CFD-Simulation of Ignition and Combustion in Lean Burn Gas Engines

Xu, Guiqing; Hanauer, Christophe; Wright, Yuri M.; Boulouchos, Konstantinos

doi:10.4271/2016-01-0800

Cited by 12 publications

(9 citation statements)

References 34 publications

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“…For the laminar flame speed, S L 0 , algebraic relations as proposed, for example, in Metghalchi and Keck 57 and Gülder 58 are often used which correlate the laminar fame speed to the unburnt temperature, pressure and lambda. However, for the conditions encountered in gas engines, large discrepancies found were shown in Mittermayer 59 and Xu et al 60 A recent study 61 also concluded that many correlations were not able to match with recent experimental data because they were based on a limited set of measurements. In this study, one-dimensional (1D) unstrained laminar flame calculations have been performed, using the PREMIX package of CHEMKIN 62 to obtain the laminar flame speed, adiabatic temperature and flame thermal thickness.…”

Section: Methodsmentioning

confidence: 95%

Characterization of combustion in a gas engine ignited using a small un-scavenged pre-chamber

Wright

Schiliro

et al. 2018

International Journal of Engine Research

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Prechamber ignition technology receives increasing attention due to its considerable improvement on engine combustion efficiency and stability. However, fundamental knowledge concerning flame propagation inside the pre-chamber and jet formation in the main chamber is still quite scarce. In this study, a small (<0.5% VTDC) un-scavenged pre-chamber was tested in a medium size gas engine with pressure transducers installed in both pre- and main chamber. Three-dimensional computational reactive fluid dynamics Reynolds-averaged Navier–Stokes simulations were carried out using a level-set combustion model –G-equation – towards improved understanding of the combustion processes occurring inside the pre and main chamber. The characteristics of the turbulence and the flame at locations just ahead of the propagating turbulent flame front were recorded and analysed by means of the well-known Borghi–Peters diagram. The results revealed that the characteristics of the flame inside the pre-chamber differed greatly from those inside the main chamber due to considerably reduced turbulent length scales. In addition, a wide range of turbulence intensity and length scales are covered throughout the combustion event, presenting a significant challenge to modelling of flame–turbulence interaction. Various turbulent flame speed ( ST) closures widely used in internal combustion engine simulation were therefore assessed and the ranges of their respective model constants explored. A correlation for ST is subsequently proposed by blending two formulations of Gülder developed for small and large scale turbulence, respectively, and compared to the well-known Peters correlation. With appropriate model constants, both successfully reproduce the pre and main chamber combustion for the reference case in terms of evolutions of cylinder pressure, heat release rate and pressure difference between pre and main chamber. Following successful calibration of the reference operating condition, variations in engine speed, load, spark timing and lambda were calculated using both correlations, demonstrating encouraging predictive capabilities of the proposed modelling strategy.

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Section: Methodsmentioning

confidence: 95%

Characterization of combustion in a gas engine ignited using a small un-scavenged pre-chamber

Wright

Schiliro

et al. 2018

International Journal of Engine Research

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“…Direct comparisons of this ignition mechanism with the dual-fuel (pilot ignition) system are also available [26] and they can be supplemented with the present results. The Large-Eddy Simulations may also be improved with better correlations for flame speed [27] if engine conditions are targeted.…”

Section: Further Discussionmentioning

confidence: 99%

“…The computation of the reaction term in the regress variable equation requires the evaluation of the laminar flame speed which was computed using the correlation by Gulder [15]. Note that this correlation may need improvement at engine-relevant conditions [16]. A spark (modelled as a sink term in the regress variable equation) of duration 5•10  s and diameter 5 mm was imposed at the beginning of the simulation to initialize the flame.…”

Section: Large Eddy Simulationmentioning

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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“…The value of the tunable parameter A is in general case-dependent, for example a value of 2.8 was recommended in [27] for a GDI gasoline engine and 3.0-3.4 was explored in [28] for a large natural gas engine in lean conditions. In the present study, flame speed tuning was performed on a single case for the baseline pre-chamber PC-C1 and a medium injection condition ID002, resulting in A=2.75.…”

Section: Combustion Processmentioning

confidence: 99%

Experimental and Numerical Analysis of Pre-Chamber Combustion Systems for Lean Burn Gas Engines

Shapiro

Tiney

Kyrtatos

et al. 2019

SAE Technical Paper Series

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The current trend in automobiles is towards electrical vehicles, but for the most part these vehicles still require an internal combustion engine to provide additional range and flexibility. These engines are under stringent emissions regulations, in particular, for the reduction of CO2. Gas engines which run lean burn combustion systems provide a viable route to these emission reductions, however designing these engines to provide sustainable and controlled combustion under lean conditions at λ=2.0 is challenging. To address this challenge, it is possible to use a scavenged Pre-Chamber Ignition (PCI) system which can deliver favorable conditions for ignition close to the spark plug. The lean charge in the main combustion chamber is then ignited by flame jets emanating from the prechamber nozzles. Accurate prediction of flame kernel development and propagation is essential for the analysis of PCI systems. A modelling approach is proposed based on the Dynamic Discrete Particle Ignition Kernel model coupled with the G-equation combustion model. The model is validated for an air/methane academic benchmark. The approach is then applied to the investigation of performance of three pre-chamber designs developed within Horizon 2020 GASON project in conjunction with the experimental investigation of these pre-chambers mounted on Rapid Compression Expansion Machine (RCEM). The investigated prechamber designs vary with respect to the tangential nozzle angle and volume. The study focusses on a lean limit of the proposed system's operation with the main charge at λ=2.0 and a variation of prechamber design and scavenging level. The comparison of the simulation results with the experimental observations demonstrates good accuracy of the developed model. In addition, the combined experimental and modelling provides insights into the effect of prechamber geometry on potential performance.

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CFD-Simulation of Ignition and Combustion in Lean Burn Gas Engines

Cited by 12 publications

References 34 publications

Characterization of combustion in a gas engine ignited using a small un-scavenged pre-chamber

Characterization of combustion in a gas engine ignited using a small un-scavenged pre-chamber

Fundamental Aspects of Jet Ignition for Natural Gas Engines

Experimental and Numerical Analysis of Pre-Chamber Combustion Systems for Lean Burn Gas Engines

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