Analysis of the Correlation between Flow and Combustion Characteristics in Spark-ignited Engine 2021-01-0463
As global emission standards are getting stringent, it is inevitable to increase the thermal efficiency through the high compression ratio in spark-ignited engines. Various researches are being conducted to mitigate knock caused by increased compression ratio, which requires an understanding of the combustion phenomena inside the combustion chamber. In particular, the flow is a major factor affecting the entire combustion process from the generation to propagation of flames. In the field of spark-ignited engine research, where interest in lean combustion concept and expansion of EGR supply is increasing, flow analysis is essential to secure rapid flame propagation speed and stable combustion process. In this study, the flow around the spark plug was measured by the Laser Doppler Velocimetry system, and then the correlation with combustion in the spark-ignited engine was analyzed.
The turbulence intensity at the position of the spark plug was calculated by measuring the flow velocity by installing the probe adaptor instead of the spark plug under motoring conditions. To measure the flow characteristics of various engine conditions, LDV measurement experiments were conducted with different engine speed, intake pressure and valve timing. In addition, the design of the intake port was changed to analyze the flow characteristics according to the tumble ratio. Compared to other engine variables, engine speed and intake valve timing have a lot of influence on the flow around the spark plug, and in engines with different tumbles, the profile of flow velocity is different. To identify the relationship between the flow characteristics and the combustion process, combustion under various conditions were compared with the flow measured with LDV system in the same engines. Under high load conditions, there was a lack of correlation between turbulence velocity and the initial combustion duration, but the partial load condition showed high correlation.
Seungil Lee, Insuk Ko, Woojae Kim, SeJin Song, Kyoungdoug Min, Jonghyeok Lee, Heechang Oh, Jinwook Son, Youngnam Kim
Seoul National University, Hyundai Motor Company