Emission Control Techniques
The need to control the emissions from automobiles gave rise to the computerization of the automobile. Hydrocarbons, carbon monoxide and oxides of nitrogen are created during the combustion process and are emitted into the atmosphere from the tail pipe. There are also hydrocarbons emitted as a result of vaporization of gasoline and from the crankcase of the automobile. The clean air act of 1977 set limits as to the amount of each of these pollutants that could be emitted from an automobile. The manufacturers answer was the addition of certain pollution control devices and the creation of a self-adjusting engine. 1981 saw the first of these self-adjusting engines. They were called feedback fuel control systems. An oxygen sensor was installed in the exhaust system and would measure the fuel content of the exhaust stream. It then would send a signal to a microprocessor, which would analyze the reading and operate a fuel mixture or air mixture device to create the proper air/fuel ratio. As computer systems progressed, they were able to adjust ignition spark timing as well as operate the other emission controls that were installed on the vehicle. The computer is also capable of monitoring and diagnosing itself. If a fault is seen, the computer will alert the vehicle operator by illuminating a malfunction indicator lamp. The computer will at the same time record the fault in it's memory, so that a technician can at a later date retrieve that fault in the form of a code which will help them determine the proper repair. Some of the more popular emission control devices installed on the automobile are: EGR valve, Catalytic Converter, Air Pump, PCV Valve, Charcol Canitiser etc. Like SI engine CI engines are also major source of emission. Several experiments and technologies are developed and a lot of experiments are going on to reduce emission from CI engine. The main constituents causing diesel emission are smoke, soot, oxides of nitrogen, hydrocarbons, carbon monoxides etc. Unlike SI engine, emission produced by carbon monoxide and hydrocarbon in CI engine is small. Inorder to give better engine performance the emission must be reduce to a great extend. The emission can be reduced by using smoke suppressant additives, using particulate traps, SCR (Selective Catalytic Reduction) etc.
2. EMISSION CONTROL IN SI ENGINE
2.1. Methods to reduce emission in SI engine.
2.1.1. Catalytic Converter
Automotive emissions are controlled in three ways, one is to promote more 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 oxidation or combustion to occur. This additional area is called a catalytic converter. The catalytic converter looks like a muffler. It is located in the exhaust system ahead of the muffler. Inside the converter are pellets or a honeycomb made of platinum or palladium. The platinum or palladiums are used as a catalyst (a catalyst is a substance used to speed up a chemical process). As hydrocarbons or carbon monoxide in the exhaust are passed over the catalyst, it is chemically oxidized or converted to carbon dioxide and water. As the converter works to clean the exhaust, it develops heat. The dirtier the exhaust, the harder the converter works and the more heat that is developed. In some cases the converter can be seen to glow from excessive heat. If the converter works this hard to clean a dirty exhaust it will destroy itself. Also leaded fuel will put a coating on the platinum or palladium and render the converter ineffective. 2.1.2. PCV Valve
The purpose of the positive crankcase ventilation (PCV) system, is to take the vapors produced in the crankcase during the normal combustion process, and redirecting them into the air/fuel intake system to be burned during combustion. These vapors...
References: 1. www.howstuffworks.com
5. Mathur & Sharma.; Internal Combustion Engine, Dhanpat rai publications.pp 774- 778
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