Combustion characteristics of supersonic strut-cavity combustor under plasma jet-assisted combustion

Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application combined with the central fuel injection method is less.In order to expand the combustion range,the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge.The effects of total pressure of strut fuel injection,total pressure of cavity fuel injection,total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain.The combustion field structure,wall pressure distribution,combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed.The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure.However,the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range.The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5−2.0 MPa,but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased.With the increased total injection pressure of the plasma jet,the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved.When the total pressure of the plasma jet is 1.25 MPa,the combustion efficiency reaches a maximum of 82.1%.The combustion-assisted effect of different plasma jet media is significantly different.When the medium of the plasma jet is O2,the combustion-assisted effect on the combustor is most significant.

Femtosecond laser-induced Cu plasma spectra at different laser polarizations and sample temperatures

Laser-induced breakdown spectroscopy(LIBS) is a good technique for detecting and analyzing material elements due to the plasma emission produced by the high-power laser pulse. Currently, a significant topic of LIBS research is improving the emission intensity of LIBS. This study investigated the effect of laser-polarization on femtosecond laser-ablated Cu plasma spectra at different sample temperatures. The measured lines under circularly polarized lasers were higher than those under linearly and elliptically polarized lasers. The enhancement effect was evident at higher Cu temperatures when comparing the plasma spectra that have circular and linear polarizations for different target temperatures. To understand the influence of laser-polarization and sample temperature on signal intensity, we calculated the plasma temperature(PT)and electron density(ED). The change in PT and ED was consistent with the change in the atomic lines as the laser polarization was being adjusted. When raising the Cu temperature, the PT increased while the ED decreased. Raising the Cu temperature whilst adjusting the laser-polarization is effective for improving the signal of femtosecond LIBS compared to raising the initial sample temperature alone or only changing the laser polarization.

Micro-impulse and plasma plume produced by irradiating aluminum target with nanosecond laser pulses in double-pulse scheme

The micro-impulse generated by ablating an aluminum target in double-pulse laser bursts with different interpulse delays was investigated using a torsion pendulum.The plasma plume was simultaneously visualized using high-speed photography to analyze the coupling mechanism of the ablation impulse.The experiment was carried out using a pulsed laser with a pulse width of 8 ns and a wavelength of 1064 nm.The experimental results show that an impulse with an interpulse delay of 60 ns is roughly 60%higher than that with no delay between the two pulses,when the energy of both laser pulses is 50 m J.Therefore,double-pulse schemes could enhance the ablation impulse under certain conditions.This is because the ablation of the first laser pulse changes the optical properties of the aluminum target surface,increasing the absorptivity.However,the ablation impulse is reduced with a time delay of 20 ns when the energy of both laser pulses is100 mJ or 150 mJ.It can be concluded that the plasma produced by ablating the aluminum with the first pulse shields the second laser pulse.To summarize,the experimental results show that different delay times in a double-pulse scheme have a significant effect on the ablation impulse.The study provides a reference for the optimization of the parameters when laser ablation propulsion with a double-pulse scheme is applied in the fields of space debris removal,laser ablation thrusters,and so on.

New kind of Hermite-Gaussian-like optical vortex generated by cross phase

We propose a new kind of optical vortex called the Hermite-Gaussian-like optical vortex(HGOV)inspired by the cross phase(CP).Theoretically,we investigate how the CP is decoupled from the phase of a cylindrical lens.We also investigate the propagation characteristics of an HGOV,which has a Hermite-Gaussian-like intensity distribution but still retains the orbital angular momentum.F urthermore,we derive the Fresnel diffraction integral of an HGOV and study the purity at infinity.Besides,we show a novel function of the self-measurement of the HGOV.Finally,we show that we can change the relative positions of singularities and the direction of an HGOV precisely,which facilitates applications in optical micro manipulation.

An efficient regulation approach for tomographic reconstruction in combustion diagnostics based on TDLAS method

For tomographic reconstruction in combustion diagnostics,it is usually necessary to solve a rank-deficient problem,where the number of non-linear dependent equations is smaller than the number of unknowns.In some reconstructions,there are grids without rays passing through.This produces artifacts during the reconstruction.In this paper,the weight of the regulation equation is modified with the number of the rays crossing the grid cells.The effect of the neighboring grid values as well as the number of rays crossing the grid cells is considered in the new regulation method.Numerical simulation results show that the new regulation method suppresses the reconstruction error of the no rays crossing grid and successfully restrains the corner distortion in four projection angles.The effects of the weight coefficient and the smoothing factor on the reconstruction are examined through a numerical study.Finally,a combustion experiment demonstrates that the new regulation method can significantly reduce the reconstructed error,especially for the nonray crossing condition,and the results are compared with thermocouple measurements and reconstructions without modified regulation.