For gasoline fueled engines, diluted and low-temperature homogeneous charge compression ignition (HCCI) techniques have opened an affordable solution to maintain their attractiveness in low NOx levels and rising demand of fuel efficiency. However, this approach is limited to a certain range of low-load engine conditions due to combustion instability and lack of autoignition controllability. To fulfill broad range of engine operating conditions while upholding such intrinsic benefits, controlled ignition techniques have been suggested to extend effectiveness of advanced compression ignition (ACI) regimes across more practical range of engine load.  Combination of the ACI with spark ignition (SI) combustion can provide a solution to meet this demand and hence arguably cover full-load range. Such a concept can be pursued in a multi-mode combustion strategy and hence requires engines to operate in two distinct combustion modes and transition between those when needed. The engines may also need to operate in mixed-mode regimes in order to boost the benefits and allow for smooth mode switch. This study explores the concept of multi-mode gasoline fueled engine by performing 3-D CFD simulations in a single cylinder GDI engine platform. To cover the varying engine load demands, first aim of the study goes to evaluating the combustion characteristics in ACI mode at low or part-load engine conditions. In this part, details of analysis and the CFD model assessment are provided in perspective of flameless auto-ignition in conjunction with thermodynamic state of mixture charge and thermal stratification. Secondly, the study is dedicated to demonstrating the validity of the level-set based combustion model to simulate the premixed charge ignition and flame propagation. The test was conditioned at stoichiometric mixture charge aiming at full-load engine conditions. The simulations are verified against the relevant experimental data available for ACI and SI mode strategies. Considering a part-load and smooth transition between SI and ACI, a strategy of mixed-mode combustion is numerically explored by creating a virtual test condition. The results discover conventional spark ignition (deflagrative flame propagation) along with assisted end-gas autoignition phase as an evidence of mixed-mode combustion; therefore this marks a regime of spark-assisted compression ignition (SACI). Further investigation in the mixed-mode combustion presents the indication of potential gain of fuel efficiency and provide scientific insights into the controllable combustion stability.


Simulations of Multi-Mode Combustion Regimes Realizable in a Gasoline Direct Injection Engine

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

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