A Comparative Study on the Thermodynamic Analysis and Performance Characteristics of a Dedicated EGR Gasoline Engine Under Various D-lambda

The concept of D-EGR (Dedicated EGR) used high EGR rate and fuel reformation to improve thermal efficiency, entire exhaust gas which supplied from a single cylinder is recirculated to the intake system and then entered into all cylinders to improve combustion. In this study, the D-EGR system is performed on a 1.5 L port fuel injection 4-cylinder gasoline engine, in comparison to the basic engine, the reduction of fuel consumption is about 20~30 g/kWh in most of the D-EGR engine operating range, a maximum 104.1 g/kWh BSFC reduction is found at 14.0bar@1800rpm, the lowest fuel consumption is decreased from 253.7 to 224.3 g/kWh by D-EGR, and the corresponding maximum brake thermal efficiency is improved from 32.6 to 36.9%. D-lambda (the lambda of dedicated cylinder) is considered as the most significant factor to influence the fuel economy and combustion stability, the suitable range of D-lambda is around 0.69~0.82 to gain better engine performance under the whole operating points. D-lambda sweeps are conducted firstly at the lowest fuel consumption point, the fuel economy, combustion characteristics, and emission performance are analyzed. It can be seen that the rise of the degree of constant volume is the dominant contributor to the enhancement of thermal efficiency. The effect of D-lambda is investigated experimentally by first and second law of thermodynamic analysis, the energy and exergy distribution of in-cylinder combustion are calculated and the thermal equilibrium is discussed also. In addition, several typical points are selected to investigate the operating characteristics of the D-EGR engine over its whole operating range.