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The combustion process of a heavy-duty DI-Diesel truck engine has been investigated using numerical simulation. The numerical modeling was based on an improved version of the KIVA-2 engine simulation code, employing a modified characteristic time-scale combustion model and a modified Kelvin-Helmholtz spray atomization model. The NO-formation process was modeled using the extended thermal Zeldovich mechanism. The simulation efforts included the effects of different injection characteristics such as varying the injection rate profile or number of injection holes and sizes. The physical sub-models used to improve the simulation of the mixture-formation and the combustion process were validated through comparison with single-cylinder engine experiments. Special attention was given to accurately model the in-cylinder flame propagation of the individual sprays and their effect on thermal NO-formation. All simulations were based on full load cases at medium speed.

High over-all efficiency, good performance together with low impact on environment and low lifecycle-costs are the major demands of truck engine customers. To fulfill these high demands, the potential of an SNCR (selective non catalytic reduction) process for NOx reduction as an alternative to catalytic exhaust treatment systems has been examined in this investigation [1]. Aqueous urea was used as the reducing species. The experimental tests were carried out on a heavy duty single cylinder research engine. The tests confirmed the applicability of a homogeneous non-catalytic selective reduction process. By injecting aqueous urea directly into the combustion chamber a maximum NOx reduction of 65% could be achieved at full load and increased exhaust gas temperature.