Kevin P. Duffy

An Experimental Investigation of In-Cylinder Processes Under Dual-Injection Conditions in a DI Diesel Engine

Fuel-injection schedules that use two injection events per cycle (dual-injection approaches) have the potential to simultaneously attenuate engine-out soot and NO x emissions. The extent to which these benefits are due to enhanced mixing, low-temperature combustion modes, altered combustion phasing, or other factors is not fully understood. A traditional single-injection, an early-injection-only, and two dual-injection cases are studied using a suite of imaging diagnostics including spray visualization, natural luminosity imaging, and planar laser-induced fluorescence (PLIF) imaging of nitric oxide (NO). These data, coupled with heat-release and efficiency analyses, are used to enhance understanding of the in-cylinder processes that lead to the observed emissions reductions. Results show that combustion of the early-injected fuel occurs in two phases: a cool-flame phase characterized by very weak chemiluminescence, followed by a premixed-burn phase characterized by localized regions of bright soot incandescence. Combustion of the early-injected fuel liberates only a fraction of its chemical energy. Spray visualization images show that this low combustion efficiency could be due at least in part to liquid fuel penetrating to and wetting in-cylinder surfaces, but NO PLIF images of the early-injection-only case also show strong interferences from unburned fuel vapor and/or condensed fuel droplets, suggesting that incomplete bulk-gas combustion and quenching in crevices also may play roles. The traditional single-injection case produced the highest NO PLIF signal levels. Both dual-injection cases reduced NO PLIF signal levels, with the reduction being most dramatic for the retarded-main-injection case.

Caterpillar Light Truck Clean Diesel Program

In 1998, light trucks accounted for over 48% of new vehicle sales in the U.S. and well over half the new Light Duty vehicle fuel consumption. The Light Truck Clean Diesel (LTCD) program seeks to introduce large numbers of advanced technology diesel engines in light-duty trucks that would improve their fuel economy (mpg) by at least 50% and reduce our nations dependence on foreign oil. Incorporating diesel engines in this application represents a high-risk technical and economic challenge. To meet the challenge, a government-industry partnership (Department of Energy, diesel engine manufacturers, and the automotive original equipment manufacturers) is applying joint resources to meet specific goals that will provide benefits to the nation. [1] Caterpillar initially teamed with Ford Motor Company on a 5 year program (1997-2002) to develop prototype vehicles that demonstrate a 50% fuel economy improvement over the current 1997 gasoline powered light truck vehicle in this class while complying with EPAs Tier II emissions regulations. The light truck vehicle selected for the demonstration is a 1999 Ford F150 SuperCab. To meet the goals of the program, the 4.6 L V-8 gasoline engine in this vehicle will be replaced by an advanced compression ignition direct injection (CIDI) engine. Key elements of the Caterpillar LTCD program plan to develop the advanced CIDI engine are presented in this paper.