Swirl, Fuel Composition, Localized Heating, and Deposit Effects on Engine Knock Location

In this investigation, recently developed techniques to locate knock origins were applied to study fuel and deposit effects as they interact with charge motion. Particularly, the individual and interactive effects of swirl, fuel composition, localized heating, and deposits on in-cylinder knock origin were studied. A Waukesha Split Head CFR engine was modified to accept four pressure transducers for calculating by triangulation the cycle resolved in-cylinder origin of engine knock. Location of the origin of knock within the combustion chamber was based on the difference in time for each pressure transducer to register the onset of knock during the combustion cycle. Computer software was developed and optimized to maximize the success rate in locating knock within 1 cm. In order to explore the difference in location of knock due to fluid dynamics within the cylinder, the shrouded intake valve of the engine was modified to create different swirl conditions within the combustion chamber. Tests for knock location were performed under counterclockwise, clockwise, and no swirl conditions. Isooctane/n-heptane and toluene/n-heptane blends were tested to determine what differences in knock location are attributable to branched-paraffin/straight-chained paraffin versus aromatic/straight-chained paraffin chemistries. Tests were also performed to investigate the influence of localized heating within the combustion chamber on knock origin. A glow plug was inserted into the combustion chamber and data was collected at several compression ratios and power inputs to the glow plug. Finally, the effects of combustion chamber deposits on knock were investigated. Deposits were allowed to build up within the cylinder by running a deposit forming engine cycle. Tests were then performed at various knock intensities to discover the influence of those deposits on the location of in-cylinder knock origin. The effects of all the above mentioned parameters and their implications on the phenomena of engine knock are discussed.