Studies have been conducted at Michigan Technological University (MTU) for over twenty years on methods for characterizing and controlling particulate emissions from heavy-duty diesel engines and the resulting effects on regulated and unregulated emissions. During that time, control technologies have developed in response to more stringent EPA standards for diesel emissions. This paper is a review of: 1) modern emission control technologies, 2) emissions sampling and chemical, physical and biological characterization methods and 3) summary results from recent studies conducted at MTU on heavy-duty diesel engines with a trap and an oxidation catalytic converter (OCC) operated on three different fuels.
Control technology developments discussed are particulate traps, catalysts, advances in engine design, the application of exhaust gas recirculation (EGR), and modifications of fuel formulations. Methods for dilution tunnel sampling, particle size analysis, chemical analysis with emphasis on polynuclear aromatic hydrocarbons (PAH) and nitro-PAK and biological characterization using mutagenic activity (Ames) assays are described, along with statistical approaches to experimental design and data analysis.
In studies at MTU, both particulate traps and an OCC have been shown to be effective for the reduction of total particulate matter (TPM), with the OCC being better at reducing an forms of hydrocarbon emissions, including PAH and nitro-PAH, and with the traps being better at removing the solids (SOL). The use of low sulfur fuel (0.01% by mass) has led to additional reductions in TPM; the low sulfur fuel has been shown to reduce the number of small, nuclei-mode particles for one of the engines tested. PAII, nitro-PAH, and mutagenic actively levels generally decreased with use of either the traps or the OCC.