Investigating the effect of EGR on HCCI combustion of n-heptane

HCCI combustion is a hybrid concept of compression and spark ignition combustions. In this mode of combustion, a lean premixed charge combusts simultaneously from multiple sites. It has no indication of flame propagation. Utilizing very lean mixtures, and the lack of any flame propagation, considerably reduces in-cylinder NOx formation. In order to make the HCCI engine a feasible alternative to the SI and CI engines,several items must be elucidated. Control of the combustion timing is one of the most important of these items to be resolved. Combustion timing should be controlled in order that heat is released at the best time in the engine cycle. In this study, a Waukesha CFR single cylinder research engine with variable EGR was studied in University of Alberta engine research facility. The main objective of the study is the investigation of how EGR percents can affect the HCCI combustion. In order to achieve this goal, a modified first law apparent heat release model, developed by the authors, was utilized. Utilizing this model, guarantee obtaining a well-behaved and accurate apparent heat release trend and magnitude in HCCI engines. Also, the influence of EGR on emissions was discussed. Results indicate that applying EGR has profound effect on combustion phasing, leading to a retarded SOC and prolonged burn duration. It is favorable regarding fuel economy, too. The influence on emission characteristics is desirable with respect to NOx formation and unfavorable in the case of CO and HC emissions.

Keywords:

HCCI , n-heptane , EGR , Heat release