What Are Combustion Emissions?

Engine pollution and its toxicity The engine's environmental pollution mainly comes from exhaust products. The main pollutants of gasoline engines are CO, NO x and HC. Lead pollution is also caused by burning leaded gasoline.

Chinese name: Engine emissions

Foreign name: engine pollution and its toxicity

Introduction to engine exhaust pollutants

Engine pollution and its toxicity The engine's environmental pollution mainly comes from exhaust products. The main pollutants of gasoline engines are CO, NO _x and HC. Lead pollution is also caused by burning leaded gasoline. The most important exhaust pollutants from diesel engines are particulates and NO _x . Another major pollutant in engine exhaust is carbon dioxide, which is the main product of normal combustion. Although carbon dioxide itself is non-toxic, it is the main component causing the "greenhouse effect", so it has attracted worldwide attention. From a health perspective, large doses of carbon monoxide can cause death, and cities must control carbon monoxide to a lower level.

Main pollutants and hazards of engine exhaust pollutants

CO CO emissions from engine CO

Carbon monoxide is an intermediate product of the combustion of hydrocarbon fuels. It is mainly produced due to the incomplete combustion of hydrocarbons under local hypoxia or low temperature conditions, and is mixed with the exhaust gas of internal combustion engines. When the car is under heavy load, running slowly or in neutral, the fuel cannot be fully burned, and the carbon monoxide content in the exhaust gas will increase significantly. Carbon monoxide is a colorless and odorless asphyxiating toxic gas with low chemical reaction ability. Its relative density to air is 0.9670, and its solubility is very small.

NOx Engine emission pollutants NOx

NO _x is a general term for nitrogen oxides such as NO and NO ₂ . The NO2 concentration in the exhaust of a gasoline engine is negligible compared to the concentration of NO, but in a diesel engine, NO2 can account for 10% to 30% of the total NOX in the exhaust. It stimulates the human eye mucous membranes and easily causes conjunctivitis, keratitis, and emphysema in severe cases. HC has a stimulating effect on the human eye and respiratory system, and is also harmful to crops.

HC Engine emissions pollutants HC

The hydrocarbons in car exhaust come from three sources. For general gasoline engines, about 60% of the hydrocarbons come from internal combustion engine exhaust emissions, 20% to 25% come from crankcase leakage, and the remaining 15% to 20% come from evaporation of the fuel system. Under certain geographic, temperature and meteorological conditions, HC and NO _x in the exhaust gas will undergo a photochemical reaction under strong sunlight, generating peroxidation products mainly composed of ozone (O ₃ ) and aldehydes, called photochemical smog . Ozone has a unique odor and strong toxicity, and aldehydes have a stimulating effect on the human eye and respiratory tract. In addition, they hinder the normal growth of organisms.

Engine exhaust pollutant particles

The main component of the particulates in the exhaust gas is a variety of polycyclic aromatic hydrocarbons (PAHs) in the adsorbate, which have different carcinogenic effects. This kind of particles is composed of carbon-containing particles (soot) generated during combustion and various organic substances adsorbed on the surface, the latter is called organic soluble component (SOF).

Among all the harmful components, CO, HC, NO _x and particulates are the main pollutants. The current emission standards and purification measures for automobiles are aimed at reducing the content of these pollutants.

Engine emission pollutants External exhaust purification measures

The so-called out-of-machine purification is to install various purification devices in the exhaust system of the car, and use physical and chemical methods to change the car's exhaust gas from the original toxic gas to a non-toxic gas, and then discharge it into the atmosphere. Reduce the pollution of automobile emissions to the atmospheric environment.

Using a catalyst, CO is oxidized to CO2, oxidized to CO2 and H2O, NOx is reduced to N2 and the like. The catalysts used are manganese oxide, copper monoxide; metal oxides such as chromium oxide, nickel monoxide, and copper monoxide; and precious metals such as white metal (platinum). They can all purify CO and HC. The three-way catalytic purifier is installed on the exhaust device of the automobile engine. When the car exhaust gas passes through the passage of the purifier, the purifier in the elementary catalytic converter will enhance the activity of three gases: CO, HC and NOx, which will promote a certain Oxidation and reduction chemical reactions, in which CO is oxidized to colorless and non-toxic carbon dioxide gas at high temperature; HC compounds are oxidized to water (H20) and carbon dioxide at high temperature; NOx is reduced to nitrogen and oxygen, making three harmful gases into The harmless gas has high purification efficiency and can purify more than 90% of harmful substances. This is by far the most effective and realistic measure. ^[1]