Numerical Analysis on Flame Kernel in Spark Ignition Methane/Air Mixtures

To accurately model the Direct Injection Spark Ignition (DISI) combustion process, it is important to account for the effects of the spark energy discharge process. The proximity of the injected fuel spray and spark electrodes leads to steep gradients in local velocities and equivalence ratios, particularly under cold-start conditions when multiple injection strategies are employed. The variations in the local properties at the spark plug location play a significant role in the growth of the initial flame kernel established by the spark and its subsequent evolution into a turbulent flame. In the present work, an ignition model is presented that is compatible with the G-Equation combustion model, which responds to the effects of spark energy discharge and the associated plasma expansion effects. The model is referred to as the Plasma Velocity on G-surface (PVG) model, and it uses the G-surface to capture the early kernel growth. The model derives its theory from the Discrete Particle Ignition (DPIK) model, which accounts for the effects of electrode heat transfer, spark energy, and chemical heat release from the fuel on the early flame kernel growth. The local turbulent flame speed has been calculated based on the instantaneous location of the flame kernel on the Borghi-Peters regime diagram. The model has been validated against the experimental measurements given by Maly and Vogel,1 and the constant volume flame growth measurements provided by Nwagwe et al.2 Multi-cycle simulations were performed in CONVERGE3 using the PVG ignition model in combination with the G-Equation-based GLR4 model in a RANS framework to capture the combustion characteristics of a DISI engine. Good agreements with the experimental pressure trace and apparent heat-release rates were obtained. Additionally, the PVG ignition model was observed to substantially reduce the sensitivity of the default G-sourcing ignition method employed by CONVERGE.

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MODELING NANOSECOND-PULSED SPARK DISCHARGE AND FLAME KERNEL EVOLUTION

Journal of Energy Resources Technology ◽

10.1115/1.4051144 ◽

2021 ◽

pp. 1-22

Author(s):

Joohan Kim ◽

Vyaas Gururajan ◽

Riccardo Scarcelli ◽

Sayan Biswas ◽

Isaac Ekoto

Keyword(s):

Electrical Discharge ◽

Internal Combustion Engines ◽

Initial Conditions ◽

Fuel Mixture ◽

Spark Ignition ◽

Combustion Stability ◽

Flame Kernel ◽

Wide Range ◽

Challenging Environment ◽

Kernel Growth

Abstract Dilute combustion, either using exhaust gas recirculation or with excess-air, is considered a promising strategy to improve the thermal efficiency of internal combustion engines. However, the dilute air-fuel mixture, especially under intensified turbulence and high-pressure conditions, poses significant challenges for ignitability and combustion stability, which may limit the attainable efficiency benefits. In-depth knowledge of the flame kernel evolution to stabilize ignition and combustion in a challenging environment is crucial for effective engine development and optimization. To date, comprehensive understanding of ignition processes that result in the development of fully predictive ignition models usable by the automotive industry does not yet exist. Spark-ignition consists of a wide range of physics that includes electrical discharge, plasma evolution, joule-heating of gas, and flame kernel initiation and growth into a self-sustainable flame. In this study, an advanced approach is proposed to model spark-ignition energy deposition and flame kernel growth. To decouple the flame kernel growth from the electrical discharge, a nanosecond pulsed high-voltage discharge is used to trigger spark-ignition in an optically accessible small ignition test vessel with a quiescent mixture of air and methane. Initial conditions for the flame kernel, including its thermodynamic state and species composition, are derived from a plasma-chemical equilibrium calculation. The geometric shape and dimension of the kernel are characterized using a multi-dimensional thermal plasma solver. The proposed modeling approach is evaluated using a high-fidelity computational fluid dynamics procedure to compare the simulated flame kernel evolution against flame boundaries from companion schlieren images.

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Numerical analysis for mixture formation in direct fuel injection spark ignition engines

JSAE Review ◽

10.1016/s0389-4304(00)00062-x ◽

2000 ◽

Vol 21 (4) ◽

pp. 477-481 ◽

Cited By ~ 1

Author(s):

Y Kihara

Keyword(s):

Numerical Analysis ◽

Fuel Injection ◽

Spark Ignition ◽

Spark Ignition Engines ◽

Mixture Formation ◽

Direct Fuel Injection

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Spark Ignition of SPP Injector Under Sub-Atmospheric Conditions

10.1115/gt2021-58699 ◽

2021 ◽

Author(s):

Qianpeng Zhao ◽

Yong Mu ◽

Jinhu Yang ◽

Yulan Wang ◽

Gang Xu

Keyword(s):

High Speed ◽

Spark Ignition ◽

Test Facility ◽

Propagation Mode ◽

Inlet Temperature ◽

Reacting Flow ◽

Atmospheric Conditions ◽

Flame Kernel ◽

Flame Development ◽

Initial Flame

Abstract The sub-atmospheric ignition performance of an SPP (Stratified Partially Premixed) injector and combustor is investigated experimentally on the high-altitude test facility. In order to explore the influence of sub-atmospheric pressure on reignition performance and flame propagation mode, experiments are conducted under different pressures ranging from 19 kPa to 101 kPa. The inlet temperature and pressure drop of the injector (ΔPsw/P3t) are kept constant at 303 K and 3% respectively. The transparent quartz window mounted on the sidewall of the model combustor provides optical access of flame signals. Ignition fuel-air ratio (FAR) under different inlet pressures are experimentally acquired. The spark ignition processes, including the formation of flame kernel, the flame development and stabilization are recorded by a high-speed camera at a rate of 5kHz. Experimental results indicate that the minimum ignition FAR grows rapidly as the inlet air pressure decreases. An algorithm is developed to track the trajectory of flame kernels within 25ms following the spark during its breakup and motion processes. Results show that the calculated trajectory provides a clear description of the flame evolution process. Under different inlet air pressures, the propagation trajectories of flame kernels share similarities in initial phase. It is pivotal for a successful ignition that the initial flame kernel keeps enough intensity and moves into CTRZ (Center-Toroidal Recirculation Zone) along radial direction. Finally, the time-averaged non-reacting flow field under inlet pressure of 54kPa and fuel mass flow of 8kg/h is simulated. The effects of flow structure and fuel spatial distribution on kernel propagation and flame evolution are analyzed.

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Laminar-to-turbulent flame transition and cycle-to-cycle variations in large eddy simulation of spark-ignition engines

International Journal of Engine Research ◽

10.1177/1468087420962346 ◽

2020 ◽

pp. 146808742096234

Author(s):

Yunde Su ◽

Derek Splitter ◽

Seung Hyun Kim

Keyword(s):

Large Eddy Simulation ◽

Early Stage ◽

Turbulent Flame ◽

Transition Process ◽

Spark Ignition ◽

Transition Model ◽

Flame Kernel ◽

Eddy Simulation ◽

Proposed Model ◽

Large Eddy

This paper investigates the effect of laminar-to-turbulent flame transition modeling on the prediction of cycle-to-cycle variations (CCVs) in large eddy simulation (LES) of spark-ignition (SI) engines. A laminar-to-turbulent flame transition model that describes the non-equilibrium sub-filter flame speed evolution during an early stage of flame kernel growth is developed. In the present model, the flame transition is characterized by the flame kernel size at which the flame transition ends, defined here as the flame transition scale. The proposed model captures the effects that variations in a turbulent flow field have on the evolution of early-stage burning rates, through variations in the flame transition scale. The proposed flame transition model is combined with the front propagation formulation (FPF) method and a spark-ignition model to predict CCVs in a gasoline direct injection SI engine. It is found that multi-cycle LES with the proposed flame transition model reproduces experimentally-observed CCVs satisfactorily. When the transition model is not considered or when variations in the transition process are neglected, CCVs are significantly under-predicted for the case considered here. These results indicate the importance of modeling the laminar-to-turbulent flame transition and the effect of turbulence on the transition process, when predicting CCVs, under certain engine conditions. The LES results are also used to analyze sources for variations in the flame transition. It is found, for the present engine case, that the most important source is the cycle-to-cycle variation in the turbulence dissipation rate, which is used to measure the strength of turbulence in the proposed model, near a spark plug. The large-scale velocity field and the variations of the laminar flame speed due to the mixture composition and thermal stratification are also found to be important factors to contribute to the variations in the flame transition.

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A Numerical Study on Effects of Electrode Gap and Heat Loss on Flame Kernel Formation in Spark Ignition Process for Methane/Air Mixtures

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.77.177 ◽

2011 ◽

Vol 77 (773) ◽

pp. 177-185

Author(s):

Shinji NAKAYA ◽

Mitsuhiro TSUE ◽

Michikata KONO ◽

Daisuke SEGAWA ◽

Toshikazu KADOTA

Keyword(s):

Heat Loss ◽

Numerical Study ◽

Spark Ignition ◽

Ignition Process ◽

Electrode Gap ◽

Flame Kernel

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Investigation of the spark ignition enhancement in a supersonic flow

Modern Physics Letters B ◽

10.1142/s0217984914502261 ◽

2014 ◽

Vol 28 (29) ◽

pp. 1450226 ◽

Cited By ~ 11

Author(s):

Zun Cai ◽

Zhen-Guo Wang ◽

Ming-Bo Sun ◽

Hong-Bo Wang ◽

Jian-Han Liang

Keyword(s):

Ignition Time ◽

Spark Ignition ◽

Dominant Factor ◽

Ignition Process ◽

Operation Condition ◽

Flame Kernel ◽

Operation Conditions ◽

Key Factor ◽

Lean Fuel ◽

Spark Energy

Ethylene spark ignition experiments were conducted based on an variable energy igniter at the inflow conditions of Ma = 2.1 with stagnation state T0 = 846 K , P0 = 0.7 MPa . By comparing the spark energy and spark frequency of four typical operation conditions of the igniter, it is indicated that the spark energy determines the scale of the spark and the spark existing time. The spark frequency plays a role of sustaining flame and promoting the formation and propagation of the flame kernel, and it is also the dominant factor determining the ignition time compared with the spark energy. The spark power, which is the product of the spark energy and spark frequency, is the key factor affecting the ignition process. For a fixed spark power, the igniter operation condition of high spark frequency with low spark energy always exhibits a better ignition ability. As approaching the lean fuel limit, only the igniter operation condition (87 Hz and 3.0 J) could achieve a successful ignition, where the other typical operation conditions (26 Hz and 10.5 J, 247 Hz and 0.8 J, 150 Hz and 1.4 J) failed.

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