CAREER: Fuels, Additives and Emissions in Low-Temperature Combustion

Brown University, Providence RI

Investigators

Abstract

CBET-1553366, Goldsmith One strategy to reduce the engine exhaust emissions is to control the combustion at a temperature lower than the conventional value. Low-temperature compression-ignition engines represent a new class of internal combustion engines that could meet the stringent and imminent fuel economy requirements. Engineers typically add additives to the fuel to improve the engine performance. The most commonly used additive contains nitrogen, yet the fate of fuel-bound nitrogen in low-temperature combustion is poorly understood. Although some of the ultimate combustion byproducts formed by nitrogen-containing additives in these engines may be comparatively benign, other byproducts are highly toxic, and the relative yield of these toxic byproducts is not known. The goal of this proposal is to discover the fate of fuel-bound nitrogen in advanced engines. Over the course of five years, the PI will combine novel experimental, theoretical, and modeling techniques to provide quantitative measurements and kinetic predictions for the combustion byproducts of nitrogen-containing additives under engine-relevant conditions. This research will provide engineers with the tools to quantify the interactions between additives and transportation fuels in internal combustion engines, and to predict how changes to the additive, the fuel, or the engine will affect the emissions. Additionally, this research will benefit atmospheric chemists by improving their forecasts of smog and related problems. Finally, the PI will develop a series of educational modules that illustrate how changing the structure of a fuel changes its combustion properties, and will create hands-on design projects in which students build different combustion devices. The most widely used fuel additive in low-temperature compression-ignition engines is 2-ethyl-hexyl nitrate (2EHN). The hypothesis is that a significant percentage of the nitrogen in 2EHN exits the cylinder as hydrogen cyanide and other highly toxic compounds. To test this hypothesis, shock tube experiments, electronic structure theory, and kinetic modeling studies will be combined to quantify the various nitrogen containing products and establish the reaction pathways that produce them. Additionally, the PI will collaborate with engineers at Argonne National Laboratory to develop computational models to predict how 2EHN will interact with real-world transportation fuels, such as n-heptane, iso-octane, and toluene. Many key pathways in low-temperature compression-ignition engines are kinetically controlled, so these engines produce different combustion byproducts than conventional, high-temperature engines. Knowledge of these pathways is particularly important for fuel additives that contain nitrogen. The majority of our understanding of nitrogen chemistry is limited either to high temperatures in excess of the thermal NOx limit, or low temperatures in the atmosphere. This proposal will fill in a crucial gap in our understanding of nitrogen chemistry by elucidating the key chemical pathways for the oxidation and reduction of nitrogen containing species below the thermal NOx threshold.