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Initial measurements of water vapor temperature using a Fourier domain mode locking (FDML) laser were performed in a carefully controlled homogenous charge compression ignition engine with optical access. The gas temperature was inferred from water absorption spectra that were measured each 0.25 crank angle degrees (CAD) over a range of 150 CAD. Accuracy was tested in a well controlled shock tube experiment. This paper will validate the potential of this FDML laser in combustion applications.

A laser-based sensor has been developed which generates short multicolored pulses for use with absorption spectroscopy techniques for the collection of thermodynamic information in an HCCI engine. Our sensor is based on supercontinuum generation which is accomplished by coupling a short-duration, high energy laser pulse (the pump) into fiber optics where colors other than the pump are generated through various nonlinear phenomena. The resulting “white pulse” is then stretched out in time by dispersive media (e.g., another fiber) to a time scale which can be collected by a high speed detector and oscilloscope. Although other multicolored (wavelength agile) laser based techniques generated by scanning mirrors or gratings have been applied to HCCI combustion [1], our supercontinuum approach offers a broad range of wavelengths with both high spectral and high temporal resolution from a source with no moving parts.