Evaluation of heavy-duty engine exhaust hydrocarbon and non-methane hydrocarbon analysis methods.

摘要

The harmful environmental and health effects of automobile exhaust constituents have necessitated their regulation in many countries. The constituents of concern from diesel fueled engines are oxides of nitrogen (NOx), hydrocarbons (HC), carbon monoxide (CO) and particulate matter. Hydrocarbons combine with the oxides of nitrogen in a photochemical reaction, aided by sunlight, to form ozone which is a major constituent of smog. However methane does not aid in smog formation and is excluded from the present United States on-road hydrocarbon regulation.; Flame ionization detectors (FID) are the preferred detectors for hydrocarbon measurement from compression ignition internal combustion engines. Regulatory requirement for non-methane hydrocarbon measurement involve the determination of total hydrocarbon using a FID-based analyzer and methane measurement using gas chromatographs (GC) and subtraction of these two values. New regulatory standards allow the use of non-methane cutter equipped analyzers for on-line determination of exhaust methane content.; The SAE J1151 standard GC method and an in-house GC method, incorporated at West Virginia University (WVU), were compared for correlation in methane measurements. The total hydrocarbon measurements from the WVU method were compared with bench analyzer results. A non-methane cutter equipped California Analytical Instruments (CAI) heated FID hydrocarbon analyzer capable of continuous methane measurements was evaluated for correlation with the SAE J1151 GC method. Day-to-day repeatability of the analyzer and SAE J1151 GC method was studied.; Good correlation was observed in the methane measurements by the two GC methods. The SAE J1151 GC methane measurements with natural gas samples were 5% lower than the WVU GC method results. A projection factor was determined to estimate THC concentration from methane concentration. The methane results from the two GC methods showed poor correlation for diesel-based fuel samples but the range of concentration in the values were within the drift limits of the detectors to make any inferences. The total hydrocarbon measurements from the WVU GC method had poor correlation with the analyzer results. The CAI HFID analyzer results agreed well with the results of the SAE J1151 GC method indicating its capabilities in methane measurement. The SAE J1151 GC method showed greater variability with transient exhaust emission test dilute bag samples but the results were within the allowable precision in the standard. The CAI analyzer showed good repeatability when tested with tunnel background samples. The Horiba total hydrocarbon analyzer showed increasing variations in day-to-day measurement in the repeatability tests. Due to the very small magnitude of brake specific methane values associated with diesel-based fuels the final brake specific NMHC concentration reported is not affected significantly by the method of methane analysis.