Plasma-assisted ignition for a kerosene fueled scramjet at Mach 1.8

By using a plasma jet (PJ) torch with 1.5 kW input power as an igniter, successful ignition for liquid-kerosene fueled combustion experiment was conducted in a direct-connected supersonic test facility. The incoming flow has total temperature of 950 K and local Mach number of 1.8, corresponding to Mach 4 flight condition. In this study, several optical techniques, including high speed photography, high speed schlieren photography, and planar laser scattering (PLS) technique, were combined to study the ignition process, flame propagation, and mixing features of liquid kerosene fuel with air around the cavity. The effect of fuel injection position, injection pressure, and feedstock gas on ignition performance has been analyzed. The results indicate that local mixing is a critical factor for ignition. It is also shown that the PJ torch with N-2 + H-2 feedstock is superior to the PJ torch with N-2 feedstock for the ignition of liquid-kerosene fuel. These results are valuable for the future optimization of kerosene-fueled scramjet engine when using a PJ torch as an igniter

Discharge characteristics and abatement of volatile organic compounds using plasma reactor packed with ceramic Raschig rings

Discharge characteristics and abatement of volatile organic compounds using plasma reactor packed with ceramic Raschig rings were investigated. It was found that the gap equivalent capacitance decreased with increasing voltage while the dielectric barrier equivalent capacitance increased initially and stabilized at about 700 pF. Compared with empty reactor, toluene removal was significantly enhanced by ceramic Raschig rings, 97% against 48%. With respect to the energy yield in the presence of padding, the efficiency was remarkably improved up to 10 g/kWh, which was 2 times higher than that of 5 g/kWh in the absence of padding with removal ratio exceeding 50%

Three-dimensional flame measurements with large field angle

A system for three-dimensional computed tomography of chemiluminescence was developed to measure flames over a large field angle. Nine gradient-index rods, with a 9 x 1 endoscope and only one camera are used. Its large field of view, simplicity, and low cost make it attractive for inner flow field diagnostics. To study the bokeh effect caused by the imaging system on reconstruction solutions, fluorescent beads were used to determine the blurring function. Experiments using a steady diffusion flame were conducted to validate the system. Three models, namely the clear-imaging, out-of-focus imaging, and deconvolution models, were utilized. Taking the bokeh effect into account, the results suggest that based on run-times the deconvolution model provides the best reconstruction accuracy without increasing computational time. (C) 2017 Optical Society of America;A system for three-dimensional computed tomography of chemiluminescence was developed to measure flames over a large field angle. Nine gradient-index rods, with a 9 x 1 endoscope and only one camera are used. Its large field of view, simplicity, and low cost make it attractive for inner flow field diagnostics. To study the bokeh effect caused by the imaging system on reconstruction solutions, fluorescent beads were used to determine the blurring function. Experiments using a steady diffusion flame were conducted to validate the system. Three models, namely the clear-imaging, out-of-focus imaging, and deconvolution models, were utilized. Taking the bokeh effect into account, the results suggest that based on run-times the deconvolution model provides the best reconstruction accuracy without increasing computational time. (C) 2017 Optical Society of America</p

Computed Tomography Measurement of 3D Combustion Chemiluminescence Using Single Camera

Instantaneous measurement of flame spatial structure has been long desired for complicated combustion condition (gas turbine, ramjet et.). Three dimensional computed tomography of chemiluminescence (3D-CTC) is a potential testing technology for its simplicity, low cost, high temporal and spatial resolution. In most former studies, multi-lens and multi-CCD are used to capture projects from different view angles. In order to improve adaptability, only one CCD was utilized to build 3D-CTC system combined with customized fiber-based endoscopes (FBEs). It makes this technique more economic and simple. Validate experiments were made using 10 small CH4 diffusion flame arranging in a ring structure. Based on one instantaneous image, computed tomography can be conducted using Algebraic Reconstruction Technique (ART) algorithm. The reconstructed results, including the flame number, ring shape of the flames, the inner and outer diameter of ring, all well match the physical structure. It indicates that 3D combustion chemiluminescence could be well reconstructed using single camera

Measurements of spectral parameters for nitrous oxide near 4.56 mu m using a quantum cascade laser

Line strengths and nitrogen (N-2)-broadening coefficients for six nitrous oxide transitions were measured using a continuous-wave quantum cascade laser (cw-QCL) operating near 4.56 mu m. The temperature dependence of the exponent n for the N-2-broadening coefficients was determined over the range 298-800 K using a sapphire-sealed optical cell. Spectral parameters were determined by fitting absorption spectra with multi-peak Voigt profiles. The line strengths for the six transitions are 0-3% larger than those in the HITRAN 2012 database, while the N-2-broadening coefficients at the reference temperature are 2-5% smaller than the HITRAN 2012 values. (C) 2016 Elsevier Ltd. All rights reserved

Experimental Study of the Transient Response of Bunsen Flame to Nanosecond Pulsed Discharges

The transient processes associated with the interaction of a Bunsen flame and nanosecond pulsed discharges (NPD) are explored experimentally with two optical methods. A nanosecond-gated schlieren system is employed to image the shockwave propagation and the hydrodynamic response of the flame to NPD while the time-resolved optical emission spectroscopy measurements are carried out to determine active species and temperature in the plasma region created by the discharges. Therefore, the unsteady process of the interaction of the flame with the discharges is recorded in real-time by the combined measurements. Numbers of experimental evidences for understanding the dynamics of non-equilibrium plasma produced by NPD and performing further numerical simulation are offered

AEROSPACE SCIENCE AND TECHNOLOGY

Scramjet design is still a great challenge for researchers. It proves to be a critical issue for scramjet combustor to avoid intensive thermal choking while increasing combustion efficiency. Focusing on this target, the relationship between combustor configuration and the performance of dual-mode combustor was investigated using a direct-connected scramjet facility. Combustor was constituted by constant area part and divergent part, while cavities equipped in the expanded wall as flame-holding device. Ethylene was injected normally into the Ma 2.5 mainstream by both wall and cavity injectors. Two critical parameters of configuration, cavity location and the divergent angle, were changed during experiments. Combustion efficiency could evaluate the combustor performance, which was measured by an optical sensor based on tunable diode laser absorption spectroscopy (TDLAS). Combined with traditional wall static pressure and schlieren measurement, combustion efficiency and possible heat release both streamwise and spanwise were analyzed for different cases. It is found that combustion apparently is well organized with smaller divergent angle. Combustor could avoid inlet unstart and get disperse heat release with double cavities, but there is still space to increase efficiency by changing the location of recirculation zone. And experimental results show that the cooperation of cavities is essential for stabilizing combustion downstream. (C) 2015 Elsevier Masson SAS. All rights reserved

Tunable diode laser absorption spectroscopy measurements of high-pressure ammonium dinitramide combustion

The working processes of the ADN-based liquid thruster are complex, utilizing catalytic decomposition in a catalyst bed and high-pressure combustion in the combustion chamber. The present study examines the experimental performance of high-pressure combustion in an ADN-based liquid thruster. Using the Tunable Diode Laser Absorption Spectroscopy (TDLAS) method, flow parameters such as gas temperature and the characteristic species concentration of CO in the combustion chamber were measured instantaneously under the atmospheric environment. The effects of propellant inlet pressure and the catalyst bed preheated temperature on the combustion process were evaluated. It was found that both an increase in the propellant inlet pressure and an increase in the catalyst bed preheated temperature led to an increase in the gas temperature and a decrease of the CO mole fraction in the combustion chamber. In a hot fire test in the vacuum chamber, the performance of the model thruster under steady operation was tested. The results showed that with the increase of propellant inlet pressure, the combustion chamber pressure and the combustion chamber wall temperature also increase. However, although the increase of the catalyst bed preheated temperature also led to the increase of the combustion chamber wall temperature, the combustion chamber pressure remained nearly constant. These results provide a better understanding of the mechanisms of high-pressure combustion with ADN-based liquid propellants, which is beneficial to the development of green aerospace propulsion techniques. (C) 2015 Elsevier Masson SAS. All rights reserved. The working processes of the ADN-based liquid thruster are complex, utilizing catalytic decomposition in a catalyst bed and high-pressure combustion in the combustion chamber. The present study examines the experimental performance of high-pressure combustion in an ADN-based liquid thruster. Using the Tunable Diode Laser Absorption Spectroscopy (TDLAS) method, flow parameters such as gas temperature and the characteristic species concentration of CO in the combustion chamber were measured instantaneously under the atmospheric environment. The effects of propellant inlet pressure and the catalyst bed preheated temperature on the combustion process were evaluated. It was found that both an increase in the propellant inlet pressure and an increase in the catalyst bed preheated temperature led to an increase in the gas temperature and a decrease of the CO mole fraction in the combustion chamber. In a hot fire test in the vacuum chamber, the performance of the model thruster under steady operation was tested. The results showed that with the increase of propellant inlet pressure, the combustion chamber pressure and the combustion chamber wall temperature also increase. However, although the increase of the catalyst bed preheated temperature also led to the increase of the combustion chamber wall temperature, the combustion chamber pressure remained nearly constant. These results provide a better understanding of the mechanisms of high-pressure combustion with ADN-based liquid propellants, which is beneficial to the development of green aerospace propulsion techniques. (C) 2015 Elsevier Masson SAS. All rights reserved.</p

Combined TDLAS and OES technique for CO concentration measurement in shock-heated Martian atmosphere

This paper describes the CO concentration and gas temperature distribution measurements behind a strong shock wave in the simulated Martian atmosphere by an optical diagnostic system. The strong shock wave (6.31 &plusmn; 0.11 km/s) is established in a shock tube driven by combustion of hydrogen and oxygen. The optical diagnostic system consists of two parts: the optical emission spectroscopy (OES) system and the tunable diode laser absorption spectroscopy (TDLAS) system. For OES system, high temporal and spatial resolution experimental spectra of CN violet system (B-2 Sigma(+)-&gt; X-2 Sigma(+), Delta v = 0 sequence) have been observed. Rotational and vibrational temperature distribution along the shock wave is inferred through a precise analysis of high-resolution experimental spectra. For TDLAS system, a CO absorption line near 2335.778 nm is utilized for detecting the CO concentration using scanned-wavelength direct absorption mode. Combined with these experimental results using OES, CO concentration in the thermal equilibrium region is derived. The detected average CO concentration is 7.46 x 10(12) cm(-3) with the average temperature of 7400 K &plusmn; 300 K, which corresponds to the center fractional absorption of 2.7%