Biodiesel has been shown to be highly effective in reducing CO, HC, PM and greenhouse gas emissions from diesel engines, decreasing dependence on petroleum imports and developing new markets for domestic agricultural products such as soybeans. Unfortunately, many research studies have also shown that biodiesel results in an increase in NOx emissions. The perceived NOx penalty associated with biodiesel threatens to limit its widespread acceptance since engine manufacturers and regulatory agencies continue to struggle with NOx emissions from mobile diesel sources. The vast majority of the literature has focused on differences in physical properties (bulk modulus, boiling point, viscosity, etc.) between biodiesel and petroleum diesel as the mechanism for increased biodiesel NOx. However, there is increasing evidence that biodiesel NOx increases are related to fundamental differences in the chemical oxidation mechanism of biodiesel (i.e. methyl esters) in comparison to petroleum diesel. Unfortunately, very little work has been done to develop detailed chemical kinetic mechanisms for long chain methyl esters and to evaluate why these molecules result in increased NOx and decreased PM. A better understanding of biodiesel NOx and soot processes, will lead to the development of even cleaner burning renewable fuels.
Intellectual Merit This Major Research Instrumentation Grant is for the purchase of a rapid compression machine (RCM) that will be used for fundamental chemical kinetic studies on biofuels. An RCM is an instrument designed to simulate the compression stroke of a single engine cycle allowing auto-ignition phenomena to be studied in a much more controllable environment than that which is possible in an actual engine. The RCM will be integrated with a novel fast response NO/NO2 analyzer that will allow time-resolved NOx measurements and a rapid quenching system that will enable sophisticated gas analysis of combustion products and intermediates. By performing experiments on biofuels (and surrogate fuels) in an RCM it will be possible to isolate the chemical kinetic effects on NOx and soot production from the variety of other processes that are present in an actual diesel engine. Moreover, data acquired using this system will be integral to developing a data base necessary for adopting a universally accepted reference fuel for biodiesel, such as methyl oleate. Development of an RCM capability dedicated to alternative fuels research will effectively bridge the gap between the handful of fundamental combustion studies on smaller biodiesel surrogates and the multitude of engine studies in which the underlying mechanisms responsible for pollutant emissions are difficult to isolate.
Broader Impacts Environmental essayist Bill McKibben rightfully suggests that global warming is the first civilization-scale challenge ever faced by the human race. While there is no single technological panacea for this omnipresent challenge, renewable fuels such as biodiesel have the potential to play a significant role in mitigating greenhouse gas emissions since they are nearly CO2 neutral. A solution to the perceived biodiesel NOx problem will result in further widespread acceptance of biodiesel by engine manufacturers and government agencies, thereby resulting in decreased greenhouse gas emissions. Decreasing PM emissions from diesel engines is an equally important issue that can be addressed through the use of biodiesel. Diesel PM has been classified as a probable human carcinogen by the World Health Organization and the USEPA, and recent studies have linked diesel PM to heart disease.
