MEASUREMENT OF PARTICULATES EMITTED FROM SGDI ENGINES

Licentiate thesis, 2014

This thesis discusses particulate emissions from spray guided, gasoline, direct-injected (GDI) engines. The aim was to measure solid particulates without the influence of volatiles. Therefore, two sampling systems were developed for sampling either low or high particulate content. This thesis discusses the use of both systems for the measurement of solid particulates, as well as a selection of results from tests performed with the two systems. The tests were conducted on a single-cylinder engine operating under stratified or homogenous mode with relatively high levels of particulate emissions and a multi-cylinder engine operating under homogenous mode with low levels of particulate emissions. The engines were operated in steady state mode. The former system was developed based on recommendations for the measurement of particulate number according to the Particulate Measurement Program [1]. The latter system was developed to enable measurements of undiluted samples in cases where the amount of particulates may be lower than the detection limit of the classifying instrument. The thesis is divided into two main parts: an introductory part and a part presenting the most significant results obtained in the tests. The introductory part discusses the theory behind GDI engines and particulate formation, as well as measurement methods and how to interpret results from engine measurements. Based on a review of the current literature, the introductory part also explains how a few factors, such as EGR, injection strategies and boosting, affect particulate emissions. The last part discusses a selection of results from the engine tests. Both engines were found to emit particulates with one distinct nucleation mode and one distinct agglomerate mode. The single-cylinder engine was found to emit particulates no larger than 100 nm in homogenous mode, whereas the multi-cylinder engine emitted particulates with a maximum size of 300 nm in homogenous mode. The single-cylinder research engine was found to emit larger particulates in stratified mode than when operated under homogenous mode. The total particulate mass was also found to be at least one order of magnitude larger in stratified mode than in homogeneous mode. The largest particulates were found to decrease in size with increasing engine speed. Both sampling systems were found to work appropriately and recommendations on their design are presented in the thesis. Two published papers are included in the thesis. The first paper discusses factors affecting particulate emissions from a single-cylinder engine operating in stratified mode. The paper was presented at the SAE conference in Capri, 2013. The second paper discusses a novel particulate sample conditioning system without sample dilution to avoid falling below the classifier’s detection limit. This paper was presented at the Fisita conference in Maastricht, 2014.