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Experimental Investigation of the Influence of Ignition System Parameters on Combustion in a Rapid Compression-Expansion Machine
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
Lean burn combustion concepts with high mean effective pressures are being developed for large gas engines so that future stringent emission limits are met while high engine efficiencies are maintained. Since these combustion concepts induce severe boundary conditions for ignition, applied research is focusing on the process of spark ignition and flame initiation in order to avoid misfiring and keep cycle-to-cycle combustion variability within reasonable limits. This paper conducts a fundamental investigation of early flame kernel development under different ignition system settings. The investigations are carried out on a rapid compression-expansion machine in which the spark ignition process can be observed under engine-like pressure and excess air ratio conditions while low flow velocities are maintained. The schlieren setup for high-speed optical investigations of the area of the spark plug electrodes is described and a suitable post-processing routine is introduced. The influence of different spark current durations on early flame kernel formation is investigated using a modulated capacitive discharge ignition (MCDI) system. The outcomes reveal that a short spark current duration results in a slower increase and higher standard deviation of the flame area during the early phase of combustion. Moreover, stable flame initiation appears to require a minimum spark current duration. The methodology introduced in this paper will be applied in detailed investigations of other spark plug geometries and ignition settings in order to examine the ignition of lean mixtures.