Specific Net Work and Mean Effective Pressure Based Thermodynamic Analysis and Optimization of Ideal Atkinson Cycle

Abstract

In this study, the criteria for maximum values of specific net work and mean effective pressure in the air standard Atkinson cycle, which is the ideal thermodynamic cycle of internal combustion engines used in hybrid electric vehicles, were examined. For this, it was assumed that the cycle operates in a certain temperature range. Thus, while the maximum temperature of the cycle is constant, the compression ratio was optimized for maximum specific net work and maximum mean effective pressure. A case study was conducted for this study. For the case study, assuming the geometric expansion ratio of 12, the maximum temperature value of the cycle was determined as 1961.923 K. Based on this maximum temperature value, the maximum values of the specific net work and the ambient effective pressure were determined as 580.139 kJ/kg and 373.857 kPa, respectively. In addition, the geometric compression ratios for the maximum values of the specific net work and the ambient effective pressure were determined as 15.462 and 31.063, respectively. Looking at the geometric compression ratio values of today's engines, it was seen that these values were closer to the compression ratio at which the maximum specific net work was achieved. It was observed that the thermal efficiency increased when the compression ratio was optimized for the conditions where the maximum average effective pressure was achieved. The results obtained from this study are particularly attractive to engine designers.