Quantitative In-Cylinder Fluid Composition Measurements Using Broadband Spontaneous Raman Scattering

A measurement technique is described which permits quantitative, multi-point, in-cylinder fluid composition measurements in an internal combustion engine. The technique is based on spontaneous Raman scattering with broadband signal collection, and provides simultaneous determination of the mole fractions of H₂O, CO₂, N₂, O₂, and fuel (C₃H₈). Calibration and data reduction procedures which largely eliminate interference between the signals from the various species are discussed. Mean mole fractions obtained in an optical access engine from the beginning of the intake stroke to the end of the compression stroke are reported. The mean mole fractions of the individual species are used to obtain independent estimates of the mean mole fraction of burnt residual gases, which, in turn, are used to evaluate the accuracy and consistency of the data. An over-prediction of the CO₂ mole fraction in hot exhaust gases is found to be the most significant shortcoming of the technique. This over-prediction is believed due to variation in the scattering cross-section of CO₂ with temperature.