Computational and Experimental Study of Oxygenated Hydrocarbon Fuel Chemistry in Non-premixed Flames

Yale University, New Haven CT

Investigators

Abstract

1133211 Pfefferle Intellectual Merit: Plants are about 50 % oxygen by weight. Thus as society inevitably moves from fossil fuels towards renewable fuels, the oxygen content of combustion fuels will increase. The presence of oxygenated hydrocarbons in the fuel introduces important combustion science and public health issues that are addressed by the proposed research. First, oxygenates may reduce emissions of soot particles. Second, they can also increase emissions of other toxic combustion byproducts such as aldehydes. In order to rationally optimize soot reductions while minimizing air toxics emissions, we need to understand the chemical mechanisms of fuel decomposition and aromatic hydrocarbon formation for oxygenates. The number of oxygenates that can be made from vegetation is large, and the sooting tendencies and fuel decomposition products vary greatly as a function of oxygenate structure; thus strictly empirical approaches for choosing among them are not reliable. A strategy that analyzes a large number of oxygenated fuels and leads to methods that can predict mechanisms and reactivity from fuel structure is needed. Although the combustion chemistry of hydrocarbons and some small oxygenates has been widely studied, little is known for most oxygenated hydrocarbons. We propose a novel approach that is based on rapid, on-line species measurements and computational simulations in co-flow flames where a small amount of the oxygenated fuel is added to a base fuel of methane. The base methane flame is has been well characterized and computations provide good agreement with experimental species measurements. Our strategy involving perturbation of a well-characterized system enables high-quality measurements and also facilitates simulations because the solutions from previously computed base methane flames can be used as a starting estimate for all of the doped flames. Importantly, our methods compare the fate of oxygenated fuel species under identical flame conditions emphasizing differences in chemical mechanisms over other factors. In earlier work we validated this methodology for regular hydrocarbons including heptanes, hexenes, hexadienes, cycloalkanes and aromatics. Here we will extend it to 100+ oxygenated hydrocarbons with up to 20 carbon atoms. Our results will provide an important comparison to other studies of oxygenates combustion chemistry, most of which use premixed flames and a limited number of oxygenated fuel structures. The analysis of a wide range of structures is required for development of structure/reactivity relationships allowing robust mechanism testing and a rational basis for oxygenated fuel selection to optimize emissions benefits. Broader Impacts: Our work sets the stage for cleaner engine design and renewable fuels utilization by expanding the database to oxygenated hydrocarbons, and by providing rational correlation and extrapolation data for the effect of fuel structure on soot production and possible toxic oxygenated emissions. We will collaborate with local industry to facilitate this. We have provided detailed results from our previous studies to numerous groups around the world who have used them to test computational models. The databases generated here will be archived for direct access to researchers around the world. Undergraduate students have participated in our previous research and will perform laboratory modules related to this project. We will also involve students from local non-PhD granting colleges and high schools in our work and helping them develop research projects at their home institutions and to interest them in continuing study in the sciences.