Effects of design and operating parameters on the performance of a quasi-realistic Diesel cycle engine

Abstract

Although Diesel engines have begun to be abandoned in the automotive industry due to the emission legislations of the world, they are still widely used in generators, work machines, agricultural machines, and heavy vehicles due to their high power density and thermal efficiency. The classical Diesel cycle, which is the thermodynamic cycle of Diesel engines, was developed by taking into account irreversibilities, heat transfer losses, friction, and gas exchange process, and a quasi-realistic Diesel cycle was obtained. Also, the working fluid of the Diesel cycle has been accepted as an air-fuel-residual gas mixture instead of air. This Diesel cycle model is very useful to examine the effect of Diesel engines' design and operating parameters on engine performance. For this study, the effect of variation in equivalence ratio, stroke-bore ratio, and compression ratio on engine performance was examined. Thermal efficiency, maximum temperature, exhaust temperature, fuel consumption, and specific fuel consumption are used as engine performance parameters. The characteristics and operating conditions of a Diesel engine in a power generator were used for the numerical study. Engine performance increased by increasing the equivalence ratio, which is the engine operating parameter. When the compression ratio, which is the structural parameter, increased, the engine performance increased, but the maximum temperature also increased, although it was not desired. Therefore, it is necessary to optimize the compression ratio and the maximum temperature. Again, when the stroke-bore ratio, which is a structural parameter, was increased, engine performance decreased, but the maximum temperature decreased as desired. For optimization of the two structural parameters, compression ratio, and stroke-bore ratio, it is necessary to decrease the stroke-bore ratio while increasing the compression ratio. The results obtained with the numerical study using the created model are guiding for engine designers.