High Temperature Sampling System for Real Time Measurement of Solid and Volatile Fractions of Exhaust Particulate Matter

摘要

This paper discusses the design and qualification of a High Temperature Sampling System (HTSS), capable of stripping the volatile fraction from a sample flow stream in order to provide for quantification of total, solid and volatile particulate matter (PM) on a near real-time basis. The sampling system, which incorporates a heated diesel oxidation catalyst, is designed for temperatures up to 450°C. The design accounts for molecular diffusion of volatile compounds, solid particles diffusion and reaction kinetics inside one channel of the oxidation catalyst. An overall solid particle loss study in the sampling was performed, and numerical results were compared with experimental data gathered at the West Virginia University Engine and Emissions Research Laboratory (EERL) and West Virginia University's Transportable Heavy-Duty Vehicle Emissions Testing Laboratory (THDVETL). Data indicated that "dry soot" aerosol streams, which were produced at a single engine operating mode on an engine test stand point using a dynamometer were largely unaffected by the sampling system. Important differences were identified in the nucleation mode between steady-state and transient tests - a smaller nucleation mode was observed in the transient operation. Depending upon the test cycle, the particle loss, on count basis, in the HTSS ranged from 10% to 26%. The HTSS was found to be very effective in scrubbing the volatile organic fraction (VOF) from the exhaust stream; hence, resulting in a 96% reduction in total PM count and 52% total PM mass under steady-state mode of engine operation. Under transient operation, the total PM count reduction was 55%, and the total PM mass reduction was 32%. The difference in the untreated sample stream and the treated sample was evident in the concentration and size distribution of nucleation mode particles. The sampling system represents a viable method for collecting nanoparticles and the larger accumulation mode particles and the opportunity to perform an extensive suite of chemical and morphological analyses.