EMISSION CONTROL TECHNOLOGY FOR INTERNAL COMBUSTION ENGINES
EMISSION CONTROL TECHNOLOGY
FOR INTERNAL COMBUSTION ENGINES
INTERNAL COMBUSTION ENGINES ARE USED IN A VARIETY OF STATIONARY APPLICATIONS RANGING FROM POWER GENERATION TO INERT GAS PRODUCTION.
BOTH SPARK AND COMP. ENGINES CAN BE FOUND.
A VARIETY OF FUELS CAN BE USED FOR I.C.ENGINES.
THE OPERATION OF I.C ENGINES RESULTS IN THE ENISSION OF HYDROCARBONS,CO,NOX,, & PARTICULATE MATTER.
TECHNIQUES USED TO CONTROL
CATALYST CONTROL TECHNOLOGY-
PRINCIPLE- USED FOR CONTROLLING THE GASEOUS EMISSION OF A STATIONARY I.C. ENGINES – THE CATALYST CAUSES CHEMICAL REACTIONS WITHOUT BEING CHANGED OR CONSUMED. CATALYST TRANSFORM POLLUTANTS INTO HARMLESS GASES.
SELECTIVE CATALYTIC REDUCTION
INTRODUCING A REDUCING AGENTS SUCH AS AMMONIA,UREA,MAKES THE NECESSARY CHEMICAL REACTIONS POSSIBLE.
THE REACTIONS ARE:-
OXIDATION CATALYSTS CONTAIN PRECIOUS METALS IMPREGNATED INTO A HIGH GEOMATRIC SURFACE AREA CARRIER AND ARE PLACED IN THE EXHAUST STREAM THEY ARE VERY EFFECTIVE IN CONTROLLING CO&HYDROCARBON EMISSION.
HELP IN REDUCING EMISSIONS
BY CONTROLLING EXHAUST BEFORE IT LEAVES THE ENGINE.
BY CONTROLLING THE AIR TO FUEL RATIO(IDEAL RATIO 14.7:1 )
HOW REDUCE POLLUTION
Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce -- carbon monoxide, VOCs and NOx molecules. The converter uses two different types of catalysts, a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream, while also minimizing the amount of catalyst required (they are very expensive).
There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads. Most cars today use a honeycomb structure.
The Reduction Catalyst
The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:
2NO => N2 + O2 or 2NO2 => N2 + 2O2
The Oxidization Catalyst
The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:
2CO + O2 => 2CO2
The third stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is an oxygen sensor mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter is. This sensor tells the engine computer how much oxygen is in the exhaust. The engine computer can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the engine computer to make sure that the engine is running at close to the stoichiometric point, and also to make sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.