What is a multi-point injection engine and what are its advantages compared with general-purpose engines?

As we all know, the EFI device of automobile engine is generally composed of fuel injection circuit, sensor group and electronic control unit. If the injector is installed in the original carburetor position, that is, there is only one gasoline injection point in the whole engine, this is a single-point EFI; If the injector is installed on the intake pipe of each cylinder, that is, gasoline is injected into the cylinder from multiple places (at least one injection point for each cylinder), this is multi-point injection. Accordingly, the engine with single-point EFI device is a single-point EFI engine, and the engine with multi-point injection device is a multi-point injection engine.

In addition to the installation position of the injector, there are also differences in performance and manufacturing cost. Gasoline engines operate by burning the mixture in the cylinder. The running quality of the engine depends largely on the quality of the mixture, and the formation of the mixture depends largely on the form of the fuel injection system. Therefore, which electronically controlled fuel injection form is adopted has a great influence on the engine performance.

The fuel in the mixture must be atomized to completely mix with air and contribute to combustion. In the fuel supply system, when fuel enters the intake manifold, it exists in the form of oil droplets and flows to the intake valve at the same time. Most oil droplets form oil mist, and a small amount of oil droplets form oil film on the intake manifold wall. In order to reduce the amount of oil film on the pipe wall, single-point injection and multi-point injection are solved in different ways.

Because single-point injection is to set the fuel injector above the throttle valve, it can only improve the atomization at the throttle valve and the temperature of the heating pipe wall to improve the degree of fuel evaporation, but it is difficult to ensure that no oil film or oil droplets are formed on the pipe wall from the throttle valve to the intake valve, so the structure of the intake manifold has a great influence on the transportation and distribution of mixed gas, and it is difficult to maintain ideal mixed gas distribution under all working conditions; Multi-point injection is that the fuel injector is located at the intake valve, and the fuel is further evaporated on the hot intake valve and fully mixed with air, and then immediately enters the combustion chamber through the intake valve, which is not affected by the intake manifold structure and can ensure the uniform distribution of the mixed gas.

Single point injection has simple structure, reliable operation and simple maintenance. An obvious advantage is that the single-point injection injector is located above the throttle valve and directly injected into the intake pipe, with high airflow speed. Because the pressure there is low (the flow rate is inversely proportional to the pressure), the injection only needs 0. 1 MP. It can be injected at low pressure, and the multi-point injection works at 0.35MPa, which means that the single-point injection system can reduce the requirements for electric fuel pumps and save costs. But in performance, multi-point injection is better than single-point injection, and multi-point injection engine has the advantages of less pollution and more fuel saving.

In order to ensure the running quality of automobile engines, the electronic fuel injection system of automobile engines mostly adopts multi-point injection, while the single-point injection system is generally only used in small cars.

At present, most domestic cars use multi-point injection engines, such as Changan Antelope, Li Jinxia, Geely Meiyan Et, Jetta, Bora, Shenlong Fukang, Picasso, Santana 2000, Polo, Sail, Prima, Familia, Brilliance China, fashionable and peculiar.

Rui (second generation), Li Xia 2000, Parrio, Fengshen Bluebird, Hongqi, Passat, Buick, Audi A6, etc.

What is a closed-loop control EFI system? What are the advantages compared with the open-loop control EFI system?

The closed-loop control of engine EFI system is a closed triangle relationship among real-time oxygen sensor, computer and oil quantity control device. The oxygen sensor "tells" the computer the air-fuel ratio of the mixture. The computer sends a "command" to the fuel control device to adjust the air-fuel ratio to the theoretical value (14.7: 1). This adjustment often exceeds the theoretical value. The oxygen sensor detects it and reports it to the computer, and then the computer sends an instruction to adjust it back to14.7: L. Because each adjustment cycle is very fast, the air-fuel ratio will not deviate from14.7: l. Once put into operation, this closed-loop adjustment will be continuous.

The closed-loop controlled EFI engine can always run under ideal working conditions (the air-fuel ratio will not deviate too much from the theoretical value), thus ensuring that the car not only has good power performance, but also saves fuel.

At the same time, closed loop is the most effective operation mode. The computer should be programmed to be as closed-loop as possible. However, in order to enter the closed-loop control, some conditions must be met: the oxygen sensor must reach the working temperature (about 3 15. c)； The engine water temperature must reach the critical temperature (about 65℃); After the engine is started, a predetermined period of time (from a few seconds to a minute or two) passes. There are other situations, such as strong acceleration and long idle time, and the computer will force the system to exit the closed loop.

Corresponding to the closed loop is the open loop. In the open-loop control mode, the input information used by the computer includes water temperature, load, atmospheric pressure and engine speed. This information determines the air-fuel ratio. Once this information is processed, the computer sends an appropriate command to the mixture control device, but the command will not change unless the input changes. In this working mode, the computer doesn't use the input information of oxygen sensor, so it doesn't know whether the "command" about air-fuel ratio can run satisfactorily, which is the weakness of open loop.

At present, in domestic cars, engines with multi-point injection technology basically adopt closed-loop control technology.

What are the usual arrangements of engine cylinders? What are the characteristics of inline 4-cylinder (L4) and V-type 6-cylinder V6 engines?

The common cylinder numbers of automobile engines are 3, 4, 5, 6, 8, 10 or 12. An engine with a displacement of less than 1 L usually has three cylinders, an engine with a displacement of 1 ~ 2.5L usually has four cylinders, an engine with a displacement of about 3 L usually has six cylinders, an engine with a displacement of about 4 L has eight cylinders, and an engine with a displacement of more than 5.5L uses 12 cylinders. Generally speaking, under the same cylinder diameter, the more cylinders, the greater the displacement and the higher the power; Under the same displacement, the more cylinders, the smaller the cylinder diameter, because the speed can be increased, thus obtaining greater lifting power.

The arrangement of cylinders mainly includes in-line, V-type and W-type.

Generally, the cylinders of engines with less than 5 cylinders are arranged in line. A few 6-cylinder engines also have in-line engines, and there have been in-line 8-cylinder engines in the past. The cylinder block of an in-line engine is arranged in a straight line. Cylinder block, cylinder head and crankshaft are simple in structure, low in manufacturing cost, good in low-speed torque characteristics, low in oil consumption and widely used, with the disadvantage of low power. Generally, gasoline engines below l L mostly use 3-cylinder inline, L ~ 2.5L gasoline engines mostly use 4-cylinder inline, and some 4-wheel drive models use 6-cylinder inline. Because of the small width, facilities such as supercharger can be arranged next to it. In-line 6-cylinder has good dynamic balance and less vibration, so it is also used in some middle and high-end cars, such as the old Shanghai brand cars.

The cylinders of 6 ~ 12 cylinder engines are generally arranged in a V shape, and V 10 engines are mainly installed in racing cars. V-type engine is short in length and height, and it is very convenient to arrange. It is generally believed that V-type engine is a relatively advanced engine and has become one of the symbols of car grade. V8 engine is rarely used because of its complicated structure and high manufacturing cost. The V 12 engine is too big and heavy, and only a few advanced vehicles are used.

In recent years, Volkswagen has developed W engines, including W8 and W 12. The cylinders of the W engine are arranged in four rows at staggered angles, which makes them more compact.

At present, the most common engines are mainly inline 4-cylinder (L4) and V-type 6-cylinder (v6) engines. Generally speaking, the displacement of V6 engine is higher than that of L4, and V6 engine runs more smoothly and quietly than L4. L4 is mainly installed on ordinary cars, and V6 is installed on middle and high-grade cars.

Domestic cars equipped with V6 models are Buick (all models of 2.5 and 3 L) and Accord 3. O, Audi 2.8 and Passat 2.8; Domestic cars equipped with L4 models are: Li Jinxia (1.3L), Li Xia 2000, America and Japan (1.3L), Fukang (all models), Picasso (all models), Santana (all models), Jetta (all models), Bora (all models) and Audi/.

What is the displacement of the engine?

The working volume of cylinder refers to the volume of gas swept by piston from top dead center to bottom dead center, also known as single cylinder displacement, which depends on cylinder diameter and piston stroke. Engine displacement is the sum of the working volumes of each cylinder, which is generally expressed in milliliters (mL).