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Enhancement of fuel/air mixing is one path towards enabling future diesel engines to increase efficiency and control emissions. Air-assist fuel injections have shown potential for low pressure applications and the current work aims to extend air-assist feasibility understanding to high pressure environments. Analyses were completed and carried out for traditional high pressure fuel-only, internal air-assist, and external air-assist fuel/air mixing processes. A combination of analytical 0-D theory and 3D CFD were used to help understand the processes and guide the design of the air-assisted setup. The internal air-assisted setup was determined to have excellent liquid fuel vaporization, but poorer fuel dispersion than the traditional high-pressure fuel injections.

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 (NOX) emissions did not decrease dramatically with partial premixing.

An experimental investigation of the effects of partial premixed charge compression ignition (PCCI) combustion and EGR temperature was conducted on a Caterpillar C-12 heavy-duty diesel engine (HDDE). The addition of EGR and PCCI combustion resulted in significant NOx reductions over the AVL 8-mode test. The lowest weighted BSNOx achieved was 2.55 g/kW-hr (1.90 g/hp-hr) using cooled EGR and 20% port fuel injection (PFI). This represents a 54% reduction compared to the stock engine. BSHC and BSCO emissions increased by a factor of 8 and 10, respectively, compared to the stock engine. BSFC also increased by 7.7%. In general, BSHC, BSCO, BSPM, and BSFC increased linearly with the amount of port-injected fuel.