Geometric Swirl Number Research Articles

Effect of swirl number on structural and emission characteristics of moderate size burner flames

An experimental investigation was conducted on the flame characteristics, thermal properties, and emissions of industrial-scale (40 kW) diesel flames. This study uniquely measured structural (flame length, diameter, volume), thermal (temperature, heat flux), and emission characteristics (COX, NOX, Unburnt HC) across various equivalence ratios (0.2–0.6) and swirling conditions (Swirl number varying from 0.73 to 1.04). Results indicated that higher swirl numbers generally led to more stable and compact flames, though structural properties were less affected during lean combustion. Notably, flame temperature varied significantly, up to 350 K, resulting in substantial difference in specified emission products. The emission reductions were achieved, particularly with a geometric swirl number of 1.04, which balanced flame performance and emission both, achieving reductions in CO (9–97 %), HC (18–96 %), NO (8–16 %), and Smoke (0.3–82 %). These findings underscore the critical impact of swirl angle on combustion efficiency and emissions, highlighting the need for meticulous optimization to mitigate harmful emissions effectively. This study provides new insights into optimizing combustion parameters for enhanced environmental sustainability in industrial processes.

Confinement effect on recirculation structures in isothermal coaxial swirling jet

The present experimental work reports first observations of effect of confinement on recirculation structures in non-reacting coaxial swirling jet in geometric swirl number range of SG= 2.14–2.88. In particular, particle image velocimetry (PIV) has been employed to study the effect of two confinement ratios (CR) viz. 1.82 and 2.73 on two types of recirculation zones (RZ) i.e., pre-breakdown dual rings (PVB) and central toroidal recirculation zone (CTRZ) observed in coaxial swirling jet. It is observed thatCR = 1.82 produces a slight radial expansion in PVB whereas significant compaction and streamwise elongation is observed in CTRZ. The difference in the observation is explained on the basis of modified Rossby number (Rom). The PVB flow state which is characterised byRom > 1 presents significant resistance to wall effect to be felt till the centerline. Contrarily, the CTRZ flow mode characterised byRom < 1allows the wall effect to be felt till the centerline, in turn affecting the RZ entirely. TheCR = 2.73 is shown to offer larger area for the RZ to spread radially outwards. Resultantly, the PVB and CTRZ are shown to significantly widen. Other significant comparisons betweenCR = 1.82 and 2.73 for PVB and CTRZ are elaborated using contour plots of axial and radial strain rates.

Research on the Gas-Liquid Two-Phase Distribution Behavior and Influencing Factors of Swirling Flow in Horizontal Pipe

Gas-liquid two-phase swirling flow is widely used for gas-liquid separation in the power, chemical, petroleum, and nuclear industries. However, the majority of current research on swirling flow focuses on identifying flow patterns and does not pay more attention to topics such as the boundary where swirling flow forms. The length and diameter of the central gas core are the main focus of the current studies as well as the distribution patterns of gas-liquid two-phase. Comparative studies on the gas-liquid distribution morphology, such as whether the gas phase is separated and the separation mode, are lacking. In this paper, a combination of visual experimental observations and numerical simulations of Computational Fluid Dynamics (CFD) is used to investigate the formation conditions of gas-liquid two-phase swirling flow in three types of cyclonic components. The results show that the minimum superficial liquid velocity for the formation of swirling flow in the horizontal tube is about 0.375~0.82 m/s when the superficial gas velocity is less than 10 m/s. The formation of swirling flow is almost independent of the geometric swirl number and superficial liquid velocity when the superficial gas velocity is greater than 10 m/s. At low inlet superficial velocities, the tangential velocity determines the transition from swirling flow to stratified flow. However, at higher inlet superficial velocities, the decay of the cyclonic field is mainly affected by the wave amplitude of the gas-liquid interface. In both co-current and counter-current horizontal inline gas-liquid cyclone separators, the flow split is related to the vortex core breakdown of the central gas core. In addition, the numerical simulation results show that the breakdown of the vortex core is related to the pressure distribution inside the separator. This work enriches the study of swirling flow and provides a basis for the performance improvement of inline gas-liquid cyclone separators.

A theoretical model for calculating particle trajectory in a vane-type separator

A vane-type separator has been successfully applied to gas-liquid and liquid-liquid separation. In order to evaluate the separation performance of the separator, a theoretical model for calculating the particle motion trajectory in the vane-type separator was developed. Firstly, the simplified steady incompressible Navier-Stokes equations were derived to acquire the equations of tangential velocity and axial velocity of continuous phase flow field. Then, the coefficients were determined by fitting the CFD results and it can be used to obtain the velocity at different swirler structure conditions. Further, the force analysis on the particle was conducted to develop the motion governing equations to predict the trajectory. The predicted separation lengths at different geometric swirl number conditions show a good agreement with the experimental results and its relative error is smaller than 3%. Besides, the effects of the key parameters including density difference, particle size and viscosity of the continuous phase on the separation length were investigated.

Effects of blade lean on internal swirl cooling at turbine blade leading edges

The blade lean technique has been extensively employed in the design of modern gas turbine blades. Since swirl cooling is a promising alternative for internal cooling techniques at the blade leading edge due to its strongly-enhanced heat transfer, it is thereby vital to completely understand the fundamental flow and heat transfer behavior of swirling flows in a leaned tube to provide guidance for improved swirl cooling design in today's advanced turbine blades. In this study, to model a realistic internal swirl passage, the flow and heat transfer patterns of swirl cooling were numerically investigated within leaned, convergent tubes. To examine the effects of blade lean levels, two leaned tubes with moderate and extra angles were considered. The simulations were carried out using the unsteady Reynolds-averaged Navier-Stokes (URANS) method for a strong geometrical swirl number of 5.3. Furthermore, to demonstrate the necessity of using the unsteady simulation in modeling swirling flows, steady and unsteady RANS simulations were compared against experimental data for a straight tube with constant cross section. Results reveal that the steady RANS method fails to capture the reverse flow in the downstream section of the tube where vortex breakdown occurs, leading to over-predicted axial velocity and under-predicted circumferential velocity. However, the unsteady RANS method provides satisfactory results for both flow and heat transfer, achieving a good compromise between computational efforts and numerical accuracy. In comparison with the straight tube, Dean vortices in the leaned tube decelerate the decay of the swirl in the upstream section, and vice versa in the downstream part by changing the axial velocity profile. In addition to the double helical vortex typically observed in the swirling flow, the inner vortex induced by strong shear in a transition layer between core and ring zones also contributes to enhanced turbulence mixing and thus improves heat transfer. The stronger swirl in the inlet regions of the leaned tubes decreases the turbulence production in the core zone, resulting in a lower flow loss relative to the straight tube. Globally, the extra-leaned tube has an increase of heat transfer coefficients by 5.3% and a reduction of pressure loss by 24.90%, while the moderate-leaned tube has a decrease of heat transfer coefficients by 6.1% and a reduction of pressure loss by 12.89%, relative to the straight tube.

NOx emissions in a swirled-stabilized magnesium flame

Alternative sources of clean energy with reduced greenhouse gas emissions have to be considered. Among them, the combustion of metal fuels such as aluminum or magnesium is promising. Nitrogen oxides (NOx) are the only undesirable gases produced during such metal combustion. The present study analyzes the amounts of NOx (NO and NO2) produced by a swirled stabilized magnesium flame. Two geometric swirl numbers are considered: 0.7 (low swirl number) and 7.3 (high swirl number). Different air–fuel ratios – equivalence ratio ranging from 0.17 to 1 – are considered, being obtained by changing the mass flow rate of the injected fuel which is a pulverized fuel of pure magnesium particles with a size fraction 50–70 µm. Thermocouples and a bichromatic pyrometer are implemented to monitor the gas temperature and the flame temperature, respectively. Oxygen (O2) is measured using an in-line paramagnetic analyzers and NOx are measured using an IR-UV analyzer.Whatever the swirl conditions and the air–fuel ratio tested, a stabilized flame of Mg is obtained. The metal combustion exhibits very stable performances. NOx emissions versus equivalent ratio follow a bell-shape curve. Under the tested experimental conditions, the amount of NOx never exceeds 7 gNOx/kWh, which is lower than the maximal value of NOx emission from a gasoline engine. The NOx mole fraction increases when the air–fuel ratio increases, as the power dissipated by the flame increases. The temperature of MgO particles in the flame reaches 2250 °C and the gas temperature never exceeds 1400 °C. The thermal NOx formation is estimated applying Zeldovich’s model. The model indicates that NOx can be produced in the gas surrounding the hot MgO particles. For the highest equivalence ratio, even if the gas temperature is still increasing, the NOx production is disfavored in the rich mixture. Based on these results, a global scheme for NOx formation is proposed which includes four successive steps.

Swirl number and nozzle confinement effects in a flat-vane axial swirler

This paper presents the results of a parametric experimental study of free swirling flow at the exit of a flat-vane axial swirler. A total of 16 data sets were acquired by combining four swirler vane angles (22°, 29°, 50.5°, and 58.3°) and four exit nozzles of different diameters (30, 40, 52, and 76 mm). Sophisticated pressure probes consisting of precise microphones and a two-component LDV system were used to investigate the effect of these geometrical parameters on swirling flow regimes characterized by the swirl number. Particular attention was paid to the precessing vortex core (PVC) phenomenon observed at the exit of the swirler nozzle. It has been shown that by varying the vane angle and the diameter of the exit nozzle, it is possible to independently control the swirl number value and the occurrence of a PVC. A distinct correlation has been found between the PVC-induced pressure pulsations detected by acoustic probes and the tangential velocity fluctuations measured by LDV. The use of microphones provides a quick way to measure the frequency response of swirl flow in a wide range of geometries and flow configurations. The PVC effect does not occur at low subcritical values of the integral swirl number (S < 0.5) and in the case of strong swirl flow (Sg = 0.9 and 1.2) in the absence of constriction by the nozzle (De/D0 = 1). The disappearance of the PVC effect for strong swirl flow without constriction is due to the extreme displacement of the flow to the nozzle walls. The absence of a PVC in the flow was inferred not only from measurements of the frequency response of the flow over a wide range of Re numbers, but also from the absence of specific markers in velocity RMS distributions. Measurement results are used to derive an empirical correlation of the integral swirl number and the Strouhal number with a modified geometric swirl number. This allows a generalization of the frequency characteristics of swirling flows with a PVC for flat-vane axial swirlers, which are widely used in engineering.

Swirler geometry effects (dh/do ratio) on synthetic gas flames. Part 2: dynamic flame behaviour at external y altered acoustic conditions

In a combustion device, unsteady heat release causes acoustic energy to increase when acoustic damping (energy loss) is not that effective, and, as a result, thermo-acoustic flame instabilities occur. In this study, effects of the swirler dh/do ratio (at different swirl numbers) on dynamic flame behaviour of the premixed 20%CNG/30%H2/30%CO/20%CO2 mixture under externally altered acoustic boundary conditions and stability limits (flashback and blowout equivalence ratios) of such mixture were investigated in a laboratory-scale variable geometric swirl number combustor. Therefore, swirl generators with different dh/do ratios (0.3 and 0.5) and geometric swirl numbers (0.4, 0.6, 0.8, 1.0 1.2 and 1.4) were designed and manufactured. Acoustic boundary conditions in the combustion chamber were altered using loudspeakers, and flame response to these conditions was perceived using photodiodes and pressure sensors. Dynamic flame behaviour of respective mixture was evaluated using luminous intensity and pressure profiles. Results showed that the dh/do ratio has a minor impact on dynamic flame behaviour.

Swirler geometry effects (dh/do ratio) on synthetic gas flames: Part 1: Combustion and emission characteristics

Swirling flows increase combustion performance via favouring flame stability, pollutant emissions, and combustion intensity. The strength of a swirling flow is characterized by a parameter known as swirl number, which is highly related to the dh/do ratio. In this study, effects of the swirler dh/do ratio on combustion and emission characteristics of the synthetic gas flames of premixed 20%CNG/30%H2/30%CO/20%CO2 mixture were experimentally investigated in a laboratory-scale swirl stabilized combustor. For this purpose, twelve different swirl generators were designed and manufactured. dh/do ratios of these swirlers were set as 0.30 and 0.50, and the geometric swirl number was varied between the values of 0.4 and 1.4 (at 0.2 intervals). All experiments were conducted at a fuel-lean equivalence ratio (ϕ = 0.6), room temperature, and local atmospheric conditions of the city of Kayseri, Turkey. A data logger was utilized to plot axial and radial temperatures and NOx, CO, and CO2 profiles, which were exploited to assess combustion and emission performance. Results showed that the dh/do ratio had a non-monotonic effect on the behaviour of combustion and emission of the tested synthetic gas mixture. Depending on the swirl number, increments and decrements were observed in temperature and emission values.

Flame and instability characteristics of high hydrogen content gas mixtures

In this study, initially, 50%H2–25%CH4–25%CO2, 60%H2–20%CH4–20%CO2 and 70%H2–15%CH4–15%CO2 mixtures were combusted in a laboratory scale-swirl stabilized-premixed combustor so as to specify combustion and emission characteristics of respective gas mixtures. Later on, such mixture flames were exposed to acoustic perturbations at different frequencies between the values of 65–205 Hz and under these conditions, flame response was evaluated. The acoustic perturbations were intentionally created by loudspeakers located in side arms of the T-shaped combustor. Two openings on the combustor walls, and photodiodes and pressure sensors assembled in the experimental apparatus enabled interpreting flame response. During experiments, inlet parameters (such as thermal power – 4 kW, equivalence ratio – 0.5, mixture temperature, etc.) and geometric swirl number (1.2) were kept constant, and tested flames were acoustically forced for 30 s at each frequency step. Results showed that thermal Zeldovich mechanism doesn’t dominate NOx formation for tested flames, and 50%H2–25%CH4–25%CO2 mixture emits nearly thirty times of magnitude of higher NO than 70%H2–15%CH4–15%CO2 mixture. Besides, the onset of flame instabilities depending on the forcing frequency isn’t controlled by gas composition. However, flame and combustion chamber acoustics weakly couple, hence pressure and heat release rate oscillations weaken as hydrogen amount in gas mixture increases.

Spray characteristics and flow topologies of high shear injector at high primary swirl

In this paper, we present detailed experimental measurements and analysis on the spray-flow interaction emerging from a newly designed high shear injector. The injector consists of a series of radial/axial entry air swirler with interchangeable flare at the exit and the fuel nozzle mounted concentric to the swirlers. The geometrical parameters concerning the swirl configuration are geometrical swirl number (SNPrim), airflow split ratio(γ), area ratio(Δ), flare angle(θ) and relative flow orientation of primary and secondary swirlers (co and counter-rotation). The time-resolved particle image velocimetry is employed to capture the spray flow field topology. The radial (W/Df) and axial (L/Df) expansion of the recirculation zone are explored with respect to the near field swirl number (SN5). The flow from the present injector indicates a negligible change in the radial expansion (W/Df) of the recirculation zone on switching the relative swirl orientation from counter to co-rotation configuration. The radial dispersion of spray illustrates nearly linear relationship with the size of the recirculation zone, whereas the droplet size distribution is insensitive across the test cases. Furthermore, the spray patternation and droplet size across all the cases indicate that a change in spray cone angle could be achieved without much deteriorating the circumferential uniformity and droplet size distribution. Finally, proper orthogonal decomposition (POD) analysis reveals that with radial expansion of recirculation zone, the peak amplitude shifts to lower frequencies and the turbulent kinetic energy contribution to flow of the different spatial coherent structures change accordingly.

Regression rate and combustion performance investigation on hybrid rocket motor with head-end swirl injection under high geometric swirl number

It is well known that head-end swirl injection can overcome the key problem of low regression rate and combustion inefficiency in hybrid rocket motor effectively. In this paper, the effect of head-end swirl injection under high geometric swirl number (above 10) has been investigated by numerical method. Three-dimensional structured mesh technology has been used. The numerical model coupled of turbulence, combustion, solid fuel pyrolysis and solid-gas coupling model was proposed in this paper. A series of cases which indicate the head-end swirl injection under high geometric swirl number can extremely improve the fuel regression rate and combustion efficiency of hybrid rocket motor are conducted. Compared to conventional axial injection, when the geometric swirl injection is 44.9, the improvement of average fuel regression rate reaches 3.23-4.93 times, and the combustion efficiency increases to 93.9-95.8% under different oxidizer mass flux. Besides, the parameters, including oxidizer mass flux, geometric swirl number and injection velocity component ratio, exert great influences on the hybrid rocket motor with head-end swirl injection in different ways. Through integrated design of the injector, the oxidizer to fuel ratio (O/F ratio) could equal to the optimal O/F ratio 1.93 approximately and be stable during the rocket motor operation, so the rocket motor performance will be in high and stable status.

Experimental Investigation of Flame Characteristics of H2/CO/CH4/CO2 Synthetic Gas Mixtures

ABSTRACT Chemical composition of synthetic gas and concentration of its components depend on gasification process and feedstock. Synthetic gas mainly consists of hydrogen (H2) and carbon monoxide (CO), and may contain trace amounts of carbon dioxide (CO2) and methane (CH4). In this study, combustion and emission characteristics of H2/CO/CH4/CO2 blending syngas mixtures with high H2/CO ratio were experimentally investigated in a swirl-stabilized premixed combustor. Furthermore, stable operating ranges (flashback and blowout equivalence ratios) of such mixtures and flame response of 67.5%H2-22.5%CO-5%CO2-5%CH4 mixture to acoustic forcing were also detected. During the experiments, CH4 amount in tested gas mixtures varied between 5% and 20% by volume (at intervals of 5%), and H2/CO ratio and CO2 concentration were kept constant at the values of 3 and 5%, respectively. As a consequence, mixtures of 67.5%H2-22.5%CO-5%CO2-5%CH4, 63.75%H2-21.25%CO-5%CO2-10%CH4, 60%H2-20%CO-5%CO2-15%CH4 and 56.25%H2-18.75%CO-05%CO2-20%CH4 were derived and tested under the same boundary and physical conditions. All experiments were conducted at 0.4 equivalence ratio (Φ) and 0.2 geometric swirl number (SN). Preliminarily, stable operating ranges of respective gas mixtures were determined to find an equivalence ratio at which all gas mixtures could be tested without causing any flame instability and then, CH4 addition effects on combustion and emission characteristics of such mixtures were evaluated via utilizing axial and radial temperature, CO and O2 profiles. Lastly, flame behavior of 67.5%H2-22.5%CO-5%CO2-5%CH4 mixture was evaluated under externally modified acoustic conditions. Acoustic field in the combustor was mechanically altered by using side-mounted loudspeakers in the frequency range of 30–200 Hz. To identify flame instabilities and to evaluate the degree of coupling between heat release and pressure oscillations, pressure sensors and photodiodes installed on combustion chamber and burner were utilized. Results of this study showed that CH4 addition to synthetic gas mixtures improves rich flammability limits, and increases flame temperature, flame height and emissions. Under externally modified acoustic conditions, flame behavior slightly alters (flashback and blowout does not occur). Additionally, pollutant emissions improve in an environment-friendly manner under such conditions.

Study of the influence of water vapour and carbon dioxide dilution on flame structure of swirled methane/oxygen-enriched air flames

In this work, the effect of dilution with water vapour H2O and carbon dioxide CO2 on the structure and stability of a methane/enriched air premix flame, confined and swirled at atmospheric pressure was studied. Measurements were carried out at constant adiabatic temperature (1773, 1873, 1973 and 2073 K), from air to oxycombustion (enrichment OI ranging from 21 to 100%), for two inlet temperatures (T0 = 373 K and 473 K), at constant equivalence ratio maintained at 0.91 and inlet aerodynamic conditions maintained constant: average inlet velocity at 30 m·s−1 and geometric swirl number at Sn = 0.90. The experimental setup is a burner used consisting of a swirled stainless steel single injector, mounted in a combustion chamber operating at atmospheric pressure. The flames were visualized by CH* chemiluminescence. From instantaneous images, the flame contour, detected with a Matlab® processing, was determined. From this flame contour, flame height (Hf) and lift-off height (Hlo) were extracted by measuring respectively the maximum height of the flame top and the minimum height of the bottom flame. The evolution of the mean macrostructure of the flame was then studied. The results of the steam dilution were detailed and compared with those obtained with carbon dioxide. Links between the laminar flame speed and the flame structure and stability were clearly established.

On the influence of geometrical parameters on the spray characteristics of high shear injectors

We discuss the influence of geometrical parameters over the performance of high shear injector. High shear injector usually consists of a series of air swirlers (primary and secondary) with diverging flare at the exit and centrally mounted fuel nozzle. In this study, we have considered only parameters pertaining to air swirler i.e. geometrical swirl number (SNgeo), flow split ratio (γ), area ratio (Δ), flare angle (θ) and flow orientation of primary and secondary swirlers (co/counter rotation). The above parameters were categorized into two paradigms, first, SNgeo, γ, Δ are designated as internal geometrical parameters, which induces variations in the bulk Reynolds number at the exit. On the other hand, parameters like flare angle (θ), flow orientation doesn’t yield any variations in bulk Reynolds number. Time resolved PIV (Particle Image Velocimetry; ~ 3500 frames/s) is employed to extract the topological structures of the flow field. The length scale (W/Df), which embodies the radial extent of the recirculation zone is governed by near field swirl number (SN10) and Reynolds number for cases with variations in SNgeo, γ, Δ. Contrarily, with variations in θ and flow orientation, (W/Df) is found to be a function of near field swirl number f (SN10) only. The spatial distribution of the spray shows linear relationship with the W/Df. Finally, the droplet size spectrum obtained from 3D PDI (Phase Doppler interferometer) also shows insensitivity with respect to the different test cases. This clearly indicates that in high shear atomizer configuration, spread of the spray can be altered without deterioration in uniformity and droplet size distribution.

Experimental Investigation of the Confinement Effect on Flashback in Multi Combustion Modes Tangential Swirl Burner

&#x0D; &#x0D; &#x0D; &#x0D; Given the importance of gas turbines in the process and amount of global energy from fossil fuels, the views were directed toward this study in addition to the availability of the liquefied petroleum gas and because of knowing many details of it is composition and behavior this type of fuel has been proven. The development of the tangential swirl burner geometry also one of the targets of this study by reducing the combustion instability include flashback and the minimizing in the burner size comparing with other classic tangential swirl burner shape include cylindrical confinement with conical cup confinement. The authors take care in previous studies in field of swirling flow either in scope of geometry characteristics or in scope of fuel issues. The geometrical swirl number which play an important factor in swirling flow had been taken in the consideration for the process of the tangential swirl burner manufacturing as well as the heat caloric value of the operating fuel. The experimental results of combustion the liquefied petroleum gas had been proved that the formal additions added in this study to development the burner nozzle mouth will reduce and improve the occurrence of the operational problems represent flashback and an increasing in the working area by increasing the flashback limits for both premixed and partial premixed combustion modes which will be clarified and the mechanism of composition in the following sections of this paper.&#x0D; &#x0D; &#x0D; &#x0D;

An experimental study on the effect of swirl number on pollutant formation in propane bluff-body stabilized swirl diffusion flames

The combustion characteristics of propane/air bluff-body stabilized swirl diffusion flames within the turbulent regime are studied experimentally to determine the effect of the swirl number on the flame dynamics and pollutant emissions. The investigated burner consists of a central bluff body with an annulus to introduce the tangential and axial air flows. Results show that in low annulus Reynolds numbers (ReS), the temperature distribution is more affected by the overall equivalence ratio (φo), which is calculated based on the flow rates of the air supplies and the fuel jet. However, by increasing ReS, the impact of swirl number becomes more apparent. Analysis of the combustion products demonstrates a reduction in CO concentration with increasing the geometric swirl number which becomes more evident in higher annulus Reynolds numbers. In addition, the trend of NO emission is strongly analogous to the temperature distribution which is an indication of thermal NO formation. Measurements demonstrate that in lower annulus Reynolds numbers, the dominant factor is the overall equivalence ratio, while with increasing the annulus Reynolds number, the swirl number represents more significance.

Combustion and emission characteristics of premixed CNG/H2/CO/CO2 blending synthetic gas flames in a combustor with variable geometric swirl number

This paper presents the results of experimental studies conducted on premixed CNG/H2/CO/CO2 blending synthetic gas flames in a laboratory scale combustor, with particular emphasis on effects of swirl number (from 0.2 to 1.6, at intervals of 0.2) and equivalence ratio (0.6, 0.8 and 1.0) on combustion and emission characteristics of such mixtures. Furthermore, effects of swirl number on lean blowout and flashback limits of studied mixtures were also investigated. Irrespective of the swirl number and equivalence ratio, H2/CO ratios of tested gas mixtures were kept constant (1.0), and mixtures of H2/CO/CNG/CO2 which were diluted with different amount of CO2 (0–20%, at intervals of 5%) were derived. Considering broadest operating range, mixture of 20%CNG/30%H2/30%CO/20%CO2 was determined as base fuel to be tested. Combustion and emission behavior of tested gas mixtures were assessed by examining axial and radial temperature, NOx, CO and CO2 distributions. Besides, swirl number and equivalence ratio effects on flame structure were evaluated by investigating instantaneous flame images (with the same focal length and exposure time). Results of this study showed that effects of swirl number on flame characteristics (temperature and pollutant emission distributions) is not monotonous, and equivalence ratio dependent flame behavior alters differently at different swirl numbers.

The Effect of Fuel Length and Geometric Swirl Number on The Local Regression Rate in Swirling-Oxidizer-Flow-Type Hybrid Rocket Using a Low-Melting-Point Thermoplastic Fuel

The Effect of Fuel Length and Geometric Swirl Number on The Local Regression Rate in Swirling-Oxidizer-Flow-Type Hybrid Rocket Using a Low-Melting-Point Thermoplastic Fuel

Hybrid Rocket Firing Experiments at Various Axial–Tangential Oxidizer-Flow-Rate Ratios

A breadboard model (BBM) of an altering-intensity swirling-flow-type (A-SOFT) hybrid rocket engine was recently developed, and static firing experiments of the BBM were performed under various axial and tangential oxidizer mass-flow rates. A-SOFTs are intended to control thrust at an optimal oxidizer-to-fuel-mass ratio and achieve a high baseline of regression rates with a fixed motor configuration. This is possible by controlling both the oxidizer mass-flow rate and the effective geometric swirl number. A simple model based on a continuous and monotonic function of oxidizer mass flux and effective geometric swirl number was able to accurately predict the performance of experiments conducted on the A-SOFT BBM. The local fuel regression behavior in the axial direction of the A-SOFT BBM was shown to be like that of a swirling-oxidizer-flow-type hybrid rocket engine. Combustion efficiency was evaluated indirectly using equations for the efficiencies of thrust and specific impulse to eliminate errors due to local pressure shifts and the centrifugal force in swirling flows. In most cases, this indirect method compensated for the overestimations of efficiency that resulted by directly using chamber-pressure data.