Document LpONOpKbQvkNLZaxXn2Ya5aYX

CHAPTER 5/THE EMISSIONS SYSTEM OBJECTIVES: levels of these pollutants which can be emitted }when you have completed this chapter, you should be able to.- List the three major emissions that are the by the cars and light trucks sold in the United States. Carbon Monoxide (CO)--Carbon monoxide by-products of internal combustion. Describe the various emission control sys is a molecule made up of equal parts of car bon and oxygen. It is a colorless, odorless tems, both pre- and post-combustion types. gas, and is one of the results of incomplete Explain the principle of the catalytic con combustion. CO is extremely poisonous. verter, how the various types of converters By weight, carbon monoxide accounts for work and what they control. about 47% of air pollution. 1 List the two types of emission control Hydrocarbons (HC)--Hydrocarbons are i filters. made up of carbon and hydrogen atoms in Describe where emission recycling system various combinations. They are the product hoses are used. of any engine that does not operate at In a society that has become increasingly 100% efficiency using a hydrocarbon fuel. dependent on the automobile, one of the Hydrocarbons are a major component in Ur| inevitable side effects has been the emission of the formation of photochemical smog. -ji] !! pollutants into the air that are the by-products of the internal combustion engine. Oxides of Nitrogen (NOx)--Oxides of nitrogen consist of nitrogen combined with ii To understand these emissions and how they're created, we must first review the process varying amounts of oxygen. NOx is produced by heat and pressure during the that takes place inside the engine. combustion process. NOx is also a main component of photochemical smog. Photochemical smog results when HC and NOx are combined in the presence of bright sunlight. Smog, originally thought to be a com bination of smoke and fog, is actually the for mation of ozone, nitrogen dioxide and nitrogen nitrate when HC, NOx and bright sunlight are combined. Exhaust systems also emit lead and carbon (soot). Lead is being eliminated from gasoline for three reasons: because it is such a hazardous pollutant, because engines are being designed which no longer need it as a lubricating agent, and because lead in an exhaust system can I (Figure 43) Combustion. rapidly destroy the efficiency of a catalytic 1 For any organic combustion to occur, three converter. | j j j basic elements are required: fuel, oxygen and heat. Under ideal conditions, combustion produces heat, carbon dioxide (C02), and water vapor (H20). But in almost every internal com- Carbon or soot is a by-product of incomplete combustion in a diesel engine. There are cur rently no federal standards for soot emissions. One reason is that a properly adjusted engine j bustion reaction, other by-products are j produced. emits very little soot. Another is that no effec tive controls have been developed to contain or The three major pollutants caused by the trap soot. operation of the internal combustion engine-- carbon monoxide (CO), hydrocarbons (HC) and EMISSION CONTROL SYSTEMS ~xides of nitrogen (NOx)--have been deter There are two basic types of emission control mined to be hazardous to human health. Legisla systems: those which prevent the formation of tion has been passed which limits the maximum pollutants ("pre-combustion" systems--the