What is direct injection? by Asiautos Auto Parts(vehicles Aftermarket Parts Expert)

1. Explanation of direct injection

The main difference between a direct injection gasoline engine and a general gasoline engine is the location of gasoline injection. The gasoline electronic injection system used in a general electronic injection gasoline engine injects gasoline into the intake manifold or intake pipe, mixes with air to form a mixed gas, and then enters the cylinder combustion chamber through the intake valve to be ignited and work.

As the name suggests, a direct injection gasoline engine injects gasoline into the cylinder. It installs the fuel injector in the combustion chamber, injects gasoline directly into the cylinder combustion chamber, and air enters the combustion chamber through the intake valve to mix with gasoline to form a mixed gas to be ignited and work. This form is similar to a direct injection diesel engine, so some people think that a direct injection gasoline engine is a pioneering work that transplants the form of a diesel engine to a gasoline engine.

2. Advantages of direct injection

The advantages of a direct injection gasoline engine are low fuel consumption and high power per liter.

The air-fuel ratio reaches 40:1 (the air-fuel ratio of a general gasoline engine is 15:1), which is what people call "lean combustion".

Half of the piston top in the engine is spherical, and the other half is a wall. After the air rushes in from the valve, it forms a vortex motion under the compression of the piston. When the compression stroke is about to end, the fuel injector at the top of the combustion chamber starts to spray fuel. Gasoline and air form a mixture under the action of the vortex motion. This rapidly rotating mixture is layered. The closer it is to the spark plug, the thicker it is, and it is easy to ignite and work.

The compression ratio is as high as 12, and the power and torque are increased by 10% compared with general engines of the same displacement.

Wide application of direct injection in the cylinder

Among the engine technologies adopted by various manufacturers recently, the most popular technology is direct injection in the cylinder. This technology derived from diesel engines has been widely used in VAG, BMW, Mercedes-Benz, GM and Toyota (Lexus) series.

Direct injection technology in the cylinder is widely used in the VAG Group. The 4.2-liter FSI engine shared by Audi RS4 and R8 is a representative work with strong performance.

Among them, the VAG Group can be regarded as the most representative example of the introduction of direct injection technology. Currently, Audi and VW have listed the FSI direct injection engine as a high-end power source for their models, and the top-level cars of Audi and VW even combine FSI with turbocharging to increase power.

The biggest advantage of the direct injection design of the fuel supply system is that the fuel is directly injected into the combustion chamber at extremely high pressure. Therefore, in addition to the structure and position of the fuel injector being different from the traditional fuel supply system, the atomization and mixing efficiency of the oil and gas are also better. In addition, the control technology of various electronic systems on the car has been greatly improved recently, and the computer's judgment and control of the intake volume and injection timing have become more accurate. Therefore, with the combination of direct injection technology to greatly improve the combustion efficiency of the engine, in addition to the engine being able to generate more power, it also has positive help for environmental protection and energy saving.

However, direct injection technology is not invincible. From an economic perspective, a fuel supply system that uses direct injection not only has to spend more money in the research and development process, but also has complex and sophisticated component structures, and the price of components is more expensive than traditional fuel supply systems. Therefore, these are also factors that future direct injection engines have yet to overcome.