Manufacturers of that era experimented with vacuum orifice restrictors and vacuum delay valves to try to find a happy medium between clean air and performance.īy 1981, closed loop computer controls were in place.
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Driveability is also improved by stopping EGR when the engine is started up cold, at idle and at full throttle.īy 1975, if you unplugged an EGR valve, you’d end up having an engine ping driveability complaint.
Most of the nitrogen is simply carried out with the exhaust gases.įor consistent driveability, it is desirable for the amount of exhaust gas flow to be proportional to the throttle opening. At lower combustion temperatures, very little of the nitrogen in the air combines with oxygen to form NOx. Since exhaust gas does not burn, this lowers the combustion temperatures and reduces NOx emissions from the engine. In subsequent issues, we will highlight the other three main internal combustion engine emission system control components - positive crankcase ventilation (PCV), air injection reactors (AIR) and the catalytic converter.Įxhaust gas recirculation is the dilution of the air/fuel mixture to control amounts of exhaust gas. In this column we will take a look at exhaust gas recirculation (EGR), one of the four major basic system control components used on all systems today. Emission controls on cars and trucks have one purpose: to reduce the amount of pollutants and environmentally damaging substances released by vehicles.
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