19-07-2012, 04:47 PM
Emission Control Techniques on IC Engines
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Abstract
Automobile exhausts are one of the major sources of air pollution. This seminar discusses about the various refinements made in automobile engines. The emission from SI engine includes oxides of nitrogen and carbonmonoxide. A most commonly used device in SI engines is a catalytic converter. The job of the catalytic converter is to convert harmful pollutants into less harmful products before they leave the exhaust. The various stages of operation are oxidation catalyst, reduction catalyst, and a closed loop control system with an oxygen sensor.
INTRODUCTION
The need to control the emissions from automobiles gave rise to the computerisation of the automobile. Hydrocarbons carbonmonoxide and oxides of nitrogen are created during the combustion process are emitted into the atmosphere from the tail pipe. There are also hydrocarbons emitted as a result of vapourisation of gasoline from the crank case of the automobile. To solve these problems governments create clean air laws that restrict the amount of pollution that automobiles can produce.
Catalytic Converter
Regardless how perfect the engine is operating there will always be some harmful by products of combustion.Automotive emission are controlled in three ways one is to promote complete combustion so that there are less by products.The second is to reintroduce excessive hydrocarbons back into the engine for combustion and the third is to provide an additional area for combustion to occur.This additional area is called a catalytic converter.The job of the catalytic converter is to convert harmful pollutants into less harmful emissions before they leaves the car’s exhaust system.The catalytic converter looks like a muffler.It is located in the exhaust system ahead of the muffler.
Effects of Closed Loop Control System on TWC Operation
To ensure that the catalytic converter has the feed gas composition it needs, the closed loop control system is designed to rapidly alternate air-fuel ratio slightly rich,then slightly lean of stoichometry.By doing this the carbonmonoxide and oxygen content of the exhaust gas also alternates with the air-fuel ratio(A/F).In short the converter works as follows: