Application of EGR cooler

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The role of EGR cooling system：

The EGR cooling system is a device designed to reduce NOx emissions from automobile exhaust, and is an exhaust gas recirculation system. At a higher speed of the car, a small amount of exhaust gas is reintroduced into the intake valve. The temperature of the exhaust gas is related to NOx emissions. The lower the temperature of the exhaust gas, the better the NOx suppression effect of the engine. The EGR cooler can reduce the temperature of the exhaust gas entering the cylinder. The lower temperature is definitely beneficial to the thermal load of the engine and reduces the engine temperature.

EGR cooler cooling principle:

Generally, a liquid / gas heat exchanger is installed in the EGR circuit to cool the recirculated exhaust gas.

The entire EGR circuit consists of oil cooling, connecting pipes and EGR valve (to control the gas flow through the system). The system is usually fixed on the intake pipe or the engine body.

In order to meet European emission standards, engine manufacturers must calibrate engines according to European ECE / EUDC cycle requirements. The characteristics of the current cooling EGR system are only determined by the control technology of the EGR valve. Due to higher and higher requirements for accurate control, the system began to use more and more electric EGR valves. The second-generation cooling EGR system adjusts the efficiency of the cooler to achieve independent control of gas flow and temperature, so it is the ideal choice for EURO IV and EURO V engines.

Working principle of EGR cooler:

The main component of the EGR system is a numerically controlled EGR valve. The numerically controlled EGR valve is installed on the right exhaust manifold. Its function is to independently and accurately control the amount of exhaust gas recirculated to the engine, regardless of the degree of manifold vacuum.

The EGR valve controls the amount of exhaust gas flowing from the exhaust manifold back to the intake manifold through three metering holes with increasing apertures to produce 7 different flow rate combinations. Each metering hole is composed of a solenoid valve and a needle valve. When the solenoid valve is energized, the armature is attracted upward by the magnet to open the metering hole. The characteristics of the rotary needle valve ensure a good seal when the EGR valve is closed.

The EGR valve is normally opened under the following conditions:

Engine warm-up operation.
The speed exceeds the idle speed. The ECM controls the EGR system based on the engine cooling water temperature sensor, throttle position sensor and air flow sensor.

Application of EGR cooler:

At present, the application of the EGR system to foreign automobile engines has been quite common.In addition to effectively reducing NOx emissions, the EGR system can also effectively reduce fuel consumption.It matches well with the EGR system on the partial load of the car gasoline engine operating conditions The engine throttle opening is increased at this time, which can reduce the engine pump air loss work. In addition, the lean combustion engine can only meet the exhaust emission standards when the EGR system is used; the use of the EGR system can reduce the consumption of precious metals in the three-way catalytic converter, and can reduce the cost of meeting the emission standards of gasoline vehicles. In recent years, foreign EGR systems have been increasingly used in diesel vehicles. Diesel engines have to meet Euro II emission standards. It is very difficult to achieve this standard without installing an EGR system. The development of EGR system is so far not a traditional pneumatic spring diaphragm mechanical valve, but an electromechanical integration product that needs to consider various control factors of the engine and the vehicle.

An exhaust gas recirculation (EGR) system is used to reduce the emission of nitrogen oxides (NOX) in the exhaust gas. Nitrogen and oxygen only react chemically under high-temperature and high-pressure conditions. The temperature and pressure in the engine’s combustion chamber meet the above conditions, especially during forced acceleration.

When the engine is running under load, the EGR valve opens, allowing a small amount of exhaust gas to enter the intake manifold and enter the combustion chamber along with the combustible mixture. At idle, the EGR valve closes and almost no exhaust gas is recirculated to the engine. Automobile exhaust gas is a non-combustible gas (without fuel and oxidant) and does not participate in combustion in the combustion chamber. It reduces the combustion temperature and pressure by absorbing part of the heat generated by combustion to reduce the amount of nitrogen oxide generated. The amount of exhaust gas entering the combustion chamber increases as the engine speed and load increase.

Development of EGR cooler:

The essence of EGR cooler is the general application of heat exchanger in cold zone EGR technology. The structure of the smooth tube heat exchanger is the simplest, and the flow smoothness is better, but its potential for heat transfer efficiency is not exerted. The threaded tube uses the principle of surface roughening to improve the heat transfer efficiency, but increases the resistance to flow; Finned tubes also increase the heat transfer efficiency, but the optimization of its structure is yet to be studied; the spiral baffle heat exchanger has been qualitatively improved compared to the bow baffle heat exchanger, and with its excellent performance has become The most popular form of EGR cooler. In recent years, people have also begun to attach importance to the research of high-efficiency heat exchangers in EGR coolers. Plate-fin EGR heat exchangers are one of them, although the application of this type of heat exchanger is compared to the shell and tube type. The heat exchanger is still slightly immature, but I believe that with the deepening of research, the shortcomings of high-efficiency heat exchangers will be improved one by one, and it will also become a more promising type of EGR cooler with its better heat exchange performance. form.

Edited by: Ryan Wu;

Copyright: SIMUWU Vacuum Furnace

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