What is the main purpose of exhaust gas recirculation?

The main purpose of exhaust gas recirculation is to reduce nitrogen oxides (NOx) in the exhaust gas and improve fuel economy at partial load.

According to the action control form of the system actuator (EGR valve), it can be divided into mechanically controlled EGR system and electronically controlled EGR system; According to the control object of the EGR valve, that is, the way of system control, it can be divided into direct control EGR system and indirect control EGR system.

The main purpose is to reduce nitrogen oxides in the exhaust gas.

no x) and improve fuel economy at partial load.

Basic principle. The basic principle of EGR purifying NOx is actually heat capacity.

Specific applications of the theory.

Due to the specific heat of triatomic gases such as CO2, H2O, and NO2 in engine exhaust.

Higher, when the fresh gas mixture and exhaust gas are mixed, the heat capacity also increases.

The heat required to heat this mixture diluted by exhaust gas increases by 1 degree Celsius, and the maximum combustion temperature decreases under the condition that the total amount of fuel combustion heat release remains unchanged. At the same time, the dilution effect of the exhaust gas on the fresh mixture reduces the concentration of oxygen, so that the generation of NOx is inhibited.

Technology. In fact, the reflux of the exhaust gas is indirectly inserted into the two flow patterns of suction and exhaust, and the opening and closing time of the control valve is used to control the increase or decrease of the flow rate. Since the high temperature exhaust gas reflux makes it possible to ignore the low efficiency of suction and filling, most large diesel engines are equipped with a cooling mechanism (cool EGR) made of a heat exchanger.

Most will be part of the engine's cooling water.

Splitting, using a cooling mechanism to dissipate the absorbed heat, but adding an additional 30% load to the radiator, so other equipment such as cooling fans must be enlarged and thus increase weight.

A turbocharger is additionally installed.

If the EGR is applied to a large fuel engine with a high load of the overfeeder, the suction pressure will be greater than that of the exhaust, and the simple valve switch will not be able to reflux, so it is necessary to install an EGR control valve check valve (check valve).

Theoretically, if the EGR amount can be changed, it is possible to eliminate the throttle valve of the fuel engine.

However, the difficulty of ignition of a large number of EGRs can easily lead to combustion instability, and the inability to achieve a steady state at idle makes it difficult to put it into practical use. EGR is highly related to lean combustion technology, and there is also the issue of how to achieve stable combustion under rarefied mixtures in direct in-cylinder injection technology.

The main purpose is to reduce the harmful gases emitted into the atmosphere by automobile exhaust, inhibit the production of nitrogen oxides (NOx), and reduce the harm of automobile exhaust to the air and human body.

The so-called exhaust gas recirculation system refers to the return of part of the exhaust gas from the engine to the intake manifold and re-enters the cylinder with the fresh mixture. Because the exhaust gas contains a large amount of CO2, and CO2 cannot be burned but absorbs a large amount of heat, the combustion temperature of the mixture in the cylinder is reduced, thereby reducing the amount of NOx generated.

NOx is formed by nitrogen and oxygen in the atmosphere under high temperature and high pressure conditions. EGR brings 10% and 20% of the exhaust gas from the exhaust pipe mold into the intake pipe, and enters the combustion chamber with the fresh mixture, so that the exhaust gas inhaled by the cylinder cannot be burned, and the maximum temperature of the Xiangzu cylinder is reduced in order to reduce NOx emissions.

Exhaust gas recirculation COPY refers to: sending exhaust gas into the cylinder when the engine is under small load, participating in the combustion of the mixture, and reducing the temperature in the cylinder to reduce the emission of harmful substances (such as nitrogen oxides) in the exhaust gas;

As for the secondary air pump, it acts on the secondary air injection system, which mainly plays a role in cold start and warm-up, and is to send air like an exhaust pipe, so that the unburned part of the air and exhaust gas can be fully combusted, and the emission of harmful substances such as carbon monoxide and carbon hydride is reduced.

Exhaust gas recirculation is the process of returning part of the exhaust gases from the engine to the intake manifold and re-entering the cylinder with the fresh mixture.

Because the exhaust gas contains a large amount of polyatomic gases such as CO2, and gases such as CO2 cannot be burned but absorbs a large amount of heat due to its high specific heat capacity, the maximum combustion temperature of the mixture in the cylinder is reduced, thereby reducing the amount of NOx generated, and the main purpose is to reduce the nitrogen oxides in the exhaust gas and can improve the fuel economy at partial load.

The function of exhaust gas recirculation: Reducing nitrogen oxides (NOx) in the exhaust gas and improving fuel economy at partial load, exhaust gas recirculation is a technology that re-inhales a part of the exhaust gas after combustion in a small internal combustion engine for automobiles.

Exhaust gas recirculation is a technology (technique or method) in which a small internal combustion engine for automobiles re-inhales a portion of the exhaust gas after combustion and is introduced to the suction side.

The main function is to reduce nitrogen oxides (NOx) in the exhaust gas and improve fuel economy at partial load.

In principle, the EGR is not effective in reducing throttle loss in diesel engines without throttle valves, but in the early 1990s, the EGR study aimed at reducing NOx found that the large amount of carbon dioxide present in the exhaust gas has a higher heat capacity than water vapor and the atmosphere, so it also has some effect on improving fuel economy.

Extended information: Since the high temperature exhaust gas return can be ignored due to the low efficiency of suction and filling, almost all large diesel engines are equipped with a cooling mechanism made of heat exchangers.

Most of them will use a cooling mechanism to dissipate the absorbed heat by a part of the cooling water flow of the engine, but it will add an additional 30% of the negative front load to the radiator, so the weight will increase due to the need to increase the cooling fan and other equipment.

In addition, if an EGR is applied to a large fuel engine equipped with a turbocharger or other combustion engine under high load, the suction pressure will be greater than that of the gas, and the simple valve switch will not be able to return the flow, so it is necessary to install an EGR control valve check valve (check valve).

Theoretically, it is possible to eliminate the throttle valve of a combustion engine by changing the amount of EGR, but it is difficult to put it into practice due to the difficulty of igniting a large amount of EGR, which tends to cause combustion instability and the inability to achieve a steady state at idle.

Photo by Pacific Automobile Network Q&A).