Abstract:

New discoveries and extraction methods have led to a dramatic rise in natural gas production across the world. Due to its low and stable cost, there is an increasing interest in natural gas fueled vehicles. Stringent emission regulations require gas engine manufacturers to move towards ultra-lean operation to reduce emissions. Ultra-lean combustion, however, gives rise to some serious challenges. As the fuel/air mixture becomes leaner, ignition becomes more difficult. Poor ignition can lead to misfires resulting in undesirable effects such as cycle-to-cycle variability, rough operation, and reduction in efficiency and increased unburned hydrocarbon emissions. An approach that can potentially solve these problems is to use a hot turbulent jet to ignite the ultra-lean mixture. A small quantity of near stoichiometric fuel/air is burned in a separate combustion chamber called the pre-chamber, and the combustion products, in the form of a hot turbulent jet, are then discharged into the main chamber filled with ultra-lean premixed fuel/air through a small diameter orifice. Compared to conventional spark ignition, the hot jet has a much larger surface area leading to multiple ignition sites which can increase the probability of successful ignition and cause faster flame propagation and heat release. This talk will discuss the fundamental mechanisms of turbulent hot jet ignition and the effect of pre-chamber design such as geometry, orifice diameter, and spark plug location on the ignition characteristics. Additionally, it was found that supersonic hot jet, which were generated by using converging-diverging (C-D) orifices, can ignite leaner mixtures, due to the creation of a high-temperature zone downstream of the shock structures. Lastly, the ignition phenomena by multiple jets generated by pre-chamber combustion are discussed.

Brief Biography:

Li Qiao earned BS and MS degrees in Engineering Mechanics from Tsinghua University in 1999 and 2001, and a PhD in Aerospace Engineering from the University of Michigan in 2007. Since then, she has been an Assistant and now an Associate Professor in the School of Aeronautics & Astronautics at Purdue University. Her research has focused on the development of new technologies and the understanding of basic science in the areas of fuels, combustion and propulsion. Her research has been funded by several government agencies including National Science Foundation (NSF), Air Force Office of Scientific Research (AFOSR), Army Research Office (ARO), American Chemical Society, and Federal Aviation Agency, as well as industries. She is the recipient of the NSF CAREER Award (2013), the AFOSR Young Investigator Award (2013) and the ARO Young Investigator Award (2010). She was a summer faculty fellow at NASA Glenn Research Center (2011) and Air Force Research Lab (2010). She is an AIAA Associate Fellow and a member of the AIAA Terrestrial Energy Systems Technical Committee.

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