Kerosene-fueled Scramjet Research Articles

Effect of pilot hydrogen on the mixing and combustion characteristics in kerosene-fueled scramjet

Scramjet engine has presented excellent advantages in hypersonic flight due to its excellent flight performance, such as simple structure, high specific impulse performance and a broad range of cruising speed. However, the stable combustion is extremely formidable in the case of supersonic flow. This work combined several flame-holding strategies, i.e., vertical injection orifices, dual cavities, pilot flame, as well as converting kerosene as supercritical state, aiming at providing a significant reference for the supersonic stable combustion. Meanwhile, as a highly reactive fuel, the effects of hydrogen addition on the mixing and combustion characteristics were investigated in detail. In the process, the total equivalence ratio of kerosene and pilot hydrogen was held constant at 0.8, and the effect of different equivalence ratios of hydrogen (ERH = 0, 0.34 and 0.47) was investigated. The results showed that the addition of hydrogen can effectively enhance the combustion intensity in the combustor. The wall static pressure reached from 230 kPa to 259 kPa with ERH increasing from 0 to 0.47. High pilot hydrogen can make the back pressure propagate toward the entrance, improving the risk to compromise the stable inlet conditions. The shock wave disk was occurred near the entrance, leading to the drastic variation of pressure, temperature and density. The consumption of supercritical kerosene was very fast, while the combustion of hydrogen was relatively lower, even uncomplete burning of hydrogen was observed at exit. With the addition of pilot hydrogen, the heat released in the combustor became less. Specifically, as the ERH increased from 0 to 0.47, the heat released in combustor reduced from 4.1 × 104 to 3.2 × 104 MJ/s, resulting in the corresponding temperature at the exit decreaing from 1777 to 1607 K, due to the decrement of combustion efficiency resulted from the addition of hydrogen.

Challenges and solutions for local flame development during spark ignition in a kerosene-fueled scramjet combustor

This study experimentally investigates the challenges and solutions related to the development of local flame into global flame during kerosene spark ignition in a scramjet combustor operating at Mach 4 flight conditions. The ignition and intensity of local flame are explored with different injection pressures. Two potential solutions have been proposed to facilitate the development. The results show that injection pressure plays a critical role in controlling fuel transport into the ignition cavity T1, affecting the local equivalence ratio and local flame formation. Higher injection pressures lead to less fuel transported into cavity T1, resulting in fuel-lean local equivalence ratios and potential ignition failure. Extending the duration of ignition and injection improves ignition reliability. The suppressive effect of dense spray on local flame is the main cause of the local flame development problem. A higher injection pressure can reduce the suppressive effect and increase the intensity of downstream cavity flames. When the downstream cavity flames reach a critical intensity, the flashback of downstream cavity flame will occur, achieving global flames. The dense spray can be thinned out by very low upstream injection pressure, which can also result in global flames.

Investigation of Unsteady Combustion Regimes in a Kerosene-Fueled Scramjet with Air Throttling

This paper describes an experimental study investigating unsteady combustion regimes in a kerosene-fueled scramjet. The results are obtained under inflow conditions of a 2.9 MPa stagnation pressure, 1900 K stagnation temperature, and a Mach number of 3.0. The air throttling position is 240 mm downstream of the combustor entrance, with an air throttling flow rate (ratio of air throttling mass flux to inflow mass flux) of 38% and a fuel equivalence ratio of 0.37. Combustion is relatively stable when air throttling is applied and is dominated by auto-ignition. When air throttling is turned off, the combustion becomes more unsteady and is dominated by flame propagation. At the same time, the combustion mode changes, and the frequency of the combustion mode transition is 286 Hz. Schlieren images and one-dimension analysis show that the effect of air throttling is the coupling of cold throat (aerodynamic throat) and hot throat (thermal throat). The proper orthogonal decomposition and dynamic mode decomposition analysis present that when air throttling is applied or removed, the frequencies of injector–flame feedback are almost the same, while the frequencies of shock–flame feedback exhibit considerable variation, which is caused by the location of the precombustion shock affected by air throttling.

Experimental and numerical investigations on controlled parameter selection methods for kerosene-fueled scramjet

Abstract In order to determine the optimal wall pressure location as the controlled parameter for kerosene-fueled scramjet, a combined approach of numerical simulation and experimental analysis was employed. The results indicate that with an increase in the equivalence ratio of kerosene, the combustor exhibits consecutive modes, including pure scramjet mode, dual-mode scramjet mode, dual-mode ramjet mode, and pressure disturbance to the isolator inlet mode. The peak pressure ratios corresponding to the mode transition boundaries are 1.95, 3.26, and 3.57, with respective isolator outlet Mach numbers of 1.62, 1.0, and 0.74. The equivalence ratio corresponding to mode transition increases with an increase in the combustor inlet total temperature. Considering the dynamic characteristics of wall pressures at different locations, the position at x/L = 0.46 demonstrates the best linearity, highest sensitivity, and greater stability. Hence, it is the most suitable choice as the controlled parameter for fuel flow in this kerosene-fueled scramjet.

Experimental study on the combustion process of a kerosene-fueled scramjet with strut injection

The ground combustion test was used to study the effects of kerosene fuel on the start-up ignition and flame stabilization of a scramjet with reverse strut injection. The test analyzed the changes of flow field wave system and flame propagation law under various working conditions after pilot hydrogen was injected into the combustor. The results showed that when hydrogen was injected into the combustor, it started to combust in only 0.0128 s. The heat released by combustion led to the generation of reverse pressure gradient, which made the wave system move forward and concentrate near the backward step. In the case of hydrogen self-ignition, the entire flow field remained stable combustion. At t = 0.07 s, kerosene was gradually injected into scramjet and ignited by pilot flame. The pressure at the monitoring point increased rapidly from 0.064 MPa to 0.135 MPa, and severe combustion occurred in the cavity. The flame began to propagate from the shear layer to the low-speed recirculation zone. Subsequently, the pressure of the monitoring point was reduced to 0.121 MPa, and the combustion flame continuously passed from the cavity downstream. When the hydrogen was removed, the pressure was reduced to 0.09 MPa, and the flame in the cavity was relatively weakened. However, the rapid ignition condition of kerosene could still be achieved, and the combustion flame continued to generate. After fuel began to be gradually removed, kerosene could not maintain continuous flame combustion due to the reduction of injection volume. The combustor changed between ignition and flameout, showing periodic oscillation with a period of 4.8 ms.

Experimental investigation of effects of air throttling on combustion characteristics in a kerosene-fueled scramjet at Ma7

Experimental investigation of effects of air throttling on combustion characteristics in a kerosene-fueled scramjet at Ma7

Experimental investigation of effects of dual-cavity configuration on ignition and flame stabilization in a kerosene-fueled supersonic combustor

The effects of two kinds of dual-cavity configuration on ignition and flame stabilization in a high Mach number (Ma) kerosene-fueled scramjet were experimentally investigated in this study. To better understand the combustion characteristics, flow structure and flame development were studied by schlieren photography, flame self-illumination photography, and wall-pressure measurement. Results were obtained with an isolator inlet Ma 3.0, total pressure 2.9 MPa, and total temperature 1900 K, which correspond to Maf 8.0 condition. The symmetrical dual-cavity configuration did not achieve kerosene auto-ignition, while the staggered dual-cavity configuration did achieve kerosene auto-ignition because shock waves were much more complex. In the staggered dual-cavity scramjet, flame stabilization was achieved after successful ignition by a lower equivalence ratio (ER) of kerosene, but when the ER of kerosene was increased to 0.8, flame stabilization was not achieved and the flow structure oscillated quasi-periodically.

Multi-channel gliding arc plasma-assisted ignition in a kerosene-fueled model scramjet engine

A multi-channel gliding arc (MCGA) plasma was utilized to ignite a kerosene-fueled model scramjet engine with an inflow of Ma2.92. High-speed photography from the top and side view of the scramjet combustor, high-speed CH* chemiluminescence imaging coupled with the electrical measurements were used to investigate the ignition process. A three-dimensional RANS simulation was used to show the distributions of velocity, temperature, and local equivalence ratio of the supersonic cold flow. In the ignition process, the formation of the flame kernel mainly depends on the discharge characteristics of the MCGA plasma, whereas the flame propagation process is mainly determined by the cavity flow. The MCGA plasma is more likely to produce a large area of the flame kernel in the spark-type discharge with the long arc column and overlaps of each channel gliding arc. The larger flame can be generated subsequently by the merging of the flame kernels ignited by the MCGA plasma, which develops into the resident flame. The resident flame is unable to be formed in a relatively high local equivalence ratio, and it is hard to spread to the back of the cavity along the shear layer due to the large velocity gradient with a relatively low temperature. The resident flame is formed several times by the MCGA plasma ignition, which increases the possibility of the flame spreading to the back of the cavity to form the mainstream flame. The local equivalence ratio can significantly affect the cavity ignition of the kerosene-fueled scramjet combustor.

Experimental investigation of effects of pulsed injection on flow structure and flame development in a kerosene-fueled scramjet with pilot hydrogen

The effects of pulsed injection on the flow structure and flame development in a scramjet were investigated experimentally with a pilot hydrogen equivalence ratio (ER) of 0.1 and a kerosene ER of 0.3; the pilot hydrogen was used to enhance the kerosene combustion. In the steady injection flow, the non-reacting flow structure changed periodically, and the monitor pressure built up rapidly when the pilot hydrogen self-ignited at t = 0.0096 s, increasing from 0.03 to 0.037 MPa. The pilot flame was stable and filled the whole cavity until the kerosene began to be injected into the combustor at t = 0.05 s; the kerosene combustion occurred only in the cavity shear layer. After a very short time, the pilot flame was blown off by the kerosene. In the pulsed injection flow, the kerosene kept burning with the help of the pilot flame, and the monitor pressure remained at a high value that was about six times that in the non-reacting flow. The mixture of pilot hydrogen and kerosene flame could propagate into the isolator, which was discontinuous and a distinct fault could be seen in the flame images. The kerosene combustion under pulsed injection was very intense, and even when the pilot hydrogen was removed, the cold room-temperature kerosene could still burn steadily for some time. Comparing with the flame development process under steady injection conditions, it is concluded that pulsed injection helps greatly to realize kerosene ignition and stable combustion.

Experimental investigation on flame stabilization of a kerosene-fueled scramjet combustor with pilot hydrogen

Flame stabilization in a kerosene-fueled scramjet combustor was investigated experimentally through Schlieren, flame luminosity, and wall pressure measurement, aiming to obtain better insight into combustion characteristics. Experiments were conducted in a direct-connected supersonic combustion facility with inflow conditions of Mach number 2.0, stagnation pressure 0.82 MPa, and temperature 950 K, simulating the flight condition of Mach number 4.0. Results revealed that kerosene was able to be ignited when the equivalence ratio of pilot hydrogen reached 0.080, but was unsuccessful when the equivalence ratio was 0.040. Once ignited, the intense combustion induced high back pressure forcing the flame to spread into the isolator. The pilot flame invariably appeared in the cavity shear layer and attached to the cavity ramp under different equivalence ratios of pilot hydrogen. With the mass flux of pilot hydrogen increased, the kerosene flame located near the cavity ramp was asymmetrical and unstable since it propagated upstream repeatedly. Therefore, the kerosene could be ignited by a suitable equivalence ratio of continuous pilot hydrogen, potentially accompanied with unstable combustion.

Experimental study on the effects of simulated flight conditions on ignition and flame stabilization in a supersonic combustor

Effects of simulated flight conditions on ignition and flame stabilization in a kerosene fueled scramjet combustor were experimentally investigated in the present paper. Simulated flight conditions were Mach 4.5 and Mach 4.0, and the isolator entrance Mach number was 2.0. Wall pressure and flame emission were made during the experiments in an attempt to better understand the combustion characteristics, air throttling was used to enhance the flame stabilization. The results showed that, the kerosene ignition was achieved successfully under the Mach 4.5 flight condition, that of Mach 4.0 flight condition was blowout before the kerosene pressure reached the max pressure. The flame in the combustor without air throttling during Mach 4.0 flight condition only existed in the cavity and near the top wall before it was blown off, that of Mach 4.5 flight condition had spread into the isolator. The flame stabilization was also only achieved under the Mach 4.5 flight condition with the aid of air throttling, the flame in the combustor with air throttling during the Mach 4.0 flight condition was blowout before the throttling air was removed. Ignition and flame stabilization were easy to be achieved under the higher flight condition.

Experimental study of flame stabilization in a kerosene fueled scramjet combustor

Kerosene flame stabilization in a Mach 2.0 model combustor was studied experimentally by using laser-induced fluorescence and high-speed photography. The interferential fluorescence in OH-PLIF was eliminated by the comparison with kerosene-PLIF. The reaction layers of flame were marked by the sharp gradient regions of fluorescence intensity in OH-PLIF. The results show that the flame is stabilized in the cavity at a lower equivalence ratio. As the equivalence ratio is increased, flame is stabilized in the cavity shear layer and spreads into the mainstream. The oscillations of the flame are quantified and correlated with the pressure fluctuations of the pseudoshock. Low-frequency oscillations are found to be amplified in the upstream propagation. As the inlet stagnation temperature rises, ram-scram transition occurs at a higher equivalence ratio. Kerosene flame is always stabilized in the cavity region without propagating upstream within the range of current inlet stagnation temperature (885–1285 K).

Experimental study on combustion characteristics of kerosene-fueled scramjet combustor

ABSTRACTKerosene-fueled ignition combustion test was carried out in a scramjet combustor under the condition of total temperature of 810 K, Mach number of 2.0 and different total pressures of 600, 700, 800 and 900 kPa. The combustor model was a dual-mode combustor with double cavity flameholder. Hydrogen was injected in the first cavity, and kerosene was injected in front of the first cavity. Hydrogen, being pilot flame, was the first to be ignited by the spark plug, and then kerosene was ignited by hydrogen. Kerosene was kept burning solely after hydrogen was stopped injecting. Combustion luminosity images were pictured in tests. The test results showed that all the combustion modes of kerosene and hydrogen were upstream cavity stabilization mode under different fueling conditions. Under the higher entrance pressure or the higher kerosene equivalence ratios, the kerosene combustions were upstream cavity stabilization mode. Under the lower entrance pressure or the lower kerosene equivalence ratios, the combustions were downstream cavity stabilization combustion mode. Under the middle entrance pressure or the kerosene equivalence ratios, oscillations of combustion mode occurred. The flameholding capacity of the kerosene-fueled combustor increases with the increase of the entrance total pressure.

Combustion characteristics of hydrogen and cracked kerosene in a DLR scramjet combustor using hybrid RANS/LES method

This paper applies a zonal hybrid RANS/LES framework to analyze supersonic combustion in a model scramjet combustor. The geometries and boundary conditions of model scramjet combustor are based on an experiment conducted at DLR, German Aerospace Center. This model scramjet combustor was designed to achieve free flight Mach number of 5.5 and total air temperature of 1500 K. Hydrogen at subcritical conditions and thermal/catalytic cracked kerosene at supercritical conditions are injected as fuel. A surrogate of thermal/catalytic cracked kerosene is composed of ethylene and methane in supercritical conditions. To remain consistent with the hydrogen-fueled case, the total equivalence ratio is set to 0.034 for both cases. The total equivalence ratio is quite small, so it is not induced flow separation in the combustor duct. The thermodynamic and transport properties of the supercritical thermal/catalytic cracked kerosene are calculated using the Redlich–Kwong Peng–Robinson cubic equation of state and Chung's model for viscosity and conductivity. This paper focuses on comparisons of the subcritical hydrogen-fueled and supercritical cracked kerosene-fueled scramjet combustors in terms of intrinsic flow and combustion features. The analysis is demonstrated via a reacting regime diagram in nonpremixed turbulent combustion, flame index contours and scatter plots of the flamelet structure. It is found that the cracked kerosene surrogate flame is more vulnerable to quenching than the hydrogen flame, and flame quenching occurs in the immediate vicinity of the injector.

Investigation of flameholding mechanisms in a kerosene-fueled scramjet combustor

Laser-induced fluorescence and high-speed photography were employed to investigate the kerosene flame stabilization mechanism in a cavity-based scramjet combustor with an inlet condition corresponds to flight Mach number of 4. Pilot hydrogen was used to ignite the kerosene fuel. The PLIF results of kerosene distribution in the reacting cases showed that the mixing process was dramatically enhanced compared to the non-reacting cases. Sharp OH gradients were observed in the shear layer and the aft region of cavity, which indicated that the flame was located at these positions. A portion of hot products participated in the recirculation of the cavity and preheated the kerosene-air mixture in the leading edge. The heated mixture was ignited in the mid-cavity and the reaction zone spread into the mainstream flow. Due to the competition between the local flame speed and the local flow speed, the high-speed images showed that the spreading location was in fluctuation. This movement was observed to cause a low-frequency wall pressure fluctuation.

Investigation of the effects of fuel injector locations on ignition and flame stabilization in a kerosene fueled scramjet combustor

The effects of fuel injector locations on ignition and flame stabilization in a kerosene fueled scramjet combustor have been investigated in the present paper. Various measurements are made during the experiments in an attempt to better understand the combustion characteristics, including wall pressure measurements and high speed color flame emission images. The results are obtained under the inflow condition of Ma number 2.0, total pressure 1.0 MPa and total temperature 1100 K which corresponds to Ma 4.5 flight condition. When the pilot hydrogen and kerosene were injected into the combustor from the injector K2 (in the cavity) and K1 (upstream the cavity), respectively, the kerosene could be ignited successfully by a lower equivalence ratio (ER) of pilot hydrogen, but the kerosene flame was blowout after the pilot flame was removed. When the injector locations of pilot hydrogen and kerosene were exchanged, the ER of pilot hydrogen must be increased to achieve successful ignition, the kerosene flame stabilization could be achieved after successful ignition. When the equivalence ratio of kerosene was decreased to 0.13, the lean blowout occurred and flame stabilization could not be achieved after the pilot hydrogen was removed.

Investigation of flameholding characteristics in a kerosene-fueled scramjet combustor with tandem dual-cavity

The flameholding characteristics in a kerosene-fueled scramjet combustor with a tandem dual-cavity were investigated experimentally under various inlet stagnation pressure conditions. Flame stabilization locations were judged by the pressure distributions and flame luminescence images. The results show that at lower and higher equivalence ratios, the flame was stabilized in the downstream and upstream cavities, respectively. While at intermediate range of equivalence ratio the flame was oscillating between the two cavities. The inlet stagnation pressure has a significant impact on the flameholding characteristics by affecting the relative pressure rise and the flame speed. The transition of flame stabilization location can occur in a higher local flow Mach number in the case of the higher inlet stagnation pressure.

Effects of Cavity Configurations on Flameholding and Performances of Kerosene Fueled Scramjet Combustor

AbstractIn this work, the effects of cavity flameholder configurations on flameholding and performances of kerosene fueled scramjet combustor were studied experimentally and numerically. For experiments, a directly connected ground facility was used and clean high enthalpy air, with a total temperature of 800 K and a total pressure of 800 Kpa, was provided by an electricity resistance heater. To investigate the effects of cavity configurations on flameholding capacity and reacting-flow characteristics, three different flameholders, one single cavity flameholder and two tandem cavity flameholders, were used in experiments. For the two combustors with tandem cavity flameholders, the location and configurations of its up-stream cavity were same with the single cavity flameholder, and the length-to-depth ratios for down-stream cavities were 9 and 11 respectively. The experimental results showed that stabilize kerosene combustion were achieved for combustor with tandem cavity flameholders mounted, and none for that with single cavity flameholder. The none-reacting and reacting flows of combustor models with tandem cavity flameholders were compared and studied with numerical and experimental results. The results showed that higher combustion efficiencies and pressure recovery ratios were achieved for the combustor with down-stream cavity length-to-depth ratio of 9.

Numerical Investigation of Various Fuel Injection Angles on Interaction in Cold Kerosene-fueled Supersonic Flow

The incident shock wave strongly affects the transversal injection field in cold kerosene-fueled supersonic flow, possibly due to its affecting the interaction between incoming flow and the fuel through various operation conditions. Optimum selection of fuel injection parameters indicates optimum interaction between incoming flow and fuel. Based on three dimensional Couple Level Set & Volume of Fluids (CLSVOF) approach, a detailed Computational Fluid Dynamics model of a cold kerosene-fueled scramjet combustor is developed in this study. Next, the effects of various injection angles on the interaction between incident shock wave and transversal cavity injection are addressed. The injection angles are specified from 45̊ to 135̊ in 45̊increments when other operation parameters, i.e. the injection diameter, velocity and pressure drop are all constant. The CLSVOF-based predictions are focused on penetration height, span-wise expansion area, angle of shock wave and sauter mean diameter (SMD) distribution of the kerosene droplets. Our findings show that the penetration depth, span-wise angle and expansion area of the transverse cavity jet all increased with the injection angle, and that the kerosene droplets are more prone to breakup and atomization at the outlet of the combustor for the injection angle of 45̊. This study demonstrates the effectiveness of CLSVOF modeling for better understanding of kerosene-fueled supersonic mixing and scramjet combustor design improvement.

Numerical investigation of scale effect of various injection diameters on interaction in cold kerosene-fueled supersonic flow

The incident shock wave generally has a strong effect on the transversal injection field in cold kerosene-fueled supersonic flow, possibly due to its affecting the interaction between incoming flow and fuel through various operation conditions. This study is to address scale effect of various injection diameters on the interaction between incident shock wave and transversal cavity injection in a cold kerosene-fueled scramjet combustor. The injection diameters are separately specified as from 0.5 to 1.5mm in 0.5mm increments when other performance parameters, including the injection angle, velocity and pressure drop are all constant. A combined three dimensional Couple Level Set & Volume of Fluids (CLSVOF) approach with an improved K-H & R-T model is used to characterize penetration height, span expansion area, angle of shock wave and sauter mean diameter (SMD) distribution of the kerosene droplets with/without considering evaporation. Our results show that the injection orifice surely has a great scale effect on the transversal injection field in cold kerosene-fueled supersonic flows. Our findings show that the penetration depth, span angle and span expansion area of the transverse cavity jet are increased with the injection diameter, and that the kerosene droplets are more prone to breakup and atomization at the outlet of the combustor for the orifice diameter of 1.5mm. The calculation predictions are compared against the reported experimental measurements and literatures with good qualitative agreement. The simulation results obtained in this study can provide the evidences for better understanding the underlying mechanism of kerosene atomization in cold supersonic flow and scramjet design improvement.