Number Concentration and Size Distributions of Nanoparticle Emissions during Low Temperature Combustion using Fuels for Advanced Combustion Engines (FACE) 2014-01-1588

Due to tightening emission legislations, both within the US and Europe, including concerns regarding greenhouse gases, next-generation combustion strategies for internal combustion diesel engines that simultaneously reduce exhaust emissions while improving thermal efficiency have drawn increasing attention during recent years. In-cylinder combustion temperature plays a critical role in the formation of pollutants as well as in thermal efficiency of the propulsion system. One way to minimize both soot and NO_x emissions is to limit the in-cylinder temperature during the combustion process by means of high levels of dilution via exhaust gas recirculation (EGR) combined with flexible fuel injection strategies. However, fuel chemistry plays a significant role in the ignition delay; hence, influencing the overall combustion characteristics and the resulting emissions. Therefore, the Fuels for Advanced Combustion Engines (FACE) Working Group of the Coordinating Research Council (CRC) specified and formulated a matrix of nine test fuels for advanced combustion engines based on the variation of three properties: cetane number, aromatic content, and 90 percent distillation temperature.

The primary objective of this study was to investigate the effects of various FACE diesel fuels on the nanoparticle formation during low temperature combustion processes. An experimental study was performed at West Virginia University's Engine and Emission Research Laboratory (EERL) to determine the FACE property effects on the low temperature combustion (LTC) process in a turbo-charged GM 1.9L light-duty compression ignition engine under steady-state operating conditions (2100rpm/3.5bar BMEP). A comprehensive test matrix was developed including intake oxygen (O₂), as a surrogate for EGR fractions, and rail-pressure parameter variations during single injection timing settings. Furthermore, the influence of varying injection timing and fuel fraction during split injection strategy onto nanoparticle formation was investigated as well.

Particle number concentrations increased with a simultaneous increase in particle diameter for both single and split injection strategies in case of FACE diesel fuels with increasing cetane number (CN) for the low NO_x, low soot and highest brake-thermal efficiency (BTE) tests. Advancing the start of injection timing led to a decrease in particle number concentration, but a simultaneous increase in nanoparticle emissions was observed for a low CN fuel.