Browse Publications Technical Papers 2019-01-0718
2019-04-02

An Investigation of near-spark-plug Flow Field and its Effect on Spark Behavior 2019-01-0718

In the recent decades, the emission and fuel efficiency regulations put forth by the emission regulation agencies have become increasingly stringent and this trend is looking to continue in future. Advanced spark ignition engines can operate under lean conditions to improve efficiency and reduce emissions. Under such lean conditions, ignition and complete combustion of the charge mixture is a challenge because of the reduced charge reactivity. Enhancement of the in-cylinder charge motion to increase the flame velocity and consequently reduce the combustion duration is one possible way to improve lean combustion. The role of air motion in better air-fuel mixing and increasing the flame velocity, by enhancing turbulence has been researched extensively. However, during the ignition process, charge motion can influence the initial spark breakdown, the resulting flame kernel formation, and flame propagation. Therefore, to estimate the flow field around the spark plug, a combined empirical and simulation study is undertaken. A steady cross flow of air across the spark gap of a conventional J-type spark plug is simulated to determine the effect of spark plug geometry on the steady flow field. The flow velocity is varied upstream of the spark plug. Resultant flow field from the simulations is compared to the optical measurements using particle image velocimetry (PIV) for validation of the numerical model. Flow characteristics are compared to the high-speed direct imaging, voltage and current measurement results of the spark channel in an effort to correlate the spark behavior with the local flow velocity. Preliminary results show that the turbulence is generated in the wake of the spark plug as expected and flow velocity in the spark gap is lower the free stream velocity. Optical measurements and voltage waveforms show the spark stretching and restrikes increase with increasing velocity.

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