Fast-spec: An infrared spectroscopic diagnostic to measure time-resolved exhaust hydrocarbon emissions from S.I. engines

An infrared spectroscopy-based system has been developed that attaches to the exhaust port of an S.I. engine and is used to make time-resolved measurements of unburned hydrocarbon emissions. Radiation from a miniaturized infrared source was coupled into modified white cell optics through sapphire windows sealing a transmission cell integrated into the exhaust manifold. The radiation absorption from the 3.4-μm vibrational stretch band common to all hydrocarbons is used to quantify the hydrocarbon concentration fluctuations throughout the exhaust process. The diagnostic system was tested in a CFR engine operated at 600 rpm using propane fuel. It measured the hydrocarbon concentration spatially averaged across the exhaust manifold. The temporal resolution of the measurements was 830 μs (3.0 crank-angle degrees). Four fuel/air equivalence ratios were examined. The peak in hydrocarbon exhaust concentration that occurs shortly after exhaust valve opening was found to have a much large magnitude and shorter duration than has been seen previously with fast flame ionization detector (fast-FID) measurements. Reasonably good agreement was found between the mass integrated HC concentrations and those measured using an FID; however, more work is needed to better quantify the accuracy of the technique. The sensitivity and signal-to-noise ratio of the system were very high with fluctuations of approximately 15 ppmc3 resolvable.