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

Merotto, L.; Balmelli, Michelangelo; Vera-Tudela, W.; Soltic, Patrik

doi:10.1016/j.combustflame.2021.111851

Cited by 23 publications

(6 citation statements)

References 39 publications

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“…Some of the mentioned limitations can be overcome by using repetitive voltage pulses of some tens of nanoseconds duration, which allow the initiation of breakdown at higher voltages and thus channel more energy into the phase where the plasma is not in thermal equilibrium. The resulting advantages are shorter ignition delays, stable ignition at higher air-to-fuel ratios or exhaust gas dilution, and faster flame propagation [6]- [8]. Computational fluid dynamic modeling of ignition from a nanosecond pulsed discharge was reported in [9], and a description of the energy delivered during the discharge was reported in [10]; nevertheless, the characterization and modeling of breakdown thresholds (e.g., probability of breakdown occurring for a pulse of given amplitude, rise time, and duration) and the distribution of delay times are lacking.…”

Section: Introductionmentioning

confidence: 99%

Breakdown of Synthetic Air Under Nanosecond Pulsed Voltages in Quasi-Uniform Electric Fields

Balmelli

Färber³

et al. 2022

IEEE Access

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The electrical breakdown of synthetic air under ultrashort high-voltage pulses (50 ns duration), as well as slowly increasing ("DC") voltages, is experimentally studied in a well-defined quasi-uniform electrode configuration (sphere-plane). The electrode spacing is varied from 0.1 to 1 mm, and the gas pressure is varied from 1.5 to 8 bar. The study's goal is to provide experimental data to develop breakdown models that predict the breakdown probability of small gas gaps under arbitrary voltage excitations. In particular, this analysis is intended for applications where statistical and formative time lags need to be considered, such as nanosecond pulsed ignition or partial discharges in inverter-fed motors. The influence of the electrode material and the presence of UV illumination are investigated for both DC and pulsed voltages. The results highlight the important role of seed electron provision for breakdown under short transient voltages. Evidence for a fieldassisted emission of seed electrons with a pressure-dependent onset field is found from time lag measurements. An empirical expression is derived based on the Fowler-Nordheim formula to quantify the seed electron generation rate. The expected dependence of the breakdown threshold on the cathode material (work function) was confirmed for breakdown under slowly increasing voltages (Townsend mechanism). Interestingly, a dependence of the breakdown voltage was also found for nanosecond pulsed voltages (dominated by the streamer mechanism). This suggests that the field emission of electrons from the cathode is the dominant source of seed electrons in large cathode electric fields.

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Section: Introductionmentioning

confidence: 99%

Breakdown of Synthetic Air Under Nanosecond Pulsed Voltages in Quasi-Uniform Electric Fields

Balmelli

Färber³

et al. 2022

IEEE Access

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“…To study the pre-ignition of lube oil, a series of measurements related to pre-ignition onset will be performed with no additional ignition sources. [17][18][19][20] In particular, the determination of the inflammation phase as well as the flame kernel growth is of interest. Moreover, implications on the subsequent combustion phase and flame propagation will be acquired.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of lube oil pre-ignition in an optical gas engine test rig

Vera-Tudela,

Süess,

Albrecht

et al. 2024

International Journal of Engine Research

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Lean-premixed gas combustion is an attractive option for meeting future emission standards toward considerably lower particulate matter and emissions while obtaining an efficiency comparable to diesel combustion. However, ignition processes still pose considerable challenges, with pre-ignition being a major issue. The pre-ignition phenomenon might result from the self-ignition of lube oil in hot zones, making it challenging to observe in real engines. To study single or sparsely separated lube oil droplets under engine-like conditions, the “Flex-OeCoS” experimental test facility was used. To be able to induce such pre-ignitions artificially a novel piezo droplet injector was developed and manufactured, which enabled the metering of minor amounts of lubricating oil or even the injection of single droplets. High-speed cameras and specially developed and partially automatable and adaptive evaluation algorithms were used to record and track the behavior of the injected droplet using overlaid schlieren and OH* chemiluminescence. During the measurement campaigns, relevant operating parameters were varied, and optical investigations were carried out with an ignitable mixture on the Flex-OeCoS test facility under engine-relevant operating conditions. Spontaneous ignition of the vaporized lubricating oil was observed, which subsequently led to ignition of the whole air-fuel mixture in the optical combustion chamber. This was especially evident for lean methane-air mixtures up to an air-fuel ratio of 2.0. With this approach, information could be gathered about the necessary internal engine conditions that lead to pre-ignition in lean mixtures and where their limits lie.

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“…There have been a number of recent studies focusing on the effects of pre-chamber ignition and turbulent jet flame on main-chamber combustion [6][7][8], and the onset of DDT [4,9] in real engines or combustion chambers under engine relevant conditions. Qin et al [6] used direct numerical simulations to study the transient mixing and ignition mechanism of methane/air mixtures in a simplified pre-chamber/main-chamber system.…”

Section: Introductionmentioning

confidence: 99%

Parametric Studies of Deflagration-to-Detonation Transition in a Pre-Chamber/Main-Chamber System

Zhu

Tang

Lai

et al. 2022

ASME 2022 ICE Forward Conference

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Numerical simulations are performed to study the process of flame propagation through a small orifice and transition to detonation in a confined pre-chamber/main-chamber system. The numerical model solves the fully compressible Navier-Stokes equations by a high-order numerical algorithm on a dynamically adapting mesh, coupled with a single-step chemical-diffusive model for a stoichiometric ethylene-oxygen mixture. Four successive stages, namely laminar flame propagation, jet flame formation, flame distortion by shock waves, and transition to detonation, are observed. Parametric studies with varying nozzle diameters and initial temperatures are tested to investigate the effect of nozzle size and the stochasticity of deflagration-to-detonation transition (DDT). The results suggest that the case with a smaller nozzle size, d = 1.5 mm, requires a longer time for the flame to evolve and transition into a detonation. A small change in the initial temperature results in clear fluctuations of flame surface length in the turbulent flame regime. In addition, the case with the smaller orifice size is shown to be more sensitive to the initial temperature. Due to the stochastic nature of DDT, the time and location for detonation initiation vary in all cases. Nevertheless, the detonation mechanism remains the same and is independent of the small variations in the initial temperature or the orifice size.

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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

Cited by 23 publications

References 39 publications

Breakdown of Synthetic Air Under Nanosecond Pulsed Voltages in Quasi-Uniform Electric Fields

Breakdown of Synthetic Air Under Nanosecond Pulsed Voltages in Quasi-Uniform Electric Fields

Experimental study of lube oil pre-ignition in an optical gas engine test rig

Parametric Studies of Deflagration-to-Detonation Transition in a Pre-Chamber/Main-Chamber System

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