Measuring and Predicting Transient Diesel Engine Emissions

Sammanfattning:  Due to its impact on human health and the nature surrounding us, diesel engine emissions have been significantly reduced over the last two decades. This reduction has been enforced by the legislating organs around the world that gradually have made the manufacturers transform their engines to today’s complex high-tech products. One of the most challenging areas to meet the legislations is transient operation where the inertia in gas-exchange system makes transition from one load to another problematic. Modern engines have great potential to minimize the problems associated with transient operation. However, their complexity also imposes a great challenge regarding optimization and systematical testing of transient control strategies in an engine test bed could be both expensive and time consuming. The objective of this project is to facilitate optimization of transient control strategies. This should be done by identifying appropriate measurement methods for evaluation of transients and by providing models that can be used to optimize strategies off-line. Measurement methods for evaluation of transients have been tested in several experiments, mainly focusing on emission but also regarding e.g. EGR flow. Applicable instruments for transient emission measurements have been identified and used. However, no method to measure soot emissions cycle resolved has yet been found. Other measurements such as EGR flow and temperatures are believed to have significantly decreased accuracy during transients. A model for prediction of NOx emissions have been used and complemented with a new approach for soot emission predictions that has been developed in this project. The emission models have been shown to be applicable over a wide range of operating conditions with exception for highly premixed combustion. It has also been shown that models developed for steady state conditions can be used for transients operation.