This paper describes a numerical study of fuel/air mixing processes for stoichiometric diesel combustion. In order to overcome the deterioration of combustion efficiency that accompanies stoichiometric diesel combustion due to poor mixing and lack of available oxygen, a new nozzle layout, namely a 2-spray-angle group-hole nozzle, which consists a grouped upper spray plume (squish spray) and a lower spray plume (bowl spray) was investigated. The KIVA code with updated physical and chemistry models, including the KH-RT breakup model, 2-step phenomenological soot model, reduced n-heptane and GRI NOx mechanisms was used for the calculations. An optimized 2-spray-angle group-hole nozzle with 170 squish spray angle and 80 bowl spray angle showed significantly improved fuel consumption (178 g/kW h(-1)) compared to the baseline nozzle layout (213 g/kW h(-1)) and the 2-spray-angle nozzle without hole-grouping (193 g/kW h(-1)). (c) 2008 Elsevier Ltd. All rights reserved.