In heavy duty diesel engines, exhaust gas recirculation is often preferred choice to contain NOx emissions, in this a part of exhaust gas is tapped from exhaust manifold or later and recirculated to air intake pipe before intake manifold. Critical to such engines is the design of air intake pipe and intake manifold combination in view of proper exhaust gas mixing with intake air. The variation in exhaust gas mass fraction at each intake port should be as minimal as possible and this variation must be contained within +/− 10% band to have a minimal cylinder to cylinder variation of pollutants.
Exhaust gas homogeneity for various intake configurations was studied using three-dimensional computational fluid dynamics for a 4 cylinder, 3.8 L, Diesel fuelled, common rail, turbocharged and intercooled heavy duty engine. Flow field was studied in the computational domain from the point before exhaust gas mixing till all the four intake ports. Exhaust gas mass fraction variation at each intake port was calculated from this analysis.
This study showed that an optimized mixing length lies in the range of five times the air intake pipe diameter. Central positioning of air intake pipe onto the intake manifold is beneficial for mixing. Also a study was carried out by introducing a manifold heater with grids at the interface of air intake pipe and intake manifold. This showed that the manifold heater deteriorates the exhaust gas homogeneity inside the intake manifold and as such carried into each intake port.