Single-Shot Temporally and Spatially Resolved Chemiluminescence Spectra from an Optically Accessible SI Engine 950105

Technological advances in fast multi-element detectors now permit single-shot temporally and spatially resolved chemiluminescence spectra to be observed from an optically accessible four-stroke single cylinder spark-ignition engine. We demonstrate three techniques using multi-element detectors. First, with a wavelength coverage of 300 - 700 nm, we have observed the chemiluminescence spectra from individual combustion events with a time-gated intensified linear photodiode array. The broad wavelength coverage allows discrete spectral peaks of multiple species (OH, CH, C₂, CN, NH) to be observed simultaneously and be distinguished from the continuum luminosity of the spectra. Second, by using a digital streak camera equipped with UV optics, the continuous time evolution of the chemiluminescence spectra was obtained from the spark gap of the engine. The temporal evolution of the plasma spectra from the spark-gap region was observed on short time scales (nanoseconds through microseconds). Third, single-shot spatially and temporally resolved chemiluminescence spectra were observed with a time-gated intensified CCD camera placed in the image plane of an image-preserving spectrometer.

Using these three techniques, we are able to determine the spatial distribution and temporal evolution of the chemiluminescence spectra from the spark-breakdown and combustion regions of the engine chamber. In the spark-gap region, CN and NH dominate the spectra for the duration of the glow discharge. In fact, the emission from the CN and NH radicals is most intense during the first 10 μsec after spark-gap breakdown in the spark region. In addition, the strong nitrogen-radical chemiluminescence is observed only during the spark discharge time interval. Away from the spark gap, chemiluminescence is strong from OH, CH and C₂. No evidence of chemiluminescence from CN or NH is observed in the flame.