EXHAUST GAS RECIRCULATION PASSAGES

To reduce the emission of oxides of nitrogen (NOx), engines have been equipped with exhaust gas recirculation (EGR) valves. From 1973 until recently, they were used on almost all vehicles
Some engines use intake and exhaust valve overlap as a means of trapping some exhaust in the cylinder as an alternative to using an EGR valve. The EGR valve opens at speeds above idle on a warm engine. When open, the valve allows a small portion of the exhaust gas (5% to 10%) to enter the intake manifold. Here, the exhaust gas mixes with and takes the place of some of the intake charge.
Recirculated exhaust gas is inert and does not enter the combustion process. The result is a lower peak combustion temperature and lowered production of oxides of nitrogen.
The EGR system has means of interconnecting exhaust and intake manifolds. The passage is controlled by the EGR valve. On V-type engines, the intake manifold crossover is used as a source of exhaust gas for the EGR system. A cast passage connects the exhaust crossover to the EGR valve.
On inline-type engines, an external tube is used to carry exhaust gas to the EGR valve.