Spectroscopic investigation of interaction between propane jets injected into a supersonic flow of air under conditions of development of a nonequilibrium discharge in one of the jets

Emission spectroscopy is used to investigate the flow arising under conditions of injection of propane jets into a supersonic flow of air in the longitudinal direction; these jets are spaced apart in the initial zone of injection, and a nonequilibrium discharge is developed in one of the jets. Experiments are performed at Mach number M = 2, static pressure of 3.47 × 10⁴ Pa, and discharge current of 1 A. Data are obtained on the composition and space distribution of radiating products arising in the process of conversion of fuel-and-air mixture in the resultant combined flow. In particular, data are given on the distribution of intensity of radiation of C₂, CN, and CH radicals, as well as of atomic hydrogen and oxygen. The investigation results enable one to give a positive answer to the previously uninvestigated question of the possibility of ignition of a fuel-and-air mixture in supersonic flow, which propagates outside of the zone of reactions, supported by the nonequilibrium discharge. It is found that the redistribution of fuel between the main flow in which no discharge is present and an auxiliary channel in which the discharge is generated may result in a higher efficiency of the processes occurring in the main flow. The employed methods make it possible to determine the geometry of arising flow in the presence of plasma-chemical reactions.     

Spectroscopic investigations of longitudinal discharge in supersonic flow of air with injection of propane into the discharge zone

Results are given of investigations of a longitudinal contracted electric discharge in a supersonic flow of air at Mach number M = 2, static pressure of 3.47 × 10⁴ Pa (260 torr), and discharge current of 1 A with injection of propane into the discharge zone via electrode located upstream. The special feature of the discharge is that only one, anode, branch is realized in this case. Emission spectroscopy is used to obtain data on the composition of radiating products arising in the process of conversion of fuel-and-air mixture in the discharge and on their space distribution. In particular, data are given on the distribution of intensity of radiation of C₂, OH, CN, and CH radicals, as well as of atomic hydrogen, oxygen, carbon, and nitrogen, in a number of discharge channel sections. It is found that the main reaction zone in such a channel is preceded by the induction zone, where the development of reactions is hampered in spite of the electron flow in this zone. The employed procedure makes it possible to determine the variation of the transverse dimensions along the discharge channel and the details of flow such as a gradual shift of the gasdynamic lines of current due to the pattern of flow past the electrodes. Analysis of distribution of radiation intensity in the spectrum of atomic oxygen in a discharge without injection of propane gives estimates of the electron temperature which turns out to be approximately 1.1–1.2 eV.     

Fuel ignition and flame front stabilization in supersonic flow using electric discharge

Recent achievements in the field of stabilization of the front of high speed combustion using electric discharge are presented. Near-surface discharge at the plane wall between electrodes installed in the plane of the wall is applied in this study. Hydrogen and ethylene directly injected from the wall to the flow with a Mach number M = 2 and an air total temperature T ₀ = 300–760 K are used as fuel. The excess fuel coefficient calculated by the total air flow rate in the channel does not exceed ER = 0.1. The value of electric power input into the discharge is W _pl/H _tot < 2% of the total flow enthalpy, while the thermal power due to combustion exceeds W _com/H _tot > 100% at a low initial gas temperature. Electric discharge is first applied to stabilize combustion under conditions of a fixed separated zone and on the plane wall of the combustion chamber. A two-stage combustion regime is demonstrated. It is shown that the application of electric discharge makes it possible to achieve complete fuel combustion η > 0.9 in a wide range of experimental parameters.     

Fine structure of carbon films deposited from a microwave low-pressure gas discharge

We have studied the conditions of synthesis and the fine structure of carbon films of various structural modifications possessing preset electrical properties. The phase diagram of polymorphous transformations is constructed for carbon films grown from the plasma of microwave discharge in low-pressure ethanol vapor. Technological factors influencing the efficiency of extracting diamondlike microcrystals from a hydrocarbon matrix have been studied. Depending on the extraction regime and initial layer thickness, the size of extracted microcrystals can vary from 10–12 to 100–120 nm, while their surface concentration may reach 1.4×10⁷ cm⁻².     

The performance analysis and design optimization of fuel temperature control for the injection combustion engine

The purpose of the paper is to analyze the performance and design optimization of fuel temperature control in the injection combustion engine. There is a fuel temperature control device designed between the injection and fuel pump to cool down or warm up the fuel. Thermoelectric module (TEC) chips are applied in the device to absorb or dissipate heat from the fuel. There are several results relating exhaust emission and engine output performance to fuel temperature in this paper to display the optimization of fuel temperature for the injection engine. The experimental results indicate that increasing fuel temperature will result in an increase in CO, HC, and in a decrease in NO_x. Increasing the fuel temperature may affect the fuel consumption and engine output for a gasoline engine at different A/F (air to fuel) ratios. With enhanced understanding and analyses, the effects of fuel temperature on engine performance, fuel consumption and emissions can be taken into account in engine design and evaluation.     

Kinetics of free radicals in the plasma of a spark discharge in methane

The kinetics of reactions in the plasma of a spark discharge in methane at atmospheric pressure is analyzed using numerical simulation, taking account of the gas-dynamic expansion of the channel. The processes leading to the formation and annihilation of CH _x radicals are investigated and the conditions under which their maximum concentration is reached are determined. The results obtained are of interest for plasma chemical technologies for processing natural gas. Pis’ma Zh. Tekh. Fiz. 25, 82–86 (October 12, 1999)     

Some peculiarities of electric discharge between a solid electrode and technical water

We present the results of experimental study of the electric discharge between metal electrodes of various geometry and technical water within the pressure range of 8 × 10³–10⁵ Pa at the saw-tooth voltage generator frequency, f = 40 MHz, and the interelectrode distance, l = 3–30 mm. We consider transfer of the streamer discharge into spark one depending on the geometry of the metal electrode and its material. We investigate the electrical characteristics of the discharge between the plate electrode and the technical water within a wide pressure range. The essential influence of the streamer discharge type on the ozone release within the investigated parameters range is discovered.     

High-frequency actuator control of air flow near a circular cylinder: Impact of the discharge parameters on the cylinder aerodynamic drag

The impact of capacitive high-frequency surface discharge on a flow around a circular cylinder is studied at airflow velocity of 20–100 m/s and the Reynolds numbers Re < 2.4 × 10⁵. The power of the discharge was modulated at a frequency of 10²–10⁴ Hz, corresponding to the Strouhal number St = 0.1–10. It is shown that the distribution of pressure in the wake behind the cylinder is significantly influenced by the discharge. A decrease in the average diameter of the wake is observed. The parameters of the discharge were measured: the gas temperature, heating rate in the discharge region, and velocity of discharge propagation.     

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NO_x) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NO_x and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.     

Singlet delta oxygen concentration and the main process of its decrease in the afterglow of a DC discharge in oxygen flow

The concentration of O₂(a ¹Δ) molecules have been measured in the direct current discharge in an oxygen flow were measured in various cross sections in the gas flow channel after the discharge. It is shown that the decrease in the concentration can be described by a quadratic dependence of rate on the O₂(a ¹Δ) concentration. The rate constant of such a process is estimated to be ∼1 × 10⁻³¹ cm⁶/sec. Potential processes are considered. A three-body process in which an O(P) atom participates as the second particle apparently plays the key role     

Laminar-turbulent transition in a supersonic boundary layer during initiation of a pulsed surface discharge

The near-surface layer structure in a supersonic airflow (M = 1.5) behind the plane shock wave has been experimentally studied in a shock tube. The flow structure was visualized using nanosecond pulsed distributed surface discharge. Different structures of plasma glow have been observed for the laminar and turbulent flow regimes in the boundary layer. The position of a region of the laminar-turbulent transition for different flow densities (0.11 and 0.19 kg/m³) has been determined and the critical Reynolds number (Re _k ～ 2.4 × 10⁵) for this transition has been evaluated.     

Electrostatic Evaluation of a Unipolar Diffusion and Field Charger of Aerosol Particles by a Corona Discharge

This article presents a unipolar diffusion and field charger by corona discharge is presented and electrostatically evaluated for charging aerosol particles. The electrostatic characteristics of the charger were investigated with an electrometer by measuring the ion number concentrations corresponding to the discharge and charging currents. The discharge and charging currents, and ion number concentration in the discharge and charging zones of the charger, increased with corona voltage. The magnitudes of the ion number concentration for positive and negative coronas in the discharge zone ranged from 1.34 × 10¹³ to 1.84 × 10¹⁵ ions/m³ and 7.34 × 10¹³ to 2.64 × 10¹⁵ ions/m³, respectively. For the charging zone, the ion number concentrations for positive and negative coronas ranged from 2.95 × 10¹³ to 1.52 × 10¹⁴ ions/m³ and 2.06 × 10¹³ to 1.47 × 10¹⁴ ions/m³, respectively. To predict the behavior of the electric field strength and lines in the discharge and charging zones of the charger, the electric field strength and distribution of the charger in the discharge and charging zones were calculated by a commercial computational fluid dynamics software package. Numerical calculation results of electric field distribution and lines through the inner electrode showed good agreement with experimental results. Also, the mean charge per particle for particle diameters were in the range of 0.01 to 50 µm for various operating conditions of the charger was theoretically evaluated. For both diffusion and field charging, lower aerosol flow rate and higher corona voltage resulted in an increase in the mean charge per particle within the charger. This simple charger proved to be particularly useful in diffusion and field charging of aerosol particles in particulate matter detector instruments for measuring PM10 and PM2.5 concentration.     

Decomposition of radioactive methyl iodide in an electric discharge field

The possibility of using electric discharge for removing radioactive iodine in the form of volatile organic compounds from air-gas streams was examined. In an electric discharge field, at the methyl iodide concentration in the range from 0.9 to 19 mg l^?1, relative humidity within 48–90%, and linear flow velocity of 0.5–3.5 cm s^?1, the decontamination factor characterizing the methyl iodide decomposition is ≥1.4 × 10⁵.     

Spectral characteristics of optical discharge in a high-speed methane–air jet

Results of gasdynamic and spectroscopic investigations of optical discharge in the subsupersonic flow of a homogeneous fuel–air (CH₄ + air) mixtures are presented. The combustion was initiated and maintained by optical discharge created using a CO₂ laser. The laser radiation propagated across the flow and was focused by a lens on the axis of the supersonic jet (M = 2). Emission-spectroscopy techniques provided data on the composition of radiating combustion products and the intensity of components emitted in the region of optical discharge. Patterns of Toepler’s visualization of the flow structure in the schlieren scheme are presented. The images were monitored by a high-speed video camera operating at an exposure time of 1.5 μs and a frame frequency of 1000 s^–1.     

Aerodynamic quality management for the NACA 23012 airfoil model using the surface high-frequency discharge

The effect of the surface capacity HF discharge on airfoil flow-around has been studied in the situation when the oncoming flow velocity is 20 m/s and the Reynolds numbers are Re = 10⁵. The power delivered to discharge was modulated with a frequency of 3 × 10²–2 × 10⁴ Hz, which corresponds to a Strouhal number of St = 1.2–80, and the average electric power (W _av) was 50–400 W. It has been indicated that the aerodynamic drag decreased and the lift increased at stall and post-stall angles of attack when the HF dielectric barrier discharge was turned on. A nonstationary stochastic change in the C _x and C _y aerodynamic characteristics was observed at a stall angle in the St = 4–10 range of Strouhal numbers when the power was insufficient (W _av ≈ 100 W).     

High-current discharge in a limited volume projectile of a railgun

A theoretical study of plasma parameters of a high-current discharge in a limited volume (in the discharge chamber) of a body moving in an electrodynamic accelerator (railgun) has been performed. The experiments have shown that in the case of a cylindrical chamber the accelerated body is destroyed. Calculations made it possible to determine factors that are responsible for the destruction; these are a rapid burnout of chamber walls and a high pressure of the plasma. A series of simulations of the parameters of the plasma in the discharge chamber with a rectangular cross section have been carried out. It has been shown that, at a ratio of the sides of the rectangle greater than 2.5, the burnout of the walls is less than 2 mm. However, the plasma pressure remains high (～10⁵ atm), which requires the chamber walls to be reinforced by a strong carcass.     

Evaluation of the nitrogen oxide emission level for a steam supply with natural gas into the combustion chamber of a gas turbine unit

Numerical simulation results on the effect of the operation parameters for a combustion chamber of a combined-cycle plant (CCP) with steam injection [1] for the combined production of heat and electric energy upon a reduction in nitrogen oxide emission are represented. Calculations are carried out for lean mixtures with α = 1.2–1.4 and great steam consumptions of 30–42%. The reaction analysis has shown that the main contribution in NO _x formation was given by reactions with the advanced Zel’dovich thermal mechanism, and the reaction contribution with the participation of N₂O into the NO formation was an order of magnitude higher than that by the mechanism of the prompt NO formation. NO₂ does not form at high temperatures and only takes part in the conversion into NO in reactions with the participation of nitric acid. It is shown that the optimum choice of operation conditions for the combustion chamber of the CCP makes it possible to obtain the NO _x content in the combustion products in some mill^?1 (ppm). According to calculations, steam injection does not increase CO emission. A comparison with the experiment is given.     

Plasma density in discharge sustained in inhomogeneous gas flow by high-power radiation in the terahertz frequency range

We have measured the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20–30 μs) in a range of background gas pressures in the discharge chamber from 10^–3 to 300 Torr. The electron concentration at low pressures (10^–3 to 7 Torr) was determined using Starkeffect induced broadening of the H_α atomic emission line (656.3 nm) of hydrogen present in discharge as a small impurity in residual gases. The maximum observed Stark broadening of the H_α line corresponded to a plasma density on the order of 2 × 1016 cm^–3, which exceeded the critical value for the given frequency of radiation sustaining the discharge. At background pressures above 7 Torr, the plasma density was estimated from analysis of the spatiotemporal patterns and waveforms of discharge glow in the visible spectral range. These estimations gave electron concentrations on the level of (1–2) × 10¹⁵ cm^–3.     

Distinctive features of operation of an internal combustion engine running on hydrogen-containing fuels

Experimental investigations have been carried out on an internal combustion engine with hydrogen added to the hydrocarbon fuel, i.e., gasoline. The possibility of improving the energy and environmental indices in the case of hydrogen feed to the engine’s air path has been shown. It has been established that increase in the fraction of hydrogen in the fuel mixture causes the operating process of the engine to improve, with the result that the flow rate of gasoline as a function of the H₂ fraction decreases by nearly 70%. Considerable reduction in the content of CO, CO₂, and CH (of approximately 5–60% depending on the amount of the added H₂) is observed. However, adding hydrogen to the fuel-air mixture leads to an increase in the content of nitric oxides in the combustion products because of the growth in the velocity of propagation of the flame and increase in the combustion temperature.     

Method for determining the gas-dynamic characteristics of a nonequilibrium hypersonic flow of nitrogen based on experimental data on the stagnation parameters

A method is developed for determining the pressure, temperature, density, velocity head, Mach number, and other gas-dynamic parameters of a nonequilibrium flow of nitrogen in a hypersonic nozzle. The method is based on experimental data on the stagnation parameters T₀, p₀ and p₀' and the gas-kinetic model adopted for nitrogen.The indices 0 and^* refer to stagnation parameters and the conditions in the minimal cross section of the nozzle, respectively.Translated from Inzhenerno-Fizicheskii Ztarnal, Vol. 56, No. 1, pp. 74–80, January, 1989.