Characterization of Exhaust Gas Recirculation for Diesel Low Temperature Combustion

Exhaust Gas Recirculation (EGR) is common on most modern diesel engines resulting in significant reduction of NOx emissions. Heavy EGR application is an enabling technique for the advanced combustion modes operating in the low temperature combustion (LTC) regime, wherein simultaneous NOx and soot emission reduction can be attained. The primary effect of EGR is the dilution of the intake charge following the displacement of fresh air by the combustion products. However, the correlation between EGR and its effectiveness is non-linear due to the lean burn nature of boosted diesel engines. This correlation is further complicated when oxygenated fuels are used for combustion in the LTC mode. In this work, the intake oxygen concentration [O2]int is selected as a representative of EGR and its effectiveness in emission abatement is shown using an array of experimental results. An EGR characterization model is developed to quantify the dynamic interaction between [O2]int and engine operating variables, namely the intake boost, exhaust gas recirculation (EGR) amount, the fueling quantity and the fuel type. The model is validated on the research engine platform in steady state and transient tests. Finally, the control of EGR effectiveness is experimentally demonstrated to achieve ultra-low NOx emissions at different engine operating points.