Time-Resolved Infrared Spectroscopy: Evaluation of Temperature for Various EGR Rates in a DI-Diesel Engine

The present paper describes IR radiation measurements carried out during the combustion of various fuels and for a number of EGR rates within the transparent Volkswagen DI-Diesel engine using a specially designed IR spectrometer of high spectral and temporal resolution. To probe the IR radiation in the spectral range of 1.2 μm to 5.3 μm, the engine was equipped with a sapphire window screwed into the glow plug bore. Three different fuels were investigated, including commercial Diesel and model fuels consisting of one or two components. The exhaust gas recirculation (EGR) rates have been varied from 0 % to 70 %. For all three fuels, the IR spectra exhibit a structure formed primarily by the main bands of H₂O, CO and CO₂ and strong continuous radiation stemming from soot particles. Soot radiation intensities vary with time and EGR rates. Assuming local thermal equilibrium and blackbody conditions, the continuum at definite wavelengths was used to evaluate temperature histories as a function of EGR rates. It was found that the maximum temperature decreases with the increase in EGR rates. The intensity of CO and CO₂ band radiation, however, is nearly independent of EGR.