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There is a significant global effort to study low temperature combustion (LTC) as a tool to achieve stringent emission standards with future light duty diesel engines. LTC utilizes high levels of dilution (i.e., EGR > 60% with <10%O2 in the intake charge) to reduce overall combustion temperatures and to lengthen ignition delay, This increased ignition delay provides time for fuel evaporation and reduces in-homogeneities in the reactant mixture, thus reducing NOx formation from local temperature spikes and soot formation from locally rich mixtures. However, as dilution is increased to the limits, HC and CO can significantly increase. Recent research suggests that CO emissions during LTC result from the incomplete combustion of under-mixed fuel and charge gas occurring after the premixed burn period [1, 2]1. The objective of the present work was to increase understanding of the HC/CO emission mechanisms in LTC at part-load.

The application of stringent requirements on emission reduction and higher fuel economy in diesel engines has led to the need for efficient energy extraction in the cylinders and reductions in exhaust gas temperatures, as well as posing challenges for energy availability for emission control systems. Internal exhaust gas recirculation (I-EGR) can increase the exhaust gas temperature and reduce engine-out gaseous emissions. The secondary opening of exhaust valves in a diesel engine produces an efficient recirculation of exhaust gases from the previous engine cycle to the cylinder mass charge during the intake stroke. However, I-EGR alone can increase exhaust gas temperature only up to a limit determined by the resulting increase in soot emissions. To obtain higher exhaust gas temperatures, I-EGR can be combined with multiple injections after the main injection event, thereby altering the heat release rate and the exothermic reactions in the exhaust stroke.