Abstract: The automobile engine will emit a lot of pollutants during its operation. The automobile engine emission control system is a device to convert the pollutants emitted by the engine into harmless substances. The emission control system consists of exhaust gas recirculation system (EGR), fuel vapor recovery device (EVAP), secondary air injection device (EAIR) and three-way catalytic converter (TWC). This paper introduces the composition, principle, maintenance methods and steps of the above devices, and analyzes their common faults with examples.

Keywords: engine emission control system principle and structural overhaul

I. Overview

(A) the main components and hazards of automobile emission pollution

The pollutants emitted by automobiles are mainly carbon monoxide, hydrocarbons, nitrogen oxides, nitrogen oxides and particulate matter (soot, lead compounds, etc.). ), which is extremely harmful to human beings: CO is a colorless, odorless but highly toxic gas produced by incomplete combustion in the engine due to insufficient air supply or other reasons. After carbon monoxide is inhaled into human body, it will combine with hemoglobin in the lungs, causing poisoning symptoms such as hypoxia, headache, dizziness and vomiting, and even death in severe cases. HC is the unburned part of automobile engine exhaust. Only when the concentration of HC is quite high will it have an impact on human body. However, when Hc and NO2 are mixed together, the high concentration ozone produced by strong sunlight will cause strong irritation to human eyes, respiratory organs and skin. Nitrogen oxides are produced by the reaction of N2 and oxygen in the air at high temperature and high pressure. NO2 has serious toxicity, which can irritate people's eyes and respiratory tract, causing wheezing, bronchitis and emphysema. In addition, nitrogen oxides and hydrocarbons react with sunlight to form photochemical smog. Photochemical smog is not only harmful to human body, but also harms plants and reduces atmospheric visibility. Particulate emissions are mainly lead compounds, sulfates and low molecular substances of gasoline vehicles. When lead compounds are inhaled and accumulated to a certain extent, it will affect hematopoietic function, cause anemia, and make the heart, lungs and other organs