Striving for reduced emissions

Enthusiasts focus on tailpipe number, appearance and exhaust acoustics, often with little thought given to their critical role in meeting emission targets. We investigate the function of the exhaust gas treatment components to achieve reduced emissions

- By Graham Eagle

EARLY DEVELOPMENTS

The introduction of the positive crankcase ventilation (PCV) system in the early 1960s was the first move towards reducing pollution from production vehicles. Fumes containing unburnt hydrocarbons from the crankcase were routed to the intake manifold, instead of being released directly into the atmosphere where they contributed to the formation of photochemical smog.

By 1966, the first exhaust emission standards followed, and the US Clean Air Act of 1970 legislated that from 1975, all cars would have to reduce emissions of CO (carbon monoxide), HC (hydrocarbons) and NOx (nitrogen oxides) by 90%. By 1974, compliance was being achieved by engine detuning, which significantly reduced engine efficiency and increased fuel consumption. It was clear catalytic converters would be required if the industry was to meet the strict 1975 targets. This was not going to be possible with the existing leaded petrol available at that time, as lead residue coated the surface of the catalysts, effectively destroying them, so the introduction of unleaded fuels was fast-tracked to allow the introduction of catalytic converters. An added benefit was that vehicles were eliminated as a source of lead poisoning.

01 Cross-section of a ceramic monolith used in three-way catalytic converters. Exhaust gas flows longitudinally through the square section channels.

THREE-WAY CATALYTIC CONVERTERS