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The potential for Low-Heat-Rejection (LHR) engines to meet current and future emission standards is a critical consideration. For the most part, NOx emissions measured both at GMR and elsewhere have been significantly higher than for conventional diesel engines, and many of the control methods for NOx increase fuel consumption. In recent studies at General Motors Research Laboratories (GMR), the LHR engine has shown potential for significant reductions in smoke and particulate emissions. In this study, data acquired from a single-cylinder LHR engine having a 2.0-L displacement and a quiescent combustion system were combined with multicylinder engine mapping data for a 1988 production truck engine to form a simulated multicylinder LHR truck engine with turbo-charging and intercooling. These data were used as input to a simulation model of the EPA heavy-duty transient test schedule to estimate LHR engine emissions and fuel consumption.