Inevitable chemical effect of balance gas in low temperature plasma assisted combustion

Abstract

Electrical discharges (or plasmas) have attracted researchers' attention to improve combustion characteristics. One of its key effects, which is not fully understood yet, is the in-situ production of chemically reactive species. Since most related low temperature kinetic studies to-date have been performed under highly diluted conditions (> 99 %), here we present the inevitable and undesirable chemical effect of a balance gas (Ar, He, N2) on the plasma-chemical kinetics. We employ a zero dimensional plasma-chemical kinetics model in combination with a (detailed and reduced) H2/O2/Ar reaction mechanism. The presented results indicate that (dissociative) quenching of excited (metastable) states dominates the H2 and O2 dissociation processes under highly diluted conditions. Additionally, in the reduced field intensity (E/N) domain, the type and amount of the balance gas significantly alters the fraction of electron energy transferred to the other species in the mixture. Therefore, we propose essential steps for the design of future kinetic studies for plasma assisted combustion.

Kinetic Study for Plasma Assisted Cracking of NH3: Approaches and Challenges

“…Regardless of the tested mechanism, the key initiation reactions for the plasma assisted decomposition of NH 3 in the presence of N 2 are the electron impact dissociation () and excitation () reactions of N 2 , whose rates are dependent on E / N rather than T g : e − + N 2 → e − + N + N normale − + normalN 2 → normale − + normalN 2 ( A 3 ) The actual decomposition of NH 3 occurs mainly through the dissociative quenching of N 2 (A 3 ) by NH 3 (), while the contribution of the direct electron impact dissociation of NH 3 (–) is an order of magnitude smaller. Note that this observed strong effect of the dissociative quenching (also known as Penning dissociation) on the conversion of NH 3 , compared to the effect of the electron impact dissociation, is attributed to the high dilution in N 2 ; this is similar to the observation in a highly diluted H 2 /O 2 mixture normalN 2 ( A 3 ) + NH 3 → normalN 2 + NH 2 + normalH normale − + NH 3 → normale − + NH …”

“…At this point, it is important to note that the (diluted) mixture of 99-% N 2 and 1-% NH 3 was chosen to limit the role of the direct electron impact dissociation of NH 3 , partly due to the high uncertainty caused by the lack of comprehensive N x H y cross-section data (discussed in 3.4.2.2). On the other hand, the result with the highly diluted mixture cannot be stretched toward mildly diluted or undiluted mixtures, because of the strong chemical effect of diluents in highly diluted mixtures . As the level of dilution decreases, the direct electron impact dissociation of NH 3 becomes more important at the expense of the diminished role of N 2 excited metastable states in the decomposition of NH 3 .…”

Combustion, Chemistry, and Carbon Neutrality

“…Fuels include hydrogen, 577,597,599 methane, 575,576,578,580,581,584,586,587,591,593,598,600 ethene, 581,589 propane, 581,590 n-heptane, 595 and other hydrocarbons, 594 methanol, 579 DME, 588 and ammonia, 582,585 and reaction systems include cells and reactors, 575,581,[588][589][590]594,596 flames, 582−584,586,593,597−599 and combustors. 576,585,592 Further aspects have been studied regarding the ion chemistry, 600 influences of the balance gases (Ar, He, N 2 ) on the chemical kinetics, 601 and spectroscopic signatures of excited states. 586 Some of the contributions have also addressed pyrolysis 589,595,596 and partial oxidation.…”

Dynamics of a Lean Flame Stabilized by Nanosecond Discharges

“…In flames, the gas composition is different, but in the conditions of the present study (premixed methane-air flame, =0.8), N2 is still the major species with a molar fraction above 72%. It is reasonable to consider that the electron energy is mainly transferred to N2 [24] and then, reaction (R1) is sufficient to represent electron-impact reactions. Nevertheless, the quenching of N2 excited states requires specific attention.…”