Quantitative soot measurements in an HSDI Diesel engine

Quantitative in-cylinder measurements of soot volume fraction in a single-cylinder HSDI Diesel engine, based on a VOLVO D5, has been carried out using the laser-induced incandescence (LII) technique using laser excitation at 1064 nm and an ICCD camera with prompt gate detection. Quantitative data was obtained by relating the LII signal response from the engine to that from a calibration flame. The aim of this paper is twofold: to present quantitative data for relevant engine operating conditions and to discuss the issues related to quantification of the LII technique using the present approach. Two different operating condition schemes were investigated. In the first, the soot production for different amounts of EGR was investigated. The in-cylinder soot volume fraction levels were found to decrease with increasing EGR ratio in the tested EGR regime, which correlates well with engine-out soot emissions. In the second part of the investigation, the injection event was divided into one pilot injection and one main injection at a constant EGR ratio of 60%. The CAD position of the pilot injection was varied, while keeping the position of the main injection constant. Early pilot injection timings resulted in excessive fouling of the optical parts, thus limiting the accuracy of quantitative measurements. Still, the flow pattern of the soot within the cylinder is presented and discussed. The corrections needed to accurately estimate soot volume fractions in an optical engine by relating the integrated LII signal to that obtained in a calibration flame are discussed. Using a heat and mass transfer model for LII, the pressure and temperature effects on the absolute LII signals are investigated. Results show that the use of a short prompt gate (30 ns) is preferable in order to decrease systematic errors due to differences in the conditions between the engine and the calibration flame. Also the systematic errors introduced by potential particle aggregation are studied and discussed.