Concentration and Size Distributions of Nanoparticle Emissions during Low Temperature Combustion using Fuels for Advanced Combustion Engines (FACE).

摘要

Due to tightening emission legislations, both within the US and Europe, including concerns regarding greenhouse gases, next-generation combustion strategies for internal combustion (IC) 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 NOx 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. The Advanced Vehicles, Fuels, and Lubricants (AVFL) committee of the Coordinating Research Council (CRC) specified and formulated a matrix of nine test fuels for advanced combustion engines (FACE) based on the variation of three properties: cetane number, aromatic content, and 90 percent distillation temperature.;The primary objective of this study was to study 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 nanoparticles was investigated as well.;Diluted exhaust gas emissions extracted from the CVS tunnel were measured continuously using a Horiba MEXA-7200D gaseous emissions analyzer and included total hydrocarbons (THC), carbon monoxide (CO) as well as carbon dioxide (CO 2) and oxides of nitrogen (NOx). NOx and O 2 concentrations were measured in the raw exhaust and intake manifold using Horiba MEXA-720 NOx analyzers, respectively.;Furthermore, the AVL Micro Soot Sensor, consisting of a measuring unit and an exhaust conditioning unit, was used to measure the soot concentration in the raw exhaust based on the photoacoustic measurement method.;Nanoparticle concentration and size distributions were determined using the Exhaust Emissions Particle Sizer (EEPS(TM)) spectrometer from TSI Inc. (model 3090) as well as the Differential Mobility Spectrometer (DMS) from Cambustion (model DMS500). Continuous exhaust gas samples were extracted from the CVS tunnel (dilution ratio DR ≈ 10) and routed through a double stage dilution system using ejector type dilutors. The first stage was maintained at 140°C (DR ≈ 6) in order to suppress condensation and particle nucleation phenomena, while the second stage utilized dilution air at ambient temperatures (∼25°C, DR ≈ 11).;Particle number concentration increased with a simultaneous increase in particle diameter for both single and split injection strategies in case of FACE diesel fuels with increasing CN for the low NOx, low soot and highest 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 low CN fuels.