Pulsed Discharge Jet Research Articles

Effects of using nanosecond repetitively pulsed discharge and turbulent jet ignition on internal combustion engine performance

Robust ignition of hard-to-ignite fuels is essential for future spark ignited internal combustion engines, particularly for introducing efficiency-enhancing diesel-like process parameters like air excess or high amounts of exhaust gas recirculation (EGR). On the one hand, novel plasma-based ignition systems like Nanosecond Repetitively Pulsed Discharge (NRPD) are promising in extending the ignition limits and the early flame development speed. On the other hand, Turbulent Jet Ignition is effective for shortening the combustion duration and decreasing the unburned hydrocarbon emissions.This article investigates experimentally the combination of NRPD ignition and TJI. The aim is to use a technology for robust inflammation (NRPD) in combination with a technology for fast combustion of the bulk charge (TJI). For this purpose, a turbocharged light-duty four-cylinder engine operated with natural gas is used. The engine can be fitted with a classical Open Chamber (OC) spark plug or with Pre-Chambers (PC). The PCs can be filled uniquely with fuel and air coming from the Main Chamber (MC) (“passive PC”), or additional fuel can be added to the PCs (“active PC”). The air-to-fuel ratio and EGR rate can be freely controlled. Five different combustion strategies are investigated with NRPD ignition and compared against an inductive discharge ignition system. The combustion strategies are passive PC with air and EGR dilution, active PC with air dilution, and Open Chamber (OC) with air and EGR dilution. HRR evaluations and a loss analyses are performed to interpret the results.Despite the faster inflammation present with NRPD ignition, similar peak efficiencies and emissions are reached in OC configuration using the inductive discharge and NRPD ignition systems, which are achieved by varying air-to-fuel ratios (AFR) and EGR rates. Above dilution levels for peak efficiency, the efficiency using NRPD ignition decreases at a slower pace and tolerates higher AFR and EGR rates, thanks to a more complete and shorter combustion.For the PC experiments using NRPD ignition, an efficiency increases and a reduction of emissions compared to inductive discharge ignition are present for the investigated AFR and EGR rates for both active and passive PC operations. The efficiency increase is present due to a stronger pre-chamber discharge and thanks to a faster end phase of combustion. Actively fueling the PC results in faster and more complete combustion that is overcompensated by the increased wall heat losses, reducing the overall efficiency. The results show that passive PC with NRPD ignition may be an ideal ignition concept that maximizes engine efficiency and minimizes emissions.

Spectroscopic detection of the gallium methylene (GaCH2 and GaCD2) free radical in the gas phase by laser-induced fluorescence and emission spectroscopy.

GaCH2, a free radical thought to play a role in the chemical vapor deposition of gallium-containing thin films and semiconductors, has been spectroscopically detected for the first time. The radical was produced in a pulsed discharge jet using a precursor mixture of trimethylgallium vapor in high pressure argon and studied by laser-induced fluorescence and wavelength resolved emission techniques. Partially rotationally resolved spectra of the hydrogenated and deuterated species were obtained, and they exhibit the nuclear statistical weight variations and subband structure expected for a 2A2-2B1 electronic transition. The measured spectroscopic quantities have been compared to our own abinitio calculations of the ground and excited state properties. The electronic spectrum of gallium methylene is similar to the corresponding spectrum of the aluminum methylene radical, which we reported in 2022.

Spectroscopic detection of the stannylidene (H2C=Sn and D2C=Sn) molecule in the gas phase.

The H2CSn and D2CSn molecules have been detected for the first time by laser-induced fluorescence (LIF) and emission spectroscopic techniques through the B̃1B2-X̃1A1 electronic transition in the 425-400nm region. These reactive species were prepared in a pulsed electric discharge jet using (CH3)4Sn or (CD3)4Sn diluted in high-pressure argon. Transitions to the electronic excited state of the jet-cooled molecules were probed with LIF, and the ground state and low-lying Ã1A2 state energy levels were measured from single vibronic level emission spectra. We supported the experimental studies by a variety of ab initio calculations that predicted the energies, geometries, and vibrational frequencies of the ground and lower excited electronic states. The spectroscopy of stannylidene (H2CSn) is in many aspects similar to that of silylidene (H2CSi) and germylidene (H2CGe).

Structural modification of NADPH oxidase activator (Noxa 1) by oxidative stress: An experimental and computational study

NADPH oxidases 1 (NOX1) derived reactive oxygen species (ROS) play an important role in the progression of cancer through signaling pathways. Therefore, in this paper, we demonstrate the effect of cold atmospheric plasma (CAP) on the structural changes of Noxa1 SH3 protein, one of the regulatory subunits of NOX1. For this purpose, firstly we purified the Noxa1 SH3 protein and analyzed the structure using X-ray crystallography, and subsequently, we treated the protein with two types of CAP reactors such as pulsed dielectric barrier discharge (DBD) and Soft Jet for different time intervals. The structural deformation of Noxa1 SH3 protein was analyzed by various experimental methods (circular dichroism, fluorescence, and NMR spectroscopy) and by MD simulations. Additionally, we demonstrate the effect of CAP (DBD and Soft Jet) on the viability and expression of NOX1 in A375 cancer cells. Our results are useful to understand the structural modification/oxidation occur in protein due to reactive oxygen and nitrogen (RONS) species generated by CAP.

Atmospheric‐pressure pulsed discharges and plasmas: mechanism, characteristics and applications

Pulsed discharge plasma and its application is one of the promising directions in civilian areasof pulsed power technology. In order to promote the research and development ofthe theory and application technology for pulsed discharge plasma, in thispaper, recent progress on the mechanism of nanosecond-pulse gas discharge andthe characteristics and applications of typical pulsed plasma at the Instituteof Electrical Engineering, Chinese Academy of Sciences is reviewed. Firstly,progress on mechanism of nanosecond-pulse discharge based on runaway electronsand measurement technology of runaway electrons is introduced. Then, thecharacteristics of three typical discharges, including direct-driven pulseddischarge, pulsed dielectric barrier discharge and pulsed plasma jet, arereviewed. Furthermore, typical plasma applications of pulsed plasma on surfacemodification and methane conversion are presented.

Detection and characterization of the tin dihydride (SnH2 and SnD2) molecule in the gas phase.

The SnH2 and SnD2 molecules have been detected for the first time in the gas phase by laser-induced fluorescence (LIF) and emission spectroscopic techniques through the Ã1B1-X̃1A1 electronic transition. These reactive species were prepared in a pulsed electric discharge jet using (CH3)4Sn or SnH4/SnD4 precursors diluted in high pressure argon. Transitions to the electronic excited state of the jet-cooled molecules were probed with LIF, and the ground state energy levels were measured from single rovibronic level emission spectra. The LIF spectrum of SnD2 afforded sufficient rotational structure to determine the ground and excited state geometries: r0″ = 1.768 Å, θ0″ = 91.0°, r0' = 1.729 Å, θ0' = 122.9°. All of the observed LIF bands show evidence of a rotational-level-dependent predissociation process which rapidly decreases the fluorescence yield and lifetime with increasing rotational angular momentum in each excited vibronic level. This behavior is analogous to that observed in SiH2 and GeH2 and is suggested to lead to the formation of ground state tin atoms and hydrogen molecules.

An experimental and theoretical study of the Ã(2)A(″)Π-X̃(2)A(') band system of the jet-cooled HBBr/DBBr free radical.

The electronic spectra of the HBBr and DBBr free radicals have been studied in depth. These species were prepared in a pulsed electric discharge jet using a precursor mixture of BBr3 vapor and H2 or D2 in high pressure argon. Transitions to the electronic excited state of the jet-cooled radicals were probed with laser-induced fluorescence and the ground state energy levels were measured from the single vibronic level emission spectra. HBBr has an extensive band system in the red which involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Π state at linearity. We have used high level ab initio theory to calculate potential energy surfaces for the bent (2)A' ground state and the linear Ã(2)A(″)Π excited state and we have determined the ro-vibronic energy levels variationally, including spin orbit effects. The correspondence between the computed and experimentally observed transition frequencies, upper state level symmetries, and H and B isotope shifts was used to make reliable assignments. We have shown that the ground state barriers to linearity, which range from 10 000 cm(-1) in HBF to 2700 cm(-1) in BH2, are inversely related to the energy of the first excited (2)Σ ((2)A') electronic state. This suggests that a vibronic coupling mechanism is responsible for the nonlinear equilibrium geometries of the ground states of the HBX free radicals.

Hyperfine rather than spin splittings dominate the fine structure of the B (4)Σ(-)-X (4)Σ(-) bands of AlC.

Laser-induced fluorescence and wavelength resolved emission spectra of the B (4)Σ(-)-X (4)Σ(-) band system of the gas phase cold aluminum carbide free radical have been obtained using the pulsed discharge jet technique. The radical was produced by electron bombardment of a precursor mixture of trimethylaluminum in high pressure argon. High resolution spectra show that each rotational line of the 0-0 and 1-1 bands of AlC is split into at least three components, with very similar splittings and intensities in both the P- and R-branches. The observed structure was reproduced by assuming bβS magnetic hyperfine coupling in the excited state, due to a substantial Fermi contact interaction of the unpaired electron in the aluminum 3s orbital. Rotational analysis has yielded ground and excited state equilibrium bond lengths in good agreement with the literature and our own ab initio values. Small discrepancies in the calculated intensities of the hyperfine lines suggest that the upper state spin-spin constant λ' is of the order of ≈ 0.025-0.030 cm(-1).

An experimental and theoretical study of the electronic spectrum of the HBCl free radical.

Following our previous discovery of the spectra of the HBX (X = F, Cl, and Br) free radicals [S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)], the Ã(2)A(″)Π-X̃(2)A(') band systems of the HBCl and DBCl free radicals have been studied in detail. The radicals have been prepared in a pulsed electric discharge jet using a precursor mixture of BCl3 and H2 or D2 in high pressure argon. Laser-induced fluorescence (LIF) and single vibronic level emission spectra have been recorded to map out the ground and excited state vibrational energy levels. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Π electronic state at linearity. We have used high level ab initio theory to calculate the ground and excited state potential energy surfaces and have determined the vibronic energy levels variationally. The theory results were used to assign the LIF spectra which involve transitions from the ground state zero-point level to high vibrational levels of the excited state. The correspondence between theory and experiment, including the transition frequencies, upper state band symmetries, and H, B, and Cl isotope shifts, was used to validate the assignments.

An experimental and theoretical study of the electronic spectrum of HPS, a second row HNO analog

The à (1)A" - X (1)A' electronic spectra of jet-cooled HPS and DPS have been observed for the first time, using a pulsed discharge jet source. Laser induced fluorescence spectra were obtained in the 850-650 nm region. Although the 0(0)(0) band was not observed, strong 3(0)(n) and 2(0)(1)3(0)(n) progressions and 3(1) hot bands could be assigned in the HPS LIF spectrum. Single vibronic level emission spectra were also recorded, resulting in the determination of all three HPS ground state vibrational frequencies. High level ab initio calculations were used to help confirm the vibronic assignments by calculation of transition energies, anharmonic vibrational frequencies, and anharmonic Franck-Condon factors. Ab initio potential energy surfaces gave an equilibrium structure for the X (1)A' state of r"(PH) = 1.4334 Å, r"(PS) = 1.9373 Å, θ" = 101.77° and for the à (1)A" state of r'(PH) = 1.4290 Å, r'(PS) = 2.0635 Å, and θ' = 91.74°. The rotational contours observed are consistent with these structures, confirming that the bond angle of HPS decreases on electronic excitation. Although the bond angles of HNO and HNS open in the excited state, in accord with the Walsh predictions for 12 valence electron HAB molecules, HPO, HAsO and now HPS all show the opposite behavior.

Heavy atom nitroxyl radicals. V. An experimental and ab initio study of the previously unknown H2PS free radical

The B̃(2)A(')-X̃(2)A(') transition of the prototypical thiophosphoryl radical, H(2)PS, was observed for the first time using laser-induced fluorescence and single vibronic level emission spectroscopy. H(2)PS and its deuterated isotopologues, D(2)PS and HDPS, were produced in a pulsed supersonic discharge jet from a precursor mixture of Cl(3)PS and H(2) or D(2) or an H(2)/D(2) mixture in high-pressure argon. High level ab initio calculations of the lowest three doublet electronic states helped in the definitive assignment of the B̃-X̃ transition, which involves electron promotion from the π to the π∗ orbital. Vibrational frequencies were determined for several modes of each isotopologue in the X̃ and B̃ states and found to be in accord with theoretical predictions. Although a line-by-line rotational analysis was not possible, the observed band contours are consistent with the geometries obtained from our ab initio calculations. Theory indicates that PS bond length increases upon electronic excitation, while the pyramidalization of the radical does not change significantly.

The electronic spectrum of the previously unknown HAsO transient molecule

The Ã(1)A('')-X̃(1)A(') electronic spectrum of the jet-cooled transient molecule HAsO and its deuterated isotopologue has been observed for the first time by pulsed discharge jet laser spectroscopy. The techniques of laser-induced fluorescence and single vibronic level emission were employed to probe the electronic properties of the species. The bending and AsO stretching frequencies have been determined in both states. A rotational analysis of the 0(0)(0) bands of both HAsO and DAsO has been completed and the following effective (r(0)) structures were derived: r(")(HAs) = 1.576(3) Å, r(")(AsO) = 1.8342(5) Å, and θ(") = 101.5(4)°; and r(')(HAs) = 1.569(4) Å, r(')(AsO) = 1.7509(9) Å, and θ(') = 93.1(10)°. In the rotational analysis, lines induced by axis-tilting were observed, and calculated spectra with an axis tilting angle of 3.0(5)° reproduced the intensity of these lines. The change in geometry on electronic excitation is similar to that observed for the molecule HPO, with an increase in the X-O bond length and a decrease in the HXO angle, but contrary to the predictions of the Walsh diagram for generic HAB triatomic molecules. Our ab initio calculations show that the correlation between orbital energy and bond angle changes upon electronic excitation, resulting in the atypical angle change.

Pulsed discharge jet electronic spectroscopy of the aluminum dicarbide (AlC2) free radical

Laser-induced fluorescence and wavelength resolved emission spectra of the C ̃(2)B(2)-X̃ (2)A(1) band system of the gas phase aluminum dicarbide free radical have been obtained using the pulsed discharge jet technique. The radical was produced by electron bombardment of a precursor mixture of trimethylaluminum in high-pressure argon. The three vibrational frequencies of T-shaped AlC(2) have been determined in both the combining states along with several of the anharmonicity constants. The 0(0)(0) band has been recorded with high resolution and rotationally analyzed. The spectrum is complicated by partially resolved spin-rotation and aluminum hyperfine splittings. Where necessary, we have fixed the spin-rotation constants used in the rotational analysis at the values predicted by density functional theory. The derived molecular structures are: r(0)('')(C-C) = 1.271(2) Å, r(0)('')(Al-C) = 1.926(1) Å, θ(")(C-Al-C) = 38.5(2)°, r(0)(')(C-C) = 1.323(2) Å, r(0)(')(Al-C) = 1.934(1) Å, and θ(')(C-Al-C) = 40.0(2)°. Unlike SiC(2), aluminum dicarbide shows no spectroscopic evidence of facile isomerization to the linear structure in the ground electronic state.

Laser induced fluorescence spectroscopy of the jet-cooled carbon dioxide cation (C12O2+ and C13O2+)

The A (2)Pi(u)-X (2)Pi(g) band systems of jet-cooled (12)CO(2)(+) and (13)CO(2)(+) have been recorded by laser-induced fluorescence (LIF) techniques. Very intense, vibrationally cold expansions of these cations have been obtained using a pulsed electric discharge jet with a precursor mixture of carbon dioxide or (13)C labeled CO(2) in high pressure argon. The LIF bands have been partially rotationally analyzed to obtain band origins which yielded an accurate measure of the excited state vibronic energy levels. The energy levels of both isotopologues were fitted with a Renner-Teller model that included spin-orbit coupling, Fermi resonance and anharmonic terms. Single vibronic level emission spectra were also recorded for the (13)CO(2)(+) ion and the ground state energy levels fitted using the same Renner-Teller model. The isotope relations have been used to test the validity of the derived parameters. The results give a through description of the vibronic energy levels in the ground and first excited electronic states of the carbon dioxide cation.

The electronic spectrum of the fluoroborane free radical. II. Analysis of laser-induced fluorescence and single vibronic level emission spectra

Subsequent to our spectroscopic detection of the HBX (X=F, Cl, Br) free radicals (S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)), the electronic spectrum of the A (2)A(")Pi-X (2)A(') system of the fluoroborane (HBF) radical in the 600-745 nm region has been studied in detail using the pulsed discharge jet technique. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Pi state at linearity. Using the results of our theoretical study of the ground and excited state vibrational energy levels and (11)B-(10)B isotope shifts (see the companion paper), the vibrational quantum numbers of the bands in the laser-induced fluorescence (LIF) spectra have been assigned. Rotational and vibrational analyses of the LIF and wavelength resolved emission spectra have been carried out, from which the linear excited state and the bent ground state equilibrium configurations have been confirmed. The ground state molecular geometry of HBF has been determined as r(0)(BH)=1.214(2) A, r(0)(BF)=1.303 4(5) A, and theta=120.7(1) degrees. Based on high-level ab initio calculations and symmetry considerations, predissociation of the excited state into H((2)S)+BF((1)Sigma(+)) on the ground state potential energy surface is identified as the cause of the breaking off of fluorescence in the LIF spectra.

Electronic spectroscopy of the jet-cooled arsenic dicarbide (C2As) free radical

The (2)Delta(r)-X (2)Pi(r) band system of the jet-cooled arsenic dicarbide (C(2)As) free radical has been recorded by laser-induced fluorescence (LIF) techniques in the 685-588 nm region. The radical was produced in a pulsed electric discharge jet using a precursor mixture of AsCl(3) vapor and methane in high pressure argon. A series of weak bands involving all three excited state vibrations was observed for both (12)C(2)As and (13)C(2)As. High-resolution spectra of the (2)Pi(12) component of the 0(0)(0) bands of both isotopomers were rotationally analyzed, leading to the conclusion that the upper state is (2)Delta with a small spin-orbit splitting (A = 2.78 cm(-1)). Ground and excited state molecular structures of r(0)(")(CC,ab initio) = 1.2933 A, r(0)(")(CAs) = 1.734(4) A and r(0)(')(CC,ab initio) = 1.2276 A, r(0)(')(CAs) = 1.830(3) A were derived from the B values and our density functional predictions of the C-C bond lengths. Single vibronic level emission spectra were recorded for many of the LIF bands and these were used to obtain the ground state vibrational frequencies and spin-orbit splittings. These data were satisfactorily fitted to a Renner-Teller model which gave (12)C(2)As parameters of epsilon = 0.695(8), omega(1) = 1704.8(20) cm(-1), omega(2) = 161.6(8) cm(-1), omega(3) = 663.6(12) cm(-1), and a spin-orbit constant A = 857.7(11) cm(-1).

The electronic spectrum of jet-cooled copper hydrosulfide (CuSH)

The electronic spectrum of copper hydrosulfide (CuSH) has been observed for the first time. CuSH and CuSD were produced in a pulsed discharge jet by the reaction of sputtered copper atoms with H(2)S or D(2)S. Strong laser-induced fluorescence bands observed in the 515-470 nm region were assigned as the ~A (1)A"-X (1)A' band system based on detailed rotational analysis and the correspondence with the predictions of our CCSD(T)6-311++G(3df,3pd) ab initio calculations. The laser-induced fluorescence and single vibronic level emission spectra consist primarily of a short progression in nu(3), the Cu-S stretching mode, indicative of only modest structural changes on electronic excitation. The rotational constants of four isotopomers of CuSH were used to determine effective zero-point structures in the combining states as r"(CuS)=2.0916(3) A, r"(SH)=1.364(3) A, theta"=93.5(3) degrees , r'(CuS)=2.172(3) A, r'(SH)=1.408(23) A, and theta'=93.5(24) degrees . A comparison of the ground state structures of the known metal hydrosulfides shows that they can be considered to be metal-substituted hydrogen sulfides. The electronic spectra and molecular structures of CuOH and CuSH are compared and contrasted.

The molecular structure and a Renner-Teller analysis of the ground and first excited electronic states of the jet-cooled CS2+ molecular ion

The A 2Pi(u) - X 2Pi(g) electronic band system of the jet-cooled CS2 + ion has been studied by laser-induced fluorescence and wavelength-resolved emission techniques. The ions were produced in a pulsed electric discharge jet using a precursor mixture of carbon disulfide vapor in high-pressure argon. Rotational analysis of the high-resolution spectrum of the 2Pi32 component of the 0(0) 0 band gave linear-molecule molecular structures of r0" = 1.5554(10) A and r0' = 1.6172(12) A. Renner-Teller analyses of the vibronic structure in the spectra showed that the ground-state spin-orbit splitting (A = -447.0 cm(-1)) is much larger than that of the excited state (A = -177.5 cm(-1)), but that the Renner-Teller parameters are of similar magnitude and that a strong nu1 - 2nu2 Fermi resonance occurs in both states. Previous analyses of the vibronic structure in the ground and excited states of the ion from pulsed field-ionization-photoelectron data are shown to be substantially correct.

Renner–Teller vibronic analysis for a tetra-atomic molecule. II. The ground state of the HCCS free radical

We have studied the tetra-atomic Renner-Teller effect in the ground state of the jet-cooled HCCS and DCCS free radicals. The reactive intermediates were produced in a pulsed discharge jet using thiophene or deuterated thiophene precursors and the ground-state vibronic energies were measured using the single vibronic level emission spectroscopy technique. In HCCS, emission and fluorescence depletion experiments proved that some previously unassigned laser-induced fluorescence (LIF) features were anomalous 2Delta32-2Pi32 transitions, which gave information on several ground-state 2Delta32 levels. In DCCS, rotational mixing of the excited state v'=0(2Pi32) level with the 4(1)(1 2Sigma12) level allowed several ground-state 2Sigma levels to be observed in emission. In addition, we have shown that some previously unassigned weak LIF bands of DCCS are anomalous 2Pi12-2Pi32 transitions which have allowed us to accurately measure the ground-state spin-orbit splitting (259.0 cm(-1)) for the first time. All of the expected ground-state 2Pi32 levels and the majority of the 2Pi12 levels up to 1700 cm(-1) have been observed for both isotopomers. The data have been fitted by an effective Hamiltonian matrix treatment that included Renner-Teller, spin-orbit coupling, anharmonicity, and Fermi resonance effects for the two bending vibrations and the CS stretching mode. This has allowed an unusually complete description of the orbital angular momentum coupling effects, including the determination of the epsilon4, epsilon5, and epsilon45 terms for the first time. Subtle effects in both the LIF and emission spectra signal the presence of Sears resonances in both the ground and excited states of these radicals.

Fourier transform microwave spectroscopy of HSiBr: Exploring the Si–Br bond through quadrupole hyperfine coupling

The 1(01)-0(00) (9-10 GHz) and 2(02)-1(01) (18-19 GHz) rotational transitions of HSi 79Br and HSi 81Br have been measured in a pulsed discharge jet expansion to an experimental uncertainty of approximately 1 kHz using Fourier transform microwave spectroscopy. The data have yielded an effective rotational constant, the centrifugal distortion constant Dj, the bromine nuclear quadrupole coupling constants, and the bromine nuclear spin-molecular rotation interaction parameter for both isotopomers. The derived parameters have been compared to their values calculated ab initio, and the nuclear quadrupole coupling tensor has been used to investigate the Si-Br bond, giving a sigma bond ionic character of 0.60, a pi bond character of 0.22, and a total Si-Br ionic character of 0.38. These bond characteristics have been compared to trends in other halosilylenes, silanes, and the analogous carbenes.