Characterization of knocking combustion and heat transfer in a spark ignition engine
Syrimis, Michalis
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Permalink
https://hdl.handle.net/2142/20406
Description
Title
Characterization of knocking combustion and heat transfer in a spark ignition engine
Author(s)
Syrimis, Michalis
Issue Date
1996
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Automotive
Engineering, Mechanical
Language
eng
Abstract
An experimental study was conducted to investigate combustion and in-cylinder heat transfer characteristics under light and heavy knocking conditions in a spark ignition engine. A special, single cylinder, Mitsubishi R52 engine was used, in its extended piston configuration. Fast response heat flux probes on the piston and the cylinder head provided instantaneous surface temperature measurements at different locations, both inside and outside the end-gas region. The knocking combustion process was characterized by several knock indices, based on the net heat release analysis of cylinder pressure, as well as, the amplitude of the knock induced pressure fluctuations. Knock initiation and development were investigated by sampling cylinder pressure data at two different locations in the chamber. The cyclic variability associated with knocking combustion was investigated by studying the variation, as well as the interdependence of the knock indices, under different knock severity conditions. Finally, the effects of knock on heat transfer were explored by studying changes in ensemble-average heat flux with increasing knock intensity, and also by the magnitude of the correlation coefficients between peak heat flux and the developed knock indices.
Evidence of multiple autoignition sites was found during the knock initiation process. Knock induced pressure waves were of acoustic nature, becoming weak shock waves in cases of violent autoignitions. Cyclic variability in knock intensity was found to be driven by variations in burn rate. The correlation between burn rate and knock intensity was higher for lower overall combustion rates. Under light knock, the ensemble-average peak heat flux at locations near the end-gas zone increased with spark advance, departing from its trend prior to the onset of knock. Under heavy knock, the ensemble-average peak heat flux increased over the entire piston crown. High statistical correlation (up to 0.80) was found between peak heat flux and certain of the autoignition indices within and near the end-gas zone. Knock was found to increase heat transfer by the 'scouring' action of the induced pressure waves on the wall thermal boundary layer. Apart from knock intensity, the location of autoignition initiation, and the characteristics of the flame and wave front patterns following autoignition were found to affect the magnitude of heat transfer changes.
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