The Sootless Diesel: Use of In-Plume Fuel Transformation to Enable High-Load, High-Efficiency, Clean Combustion

The emission of solid carbonaceous particulate matter (i.e. soot) is a world-wide problem that effects both human health and global environmental health alike. Although a number of sources contribute to the concentration of soot in the atmosphere, Diesel engines play a significant role. Diesel engines, or direct-injection compression-ignition engines, are the primary power plant for delivering the work required for heavy-duty transportation. In other words electrification is highly unlikely, and thus internal combustion of fuels, namely hydrocarbons, will continue to be required well into the foreseeable future. The research conducted under the Sootless Diesel project is aimed at understanding the available strategies for reducing, if not eliminating, soot emissions. Understanding the fundamental nature of soot formation within a directly-injected fuel jet is of critical importance. A model has been developed that includes rapid mixing due to turbulence effects, the ability to handle complex chemical kinetic mechanisms, as well as a phenomenological soot model. This tool can provide insight into how different fuels behave, what the effect of ambient gas conditions and composition are, and perhaps how to prepare the fuel with an additive or moderator that could effect soot-forming chemical pathways. In addition, this project has worked at making a practical connection to the heavyduty engine industry by demonstrating emissions goals with measurements from a reciprocating single-cylinder research engine. This testbed has been used to show that both methanol and ethanol can be used in a Diesel engine while emitting belowregulation-limit levels of soot. This remains true even at stoichiometric proportions of fuel and air, which maximizes the work output from the engine. In addition, the combustion efficiency, or ability for the fuel to fully oxidize, remains very high. The implications for the future are that clean, high-load Diesel engines operating on alternative fuels with minimal aftertreatment are absolutely realizable.