Vivek Gautam

Cryogenic Flow and Atomization from a Coaxial Injector

The global flow characteristics of the cryogenic flow injected from a single-element coaxial injector have been examined experimentally to simulate the flow andmixing behavior before ignition and combustion in characteristic rocket engines. The injector simulated one element of the cryogenic rocket engine injectors under realistic operating conditions. This work focuses specifically on the evolution of liquid nitrogen jet instability, spreading, and its atomization and mixing with the surrounding coaxial gaseous jet under steady-state atmospheric conditions. The effect of some important flow parameters, such as velocity ratio and momentum ratio between jets, on the potential core length of the liquid nitrogen jet and shear angle of the flow have been analyzed. The results showed a significant role of these parameters on the instability and breakup of the liquid nitrogen jet, along with the strong heat transfer effect of the surrounding atmosphere on the cryogenic liquid nitrogen jet. The shear angle of the flow remained constant along the longitudinal axis of the injector, thus confirming fully developed steady-state jet under atmospheric conditions. The mean value of the shear angle showed the transcritical nature of the liquid nitrogen jet under atmospheric conditions. The shear angle of the flow also reduced with introduction of the helium jet and decreased uniformly with increase in helium jet velocity, which supports the effect of surrounding gas density on the jet spreading as predicted by previous researchers. The potential core length of the cryogenic liquid nitrogen showed a local peak as a function of velocity of the gaseous jet and decreased exponentially with momentum ratio for values close to and higher than one.

Simulat ion of Flow and Mixing from a Coaxial Rocket Injector

Characteristi c coaxial injector geometry has been used to examine the flow and mixing behavior under non -reacting conditions for simulating the mixing performance in cryogenic rocket engines . The effects of partial or full confinement of the flows as well as momentum ratio between the inner and outer fluids from the injector have been examined at atmospheric pressure condition . The fluids used in injector s are often cryogenic liquid O 2 (LOX) through the inner tube and gaseous hydrogen through the outer annulus. In this paper we simulate th is cryogenic injector fluid mixing behavior with liquid nitrogen (LN 2) flowing through the inner tube while gaseous N 2, CO 2 or He lium (He) injected through the outer annulus. High speed cinematography has been used to examine the dynam ic al behavior of the LN 2 jet flow surround ed by a coaxial gaseous stream . Infrared ( IR ) thermal imaging technique has been used to determine the thermal field distribution associated with LN 2 jet upon its discharge from the injector exit into the surroundi ng gas flow . The role of injector -injector interaction was simulated by partial and full confinement of the injector fluids. The confinement significantly alters the dispersion of liquid jet into gaseous stream to impact flow dispersion, expansion and mixi ng. The LN 2 jet stream upon exit from the injector nozzle dispersed into ligaments and droplets prior to its vaporization . For the fully confined case the LN 2 jet persist ed over longer distances downstream of the injector exit than the unconfined or partia lly confined case s. Confinement altered the heat transfer from the surroundings to delay LN 2 vaporization in addition to expected reduction in entrainment of the surrounding air . The expansion of LN 2 jet beg an earlier with increase in momentum ratio betwee n inner and outer jets while its mixing with surrounding gases is reduced with increase in momentum ratio . These results assist one to examine flow and mixing between a cryogenic fluid and different gas density fluids as well the role of momentum ratio bet ween jets to simulate the performance at different injector operational conditions.

Cryogenic Flow and Mixing from a Single Element Coaxial Rocket Injector

The flow and mixing behavior of cryogenic fluid from a single element co -axial injector is examined . The injector simulated one element of the cryogenic rocket injector under realistic operating conditions. In case of real injector s t he flow consists of a cen tral liquid oxygen (LOX) core surrounded by annular gaseous hydrogen. In this paper, t he flow, mixing and thermal behavior of the cryogenic propellant has been simulated by using liquid nitrogen (LN 2) flowing through the inner tube and gaseous Helium (He) through the outer annulus of the injector . Specifically we have examined the evolutionary behavior of liquid nitrogen (LN 2) jet flow instability, jet breakup and mixing with the surrounding coaxial gaseous jet under steady state at atmospheric pressure con ditions . The effect of some important parameters such as, momentum ratio, density ratio and swirl in the surrounding gas flow on the behavior of liquid nitrogen (LN 2) jet in a coaxial gaseous stream has been analyzed. The results provide the role of these parameters on the instability and breakup of LN 2 jet and its subsequent effect on mixing with the surrounding gas eous stream. The experimental diagnostic techniques used here inclu de high speed Schlieren imaging and IR thermal imaging. High speed Schlieren technique is used to analyze the formation of vortical structures and instability of LN 2 jet whereas IR thermal imaging technique is used to analyze the cooling effect of cryogenic LN 2 jet on the surrounding gases and flow entrainment.

Cryogenic Flow from a Coaxial Injector under Low -Pressure In -Space Conditions

The effect of near -vacuum operating pressure on the evolutionary behavior of cryogenic fluid injected from a single -element coaxial injector has been examined experimentally . The investigated injector simulate s one element of the injector array of cryogenic rocket engine s under realistic operating c onditions. Actual rocket -engine propellants, liquid oxygen and gaseous hydrogen , are simulated by chemically inert and safe to operate liquid nitrogen and helium. This work focuses specifically on the transient evolution of liquid nitrogen jet under in -spa ce conditions. The diagnostic technique s utilized here are high -speed Mie -scattering and Schlieren imaging. The results showed that the behavior of liquid nitrogen jet wa s significant ly affected by the low -pressure conditions as well as the strong heat shi elding effect of coaxial helium jet . The cryogenic jet undergoes extraordinary jet expansion at sub -atmospheric pressures . Initial freezing of liquid nitrogen droplets and ligaments was observed close to the injector exit . The heat transfer from the warm surroundings to cold liquid nitrogen jet wa s reduced significantly in the presence of coaxial gaseous jet, which confined the cold liquid nitrogen jet and prevented its expansion to some extent .

Characterization of Cryogenic Flow and Atomization from a Coaxial Rocket Injector

The effect of some of the important flow parameters, such as, velocity ratio, density ratio and momentum ratio have been examined experimentally on potential core length of the cryogenic fluid injected from a single-element coaxial injector. The injector simulated one element of the cryogenic rocket engine injectors under realistic operating conditions. This work focuses specifically on the evolution of liquid nitrogen jet instability and breakup under steady state atmospheric conditions. The results showed significant role of velocity ratio, density ratio, momentum ratio along with the strong heat transfer effect of the surrounding atmosphere on the cryogenic liquid nitrogen jet behavior. The potential core length of the cryogenic liquid nitrogen showed a local peak as a function of velocity of the gaseous jet. However, the core length showed insensitivity to changes in density of the gaseous jet. The results also provided a strong evidence of the heat-shielding effect of the coaxial gaseous jet. The heat transfer from the surroundings to the cold LN2 jet is reduced significantly by the presence of the gaseous jet, which strongly affects the potential core length of liquid nitrogen jet. The experimental diagnostic technique used here is Schlieren imaging using a high speed camera to analyze the global flow behavior of liquid nitrogen jet. The Schlieren images were processed using image processing techniques to obtain quantitative information of the flow.

Simulation of Mixing in Rocket Engine Injectors under In-Space Conditions

Shear layer mixing between two coaxial jets of different density gases has been examined to simulate and analyze mixing and ignition between fuel and oxidizer from a single element injector of a rocket engine. An experimental combustion facility has been designed and fabricated to simulate the behavior of single element coaxial injector. The flow and mixing characteristics of this injector are examined under non-reacting conditions at normal atmospheric pressure. PIV (Particle Image Velocimetry) diagnostics is used to obtain the flowfield distribution of two different density gases that simulates the behavior of gaseous H2/O2 flows from the injector. The results are then used to validate the calculated results obtained from a CFD -model. A RANS type code has been used to simulate the dynamics of the 2-D axisymmetric simulated coaxial injector used in rocket combustors. The model can predict flowfield, turbulence characteristics and species distribution inside the combustor for a range of operating conditions. The code is then used to obtain the flow dynamic behavior as well as species distribution of H2/O2 flows inside a combustion chamber under sub-atmospheric conditions. These results provide useful information on the mixing, ignition and combustion for in-space combustion conditions. The model can be extended to include more realistic operational conditions for the injector as well as the injector-wall interactions.

Fate of Cryogenic Fl uid Flow and Atomization from a Sheer Coaxial Injector under Pre -Ignition Conditions

The transient and steady evolutiona ry beha vior of cryogenic fluid from a sheer coaxial injector has been examined experimentally under pre -ignition (on earth and simulated in -space ) conditions . The investigated inject or simulates one element of typical cryogenic rocket injectors under reali stic pressure conditions. The diagnostic technique utilized here is high -speed Schlieren imaging to analyze the density gradients in the flow . The cryogenic jet formed distinct vortical structures upon initial emergence from the injector reve aling the onse t of unsteady behavior and strong effect of heat transfer between cold liquid nitrogen and warm surroundings . The behavior of liquid nitrogen jet was significantly affected by the low -pressure in -space conditions. The cryogenic jet undergoes extraordinary jet expansion at sub atmospheric pressure (in -space) conditions . Initial freezing of liquid nitrogen droplets and ligaments was observed close to the injector exit at low pressure operating conditions . The shear angle measurements of the steady -state flow showed the trans critical nature of the cryogenic fluid along with its cooling effect on surrounding gases. The measured jet spreading/ shear angles for the atmospheric case matched very closely with the prior results and confirmed the effects of surroundin g gas density on cryogenic jet expansion as predicted by the correlations . The potential core length measurements of the cryogenic LN 2 showed strong evidence of heat -shielding effect of the coaxial gaseous jet for momentum ratios lower than one while the c ore lengths decreased exponentially with momentum ratio v alues close to and higher than one .

Thermal Field Analysis of Hydrocarbon Flames for Propulsion Applications

Thermal field distribution of turbulent hydrocarbon flames has been analyzed for various fuel/air equivalence ratios. An experimental double concentric swirl burner with centrally located fuel injection was used that simulates one injector cap of a practical gas turbine combustor. Flame temperature distributions have been examined at three different fuel/air equivalence ratios, i.e., fuel-lean (φ = 0.625), stoichiometric (φ = 1.0), and fuel-rich (φ = 1.2). Each flame is examined for co-swirl and counter-swirl configurations, Mean and fluctuating temperature maps and thermal time scales are obtained using thermocouple measurements compensated with time constant measurements in order to achieve high frequency response. Direct flame photographs and infrared (IR) thermal images have been obtained to determine the global flame characteristics, and thermal flame shape/size, intensity and temperature distribution of the various flames. The results showed strong dependence of fuel/air equivalence ratio on global features and temperature distribution inside the flame. Flame volume increased significantly with increase in fuel-air equivalence ratio but the flame became non-uniform and unstable. As expected the maximum temperatures are found for stoichiometric case. The reaction zone of the flame moved downstream of the burner with increase in fuel-air equivalence ratio. For all the fuel-air equivalence ratios counter-swirl case provided compact reaction zones than the corresponding co-swirl case. Mean and fluctuating temperature maps showed that maximum temperatures inside the flame occur at mixing interface and downstream regions of the flame. Fluctuating temperature are found higher inside shear layer and post flame region. Both mean and fluctuating maps are asymmetrical which suggests higher turbulence and presence of large vertical structures in some regions of the flame. Integral- and micro-thermal scales also supported the above mentioned results.