A scramjet combustor with double cavitybased flameholders was experimentally studied in a directconnected test bed with the inflow conditions of M = 2.64,Pt = 1.84 MPa,Tt = 1 300 K.Successful ignition and selfsustaine...A scramjet combustor with double cavitybased flameholders was experimentally studied in a directconnected test bed with the inflow conditions of M = 2.64,Pt = 1.84 MPa,Tt = 1 300 K.Successful ignition and selfsustained combustion with room temperature kerosene was achieved using pilot hydrogen,and kerosene was vertically injected into the combustor through 4×φ 0.5 mm holes mounted on the wall.For different equivalence ratios and different injection schemes with both tandem cavities and parallel cavities,flow fields were obtained and compared using a high speed camera and a Schlieren system.Results revealed that the combustor inside the flow field was greatly influenced by the cavity installation scheme,cavities in tandem easily to form a single side flame distribution,and cavities in parallel are more likely to form a joint flame,forming a choked combustion mode.The supersonic combustion flame was a kind of diffusion flame and there were two kinds of combustion modes.In the unchoked combustion mode,both subsonic and supersonic combustion regions existed.While in the choked mode,the combustion region was fully subsonic with strong shock propagating upstream.Results also showed that there was a balance point between the boundary separation and shock enhanced combustion,depending on the intensity of heat release.展开更多
Cavity-based flameholder is expected to be applied for ramjets or afterburners,which could work efficiently in the high-altitude space with low pressure.The detailed fluid structure helps to understand the flame stabi...Cavity-based flameholder is expected to be applied for ramjets or afterburners,which could work efficiently in the high-altitude space with low pressure.The detailed fluid structure helps to understand the flame stability principle of the flameholder.The fluid structure in the center section and side section of the cavity-based flameholder is experimentally measured at the inlet pressure of 0.04–0.10 MPa,Mach number of 0.1,and temperature of 300 K.Results indicate that the inlet pressure has a significant effect on the fluid-structure in the cavity.The bluff body affects the generation of the vortex in the cavity.As the inlet pressure decreases from 0.10 MPa to 0.04 MPa,the classical dual-vortex maintains excellent stability in the side section of the cavity.Whereas the single-vortex in the center section gradually becomes incomplete with the inlet pressure varying from 0.10 MPa to 0.06 MPa,and it disappears at 0.04 MPa.The reason is that with the reduction of inlet pressure,the density decreases as well,and the proportion of the mass flow rate attracted to the low-pressure area downstream of the bluff body increases,which leads to the vortex being gradually pulled and destroyed.展开更多
Numerical simulations were performed to model the non-reacting and reacting flow behind a rearward step flameholder in Mach 1.6 supersonic flow with fuel injection at the step base.The combustor geometry was based on ...Numerical simulations were performed to model the non-reacting and reacting flow behind a rearward step flameholder in Mach 1.6 supersonic flow with fuel injection at the step base.The combustor geometry was based on the University of Florida scramjet experimental facility.Turbulence was modeled using k-u shear stress transport(SST),laminar flamelet was used for combustion modeling.Wall static pressure showed good agreement with experimental data for non-reacting and reacting flow.For non-reacting flow,dummy fuel helium mole fraction distribution in the recirculation region behind the step was validated with planar laser induced fluorescence(PLIF)images in experiments.To improve the combustion characteristics,air was injected in tandem with hydrogen at step base using various configurations.With all fuel injection as baseline,the case with 2 air jets around each fuel jet and air injected at 2 times the stagnation pressure of fuel showed the most improvement compared to other cases.It was most effective in reducing the local fuel richness,shortening the flame length and increasing combustion efficiency.展开更多
文摘A scramjet combustor with double cavitybased flameholders was experimentally studied in a directconnected test bed with the inflow conditions of M = 2.64,Pt = 1.84 MPa,Tt = 1 300 K.Successful ignition and selfsustained combustion with room temperature kerosene was achieved using pilot hydrogen,and kerosene was vertically injected into the combustor through 4×φ 0.5 mm holes mounted on the wall.For different equivalence ratios and different injection schemes with both tandem cavities and parallel cavities,flow fields were obtained and compared using a high speed camera and a Schlieren system.Results revealed that the combustor inside the flow field was greatly influenced by the cavity installation scheme,cavities in tandem easily to form a single side flame distribution,and cavities in parallel are more likely to form a joint flame,forming a choked combustion mode.The supersonic combustion flame was a kind of diffusion flame and there were two kinds of combustion modes.In the unchoked combustion mode,both subsonic and supersonic combustion regions existed.While in the choked mode,the combustion region was fully subsonic with strong shock propagating upstream.Results also showed that there was a balance point between the boundary separation and shock enhanced combustion,depending on the intensity of heat release.
基金supported by the National Science and Technology Major Project(No.2017-III-0008-0034)。
文摘Cavity-based flameholder is expected to be applied for ramjets or afterburners,which could work efficiently in the high-altitude space with low pressure.The detailed fluid structure helps to understand the flame stability principle of the flameholder.The fluid structure in the center section and side section of the cavity-based flameholder is experimentally measured at the inlet pressure of 0.04–0.10 MPa,Mach number of 0.1,and temperature of 300 K.Results indicate that the inlet pressure has a significant effect on the fluid-structure in the cavity.The bluff body affects the generation of the vortex in the cavity.As the inlet pressure decreases from 0.10 MPa to 0.04 MPa,the classical dual-vortex maintains excellent stability in the side section of the cavity.Whereas the single-vortex in the center section gradually becomes incomplete with the inlet pressure varying from 0.10 MPa to 0.06 MPa,and it disappears at 0.04 MPa.The reason is that with the reduction of inlet pressure,the density decreases as well,and the proportion of the mass flow rate attracted to the low-pressure area downstream of the bluff body increases,which leads to the vortex being gradually pulled and destroyed.
文摘Numerical simulations were performed to model the non-reacting and reacting flow behind a rearward step flameholder in Mach 1.6 supersonic flow with fuel injection at the step base.The combustor geometry was based on the University of Florida scramjet experimental facility.Turbulence was modeled using k-u shear stress transport(SST),laminar flamelet was used for combustion modeling.Wall static pressure showed good agreement with experimental data for non-reacting and reacting flow.For non-reacting flow,dummy fuel helium mole fraction distribution in the recirculation region behind the step was validated with planar laser induced fluorescence(PLIF)images in experiments.To improve the combustion characteristics,air was injected in tandem with hydrogen at step base using various configurations.With all fuel injection as baseline,the case with 2 air jets around each fuel jet and air injected at 2 times the stagnation pressure of fuel showed the most improvement compared to other cases.It was most effective in reducing the local fuel richness,shortening the flame length and increasing combustion efficiency.
