Date of Award

11-29-2018

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Supervisor

David Ting

Supervisor

Ming Zheng

Rights

info:eu-repo/semantics/openAccess

Abstract

Advanced spark ignition (SI) engines can operate under lean conditions in order to improve the efficiency and reduce the emissions. Under extensive lean conditions, the ignition and complete combustion of the charge mixture is a challenge, because of the reduced cylinder charge reactivity. The enhancement of the in-cylinder global motion and local turbulence is an effective way to increase the flame velocity, and consequently shorten the combustion duration. The role of air motion in improving air-fuel mixing and combustion has been researched extensively. However, during the ignition process, the excessive charge motion can hinder the spark discharge, the resulting flame kernel formation, and propagation. Therefore, a combined empirical and simulation study is undertaken to elucidate the flow field around the spark gap, and its effect on the spark discharge. The flow field generated by a steady flow of air across the spark gap of a conventional J-type spark plug is studied under ambient conditions. Optical particle image velocimetry (PIV) measurements and computational fluid dynamics (CFD) simulations are performed alongside the high-speed direct imaging. Voltage and current waveforms of the spark channel have been measured, in order to correlate the spark behavior to the local flow velocity. The flow field near the spark gap in an SI engine under motoring conditions is simulated. The results are compared to the empirical current and voltage measurements taken during engine operation. The results show that the turbulence is generated in the wake of the spark plug and flow velocity in the spark gap is higher than the free stream velocity. The optical and electrical measurements show the spark stretching and restrikes increase, and the discharge duration decreases with an increase in flow velocity. Similar behavior is observed during engine operation as well.

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