Availability analysis of n-heptane and natural gas blends combustion in HCCI engines

One of the major problems associated with HCCI combustion engine application is lack of direct control for combustion timing. A proposed solution for combustion timing control is using a binary fuel blend in which two fuels with different auto-ignition characteristics are blended at various ratios on a cycle-by-cycle basis.The aim of this research is to investigate the exergy analysis of HCCI combustion when a blended fuel, which consists of n-heptane and natural gas, is used. In order to accomplish this task, a single-zone combustion model has been developed, which performs combustion computations using a complete chemical kinetics mechanism.The study was carried out with different percentages of natural gas in blended fuels and EGR (exhaust gas recirculation) ranging from about 45 to 85 percent and 0 to 40 percent, respectively. The results reveal that, when mass percentage of natural gas increases, exergy destruction is decreased increasing the second-law efficiency. Introducing EGR into the intake charge of dual fuel HCCI engine up to some stage (optimum value) enhances the second-law performance of the engine in spite of a reduction in work.

► A single-zone model is developed for studying the availability analysis of a HCCI engine fueled with natural gas and n-heptane. ► When mass percentage of natural gas in the fuel blend increases, exergy destruction is decreased increasing the second-law efficiency. ► Introducing EGR into the intake charge of dual fuel HCCI engine up to an optimum value enhances the exergetic efficiency. ► The EGR values above this could deteriorate the engine performance.