An Experimental Investigation of PCCI-DI Combustion and Emissions in a Heavy-Duty Diesel Engine

An experimental investigation of partial premixed charge compression ignition (PCCI) in combination with direct fuel injection was conducted on a Caterpillar C-15 heavy-duty diesel engine (HDDE). The intent of the program was to investigate the performance, emissions, and efficiency characteristics of the concept. A portion of the fuel was delivered to the intake manifold using air-assist port fuel injectors. The spray droplet characteristics were measured, for several different injector geometries, over a range of thermodynamic conditions. Subsequently, the optimized port fuel injector (PFI) was utilized in the engine tests. The engine tests were run at conditions ranging from 1200 - 1800 RPM, loads ranging from 25 - 75%, and PFI quantities ranging from approximately 10 - 70%. The tests showed that oxides of Nitrogen (NO_X) emissions did not decrease dramatically with partial premixing. It is suspected that this is a result of the local gas temperatures (prior to the diffusion combustion) being elevated due to the HCCI combustion that precedes this classic mixing controlled phase. The test results also showed the inherent tradeoff of NO_X pollutants and incomplete products of combustion (i.e. carbon monoxide, CO, and unburned hydrocarbons, UHC) with partial premixing. It was also found that a slight increase in BSFC resulted not only from the incomplete combustion but also from the non-optimized spontaneous ignition of the premixed charge.