8/9/2019 Emission Control Systems for Petrol

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EMISSION CONTROL SYSTEMS

by Fred Bordoffhe need to control the emissions from automobiles gave rise to the computerization of the automobile.ydrocarbons, carbon monoxide and oxides of nitrogen are created during the combustion process and aremitted into the atmosphere from the tail pipe. There are also hydrocarbons emitted as a result ofaporization of gasoline and from the crankcase of the automobile. The clean air act of 1977 set limits as toe amount of each of these pollutants that could be emitted from an automobile. The manufacturers anseras the addition of certain pollution control devices and the creation of a self ad!usting engine. 19"1 sa therst of these self ad!usting engines. They ere called feedback fuel control systems. #n oxygen sensor asstalled in the exhaust system and ould measure the fuel content of the exhaust stream. $t then ould sendsignal to a microprocessor, hich ould analyze the reading and operate a fuel mixture or air mixtureevice to create the proper air%fuel ratio. #s computer systems progressed, they ere able to ad!ust ignitionpark timing as ell as operate the other emission controls that ere installed on the vehicle. The computeralso capable of monitoring and diagnosing itself. $f a fault is seen, the computer ill alert the vehicle

perator by illuminating a malfunction indicator lamp. The computer ill at the same time record the fault ins memory, so that a technician can at a later date retrieve that fault in the form of a code hich ill helpem determine the proper repair. 'ome of the more popular emission control devices installed on the

utomobile are( EGR VALVE, CATALYTIC CONVERTER, AIR PUMP, PCV VALVE,CHARCOAL CANISTER.

CATALYTIC CONVERTER

utomotive emissions are controlled in three ays, one is to promote more complete combustion so thatere are less by products. The second is to reintroduce excessive hydrocarbons back into the engine for

ombustion and the third is to provide an additional area for oxidation or combustion to occur. This additionalrea is called a catalytic converter. The catalytic converter looks like a muffler. $t is located in the exhaustystem ahead of the muffler. $nside the converter are pellets or a honeycomb made of platinum or palladium.

he platinum or palladium are used as a catalyst ) a catalyst is a substance used to speed up a chemicalrocess*. #s hydrocarbons or carbon monoxide in the exhaust are passed over the catalyst, it is chemicallyxidized or converted to carbon dioxide and ater. #s the converter orks to clean the exhaust, it developseat. The dirtier the exhaust, the harder the converter orks and the more heat that is developed. $n someases the converter can be seen to glo from excessive heat. $f the converter orks this hard to clean a dirtyxhaust it ill destroy itself. #lso leaded fuel ill put a coating on the platinum or palladium and render theonverter ineffective. This is hy, in the +.'.#., all fuels designed for automobile engines are no unleaded.

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PCV VALVE

he purpose of the positive crankcase ventilation )-* system, is to take the vapors produced in therankcase during the normal combustion process, and redirecting them into the air%fuel intake system to beurned during combustion. These vapors dilute the air%fuel mixture so they have to be carefully controlled andetered in order to not affect the performance of the engine. This is the !ob of the positive crankcase

entilation )-* valve. #t idle, hen the air%fuel mixture is very critical, !ust a little of the vapors are alloedto the intake system. #t high speed hen the mixture is less critical and the pressures in the engine are

reater, more of the vapors are alloed in to the intake system. /hen the valve or the system is clogged,apors ill back up into the air filter housing or at orst, the excess pressure ill push past seals and createngine oil leaks. $f the rong valve is used or the system has air leaks, the engine ill idle rough, or at orst,ngine oil ill be sucked out of the engine.

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8/9/2019 Emission Control Systems for Petrol

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EGR VALVE

he purpose of the exhaust gas recirculation valve )02* valve is to meter a small amount of exhaust gasto the intake system, this dilutes the air%fuel mixture so as to loer the combustion chamber temperature.xcessive combustion chamber temperature creates oxides of nitrogen, hich is a ma!or pollutant. /hile the2 valve is the most effective method of controlling oxides of nitrogen, in it&s very design it adversely affectsngine performance. The engine as not designed to run on exhaust gas. 3or this reason the amount of

xhaust entering the intake system has to be carefully monitored and controlled. This is accomplishedrough a series of electrical and vacuum sitches and the vehicle computer. 'ince 02 action reduceserformance by diluting the air %fuel mixture, the system does not allo 02 action hen the engine is coldr hen the engine needs full poer.

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EVAPORATIVE CONTROLSasoline evaporates 4uite easily. $n the past, these evaporative emissions ere vented into the atmosphere.6 of all H- emissions from the automobile are from the gas tank. $n 1976 legislation as passed,rohibiting venting of gas tank fumes into the atmosphere. #n evaporative control system as developed toiminate this source of pollution. The function of the fuel evaporative control system is to trap and storevaporative emissions from the gas tank and carburetor. # charcoal canister is used to trap the fuel vapors.he fuel vapors adhere to the charcoal, until the engine is started, and engine vacuum can be used to drae vapors into the engine, so that they can be burned along ith the fuel%air mixture. This system re4uirese use of a sealed gas tank filler cap. This cap is so important to the operation of the system, that a test ofe cap is no being integrated into many state emission inspection programs. re81976 cars released fuel

apors into the atmosphere through the use of a vented gas cap. Today ith the use of sealed caps,edesigned gas tanks are used. The tank has to have the space for the vapors to collect so that they can thene vented to the charcoal canister. # purge valve is used to control the vapor flo into the engine. The purgealve is operated by engine vacuum. ne common problem ith this system is that the purge valve goes badnd engine vacuum dras fuel directly into the intake system. This enriches the fuel mixture and ill foul thepark plugs. :ost charcoal canisters have a filter that should be replaced periodically. This system should behecked hen fuel mileage drops.

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AIR IN!ECTION

nce no internal combustion engine is 166 efficient, there ill alays be some unburned fuel in thexhaust. This increases hydrocarbon emissions. To eliminate this source of emissions an air in!ection systemas created. -ombustion re4uires fuel, oxygen and heat. /ithout any one of the three, combustion cannotccur. $nside the exhaust manifold there is sufficient heat to support combustion, if e introduce somexygen than any unburned fuel ill ignite. This combustion ill not produce any poer, but it ill reducexcessive hydrocarbon emissions. +nlike in the combustion chamber, this combustion is uncontrolled, so if

e fuel content of the exhaust is excessive, explosions, that sound like popping, ill occur. There are timeshen under normal conditions, such as deceleration, hen the fuel content is excessive. +nder theseonditions e ould ant to shut off the air in!ection system. This is accomplished through the use of averter valve, hich instead of shutting the air pump off, diverts the air aay from the exhaust manifold.nce all of this is done after the combustion process is complete, this is one emission control that has no

ffect on engine performance. The only maintenance that is re4uired is a careful inspection of the air pumprive belt.

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