Numerical Characterization of Corona Spark Plugs and Its Effects on Radicals Production

Abstract

A mono-dimensional code for the simulation of the effects of High Frequency Ignition systems (HFI) on the production of chemical radicals was developed and here presented. The simulations were carried out by considering the typical environmental thermodynamic conditions of a nowadays engine at full load. An electron transport model is linked with a Boltzmann solver coupled with a chemistry solver, affecting the Electron Energy Distribution Function (EEDF) in order to obtain the physical conditions leading to the production of radical components for a given fuel mixture. The transport equations for the electrons, the positive and the negative ions, and the Gauss’ law in a steady-state plasma region. Then the Boltzmann equation for the electrons, in a spatially homogeneous steady-state case, is solved in order to obtain the EEDF. Finally the chemical kinetics model is employed assuming a fuel-air mixture neglecting the fuel carbon atoms due to the assumption that electron-impact dissociation reactions, which initiate the combustion, exhibit a greater reaction rate compared to those based on hydrocarbon thermal dissociation and therefore can be neglected in this work. Results show the production of the hydrogen (H), nitrogen (N), and oxygen (O) radicals and the radius of the initial discharge under different simulated engine operating conditions characterizing the role of a plasma corona effect for the induced chemical ignition in gasoline-powered engines.

Numerical Evaluation of the Effect of Fuel Blending with CO2 and H2 on the Very Early Corona-Discharge Behavior in Spark Ignited Engines

“…Those results are in line with the evidence shown in [29]. The Boltzmann solver validation has already been performed in the previous work [21], with comparison between the implemented in-house solver and two different open software options. The procedure also compared total ionization and attachment collision rates showing good matching of the results.…”

“…The current paper aims to extend the previous work by the same authors [21] on the characterization of radical species production from Corona discharge generated by a one-tip HFI device under engine-like environmental conditions. In the previous work, a reduced chemical kinetics set accounting for H 2 , N 2 , and O 2 , representing fuel and air, was considered.…”

“…Along the radial coordinate, the domain is bounded by the tip of the HFI plug device on the one side, and the piston crown on the other side, which is considered as the grounded surface. The grid independence test, which has already been performed in [21], revealed that the species distribution produced by adopting the typical size used in CFD simulations in the spark plug proximity for classical ignition simulation (around 0.1-0.15 mm) were slightly different from those achieved with grid element size in the range 0.01-0.005 mm, which instead have shown almost overlap results. As a consequence, the size of each element promoting mesh convergence while accurately capturing radial variation of the molar fractions was set to 40 µm with a uniform distribution.…”

“…As a consequence, the size of each element promoting mesh convergence while accurately capturing radial variation of the molar fractions was set to 40 µm with a uniform distribution. For the punctual description of the features of the preexisting physical model, the interested reader can refer to [21].…”

“…This work deals with the use of an in-house developed one-dimensional model for the steady state simulation of Corona discharge able to predict the initial discharge radius and the spatial distribution of the discharge-induced radical species, which was tested on mixtures consistent with next low-carbon fuel blends. The code was presented and discussed in a previous work of the present authors [21]. The additional contribution of this work lies in the fact that the chemical kinetics core integrated in the model was improved to address the simulation of renewable fuel mixtures in CO 2 -rich environment.…”