Demonstration of a dual-pulse laser heating technique for ignition of propane-air mixtures
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2017 Eastern States Section of the Combustion Institute. All Rights Reserved. The present contribution represents a study of the flame aerodynamics induced by laser ignition of fuel mixtures. A comparative study between laser breakdown/spark ignition and a novel dual-pulse technique demonstrates that the flame stretching effects governed by the plasma induced flow has a great influence on the combustion process. The dual-pulse technique presented herein uses one UV pulse (? = 266 nm) for achieving gas pre-ionization (through multiphoton ionization) and an overlapped NIR pulse (? = 1064 nm) for energy addition into the pre-ionized gas. It is demonstrated that this new technique displays certain advantages when compared to the well-established laser spark ignition method. We are showing for the first time that in the laser spark ignited mixtures the flame kernel breaks apart under lean conditions with detrimental effects on the subsequent flame propagation. In contrast, the dual-pulse laser ignition technique allows one to control the plasma dynamics by careful alignment of the two beams. This leads to an extension of the lean limit and an increase in combustion efficiency while the laser energy requirements are lowered. Finally, it was found that the flames ignited using the dual-pulse exhibit lower stretching and the flame speed is also reduced.