according to the number of plungers
  • plunger which functions to increase fuel pressure
  • Fuel barrel, a small space where the fuel is ready to be sent to the injector.

The way it works, when the crankshafy rotates, the camshaft pump also rotates. The rotation of the camshaft will cause the cam to press against the plunger alternately.

When the plunger is pressed against the cam, the fuel pressure rises immediately so that the fuel is sprayed from the injector.

2. Distributor pump type

Distrubutor pump is a type of injection pump with smaller design. The main purpose of the distributor pump, as a solution for vehicles with limited space.

The main feature of the distributor pump is the injection system. The inline type uses one plunger for one injector, but the distributor type uses a single plunger for all injectors.

The way it works, this plunger will press all the fuel in each fuel barrel alternately. The fuel barrel is placed around the pump shaft.

When the pump shaft rotates, the plunger will press the fuel in the fuel barrel alternately according to the ignition timing.

Even though it has a smaller design, the distributor pump does not have high fuel pressure. Therefore, this type is rarely used for high capacity diesel engines.

3. Continuous pump

Continuous pump is the latest type of diesel injection pump. As I said earlier, this type is actually the most widely applied today.

Continuous pump is an injection pump that is applied to the common direct injection system.

Judging from the physical, this pump has the smallest form of all types that we discuss. The reason is this pump only has a single function.

Its function is only to increase fuel pressure stably at high pressure. The pressure generated is also very high (30,000 - 40,000 PSI)

While the two types above, in addition to increase fuel pressure also regulates the timing and volume of sprayed fuel. So it's reasonable that the form is quite concise.

The way this pump works is like a water pump that uses a turbine even though some types also use membranes. The pump will suppress the fuel and hold the fuel pressure at the applied limit.

How is the fuel spraying technical?

On the common rail system, to spray the fuel is regulated by the injector directly with the ECU command. So, the pump duty only ensures maximum fuel pressure so that once the ECU opens the injector, fuel can be atomized.

5 Types of Fuel Injection System in Diesel Engine

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.


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


  • 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
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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.

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.

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

3 Type of Fuel Injectors With Difference and Definition

Electronic fuel injection (EFI) system has been applied to almost all recent vehicles. The good performance and economical fuel uses are the main reasons why EFI systems are implemented.

The fuel injection system works using an injector, where each injector will spray fuel with an ideal volume in the intake manifold.

The content about the injector we discussed earlier, you can read here; Understanding Fuel Injector Working Principle

However, do you know that the fuel injector consists of several types.

This is what will be our topic, so read more below

Type Of Fuel Injector On Engine

There are three types of injectors that are most commonly used (either on diesel engines or petrol engines), namely, spring type injectors, magneto injectors, and pizeo electric injectors

1. Spring type injector

As the name suggests, spring type injector is an injector that use spring. The spring properties is flexible, and this flexibility is used to press the nozzle to close.

Maybe you already understand, the injector can spray fuel because there is a small gap in the nozzle. In the OFF condition, the gap will be closed but when the injector is ON, the gap is open and the fuel is sprayed.

In this type, the spring is used to press the nozzle to close the gap. But when the fuel pressure rises spontaneously, the spring will rise. That causes the nozzle to lift and the gap is open.

Simply, the diagram is as shown below

From the picture above, it show there is a spring inside the injector body. Under the spring there is a shim, while in the bottom is a nozzle.

Shim has a functions to recover the injector performance, this is because the spring elasticity will weaken when the injector is used continuously. If the spring weakens, the gap on the nozzle will be wider. And this causes less fuel atomization.

So as a recovery, a thicker shim is used.

Spring type injectors are used in conventional diesel engines, this type requires a high pressure pump with individual controls.

So before ignition timing is achieved, the fuel pressure inside the injector is low. This makes the spring press the nozzle to close. However, when ignition timing is achieved, a high pressure pump will increase fuel pressure spontaneously.

It can be said that the injector becomes passive part, because the controller of fuel spray is a high pressure pump.

2. Magneto injector

Magneto injector is a type of injector that uses magnetism to open the nozzle gap.

It is also called a solenoid injector, because it uses a solenoid to produce magnetism.

Magneto injector works when the solenoid is given a voltage, magnetism will occur. The magnetism will move the iron core in the middle of the solenoid.

The movement of the iron core will open the nozzle gap.

In simple terms, the magneto injector diagram is as follows.

From the picture above, it can be seen that the injector control is located on the solenoid. When solenoid is OFF, the nozzle gap is closed but when the solenoid is ON the nozzle is opened.

The most striking difference is in fuel pressure. In the first type,the  typical of fuel pressure is frequency because the pressure will rise when ignition timing is achieved.

But on the magneto injector type, the fuel pressure is made stable to keep it high because each injector will spray it.

This type of magneto is the most common type used in all vehicles, either diesel (common rail) or petrol engine (EFI).

3. Pizeoelectric injector

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Basically, the third type is the same as the magneto injector where the main control is located on the injector.

However, the injector does not use magnetism to open the nozzle gap but uses special material that can deflate when energized.

The material is piezeo slice, when given a voltage of thousands of pizeo slices inside the injector body will collapse. The deflation will pull the nozzle up, and it make the nozzle gap is openned.

This type is new so that only a few manufacturers use this type of injector.

Understanding Fuel Injector Working Principle and Diagram

Electronic fuel injection system is a series of fuel systems that utilize electro-mechanical parts to deliver fuel from the tank to the cylinder with an ideal ratio.

One of the main parts on the EFI system is the injector. Then, what is the definition of the injector? how does the injector work on the engine? check the content below

Definition and Function of Fuel Injector

A fuel injector is an electro-controlled valve that uses to spray out the fuel. In the petrol fuel injection system, the injector acts as a door to spray fuel from fuel lines into the intake manifold.

The injector function is not only a sprayer, but the injector also atomizes the fuel in the intake manifold. When fuel is in atomization form, the molecules can mix better with air.

When the injector is energized, the nozzle will open so that the high pressure fuel inside the injector can be sprayed out in the form of atomization.

Then who controls the performance of the injector? it is the job of the ECU. ECU (electronic control unit) will regulate the injector opening, and it’s . But ECU needs help from a series of sensors.

So the scheme, the sensor will detect several engine conditions such as engine temperature, intake air temperature, intake air period and others. Then the sensor will send data to the ECU, the data is processed by the ECU and the output will be sent for enegized injectors.

Further more, Understanding fuel injection system in petrol engine

The Injector Working Principle

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An injector works using electrical energy, when the voltage is applied to the injector the nozzle will open so that the fuel is sprayed. How long is the duration of the voltage given, affecting the volume of sprayed fuel.

There are three main components to the injector;

  • The tube
  • Solenoid
  • Nozzle

The tube is the main body of an injector (it’s cylindrical part), here is where the fuel terminated.

Solenoid is a magnetic coil that can convert electrical energy into motion energy. In the process, the voltage from the ECU enters the solenoid. On solenoids, electromagnetic forces occur from electricity flowing through the coil.

The electromagnetic force will move an iron core in the middle of the coil, this movement opens the nozzle.

While the nozzle is a needle-like component (tapered). Under normal conditions (the injector is off), the nozzle will close the tube gap. However, when the nozzle is slightly runny, the tube gap will open.

That causes the fuel sprayed.

One thing that should not be forgotten, fuel sprayed in the form of atomization.

This happens because the gap on the tube is very small and the shape is circular. With high fuel pressure, the fuel will atomize.

Type of Fuel Injector

There are three types of injectors that are widely applied;

1. Spring type injector

This type is also called a mechanical injector, it is caused by by its works which do not use electrical energy but instead utilize the existing fuel pressure.

The main component in this injector is spring, where in the injector off, the spring will push down the nozzle, and it causes the tube close. However, when the fuel pressure is increased spontaneously, the nozzle automatically opens.

But the opening of the nozzle is also very minimal because the spring is still held.

Because it works only when the fuel pressure rises spontaneously, the fuel pressure on this injection system cannot be held continuously. Fuel pressure will be increased only when ignition timing is achieved.

So, how controlled the timming and the duration of injector ?

It’s the job off high pressure injection pump. The pump will raises the pressure spontaneously when the timming reach, while the duration is controlled by the fuel barel inside the pump that the volume can be change depending on the gas pedal opening.

This type is widely applied to conventional diesel engines

2. Solenoid injector

Solenoid injectors work using electromagnetic principles, the process as described above. Where electrical forces will be converted into mechanical movements through magnetic coil.

The difference with the first type, the solenoid type has stable fuel pressure (continously). That is because the injector is controlled by ECU.

This type is widely applied to the EFI petrol engine, as well as the common rail diesel injection system.

3. Pizeo fuel injector

Pizeo fuel injector is an injector that uses pizeo slice material. Pizeo slice is a material that can change its volume when energized.

In this case, thousands of pizeo slices are placed in the injector. When the ECU provides a voltage, this pizeo slice will deflate. The deflate will make a minimum movement, and the movement is used to move the nozzle so that the nozzle gap is open.

This type is relatively new, so there are still few developers who use this model.

Understanding Fuel Injection System in Diesel Engine

The diesel engine can generate power from the combustion process. The combustion can appear because there are diesel fuels that are sprayed into high pressure air.

You may already understand, that diesel engines are self ignited. This means that there is no need to trigger a fire to cause burning.

This happens because the air temperature in the cylinder exceeds the burnl point of the diesel fuel.

Then what about the fuel system in a diesel engine? Is it the same as the fuel injection system in the petrol engine? see content below

The working principle of the diesel engine fuel system

The diesel engine fuel system works using the principle of pressure, in this case there are two chambers, namely cylinder space and fuel lines.

The cylinder chamber is filled by high pressure air, while the fuel lines is filled by diesel fuels that ready to be sent to the cylinder.

In order for the diesel fuel to come out into the cylinder, the pressure in the fuel lines must be made higher.

So that when the nozzle is open, diesel fuel can come out towards the cylinder.

To be undestand easilly, we divide the diesel fuel injection system into several components.

  • Fuel pump
  • Fuel hoses
  • High pressure pump
  • Injector

Fuel pumps is used to deliver fuel from tanks to fuel injection lines. Fuel pump works using an electric motor.

While a high pressure pump is a special pump that has high pressure. Its function is to increase the fuel pressure inside the injector up to 1,500 bars.

Increased fuel pressure means that the fuel can get out into the cylinder during the combustion step, as you read above that the air pressure inside the cylinder when the combustion step is high. So that require higher fuel pressure.

How does the injector work?

The injector functions only as a diesel fuel exit from the fuel lines to the cylinder. However, the fuel released must be in the form of atomization.

It aims to make diesel fuel easily burn and more spontaneous.

To get that, there is a noozle at the end of the injector. It is a tapered needle that closes a hole. When the needle nozzle is slightly raised, there is a slight opening.

With high fuel pressure, the fuel will atomize through the nozzle gap.

Further explanation, Learn How Fuel Injector Works with Diagram

Difference between diesel engine injection and petrol engine injection systems

In recent vehicle, fuel injection systems are not only applied to diesel engines but also applied to petrol engines. Then what is the difference?

1. Position of the injector

The position of the injector in the diesel engine, is inside the cylinder. This means that the cylinder will interact directly with the combustion in the cylinder.

While the injector on the petrol engine is located in the intake manifold.

2. Timming

The combustion on the diesel engine occurs because the diesel fuel sprayed into high temperature air inside the cylinder. That means, diesel fuel sprayed at the beginning of the combustion step.

While combustion in the petrol engine occurs because spark plugs are sparked in high pressure air fuel mixture (AFM). That means, petrol engine fuel comes out during the suction step.

3. Fuel pressure

Diesel engines require a high fuel pressure of 1,500 bars, because the fuel will be sprayed directly in high pressure air. While the petrol engine only requires fuel pressure around 100-200 bar because the fuel is sprayed into the intake which has low pressure.

4. Air fuel ratio

The average A / F ratio on the gasoline engine is around 14.6: 1. This means that 14.6 air molecules equal 1 gasoline molecule. While the diesel engine works on lean mixture . The A / F ratio of the diesel engine is greater than 18 (1 molecule fuel equal to 18 molecules of air or greater)

Type of fuel injection system on diesel engines

There are several types of fuel injection systems in diesel engines, where each type has character and strength.

In general, there are two types

1. Conventional injection system

Conventional injection systems work mechanically. The most dominant component is a high pressure pump, where this component will regulate everything.

The fuel spraying timing is regulated by a high pressure pump, then the amount of fuel sprayed is also regulated by a high pressure pump.

The way it works, a high pressure pump will increase the pressure of the fuel inside the injector only at certain times. The time is when the initial combustion process

Here, the injector acts as a passive part that will spray fuel when fuel pressure increases.

Conventional injection systems are also divided into two types,

Inline injection system, this type has a high pressure pump with a line configuration.
Rotary injection system, this type has a high pressure pump with a rotating configuration (such as a distributor in conventional ignition)

This conventional type has advantages in the life span which is fairly durable, and easy to maintain.

However, it is lacking in terms of efficiency and emissions. Therefore, this type is widely applied to trucks or buses.

2. Common rail injection system

Common injection system works electronically. That is, everything is regulated by a series of Sensor-ECu-Actuators (same as the EFI engine).

In this type, a high pressure pump only works to increase fuel pressure continuously. That is, when the engine is running, high pressure pump will press the full more stable.

Meanwhile to regulate timming and volume of fuel, it is regulated by injectors (which are controlled by ECU).

The way it works, the fuel pump will increase fuel pressure to 2,500 bars so that the pressure in the fuel rail is stable at 2,500 bars (the pressure is  greater than conventional type). When ignition timing is achieved, the ECU will open the nozzle so that the fuel can be sprayed into the cylinder.

The advantages of the common rail injection system are more efficient, more maximum performance and better emissions.

But for more complicated and expensive treatments.

Therefore, this commonrail is mostly applied to SUV, MPV and some on heavy machines.

Understanding Fuel Injection System in Petrol Engine (Working Principle + Diagram)

Fuel injection system is a system for supplying fuel into the engine through the spraying path.

Most of fuel injection systems are applied to diesel engines. You may already be very familiar with the injectors found in all diesel engines. But the petrol engine also has a fuel injection system.

Is the fuel injection system in the petrol engine the same as a diesel engine? let's discuss in detail.

Definition of Fuel Injection Systems in Petrol Engines

Petrol engine uses gasoline as fuel, gasoline will be inserted into the cylinder along with fresh air at the suction step.

In older vehicles, there is one component called a carburetor, its function as a mixer of air and gasoline.

The carburetor will supply gasoline into the intake manifold based on the pressure difference. The pressure inside the intake is lower because there is air flow acceleration which makes the gasoline sucked into the intake manifold. The result is fresh air and gasoline can be mixed.

While the fuel injection system, the same in principle. However, the fuel injection system does not use air flow acceleration to enter gasoline, but uses an injector which directly injects gasoline into the intake manifold.

This injector is like a water tap, which can emit fluid with varying volumes.

The injector is able to spray gasoline with varying volumes, the one that regulates the volume of sprayed gasoline is ECU (electronic control unit).

How Does The Fuel Injector Work?

As explained above, the fuel injector is similar to a water tap that can emit fluid with varying volumes.

An injector consists of a pipe, nozzle, and solenoid.

  • Pipe, used as a container of gasoline from a gasoline hose.
  • Nozzle, is the small end of the injector to create an atomize effect.
  • Soleniod, a magnetic coil to open and close the nozzle.

The injector can spray gasoline in the form of atomize. This happens because there is a high pressure inside the gasoline hose. So that when the tip of the nozzle opens, the gasoline will come out in the form of atomize.

To open the tip of the nozzle, it is the solenoid jobs. This solenoid can convert electrical energy into motion energy, when it given a voltage the solenoid will pull the needle nozzle so that the tip of the nozzle opens.

For more info, you can read Understanding fuel injector working with diagram

Who gave the nozzle a voltage?

That is the task of the ECU, the ECU is a controller or processor on the EFI Engine. The ECU also determines when and how long the injector is open.

For more info, you can read the following article Electronic Fuel Injection Working and Diagram

Petrol Fuel Injection System Diagram

The injection system in the petrol engine consists of several parts including;

  1. Fuel tank
  2. Fuel pump
  3. Fuel filter
  4. Gasoline hose
  5. Delivery pipe
  6. Sensor
  7. ECU
  8. Injectors

The fuel pump does not only act as a gasoline distributor from the tank, but also increases the gasoline pressure inside gasoline hose.

So that when the tip of the nozzle opens, there will be a spray effect that will atomize the gasoline on small molecules in the intake manifold. The gasoline atomization will mix with air molecules in the intake manifold.

During the suction step, the piston can suck mixed material (AFM / air fuel mixture).

Difference between petrol and diesel fuel injection system

Both have the same working principle but the scheme is different. The most striking difference is only on timming.

The diesel engine will release fuel during the combustion step, while the petrol engine will spray gasoline at the suction step.

Another difference is the fuel pressure, the diesel engine has a much higher fuel pressure than the petrol engine. That is because, the fuel in the diesel engine is released inside the combustion chamber at the end of the compression step (the air pressure is the highest).

So that the pressure of sprayed diesel fuel must be much higher than the air pressure inside the combustion chamber.

While the petrol engine, the gasoline take out  when the suction step inside the intake manifold with low air pressure, so it does not need high fuel pressure.

To compare, you can read Understanding fuel injection system in Diesel engine

4 Type of Fuel Injection System on Petrol Engine

In general, there are 4 types of fuel injection systems in the gasoline engine

1. Single point injector

Single point injector only has one injector even though the number of cylinders is 4. An injector is placed under the throtle valve, so that it can serve all the intake channels.

2. Multi point fuel injectors (MPFI)

Multi point inectors use one cylinder for each cylinder, so if an engine has 4 cylinders there will be 4 injectors. This injector is placed in each intake channel, usually in front of the inlet valve to trim the gasoline spraying line.

Although using an injector in each cylinder, all injectors work together. This means that the four injectors will spraying fuel at the same time.

3. Sequential injection system

Sequential injection system is a new scheme that is applied to MPFI, so it has sameis diagram as MPFI where each cylinder will be served by one injector.

But all injectors work alternately according to timming for each cylinder. So if cylinder 1 is in the suction step, the injector 1 will automatically spray fuel but the other three injectors are idle.

This scheme allows the use of fuel to be more economical.

4. Gasoline direct injection (GDI)

The recent technology in the fuel injection system is GDI. GDI is similar to the direct injection diesel engine where the injector is placed inside the combustion chamber (inside the cylinder).

It is intended that all sprayed fuel can enter the cylinder, because if the fuel is sprayed inside the intake manifold, then there is the potential for fuel to condense on the intake. And this clearly lowers fuel economy.

The solution, the fuel is sprayed directly inside the cylinder during the suction step.

4 Types of Fuel Injection System With Differences and Explanations

To adjust the engine RPM, it is done by adjusting the amount of air and fuel that will be inserted into the cylinder.

To adjust the amount of air, the throtle body is done temporarily to adjust the amount of fuel completed by the fuel injection system.

In the previous article we discussed how fuel injection works, in that article it was explained that the fuel injection system works using an injector that can spraying fuel into the intake manifold.

But if discussed further, we will find 4 types of fuel injection systems. Then what? and what is the difference? let's discuss it.

4 Types of Fuel Injection System

1. Single point injection system

Single point injection system is one type of injection system that uses an injector. Even though the engine has 4 cylinders, the number of injectors remains one.

This system was found in the early discovery of injection systems in vehicle engines. At that time, an injector was placed on the throtle body as a substitute for playing a jet carburetor.

The result is the same as the carburetor system. Gasoline can be sprayed into the throtle body room but this gasoline comes out of an injector not from carburetor jet.

When compared to the carburetor type, it is clearly better because how much the volume of gasoline has been calculated before by ECU.

So that it can be more accurate.

However, because it only uses one injector, the engine's performance at high RPM is also slightly disturbed.

2. Multi point fuel injection

Multi point fuel injection (MPFI) is a newer technology than the single point type. Basically, this type is the same as the first type but the number of injectors is adjusted to the number of cylinders.

This means that for a 4 cylinder engine using 4 injectors.

Multi point injectors have the same scheme as a single point injector. But in this type, the actuator (injector) is added to more.

The advantages of multi-point injectors, fuel is more effectively channeled to the engine because the location of each injector is inside the intake manifold (in front of the inlet valve). So that when the fuel sprayed, the fuel can go directly into the cylinder .

But it has disadvantage, this type works at one time exactly like a single point. That is, all injectors will spray fuel at the same time. This will keep the fuel sprayed even if one of the cylinders is in the combustion step.

The result is wasteful fuel uses.

But for performance problems, this type is definitely better than the single point type.

3. Sequential fuel injection

Sequential injection system is the type of fuel injection that is most widely applied to recent vehicles .

Basically, the sequential fuel injection system is the same as MPFI, but this type already has individual injection. In other words, each injector does not work together but works individually according to the steps of each piston.

For example in a 4 cylinder engine, when cylinder 1 is in the suction step, only injector 1 works. While the other injectors are idle.

This can be interpreted that each injector works alternately according to the timings of each cylinder.

From the mechanism, it is exactly the same as MPFI but the scheme controller is very different. The sequential type has a more complex controller scheme because it use timming indicators for each cylinder.

However compared to the MPFI, the sequential type has better performance and better use of fuel.

4. Direct injection system

The direct injection system is a fuel injection system mechanism that placing the injector directly into the cylinder.

So that it looks like a diesel engine, where the injector will spray fuel directly in the cylinder.

This main advantages on this type is in fuel economy, because in the previous type fuel sprayed in the intake, so there is potential for fuel to condense on the intake. But on the DI system, all the fuel goes into the cylinder so that it can be more economical.

From the performance sector it is also the same as MPFI even in the system can have better performance depending on the volume of fuel that comes out.

This is the latest type of fuel injection system, in early DI was applied to diesel engines. But now, the DI system can be applied to the petrol engine, but still the fuel only comes out during the suction step.

At the petrol engine, this system is known as GDI (gasoline direct injection).