UBC Theses and Dissertations
Spark ignition of partially stratified gaseous fuel-air mixtures Chan, Edward C.
The Partially Stratiﬁed Charge (PSC) strategy aims to stabilize the spark ignition of lean-burn natural gas fueled internal combustion engines. This results in an extension of unthrottled load control, as well as a reduction in regulated pollutant and carbon dioxide emissions. While engine experiments demonstrated the feasibility of this technology, its fundamental enabling mechanisms have yet to be identified. An experimental / numerical approach was taken for the current investigation, using an idealized PSC ignition system. The PSC injection took place in a constant volume combustion chamber (CVCC) into an initially quiescent bulk mixture. A customized injection system was also developed. Experimental results indicated that stable combustion could be achieved with PSC at an air-to-fuel ratio of λ = 2.0. Furthermore, the use of double PSC injection facilitated additional consumption of the bulk fuel. The experiments also identified three primary enabling mechanisms under which PSC assists in ultra-lean spark ignited combustion. Additional insights were provided through numerical modeling. The PSC jet was modeled using the standard k−epsilon model and was found to be in excellent agreement with the experimental results in terms of penetration and entrainment. Meanwhile, the Eddy Dissipation Concept (EDC) model was used to simulate the combustion under PSC. While the computational model lacked the ability to properly predict combustion rates in the turbulent-to-laminar ﬂame transition, the ignition and early combustion phases were properly captured. The numerical framework was applied to engine conditions, and the modeled data were validated using existing experimental results. A semi-analytical ignition model was developed using detailed chemical kinetic mechanisms. A turbulent ignition parameter was derived accordingly to characterize the likelihood of an ignition event leading to combustion. The engine simulation results also provided further information in PSC charge formation, as well as ﬂame propagation. The results of this research gave rise to an improved design for future generation PSC injection / ignition devices.
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