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Low temperature combustion (LTC) modes for reciprocating engines have been demonstrated with relatively high thermal efficiencies. These new combustion modes involve various combinations of stratification, lean mixtures, high levels of exhaust gas recirculation (EGR), multiple injections, variable valve timings, two fuels, and other such features. LTC engines may be attractive in combination with low heat rejection (LHR) engine concepts. The current work is aimed at evaluating the thermodynamic advantages of such a LTC-LHR engine. A thermodynamic cycle simulation was used to evaluate the effect of cylinder wall temperature on the engine performance, emissions and second law characteristics. An automotive engine at 2000 rpm with a bmep of 900 kPa was considered. Both a conventional and a LTC design were compared. The LTC engine realized small gains in efficiency whereas the conventional engine did not realize any significant gains as the cylinder wall temperature was increased.

The uses of lean mixtures and exhaust gas recirculation (EGR) are known to increase thermal efficiency and reduce emissions. Often the two approaches are used simultaneously. This investigation is aimed at establishing a better understanding of the fundamental thermodynamic aspects of these approaches. A 5.7 liter, spark-ignition, automotive engine was selected for this study. Using a thermodynamic engine cycle simulation, the thermal efficiencies and other engine parameters were determined as functions of equivalence ratio and EGR levels. The results also are shown as functions of parameters which reflect the temperature decrease associated with decreasing equivalence ratio and increasing EGR levels. The results show that the two approaches provide lower temperatures which result in lower heat losses, reduced pumping losses, higher ratio of specific heats (“gamma”), and lower nitric oxide emissions.