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.Initial simulation results indicated that the LHR engine would have NOx emission levels more than three times that required to meet future NOx emission standards, but with particulate emission levels below any existing future emission standard. To reduce NOx emissions, injection timing retard was considered as the most practical approach for a heavy-duty engine. For the LHR engine to reach the 1991-94 NOx heavy-duty emission standard of 5.0 g/bhp-h, static injection timings of around top dead center were required. With such timing, fuel consumption of the base LHR engine increased by more than 20% relative to the best-efficiency timing of the engine, and particulates rose to levels considerably higher than required to meet 1994 heavy-duty emission standards.