Biodiesel combustion: Advances in chemical kinetic modeling

Burgeoning global demand for energy has increased concerns about the fuel security issues and deleterious environmental impacts that result from the ubiquitous use of fossil fuels to meet these needs. This article is a review of completed work towards the goal of creating chemical kinetic mechanisms for biodiesel, which will aid in the development of clean and efficient combustors that utilize alternative fuels. As the composition of biodiesel is too complex to directly model, efforts have instead focused on the development of mechanisms for surrogates, simpler molecules that can produce the primary characteristics of biodiesel combustion. Research initially targeted smaller molecules like methyl butanoate to investigate the role of the characteristic ester group that is present in the fatty acid alkyl esters that comprise biodiesel. The study of isomers and similar unsaturated compounds elucidated the effects of molecular structure on combustion. Subsequent efforts involved the study of larger molecules that are close in scale to biodiesel molecules, such as methyl decanoate, as well as molecules that are present in biodiesel, such as methyl stearate. Applications of kinetic modeling demonstrate its utility in the study of combustion through, for example, revealing the chemistry in the early formation of CO₂ in biodiesel and its soot reduction tendencies. The results of this review illustrate key limitations in kinetic modeling, namely a need for high-pressure kinetic methodology and a need for continuous improvement of kinetic mechanisms through theory and experiment. These limitations suggest direction for future research; further experimental and theoretical work will produce accurate mechanisms for appropriate biodiesel surrogates. All of these efforts represent significant advances in kinetic modeling that are important towards the goal of building a predictive capability for biodiesel combustion. Such predictive capability will aid the development of combustion technologies that will help society meet its energy needs in an environmentally conscious manner.