CONTROL OF OXIDES OF NITROGEN FROM DIESEL-ENGINES USING DILUENTS WHILE MINIMIZING THE IMPACT ON PARTICULATE POLLUTANTS

The investigation was conducted on a high-speed direct-injection diese l engine and was concerned with the effects of exhaust gas recirculati on (EGR) on diesel engine combustion and emissions. In particular, the effects on combustion and emissions of carbon dioxide (CO2) and water vapour (H2O), principal constituents of EGR, were analysed and quanti fied experimentally. The effects of increased inlet temperature and th ermal throttling of the inlet charge, both arising from the use of hot EGR, were also investigated. Finally, tests were carried out during w hich the CO2 added to the engine air flow increased the charge mass fl ow rate to the engine, rather than displacing some of the oxygen (O-2) in the inlet air. It was found that when CO2 or H2O displaced O-2 in the inlet charge, both the chemical and thermal effects on exhaust emi ssions were small. However, the dilution effect was substantial, and r esulted in very large reductions in exhaust NOx at the expense of high er particulate and unburnt hydrocarbon emissions. Higher inlet charge temperature increased exhaust NOx and particulate emissions, but reduc ed unburnt hydrocarbon emissions. Reduction in the inlet charge due to thermal throttling reduces NOx emissions but raises all the other pol lutants. Finally, when CO2 was additional to the inlet air charge (rat her than displacing O-2), large reductions in NOx were recorded with l ittle increase in particulate emissions. (C) 1998 Elsevier Science Ltd . All rights reserved.