Development and application of a time and space resolved optical diagnostic for soot temperature and concentration in a spark-ignited direct-injection engine

Soot temperature and concentration in a spark-ignited direct-injection engine have been studied using time- and space-resolved soot luminosity, radiating from hot soot particles. The study starts with a sensitivity and uncertainty analysis, where the applicability of the two-color technique was evaluated. Quantitative analysis of the sensitivity of the two-color technique was inferred from soot particle size probability-distribution functions in a zero-dimensional space and the variation in the temperature range using a fixed distribution in particle sizes. Using the results from this analysis, it was found that the sensitivity of the measured temperatures to particle size distribution will remain within 0.4--9%. In addition, Monte Carlo model was used to provide a direct three-dimensional simulation of the amount of the transmitted light along the line of sight through a fictitious cloud of soot particles. The results show that the uncertainty in the measured temperature at the bottom of the particle system is within acceptable limits. The analysis also showed that sensitivity of the measured relative soot concentration with respect to temperature distribution along the line of sight could be as high as 33%.; After quantifying the measurement limits of the two-color technique, a systematic evaluation of the usefulness of the two-color pyrometry technique was conducted over a number of different operating conditions in a wall-guided SIDI engine. The study provided a meaningful comparison with fuel-film and equivalence ratio measurements previously conducted in this engine, which was beneficial in obtaining a better understanding of the physical process that lead to soot formation and oxidation. The study was also instrumental in demonstrating practical benefits of the two-color-technique in this engine, by identifying the influence of fuel injection timing, the amount of intake air swirl, and injector type on in-cylinder soot formation and oxidation. These measurements successfully identified pool fires as the major source of engine-out soot emissions for this engine.