Exhaust Gas Recirculation System
To improve NOx emission exhaust gas recirculation becomes a key measure.EGR systems work by adding exhaust gas back into the engine intake manifold. The turbocharger, a pneumatic or an electronic valve has to ensure the pressure difference between exhaust and inlet manifolds to drive the EGR is maintained.
Cooling The Recirculate Gas
Lowering the amount of oxygen in the cylinder and the combustion temperature, NOx emission is reduced therefore at the source of origin. Cooling the recirculate gas, enhances the effectiveness of EGR and thus the further reduction in NOx. As shown in Figure 1, intensified EGR cooling serves to reduce NOx and exhaust smoke particularly at higher loads.
Increased EGR cooling has practically no effects on NOx and smoke emission at very low loads (1000 rpm, 2 bar), nevertheless this causes increased HC and CO emissions. Therefore, to control these emissions, an EGR cooler by-pass has to be installed. This by-pass serves to conduct partial flow or full flow of the exhaust gas depending on the load and speed. The EGR cooler will also be by-passed for engine cold start and warm-up.