Time-resolved infrared imaging and spectroscopy for engine diagnostics

Abstract

Molecular emissions in the infrared spectral region can provide access to a range of quantities that are of interest in internal- combustion engine research and development. Molecules; such as water, carbon dioxide, carbon monoxide, and hydrocarbons; provide the strongest signals in the range from 1.0 to 5.5 μm. We describe several imaging experiments that employed high-frame-rate infrared cameras to capture spectrally resolved and spectrally integrated signals from both optical and production engines. Spectrally resolved infrared emissions that were recorded at kHz rates (i.e., crank-angle steps) in an optically accessible, propane-fueled, single-cylinder engine are used to guide the development and validation of a radiative-emission model that is integrated into large-eddy simulations (not discussed in this paper). The emissions were dispersed with a spectrometer, and the spectra were recorded with an InSb camera. Clear spectral signatures from water and carbon dioxide were recorded, and the spectra reveal the evolution of combustion through each of 100 consecutive cycles for each engine run. Furthermore, at any wavelength of these spectra, cycle-to-cycle variation can be extracted readily. Cycle- to-cycle variation was of particular interest in a study of a production heavy-duty engine fueled by natural gas.The addition of two borescopes outfitted with high-frame-rate In- GaAs cameras enabled spectrally integrated measurements from 1.0-1.7 μm. The images allow cycle-resolved observations of ignition and flame growth. The intent of this work was to identify and quantify the impact of a range of ignition systems on lean and/or dilute operation limits from a combustion development and stability point of view.