Advanced combustion methods for simultaneous reduction of emissions and fuel consumption of compression ignition engines

Abstract

In this work, advanced combustion modes i.e. improved low-temperature combustion (LTC) and reactivity controlled compression ignition (RCCI) have been achieved in a diesel engine. LTC mode has been improved using oxidized EGR (OEGR). Studies were carried out for a pre-optimized set of operating parameters of the engine. Reduction in NOx and PM, improved LTC, was achieved with higher OEGR percentages. Higher concentrations of CO2 and lower concentrations of reacting species with increased OEGR created higher ignition delays, and hence, lower PM. Results also showed the importance of catalytic converter in reduction of tail-pipe HC, CO and PM. RCCI has been achieved using fuels with different reactivities. Liquefied petroleum gas (LPG) with low reactivity was inducted along with air, and diesel with high reactivity was injected into the cylinder. Percentage of LPG was varied from 0 to 40 % with step size of 10 %. Results showed that PM, NOx and CO were reduced with increased LPG. Due to the possibility of a minor amount of LPG-air mixture being trapped in crevices during the compression stroke, HC was increased and BTE was decreased with increased LPG percentage. The results indicate that RCCI achieved with lower amount of LPG (~10 %) is more beneficial for the reduction of PM, NOx and CO with acceptable change in values of HC and BTE. A reduction in premixed heat release peak and minor increase in ignition delays were observed with increased LPG percentage. It indicates that LPG slows down the reaction rate during premixed combustion.