Second-law analysis of the reforming-controlled compression ignition

This paper presents the optimization of energy conversion in a novel reforming-controlled compression ignition system, combining the benefits of low-temperature combustion with high-pressure thermochemical recuperation (mostly from the perspective of the second law of thermodynamics). Further, new insights into ways of improving efficiency are provided. A promising renewable fuel dimethyl ether is analyzed for the first time as a primary fuel. A comprehensive analysis of various factors influencing exergy destruction in the reforming-controlled compression ignition system in their complex interdependence is also performed for the first time. Exergy mapping results show that approximately 33% of the exergy supplied to the system is destroyed owing to irreversible processes in the cylinder itself, and approximately 5% is destroyed in the reforming system (intercooler, vaporizer, and reformer). The reformer is the main source of exergy destruction in the reforming system. Approximately 45% and 38% of the engine exergy destruction is related to chemical reaction and in-cylinder-walls heat interaction, respectively. The results indicate that the efficiency improvement due to second-law optimization reaches up to 7.1%, and if the compression ratio is increased to 18:1 instead of 16:1, this reaches up to 9.2%. The higher improvement is achieved at the highest loads.