Exhaust Gas Recycling

This technology lowers combustion temperature and thereby decreases fuel consumption. But it can cause engine problems.

- Jake Venter

Many modern engines are equipped with devices that recycle a portion of the exhaust gas from the justcompleted power stroke back into the intake manifold, in order to reduce the oxygen available for combustion. This reduces the maximum temperature during combustion, thereby reducing the amount of NOX formed in the combustion chamber.

NOX is the collective symbol for nitrogen oxide (NO) and nitrogen dioxide (NO2). The former is a sharp, sweet-smelling colourless gas and the latter is a reddish-brown gas with an irritating odour. Both are formed at high temperatures and are harmful to humans.

PETROL ENGINES

In most petrol engines, the exhaust gas recycling (EGR) injection rate is between 5% and 15% per volume of exhaust gas released each time the exhaust valves open. This quantity is regulated by a vacuum- or electronically operated EGR valve on the outside of the intake manifold.