TY - JOUR
T1 - Study of engine knocking combustion using simultaneous high-speed shadowgraph and natural flame luminosity imaging
AU - Tang, Qinglong
AU - Shi, Hao
AU - Uddeen, Kalim
AU - Sharma, Priybrat
AU - Yao, Mingfa
AU - Turner, James W. G.
AU - Magnotti, Gaetano
N1 - KAUST Repository Item: Exported on 2023-08-31
Acknowledged KAUST grant number(s): URF/1/3710-01-01
Acknowledgements: This work was funded by competitive research funding (URF/1/3710-01-01) from King Abdullah University of Science and Technology (KAUST) and the National Natural Science Foundation of China (NSFC) through its projects of 52206166.
PY - 2023/8/25
Y1 - 2023/8/25
N2 - Engine knocking is a classical but significantly impactful combustion phenomenon that arouses unfailing research interests. An in-depth understanding of the knocking mechanism holds the key to the next-generation high-efficiency spark ignition engines adopting a high compression ratio. In this study, a novel 72 kHz imaging system of simultaneous shadowgraph and natural flame luminosity (NFL) was implemented on an optical engine. The key combustion parameters that affect the engine knock intensity were investigated based on the heat release analysis. The shadowgraph image velocimetry (SIV) was utilized to measure the in-cylinder flow field. The end gas autoignition process in the engine knocking combustion was studied under knock intensity as high as 18.1 bar. The results indicate that there is an “optimum” combustion phasing that produces the highest knock intensity. The cases with more end gas mass at knock onset, though having lower mean temperatures, generally produce higher knock intensity. The knock intensity can be significantly different under the same end gas mass and mean end gas temperature, possibly due to the different temperature gradients in the end gas. The simultaneous shadowgraph and NFL imaging succussed in differentiating the density variation zone in the end gas caused by the low-temperature heat release from the hot flame zone before auto-ignition. An intense density variation zone is witnessed around the center of the cylinder under higher engine knock intensity by the shadowgraph images, showing a dark region that oscillates together with the local pressure oscillations. The coupling among the local density variation, pressure oscillation, and NFL intensity oscillation is observed during the engine knocking combustion. The velocity distribution of the flow field indicates that the engine knocking combustion enhances the in-cylinder flow, which may cause more convective heat transfer loss and flow loss.
AB - Engine knocking is a classical but significantly impactful combustion phenomenon that arouses unfailing research interests. An in-depth understanding of the knocking mechanism holds the key to the next-generation high-efficiency spark ignition engines adopting a high compression ratio. In this study, a novel 72 kHz imaging system of simultaneous shadowgraph and natural flame luminosity (NFL) was implemented on an optical engine. The key combustion parameters that affect the engine knock intensity were investigated based on the heat release analysis. The shadowgraph image velocimetry (SIV) was utilized to measure the in-cylinder flow field. The end gas autoignition process in the engine knocking combustion was studied under knock intensity as high as 18.1 bar. The results indicate that there is an “optimum” combustion phasing that produces the highest knock intensity. The cases with more end gas mass at knock onset, though having lower mean temperatures, generally produce higher knock intensity. The knock intensity can be significantly different under the same end gas mass and mean end gas temperature, possibly due to the different temperature gradients in the end gas. The simultaneous shadowgraph and NFL imaging succussed in differentiating the density variation zone in the end gas caused by the low-temperature heat release from the hot flame zone before auto-ignition. An intense density variation zone is witnessed around the center of the cylinder under higher engine knock intensity by the shadowgraph images, showing a dark region that oscillates together with the local pressure oscillations. The coupling among the local density variation, pressure oscillation, and NFL intensity oscillation is observed during the engine knocking combustion. The velocity distribution of the flow field indicates that the engine knocking combustion enhances the in-cylinder flow, which may cause more convective heat transfer loss and flow loss.
UR - http://hdl.handle.net/10754/693865
UR - https://linkinghub.elsevier.com/retrieve/pii/S1359431123014692
U2 - 10.1016/j.applthermaleng.2023.121440
DO - 10.1016/j.applthermaleng.2023.121440
M3 - Article
SN - 1359-4311
SP - 121440
JO - Applied Thermal Engineering
JF - Applied Thermal Engineering
ER -