Ignition by transient hot turbulent jets: An investigation of ignition mechanisms by means of a PDF/REDIM method

Ghorbani, Asghar; Steinhilber, Gerd; Markus, Detlev; Maas, Ulrich

doi:10.1016/j.proci.2014.06.104

Cited by 48 publications

(19 citation statements)

References 22 publications

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“…This hot-products jet may then lead to ignition as it mixes with the already-ejected pre-chamber fluid and the main chamber mixture, however this ignition method is expected to lead to a lower ignition probability. Modelling of this problem for laminar [20] and turbulent [21,22] jets has been attempted, but critical conditions for ignition have not been extensively developed yet.…”

Section: Further Discussionmentioning

confidence: 99%

Fundamental Aspects of Jet Ignition for Natural Gas Engines

Mastorakos

Allison

Giusti

et al. 2017

SAE Int. J. Engines

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Large-bore natural gas engines may use pre-chamber ignition. Despite extensive research in engine environments, the exact nature of the jet, as it exits the pre-chamber orifice, is not thoroughly understood and this leads to uncertainty in the design of such systems. In this work, a specially-designed rig comprising a quartz pre-chamber fit with an orifice and a turbulent flowing mixture outside the pre-chamber was used to study the pre-chamber flame, the jet, and the subsequent premixed flame initiation mechanism by OH* and CH* chemiluminescence. Ethylene and methane were used. The experimental results are supplemented by LES and 0D modelling, providing insights into the mass flow rate evolution at the orifice and into the nature of the fluid there. Both LES and experiment suggest that for large orifice diameters, the flow that exits the orifice is composed of a column of hot products surrounded by an annulus of unburnt pre-chamber fluid. At the interface between these layers, a cylindrical reaction zone is formed that propagates in the main chamber in the axial direction assisted by convection in the jet, but with limited propagation in the cross-stream direction. For small orifice diameters, this cylinder is too thin, and the stretch rates are too high, for a vigorous reaction zone to escape the pre-chamber, making the subsequent ignition more difficult. The methane jet flame is much weaker than the one from ethylene, consistent with the lower flame speed of methane that suggests curvature-induced quenching at the nozzle and by turbulent stretch further downstream. The velocity of the jet is too high for the ambient turbulence to influence the jet, although the latter will affect the probability of initiating the main premixed flame. The experimental and modelling results are consistent with ongoing Direct Numerical Simulations at ETH Zurich.

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Section: Further Discussionmentioning

confidence: 99%

Fundamental Aspects of Jet Ignition for Natural Gas Engines

Mastorakos

Allison

Giusti

et al. 2017

SAE Int. J. Engines

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“…The net effect is accelerated combustion leading to higher peak pressures. Transactions of the ASME However, in the case of PCLI, the partially combusted jets issuing from the prechamber introduce spatially distributed ignition sites at multiple locations, especially at the jet head vortices [10], leading to earlier and much faster combustion. This results in peak cylinder pressures approximately 20 bar larger than in SI or LI.…”

Section: Resultsmentioning

confidence: 99%

Prechamber Equipped Laser Ignition for Improved Performance in Natural Gas Engines

Almansour

Vasu

Gupta

et al. 2017

Journal of Engineering for Gas Turbines and Power

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Lean-burn operation of stationary natural gas engines offers lower NOx emissions and improved efficiency. A proven pathway to extend lean-burn operation has been to use laser ignition (LI) instead of standard spark ignition (SI). However, under lean conditions, flame speed reduces, thereby offsetting any efficiency gains resulting from the higher ratio of specific heats, γ. The reduced flame speeds, in turn, can be compensated with the use of a prechamber to result in volumetric ignition and thereby lead to faster combustion. In this study, the optimal geometry of PCLI was identified through several tests in a single-cylinder engine as a compromise between autoignition, NOx, and soot formation within the prechamber. Subsequently, tests were conducted in a single-cylinder natural gas engine comparing the performance of three ignition systems: standard electrical spark ignition (SI), single-point laser ignition (LI), and PCLI. Out of the three, the performance of PCLI was far superior compared to the other two. Efficiency gain of 2.1% points could be achieved while complying with EPA regulation (BSNOx < 1.34 kWh) and the industry standard for ignition stability (coefficient of variation of integrated mean effective pressure (COV_IMEP) < 5%). Test results and data analysis are presented identifying the combustion mechanisms leading to the improved performance.

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“…However, the ignition core may be transported towards the lateral face of the jet as the tip advances within the cold environment [11,12]. Through a comparative assessment of literature, the authors of present work speculate about the effect of Damkohler number on the probability of ignition at the vortex or shear layer of trailing jet.…”

Section: Introductionmentioning

confidence: 84%

“…Ghorbani et al [11] it is stated that for jet ignition of hydrogen-air mixture, the ignition delay varies in the range 0.1-0.4 ms, depending on the jet entrance temperature. In the present work, for the hydrogen-dominated mixtures (70%H2-30%CH4), the ignition delay is approximately 0.8 ms which reasonably agrees with Ghorbani's.…”

Section: Problem Description and Numerical Methodologymentioning

confidence: 99%

Three-Dimensional Simulation of Turbulent Hot-Jet Ignition for Air-CH4-H2 Deflagration in a Confined Volume

Feyz

Nalim

Khan

et al. 2018

Flow Turbulence Combust

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This work describes essential aspects of the ignition and deflagration process initiated by the injection of a hot transient gas jet into a narrowly confined volume containing air-CH4-H2 mixture. Driven by the pressure difference between a pre-chamber and a long narrow constant-volumecombustion (CVC) chamber, the developing jet or puff involves complex processes of turbulent jet penetration and evolution of multi-scale vortices in the shear layer, jet tip, and adjacent confined spaces. The CVC chamber contains stoichiometric mixtures of air with gaseous fuel initially at atmospheric conditions. Fuel reactivity is varied using two different CH4/H2 blends. Jet momentum is varied using different pre-chamber pressures at jet initiation. The jet initiation and the subsequent ignition events generate pressure waves that interact with the mixing region and the propagating flame, depositing baroclinic vorticity. Transient three-dimensional flow simulations with detailed chemical kinetics are used to model CVC mixture ignition. Pre-ignition gas properties are then examined to develop and verify criteria to predict ignition delay time using lower-cost non-reacting flow simulations for this particular case of study.

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Ignition by transient hot turbulent jets: An investigation of ignition mechanisms by means of a PDF/REDIM method

Cited by 48 publications

References 22 publications

Fundamental Aspects of Jet Ignition for Natural Gas Engines

Fundamental Aspects of Jet Ignition for Natural Gas Engines

Prechamber Equipped Laser Ignition for Improved Performance in Natural Gas Engines

Three-Dimensional Simulation of Turbulent Hot-Jet Ignition for Air-CH4-H2 Deflagration in a Confined Volume

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