Numerical simulation of spark ignition including ionization

Journal of Physics: Conference Series, 2019

This paper presents a 0-D kinetic model of electrostatic spark discharges consisting of the time-dependent Boltzmann equation of electrons, a discharge-circuit equation, and heavy particles’ kinetic equations to investigate the energy-transfer mechanisms from the electrostatic energy given to the energy of gases by the spark discharge. In this report, the model is applied to the discharges in atmospheric-pressure air under optimum conditions corresponding for the minimum ignition energies of the typical flammable gases, hydrogen, ethylene and propane, in three types of explosion groups for gases.

Detailed ignition modeling has been traditionally left out of the combustion simulations, mainly due to its relatively small time and length scales that could not be integrated into much larger length and time scales of combustion and fluid dynamics. Although the advancements in computing power has now made possible to integrate ignition and combustion modeling, not many researchers have shown interest due to the wide scope of knowledge it needs in both plasma physics and combustion dynamics. In this paper, we are reporting a preliminary analysis of an integrated ignition+combustion model for both spark ignition (SI) and laser-induced spark ignition (LISI) combustion chambers. A common aspect of both SI and LISI is the use of equation-of-state (EOS) tables at temperatures up to 5 times higher than those assumed in most combustion codes. We report use of an atomic physics code to generate EOS tables needed for our combustion and ignition simulations.

Combustion and Flame, 2016

This article presents a model to describe the effects of non-equilibrium plasma discharges on gas temperature and species concentration, in the set of equations governing the combustion phenomena. Based on the results reported in the literature, the model is constructed by analysing the channels through which the electric energy is deposited. The two main channels by which the electrons produced during the discharge impact the flow are considered: (1) the excitation and the subsequent relaxation of electronic states of nitrogen molecules which leads to an ultrafast increase of gas temperature and species dissociation within the discharge characteristic time; and (2) the excitation and relaxation of vibrational states of nitrogen molecules which causes a much slower gas heating. The model is fully coupled with multi-dimensional flow balance equations with detailed transport coefficients and detailed combustion chemical kinetic mechanisms. This high level of NRP discharge modelling allows computing high Reynolds flows by means of Direct Numerical Simulations and, therefore, a better understanding of plasma-assisted ignition phenomena in practical configurations. A sequence of discharge pulses in air and methane-air mixture in quiescent and turbulent flow configurations are studied with this model. The results show the minor impact of the vibrational energy on mixture ignition and how the increase of the turbulence spreads this vibrational energy and intermediate combustion species around the discharge zone, minimizing the cumulative effect of multiple pulses. In contrast, the production of O atoms during the discharge has a strong impact on the ignition delays and ignition energies (number of discharge pulses). The results also underscore the impact of the initial turbulent flow Reynolds number and the spatial distribution of turbulent eddies, relative to the discharge channel, on the number of pulses needed to ignite the mixture.

Proceedings of the Combustion Institute, 2019

In order to guarantee good re-ignition capacities in case of engine failure during flight, it is of prime interest for engine manufacturers to understand the physics of ignition from the spark discharge to the full burner lightning. During the ignition process, a spark plug delivers a very short and powerful electrical discharge to the mixture. A plasma is first created before a flame kernel propagates. The present work focuses on this still misunderstood first instants of ignition, i.e., from the sparking to the flame kernel formation. 3D Direct Numerical Simulations of propane-air ignition sequences induced by an electric discharge are performed on a simple anode-cathode setup. An Analytically Reduced Chemistry (ARC) including 34 transported species and 586 irreversible reactions is used to describe the coupled combustion and plasma kinetics. The effect of plasma chemistry on the temperature field is found to be non-negligible up to a few microseconds after the spark due to endothermic dissociation and ionization reactions. However, its impact on the subsequent flame kernel development appears to be weak in the studied configuration. This tends to indicate that plasma chemistry does not play a key role in ignition and may be omitted in numerical simulations.

Numerical Simulations - Examples and Applications in Computational Fluid Dynamics, 2010

Journal of Physics D: Applied Physics, 1996

The objective of this paper is the formulation of general macroscopic models that can be used in numerical simulation of spark discharge processes in inert gases. The governing equations for a non-polar single-substance continuum material body exposed to thermo-mechanical and electromagnetic actions are formulated in the Eulerian, as well as in the Lagrangian, description. One-dimensional, cylindrically symmetric models are derived in both descriptions. The previously given model of Plooster is reviewed and corrected. Results from simulations are presented, verifying the fact that significant dissimilarities concerning amplitude and speed of the shock will appear when the correct governing equations are not used in the simulation.

Journal of Physics D: Applied Physics

A self-consistent 1D theoretical framework for plasma assisted ignition and combustion is reviewed. In this framework, a "frozen electric field" modeling approach is applied to take advantage of the quasi-periodic behaviors of the electrical characteristics to avoid the recalculation of electric field for each pulse. The correlated dynamic adaptive chemistry (CO-DAC) method is employed to accelerate the calculation of large and stiff chemical mechanisms. The time-step is updated dynamically during the simulation through a three-stage multitimescale modeling strategy, which takes advantage of the large separation of timescales in nanosecond pulsed plasma discharges. A general theory of plasma assisted ignition and combustion is then proposed. Nanosecond pulsed plasma discharges for ignition and combustion can be divided into four stages. Stage I is the discharge pulse, with timescales of O(1-10 ns). In this stage, most input energy is coupled into electron impact excitation and dissociation reactions to generate charged/excited species and radicals. Stage II is the afterglow during the gap between two adjacent pulses, with timescales of O(100 ns). In this stage, quenching of excited species not only further dissociates O2 and fuel molecules, but also provides fast gas heating. Stage III is

Energies, 2022

Reducing green-house gases emission from light-duty vehicles is compulsory in order to slow down the climate change. The application of High Frequency Ignition systems based on the Corona discharge effect has shown the potential to extend the dilution limit of engine operating conditions promoting lower temperatures and faster combustion events, thus, higher thermal and indicating efficiency. Furthermore, predicting the behavior of Corona ignition devices against new sustainable fuel blends, including renewable hydrogen and biogas, is crucial in order to deal with the short-intermediate term fleet electric transition. The numerical evaluation of Corona-induced discharge radius and radical species under those conditions can be helpful in order to capture local effects that could be reached only with complex and expensive optical investigations. Using an extended version of the Corona one-dimensional code previously published by the present authors, the simulation of pure methane and ...

2016

Plasma-assisted combustion has received increasing attention in both plasma and combustion communities. Nanosecond Repetitively Pulsed (NRP) discharges are a promising and efficient technique to initiate and control combustion processes particularly when conventional ignition systems are rather ineffective or too energy costly. Even though a promising technique, the phenomena occurring in NRP discharges-assisted combustion are still poorly understood. The numerical studies presented in the literature are limited to 1-D and 2-D simulations in quiescent conditions. The problem complexity increases in practical configurations as ignition phenomena are also controlled by the flow and mixing field characteristics in and around the discharge channel. Direct Numerical Simulations (DNS) is a powerful research tool to understand these plasma/combustion/flow interactions. However, the computational cost of fully coupled detailed non-equilibrium plasma and combustion chemistry, and high Reynol...

International Journal of Hydrogen Energy, 2018

The paper presents numerical studies on forced (spark) ignition in a temporally evolving mixing layer between a fuel (mixture of hydrogen and nitrogen) and air. The research was performed in the framework of low Mach number approximation using implicit large eddy simulation (ILES) approach with detailed chemistry for hydrogen combustion (9 species, 19 reactions) for which the filtered source terms were computed directly using filtered quantities. The computations were performed applying a high-order numerical code on a numerical mesh with cell sizes close to the Kolmogorov scale, thus ensuring that the ILES results were credible. The spark was modelled by an energy deposition model and we considered various sizes and energies of the sparks. We analyzed the impact of these parameters on a success of ignition and flame development process. In case of successful ignition events we observed that depending on the spark locations and its characteristic the maximum temperature during the spark deposition (0.5 ms) varied in the range 2000 Ke4000 K and stabilized around 1800K shortly after the spark has been switched-off. It was found that the location of the spark in the flow region characterized by low turbulence intensity and proximity of the stoichiometric regimes almost always resulted in successful ignition, independently of the spark parameters (the energies 1mJ-4.5 mJ and sizes 1.2mm-3.3 mm). On the other hand, in the regions of high turbulence the maximum energy of the spark had to be large to ignite the flow. From this point of view it was observed that in the cases in which the total amount of energy supplied to the sparks was defined a priori, the sparks which were smaller but more intense were more effective than the sparks larger in size but weaker. We found that development of the flame and its growth after switching-off the spark cannot be directly related to the maximum temperature levels during the ignition. It was shown that in this respect the locations of the sparks relative to vortical structures play much more important role.