Jul 23 2018 04:00 PM
Jul 23 2018 05:00 PM
Modeling of Pre-ignition and Super-knock in Spark Ignition Engines
Mohammed Jaasim Mubarak Ali, Ph.D. Candidate Supervised by Prof. Hong G. Im
Monday, July 23, 2018
04:00 PM - 05:00 PM
LocationAl Kindi Building, Bldg 4, Level 5, Room 5209
Advanced combustion concepts are required to meet the increasing global energy demand and stringent emission regulations imposed by the governments on automobile manufacturers. Improvement in efficiency and reduction in emissions can be achieved by downsizing the Spark Ignition (SI) engines. The operating range of SI engine is limited by occurrence of knock, pre-ignition and the following super-knock due to boosting of intake pressure, to account for the reduction of power, as a result of downsizing the engine. Super-knock, which represents high momentary pressure accompanied with pressure oscillations, is known to permanently damage the moving component of the engines. Therefore fundamental comprehensive understanding of the mechanism involved in pre-ignition and super-knock are required to design highly efficient spark ignition engines with lower emissions that can meet the increasing government regulations.
The thesis focuses on auto-ignition characteristics of endgas and the bulk mixture properties that favor transition of pre-ignition to super-knock. Direct numerical studies indicate that super-knock occurs to due to initiation of premature flame front that transition into detonation. In literature, many sources are reported to trigger pre-ignition. Due to the uncertainty of the information on the sources that trigger pre-ignition, it is extremely difficult to predict and control pre-ignition event in SI engines. Since the information on the source of pre-ignition is not available, the main focus of this work is to understand the physical and chemical mechanisms involved in super-knock, factors that influence super-knock and methods to predict super-knock.
Pre-ignition was initiated at known locations and crank angle using a hotspot of known size and strength. Different parametric cases were studied and the location and timing of pre-ignition initiation is found to be extremely important in determining the transition of pre-ignition event to super-knock. Pre-ignition increases the temperature of the endgas and the overall bulk mixture, that transitions the pre-ignition flame front to a detonation. The transition of the flame propagation mode from deflagration to detonation was investigated with different type of analysis methods and all results confirmed the transition of pre-ignition flame front to detonation that results in super- knock.
Methods to predict super-knock is numerically investigated with predictive criteria based on Zel’dovich theory and the Sankaran number. The effect of temperature, mixture and turbulent velocity fluctuations were found to be of paramount importance to trigger detonation that results in super-knock. Probability of detonation is calculated based on the predictive criteria and is found to be consistent with results obtained with pre-ignition simulations.
Mohammed Jaasim received his Bachelor degree in Aeronautical Engineering on May 2010 from the Anna University, India. On September 2010 he started his Master's degree in Aeronautical Engineering at Anna University and graduated in May 2013. He started his PhD at KAUST with Prof. Hong G. Im as his supervisor in March 2014 in Clean Combustion research Center (CCRC).