RAMAN SPECTROSCOPY IN A COMBUSTING SPARK IGNITION ENGINE

$^{1}$J. R. Smith, AIAA Journal, Vol. 18, No. 1, January 1980 $^{2}$J. R. Smith, SAE paper no. 800137, February 1980.Author Institution:The hostile environment of the Otto cycle engine presents a challenge to acquiring Raman spectra. This work demonstrates methods of background light rejection and data processing to record useful Raman signals. Both time-averaged spectra and single shot measurements are presented. The single shot nitrogen Stokes vibrational scattering signal is used to determine density $fluctuations^{1}$. Simultaneously, the single shot anti-Stokes and Stokes nitrogen intensities are ratioed to determine temperature and probability density functions of $temperature^{2}$. This is accomplished with spatial resolution of the order of a millimeter and time resolution of 10 nanoseconds. A pulsed Nd:YAG laser is used to produce the Raman scattering. Detection is done with a single spectrometer and two GaAs photo-multiplier tubes. Special electronics are used to make a differential measurement of the charge output of each PMT which effectively rejects the high luminosity of the combustion process in the engine. A mini-computer records the anti-Stokes and Stokes signals, normalizes them by the energy of each laser pulse and converts them to engineering units. This is done once each engine cycle at 1200 rpm (i.e. 10 pulses per second). This work supported by Department of Energy