A fuel system is a vital part of the vehicle engine. It is responsible for delivering fuel to the engine. There are multiple types of fuel injection systems, and a direct fuel injection system is one of them. A direct injection fuel system is an air-fuel mixture creation system for petrol-powered IC engines where fuel is directly injected into the combustion chamber. This article explains the direct injection system working, components, and applications.
What is a Direct Injection System?
A direct injection system is a fuel injection system that injects fuel directly above the piston into the engine combustion chamber. The PDI (petrol direct injection) is also called a Gasoline Direct Injection (GDI).
It is an air-fuel mixture creation system for IC engines that run on petrol. This system directly injects fuel into the combustion chamber of the engine.
The direct injection system is most commonly used in petrol engines, but with the technology development, it has been successfully employed in diesel engines. These systems are employed in Otto engines to reduce emission rates and increase specific power and engine efficiency.
In 1925, the direct petrol engine was designed for low-compression truck engines. In the 1950s, some German cars also started to use Bosch’s mechanical GDI system.
In 1996, when Mitsubishi initiated the electronic GDI system in production cars, this technology became more popular. In the recent few years, many automotive industries have been started to use this technology.
The principle of direct injection was first implemented in diesel engines. The direct injection system is basically used in diesel engines. In the basic DI diesel engines, the fuel injects directly into the combustion chamber onto the top of a piston.
In a diesel engine, the piston reciprocating in the combustion chamber highly compresses the air and makes the air temperature of more than 400 degrees Celsius. As the air is fully compressed, the direct injection system immediately injects the diesel fuel into the combustion chamber.
This fuel injection technology permits the gasoline engine to burn fuel more efficiently with a low emission rate, resulting in higher power output, increased engine performance, and lower fuel consumption rate.
Working of Direct Injection Engine
The direct injection working process is very easy. A petrol engine works by introducing a mixture of petrol and air into the compression cylinder. This cylinder has a reciprocating piston that compresses the mixture up to the desired level.
When the mixture is compressed, a spark plug delivers a spark to start the combustion process. The power produced by the air-fuel mixture moves the piston down and creates a force.
The direct injection system has a simple working. Usually, in indirect fuel injection systems, air and gasoline are premixed in a cylinder out of the combustion chamber called the intake manifold.
While in direct injection system, gasoline and air don’t premix. In this system, fuel directly injects into the combustion chamber while air introduces via the intake manifold. The air and fuel mixing process occurs in the combustion chamber.
The combustion chamber uses a fuel distribution mechanism called charge mode. There are two types of charging methods:
- Stratified charge mode
- Homogeneous charge mode
In a homogeneous charge mode, multiple injections mix fuel with air evenly throughout the combustion chamber. However, in stratified charge mode, there is an area of high fuel density around the spark plug, keeping the leaner air-fuel mixture (lower fuel density) away from the spark plug.
Functions of Direct Injection System
The main function of direct injection in an automotive engine is given below:
- It burns fuel efficiently
- It improves the engine performance.
- Help the engine to produce more power
- It increases fuel economy.
- Reduces emission rate
Components of Direct Injection System
The direct injection system has the following major parts:
- Governor
- Injectors
- Fuel filter
- Fuel feed pump
- Fuel lines
- Fuel pump
- Fuel tank
Advantages of Direct Injection System
- The direct injection system engine needs low maintenance.
- It has high low-end torque
- This system increases the engine life
- It reduces the engine emission rate.
- It increases the performance of the engine.
- These systems handle fuel at a significantly high pressure than indirect injection systems.
Disadvantages Direct Injection System
- The main disadvantage of a direct injection system is that direct injection can clog the fuel system and cause carbon buildup in the engine. This carbon builds up on the inlet valve.
- As plaque builds up in the arteries, reducing blood flow to the heart and causes a heart attack. The accumulation of carbon works in the same way. The carbon accumulation on car intake valves decreases the fuel supply to the engine, which can cause engine damage or failure.
- Direct injection engines have high costs and complex designs.
Direct injection Vs Port injection
Port fuel injection delivers an excellent, more stable air-fuel mixture at low engine speed for smoother starting. Direct injection offers more power and more cooling at a higher engine speed to reduce knocking.
The main difference between direction injection and port injection is how they work. The direct injection works with very high pressure and injects fuel directly into the area of the spark plug so that it ignites. In contrast, port fuel injection utilizes heat from the valve to inject fuel into the cylinder as the valve opens.
The main advantage of direct injection is that it injects a cooler air/gas mixture into the cylinder.
One of the disadvantages of port fuel injection is that the fuel becomes a puddle and is absorbed by the environment, making it difficult to control.
Direct Injection Vs. Indirect Injection
The main difference between direct injection and indirect injection is given below:
| Direct Injection | Indirect Injection |
|---|---|
| The direct injection system injects fuel directly into the combustion chamber. | The indirect injection system first mixes the air and fuel in the intake manifold and then sends the mixture into the combustion chamber. |
| In this system, gasoline and air aren’t premixed. | In this system, the air and gasoline are premixed in the intake manifold. |
| This system has a complex design. | It has an easy design. |
| It has more cost than an indirect injection system. | It has a low cost. |
| This system highly increases engine performance. | It can’t increase engine performance as much direct injection system. |
FAQ Section
What is Direct Injection?
An injection process in which the fuel is directly injected into the combustion chamber is known as direct injection.
Is direct injection bad?
The direct injection system is bad because direct injection clogs the fuel system and causes carbon buildup in the engine. This carbon builds up on the inlet valve.
As plaque builds up in the arteries, reducing blood flow to the heart and causes a heart attack. The accumulation of carbon works in the same way. The carbon accumulation on car intake valves decreases the fuel supply to the engine, which can cause engine damage or failure.
Which is better direct injection or port injection?
Port fuel injection provides an excellent, more air-fuel stable mixture at low engine speed for smoother starting. At higher engine speeds, direct injection offers more power and more cooling to reduce knocking.
Which is better fuel injector or carburetor?
The fuel injection system is designed to deliver fuel with precision, ensuring the optimal amount is supplied while making adjustments based on various parameters. This results in improved fuel efficiency and reduced fuel wastage. On the other hand, a carburetor lacks the ability to adjust the fuel ratio based on the changing engine conditions.
What is the disadvantage of direct fuel injection?
One of the major disadvantages of the direct fuel injection system is their complex design and high cost than conventional fuel injection systems.