Comparison of ignition and early flame propagation in methane/air mixtures using nanosecond repetitively pulsed discharge and inductive ignition in a pre-chamber setup under engine relevant conditions

A B S T R A C T An optically accessible pre-chamber setup was used to investigate the ignition occurrence and early flame propagation in methane/air mixtures at density conditions relevant to engine application. Two Schlieren setups coupled with fast recording cameras allowed the visualization of the combustion chamber and a close up of the ignition location, respectively. A spectroscopy-based ignition diagnostic was simultaneously applied to characterize the mixture composition near the spark plug. Nanosecond Repetitively Pulsed Discharge (NRPD) ignition with different pulse patterns in terms of pulse number and repetition frequency was applied. Conventional inductive ignition and NRPD-assisted ignition in a pre-chamber setup were compared for the first time in terms of ignition occurrence and early flame propagation in engine-relevant conditions. The effect of different air to fuel ratios was assessed in both laminar and turbulent conditions. Results showed that the discharge dynamics strongly affects the effectiveness of the ignition event and consequently the later combustion stages, suggesting the path for an optimization of the NRPD control parameters based on the specific case. The NRPD ignition is shown to be advantageous for stable ignition especially in lean laminar conditions due to the increased local concentration of radicals provided by multiple discharges. This suggests that the use of NRPD gives an advantage in ignition onset especially in diluted conditions and where there is a low mixing level due to reduced turbulence. The simultaneous application of spectral and Schlieren techniques allowed gaining fundamental understanding of the processes involved in NRPD ignition of gas mixtures, useful to validate simulations and ultimately for predicting and controlling such ignition systems in practical applications. (c) 2021 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )