Publications

The use of close-coupled post injections is an in-cylinder soot-reduction technique that has much promise for high efficiency heavy-duty diesel engines. Close-coupled post injections, short injections of fuel that occur soon after the end of the main fuel injection, have been known to reduce engine-out soot at a wide range of engine operating conditions, including variations in injection timing, exhaust gas recirculation (EGR) level, load, boost, and speed. While many studies have investigated the performance of post injections, the details of the mechanism by which soot is reduced remains unclear. In this study, we have measured the efficacy of post injections over a range of load conditions, at constant speed, boost, and rail pressure, in a heavy-duty optically-accessible research diesel engine. Here, the base load is varied by changing the main-injection duration. Measurements of engine-out soot indicate that not only does the efficacy of a post injection decrease at higher engine loads, but that the range of post-injection durations over which soot reduction is achievable is limited at higher loads. Optical measurements, including the natural luminescence of soot and planar laser-induced incandescence of soot, provide information about the spatiotemporal development of in-cylinder soot through the cycle in cases with and without post-injections. The optical results indicate that the post injection behaves similarly at different loads, but that its relative efficacy decreases due to the increase in soot resulting from longer main-injection durations. Copyright © 2014 by ASME.

Abstract not provided.

Low-temperature combustion (LTC) achieved by using exhaust-gas recirculation (EGR) is an operating strategy of current interest for heavy-duty and other compression-ignition (diesel) engines because it offers low nitrogen oxides (NOx) and soot emissions compared to conventional diesel combustion. While the long ignition-delay of EGR-LTC helps increase pre-combustion mixing to reduce soot formation, other emissions, including unburned hydrocarbons (UHC), can be problematic. Particularly an issue at low-load conditions, a considerable portion of UHC emissions in large-bore diesels is often due to overly-lean fuel/air mixtures formed near the injector during the long ignition delay. In this study, we explore the use of multiple post-injection strategies, which have a large main injection and one or two smaller post injections, to help reduce engine-out UHC emissions. The short post-injections closely timed after the end of the main injection help to enrich the overly-lean region near the injector, allowing for more complete combustion of a greater portion of the fuel/air mixture. Optical results from formaldehyde and OH planar laser-induced fluorescence provide evidence of the in-cylinder spatial and temporal progression toward complete combustion.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.