With the increasingly stringent emission regulations, automobile manufacturers no longer pursue large displacement engines. Many years ago, large displacement cars gradually disappeared in the market. Nowadays, the displacement of family cars is basically below 2.0L. However, with each replacement, manufacturers must improve the power of vehicles to attract consumers. At this time, they have to invest heavily in engine efficiency, In recent years, we can often see a word about fuel, that is “GDI direct injection”. According to the survey, in the past 20 years, the proportion of GDI technology in engine output has increased from 1% to 60%. Compared with the traditional PFI electronic manifold injection, what are the advantages of GDI and how to choose when buying a car? Today, we will make a detailed analysis of the car selection detective.
1. What is the difference between GDI and PFI?
In the 100 year history of automobile, the internal combustion engine using PFI electronic manifold injection occupies the main position. PFI means that fuel is injected into the intake manifold to mix with air. The fuel injector in PFI engine is usually installed in the intake manifold. When the intake valve is opened, the air / fuel mixture is sucked into the cylinder head. In GDI engine, the injector is located in the cylinder head, the fuel is injected into the cylinder directly, and then mixed in the cylinder to form air / fuel mixture.
Although it seems that the two engines only change the position of the fuel injector, the structure is completely different. The fuel system of GDI engine needs to choose higher level hardware, high temperature (above 1400 ℃) and high pressure in the cylinder, so it needs the fuel injector and high pressure fuel pump that can withstand higher temperature and pressure. The fuel injector is usually designed with multiple holes, which helps to accurately deliver fuel to the cylinder. The position of the fuel injector is also crucial to the efficiency of the system. Generally, the fuel injector can be side mounted or installed at the top dead center of the cylinder. According to different injection modes, the overall fuel efficiency of the vehicle will also change. The electronic injection has no requirement on the strength of the manifold, so the stiffness is lower, and the overall cost of PFI engine is lower than that of GDI engine.
2. What are the advantages and disadvantages of GDI?
Compared with PFI design, GDI has many advantages, the most important of which is fuel economy and power output. Because GDI system combines higher injection pressure and can deliver fuel to piston cylinder more accurately, the fuel injected into cylinder is atomized more finely. The whole combustion process occurs when gasoline vapor is mixed with oxygen, so it can be ignited almost instantaneously. At the same time, the advanced computer system in the direct injection system can control the multiple injection and injection quantity of fuel, so the fuel combustion is more sufficient, so the output power is higher and the fuel consumption is more economical.
In order to further improve the performance, many GDI engines are combined with turbochargers. Turbochargers use the exhaust gas from vehicles to drive the turbine to provide power for the air compressor, thus forcing more oxygen-containing air into the cylinder to achieve higher fuel combustion rate. Under the same displacement, GDI engines have higher power and lower fuel consumption, Do these engines have any disadvantages? The answer is yes. GDI engine also has very obvious disadvantages.
When the fuel enters the cylinder from the intake manifold, the gasoline has the function of valve cleaning. The gasoline of PFI engine can be used as a cleaning agent, while GDI lacks the cleaning effect, which will lead to the increase of carbon deposition in the engine over a long period of time. In addition, for GDI engines, the ability to generate peak power at high speeds is more limited because the injection time is shorter. In the manifold injection, fuel can be added to the intake mixture at any time. However, GDI engine only injects fuel in the intake and compression stages, so it will appear the phenomenon of high-speed powerlessness. This does not have much impact on family cars, but it is a serious defect for some high-performance cars pursuing fun. In terms of environment, GDI engine will produce more black carbon aerosols than PFI engine. Black carbon is a strong absorber of solar radiation and has the characteristics of warming the climate. Therefore, GDI engine needs to be improved in the future.
Car selection detective point of view: from a comparative point of view, for family cars, in cylinder direct injection is more efficient, but the usual maintenance needs to pay attention to regularly clean up the carbon deposit, and the later maintenance cost is higher. The two types of engines are not absolutely good or bad. At present, some engines have used dual injection technology to complement the shortcomings of GDI and PFI, which is also the development direction of internal combustion engine in the future. Which do you think is better, di or EFI? Welcome to the discussion.