Spray Combustion Chamber with Optical Access, Ignition Zone Visualization and First Raman Measurements of Local Air-Fuel Ratio

Exhaust gas quality and efficiency of diesel combustion are primarily influenced by the mixture formation process during fuel injection. The first step in understanding the mechanisms of pollutant formation is analyzing the atomization, self-ignition and burning of the injected spray. This paper presents the details of a combustion chamber developed to inject fuel into quiescent air and allow air pressures to 60 bar (900 psi) and air temperatures to 600°C (1100°F). The special design enables four-sided optical access for the visualization of the diesel spray movement and self ignition zones by high speed photography including Schlieren techniques. For different injected fuels (diesel fuel, methanol and n-heptane) the ignition delay has been determined and the dependence on pressure and temperature are shown. At those positions where ignition occurs, measurements of the local airfuel ratio have been performed with spontaneous Raman spectroscopy. To the knowledge of the authors, this is the first such application of Raman spectroscopy and the results demonstrate the usefulness of this method in the analysis of fuel sprays.