Gas Chromatograph-Based System for Measuring the Methane Fraction of Diesel Engine Hydrocarbon Emissions

摘要

An instrument has been developed (termed the 'methane analytical system') enabling diesel methane emissions to be quatified separately from total unburned hydrocarbon emissions. The instrument employed gas chromatographic principles whereby a molecular sieve column operating isothermally separated methane from the nonmethane hydrocarbons. Direct on-line sampling occurred via constant volume sample loops. The effluent was monitored with a flame ionization detector. The instrument was fully calibrated (i.e., extremely linear response over a large concentration range) for use with Diesel engines as part of an on-going alternative fuels research program. Methane emissions from a light-duty, multi-cylinder, indirect-injected Diesel engine fumigated with natural gas were measured on-line using the methane analytical system. Methane emissions were found to range from as low as 250 ppm to a high of nearly 2%. The nonmethane hydrocarbon emissions were determined by subtracting the methane level from the total unburned hydrocarbon level. In the event that the federal engine certification procedures are changed to be based on nonmethane hydrocarbon emissions, a methane analytical system such as the one described here would have great utility.