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Manufacturers of heavy-duty diesel engines for sale in the United States face an unprecedented reduction in emissions in 2007 and in 2010. Compared to today's levels, a 90% reduction in particulate matter (PM) must be achieved by 2007, and a 90% reduction in nitric oxides (NOx) must be achieved by 2010. This paper focuses on the technology solutions possible for engine makers for the interim 2007-2009 timeframe and discusses the additional NOx reduction strategies for a 2010 compliant engine. The possibility of achieving a larger portion of the interim 2007-2009 NOx standard through in-cylinder control methods rather than by NOx exhaust treatment is discussed. High levels of exhaust gas recirculation (EGR) and advanced injection strategies to modify the conventional diesel combustion process are just two processes that can be accommodated in many of today's engine designs.

Because only the unburned gases in the crevices can contribute to hydrocarbon emissions, a model was developed that can be used to determine the temporal and spatial histories of both burned gas and unburned gas flow into and out of the piston-liner crevices. The burned fraction in the top-land is primarily a function of engine design. Burned gases continue to get packed into the inter-ring volume until well after the end of combustion and the unburned fuel returned to the chamber from this source depends upon both the position of the top ring end gap relative to the spark plug and of the relative positions of the end gaps of the compression rings with respect to each other. Because the rings rotate, and because the fuel that returns to the chamber from the inter-ring crevice dominates the sources between BDC and IVO when conditions are unfavorable to in-cylinder oxidation, these represent two sources of variability in the HC emissions.

A recently developed in-cylinder fuel injection probe was used to deposit a small amount of liquid fuel on various surfaces within the combustion chamber of a 4-valve engine that was operating predominately on liquefied petroleum gas (LPG). A fast flame ionization detector (FFID) was used to examine the engine-out emissions of unburned and partially-burned hydrocarbons (HCs). Injector shut-off was used to examine the rate of liquid fuel evaporation. The purpose of these experiments was to provide insights into the HC formation mechanism due to in-cylinder wall wetting. The variables investigated were the effects of engine operating conditions, coolant temperature, in-cylinder wetting location, and the amount of liquid wall wetting. The results of the steady state tests show that in-cylinder wall wetting is an important source of HC emissions both at idle and at a part load, cruise-type condition. The effects of wetting location present the same trend for idle and part load conditions.