The influence of Exhaust Gas Recirculation (EGR) on combustion and emissions of n-heptane/natural gas fueled Homogeneous Charge Compression Ignition (HCCI) engines

In Homogeneous Charge Compression Ignition (HCCI) combustion, a lean premixed charge combusts simultaneously in multiple sites. Utilizing highly diluted mixtures, and lack of any significant flame propagation, in-cylinder NOx formation is reduced. Making HCCI engine a feasible alternative to conventional engines requires several challenges to be resolved. Combustion timing control is one of the most important of these items. It should be done in order that heat is released at the most optimum phasing for efficiency and emissions. In this study, a Waukesha Cooperative Fuel Research (CFR) single cylinder research engine was used to be operated in HCCI combustion mode fueled by natural gas and n-heptane. The main goal of the experiments was to investigate the possibility of controlling combustion phasing and combustion duration using various Exhaust Gas Recirculation (EGR) fractions. For the analysis of the results, a modified apparent heat release model was developed. The influence of EGR on emissions was discussed. Results indicate that applying EGR reduces mean charge temperature and has profound effect on combustion phasing, leading to a retarded Start of Combustion (SOC) and prolonged burn duration. Heat transfer rate decreases with EGR addition. Under examined condition EGR addition improved fuel economy, reduced NOx emissions and increased HC and CO emissions.

The paper investigates the effect of EGR on performance, combustion, and emission characteristics of dual-fuel HCCI combustion based on an improved heat release model.Figure optionsDownload as PowerPoint slideHighlights
► A new apparent heat release model developed for HCCI combustion engines is utilized as a diagnostic tool.
► Applying EGR has profound effect on combustion phasing, leading to a retarded SOC and prolonged burn duration.
► Applying EGR is favorable regarding fuel economy.
► The influence on emission characteristics is desirable with respect to NOx formation and unfavorable in the case of CO and HC emissions.