The effect of heat transfer on performance of the Diesel cycle and exergy of the exhaust gas stream in a LHR Diesel engine at the optimum injection timing

Abstract

In this study, a Diesel cycle analysis taking combustion and heat transfer into account on performance has been performed. The effect of heat transfer is analysed in terms of design parameters such as compression ratio and cut-off ratio. The effects of heat transfer from the cylinder on exhaust temperature were also investigated for different heat transfer and combustion modes. It was observed that the work output and exhaust temperature proportionally increase with the decrease of heat transfer for a fixed combustion rate and cut-off ratio. In the experimental study, it was found that the minimum fuel consumption in the LHR engine compared to the standard (STD) engine was obtained with a 4° crank angle (CA) retardation of the injection timing from the 38° (CA). The decrease in specific fuel consumption at this injection timing reached 6%, and the increase in brake thermal efficiency was 2%. The exhaust temperature of the LHR Diesel engine with the injection timing of 38° CA was 10.8% higher than that of the STD engine, whereas, the increase in the temperature reached 22.8% at 34° CA. Thus, as a consequence of its great potential for optimisation of system performance, a comparative exergy analysis has been performed with the purpose of calculating the amount of available energy of the exhaust gas stream at the optimum injection timing (34 CA) for the LHR engine. While the maximum amount of available energy in the LHR engine exhaust gas stream with the injection timing of 38° CA was 13.45%, the increase at the optimum injection timing of 34° CA was found to reach 38%. It was concluded that the exhaust gas stream of a low heat rejection (LHR) Diesel engine is the most important source of available energy, which must be recovered via a secondary heat recovery system.