Recent progress and challenges in fundamental combustion research

Abstract

More than 80% of world energy is converted by combustion. Development of efficient next generation advanced engines by using alternative fuels and operating at extreme conditions is one of the most important solutions to increase energy sustainability. To realize the advanced engine design, the challenges in combustion research are therefore to advance fundamental understanding of combustion chemistry and dynamics from molecule scales to engine scales and to develop quantitatively predictive tools and innovative combustion technologies. This review will present the recent progresses and technical challenges in fundamental combustion research in seven areas including advanced engine concepts using low temperature fuel chemistry, new combustion phenomena in extreme conditions, alternative and surrogate fuels, multi-scale modeling, high pressure combustion kinetics, experimental methods and advanced combustion diagnostics Firstly, new engine concepts such as the Homogeneous Charge Compression Ignition (HCCI), Reactivity Controlled Compression Ignition (RCCI), and pressure gain combustion will be introduced. The impact of low temperature combustion chemistry of fuels on combustion in advanced engines will be demonstrated. This is followed by the discussions of the needs of fundamental combustion research for new engine technologies. Secondly, combustion phenomena and flame regimes involving new combustion concepts such as fuel and thermal stratifications, plasma assisted combustion, and cool flames at extreme conditions will be analyzed. Thirdly, alternative fuels and methodologies to formulate surrogate fuel mixtures to model the target combustion properties of real fuels will be presented. A new concept of radical index and transport weighted enthalpy will be introduced to rank the fuel reactivity and to assess the impact of molecular structure on combustion properties The success and limitations of the current surrogate fuel models will be discussed by using jet fuels and biodiesels as examples. Fourthly, the difficulty of modeling large kinetic mechanism of real fuel will be discussed The multi-time scale (MTS) method and the correlated dynamic adaptive chemistry (CO-DAC) method for kinetic model reduction and computationally efficient modeling will be compared and analyzed. Fifthly, the progress and challenges of high pressure combustion kinetics for hydrogen and larger hydrocarbons will be discussed. The important pressuredependent reaction pathways and key intermediate species at high pressure will be analyzed. Fundamental experimental methods for combustion and their uncertainties in acquiring combustion properties for the validation of kinetic mechanism will be discussed. Finally, recent progress in diagnostics of HO2, H2O2, RO2, ketohydroperoxide, and other key intermediate species for high pressure kinetic mechanism development will be summarized. Conclusions and opportunities of future combustion research will be made.