Active fuel design—A way to manage the right fuel for HCCI engines

Abstract

Homogenous charge compression ignition (HCCI) engines feature high thermal efficiency and ultralow emissions compared to gasoline engines. However, unlike SI engines, HCCI combustion does not have a direct way to trigger the in-cylinder combustion. Therefore, gasoline HCCI combustion is facing challenges in the control of ignition and, combustion, and operational range extension. In this paper, an active fuel design concept was proposed to explore a potential pathway to optimize the HCCI engine combustion and broaden its operational range. The active fuel design concept was realized by real time control of dual-fuel (gasoline and n-heptane) port injection, with exhaust gas recirculation (EGR) rate and intake temperature adjusted. It was found that the cylinderto-cylinder variation in HCCI combustion could be effectively reduced by the optimization in fuel injection proportion, and that the rapid transition process from SI to HCCI could be realized. The active fuel design technology could significantly increase the adaptability of HCCI combustion to increased EGR rate and reduced intake temperature. Active fuel design was shown to broaden the operational HCCI load to 9.3 bar indicated mean effective pressure (IMEP). HCCI operation was used by up to 70% of the SI mode load while reducing fuel consumption and nitrogen oxides emissions. Therefore, the active fuel design technology could manage the right fuel for clean engine combustion, and provide a potential pathway for engine fuel diversification and future engine concept.

Autoignition Comparison of n-Dodecane/Benzene and n-Dodecane/Toluene Blends in a Constant Volume Combustion Chamber

“…Autoignition propensity is an important property for the fuels used for diesel combustion engines because the combustible mixture in diesel engines is prepared through direct fuel injection in the compression stroke and ignited by piston compression. Fuel autoignition propensity is particularly of importance in the advanced diesel combustion strategies, for example, low-temperature combustion, , premixed charge compression ignition, , and stratified charge combustion ignition. , In these advanced combustion concepts that require a more uniform mixture distribution, the fuel and charge mixing quality highly depends on the length of the ignition induction period that is significantly influenced by fuel autoignition propensity. Therefore, researches have been conducted to investigate the diesel autoignition characteristics and chemical kinetics − and the influential factors to control the fuel ignition delay (ID) times in the engine cylinder. − …”

Effects of Mixture Stratification on Combustion and Emissions of Boosted Controlled Auto-Ignition Engines

“…Since that time, a lot of effort has been put into understanding and development of the CAI combustion concept. CAI operation has been also investigated using a wide range of fuels [8][9][10][11][12].…”