Fuel Injection Port Research Articles

Towards bespoke gas permeability by functionally graded structures in laser-based powder bed fusion of metals

Permeable, media transporting, components are an integral part in numerous technical applications. In gas turbines combustors, for example, gaseous oxidizer and fuel are transported separately into the burner, where they are injected and mixed, and subsequently combusted. The mixture homogeneity strongly affects the combustion performance and emissions formation and is, amongst other, determined by the spatial distribution of fuel injection ports. In this context, porous media provide the limiting case for a spatial distribution of media-injecting pores, yet is typically associated with a high pressure drop that yields a loss in efficiency. In this study, possibilities of achieving gas permeability in additively manufactured porous structures are investigated. The objective is to selectively functionalize the permeable layers for gaseous media supply with low pressure loss and, when needed, enable a targeted mixing of different gas streams. For this purpose, a laser-based powder bed fusion process (PBF-LB/M) was used in this study. It offers the opportunity to manufacture varying porosities inside complex monolithic metal parts. To produce the porous structures and to achieve gas permeability, the effect of scan rotation angle, hatch distance, build-up direction and length of the porous specimen is investigated. Due to the high temperatures present in combustion systems, the present work utilizes Inconel 718 material. The AM gas permeable specimen are experimentally characterized by means of surface topography, micro X-ray computed tomography (µXRCT) as well as flow and pressure loss test. The results show, that the AM process parameter provide effective control parameters to adjust the permeability. The strongest effect originates from the hatch distance for a given build-up direction. Depending on the scan rotation, the flow transitions from a turbulent pipe flow to a Darcy flow as present in conventional porous media. A structured alignment and connectivity of pores can be realized as evident in the µXRCT results, surface topography and the flow measurements. Residual powder, powder adhering to the pore walls and stochastic closure of pores or channels lead to deviations and need to be considered when designing respective parts. Nonetheless, the results further show that a directional dependence of the permeability and the build-up direction can be realized and controlled. Consequently, when considering the AM build-strategy in the design of components, this directed permeability can be functionalized in the generation of gas transporting and gas mixing layers separately by adjusting the AM processing parameter.

Experimental research on effects of multi-layer injection of the high-temperature preheated pulverized coal on combustion characteristics and NOx emission

Under the background of carbon peak and carbon neutrality, cleanandefficientutilization ofcoal is imperative in China. As a novel combustion technology, the coal self-preheating combustion technology has broadprospectsforapplication, nevertheless, previous studies have mainly focused on limiting NOx generation by simply applying air staging method in the combustor, which made further NOx reduction difficult to achieve. Combining the advantages of reburning technology, this study firstly realized the multi-layer injection of the high-temperature preheated fuel (PF), and investigated the effects of the reburning fuel fraction (RFF), the location of the reburning fuel injection port (RFL) and the coal type on combustion characteristics and NOx emissions. The results revealed that the generated high-temperature PF could continuously and stably enter the down-fired combustor (DFC) for subsequent combustion. In the intensely reducing atmosphere inside the self-preheating device, the released fuel-N was mainly converted to N2, and the combustion performance of the preheated coal char which could be used as an excellent fuel close to gas reburning effect was greatly modified compared with raw coal. To simultaneously achieve efficient and clean combustion of pulverized coal, the favorable RFF and RFL were 10.62%∼15.48% and 600 mm ∼ 800 mm, respectively, corresponding to the residence time in the primary combustion zone and the reburning zone in the range of 0.91 ∼ 0.99 s and 0.87 ∼ 1.11 s, respectively. What’s more, under the same reburning parameters, Alxa lignite coal had the largest NOx reduction rate (32.15%), with NOx emission of 51.36 mg/m3 (@6%O2), while Jincheng anthracite coal had the lowest NOx reduction rate (5.34%) and the highest NOx emission (149.91 mg/m3, @6%O2), and Shenmu bituminous coal achieved ultra-low NOx emission (45.75 mg/m3, @6%O2) with the NOx reduction rate of 28.05%, suggesting that on the basis of air staging, multi-layer injection of PF had more advantages for clean and efficient combustion of high volatile coal.

On cavitation in the radial flow of a thin lubricating film between two overlying disks

This study is focused on the characterization and modeling of aviation fuel cavitation physics in radial flow in a thin layer between two disks—a geometry highly relevant to aviation fuel pump systems. This involves a lower circular disk with a centrally located fuel injection port and a matching disk resting on top of the lower disk. In the described experiments, we have quantified and compared cavitating disk behavior for distilled water and JP-5 fuel at various inlet supply pressures via high-speed imaging and radial pressure measurements. High-speed imaging data were used to quantify the radial collapse location of cavitation voids. An enhanced gradient shadowgraphy method was employed to obtain the spatial–temporal evolution of propagating bubbly shock waves. This technique revealed unsteady shock waves propagating in a spiral motion in JP-5 fuel, while a standing bubbly shock was observed in water. In our modeling efforts, the Rayleigh–Plesset equation was adapted to a spatial form in order to predict the radial location of cavitation bubble collapse. Further work incorporated the spatial Rayleigh–Plesset equation into the barotropic model that has been used previously for cavitating nozzle flows and generalized it to radial flow geometry in order to reproduce radial pressure profiles obtained from the experiment. The model predictions of the radial location of bubble collapse and the radial pressure profiles are shown to be in excellent agreement with the experiments. This approach will be valuable for predicting aviation fuel cavitation in complex fuel system geometries.

INSTABILITIES OF SUPERSONIC COMBUSTION AT PLASMA-BASED FLAMEHOLDING

Two types of supersonic combustion instabilities identified in a M = 2 reacting flow at direct injection of gaseous hydrocarbon fuel and quasi-direct-current (Q-DC) plasma assistance have been considered: a global instability triggered by a mechanism of flow-combustion-plasma coupling and a fast instability of a thermoacoustic nature. The experiments were performed at SBR-50 supersonic combustion facility at variable conditions: pressureP0 = 1-4 bar, temperature T0 = 300-750 K, and fuel mass flow rate m‘ = 1-8.5 g/s. Diagnostics includedpressure measurements, filtered fast camera imaging, schlieren visualization, and spectroscopic observations. The global instability develops with a characteristic time of about 10 ms and is related to the interaction of the combustion-based separation zone with the reflected shock wave (SW) and electric discharge. It is shown that this instability could be effectively controlled by electrical discharge power. The thermoacoustic instability is developed with a characteristic time less than 1 ms. The analysis of pressure data reveals a resonant acoustic wave presence in the combustion zone between the fuel injection ports and the test section diffuser.

Modes of plasma-stabilized combustion in cavity-based M = 2 configuration

This paper considers the modes of plasma-stabilized supersonic combustion in a cavity-based flameholding configuration. The testing was performed in the SBR-50 supersonic facility at the University of Notre Dame under the following conditions: Mach number M = 2, stagnation pressure and temperature P0 = 1–3.2 bar, T0 = 295–750 K, and an ethylene injection rate of ṁC2H4 = 0–8 g/s. A rail type electric discharge is employed in this work, which represents a modification of the previously explored quasi-DC (Q-DC) configuration. Two principally different cases are realized and described in detail: in- or over-the-cavity combustion, and bulk combustion characterized by a significant increase of pressure downstream of the fuel injection ports. Rail discharge performance is compared to the performance of Plasma-Injection Modules (PIMs) using a 1D analysis. Dimensionless analysis of the plasma-assisted combustor performance indicates reasonable agreement of the in-cavity combustion mode with the Ozawa stability diagram, while the plasma-assisted bulk combustion is essentially distinct from this formalism.

Effect of transverse fuel injection system on combustion efficiency in scramjet combustor

Supersonic mixing layer behind the hydrogen fueled wedge shaped strut has been demonstrated by means of combined fuel injection strategy. Numerical investigation on the Effect of wall transverse fuel injection system in addition with parallel fuel injection approach have been found suitable for stable flame and combustion performance. The experimental supersonic combustor observation was performed by Waidmann et al. in German Aerospace Centre (DLR), which has been utilised in validation section to examine the accuracy and applicability of present computational work. Non-reacting and reacting both types of flow field characteristics are analysed to complete the validation. Good agreement was found in the contour plots towards oblique shock incident location moreover expansion fan behaviour at the end tip of the strut was observed. Pressure graph near the combustor walls and mid plane of the combustor were well matched with numerical observation however velocity graph was best suitable for near wake region instead of far-field region. Thus Ansys 14.0 fluent software has been chosen to compare the experimental data from the literature with numerical analysis. Two-dimensional computational combustor geometry has been taken with involving steady state, SST k-ω two equation based turbulence model analysis. Finite rate-eddy dissipation chemistry based combustion model is used to analyse the combustion process. Parallel fuel injection location is engaged at the same point and the change of wall transverse fuel injection port position have been analysed. Variations can be visualised in the numerical analysis outcome of combustion and mixing performance. The combustion efficiency plot is divided in to two section i.e. rapid change in chemical reaction in all four cases and second is gradual consumption of fuel. The outcome shows that the abrupt change in 68 mm transverse fuel injector model with 96% combustion efficiency.

Investigation of peripheral vortex reverse flow (PVRF) combustor for gas turbine engines

In a reverse flow combustor air is injected from the exit side so that the bulk gas flow reverses its direction while exiting the combustor. In the combustor investigated here, a dominant peripheral vortex away from the exit is stabilized by carefully choosing the location of the air jet. Combustion is stabilized due to internally recirculated hot product gases in this peripheral vortex. The fuel is injected in the peripheral vortex region at high velocity and rapid mixing of injected fuel with the oxidizer results in avoidance of hot spot regions and leads to overall lean combustion and low pollutant emissions. Due to reverse flow geometry, along with the presence of the peripheral vortex, favourable residence time distribution of gases is achieved (shown numerically). This resulted in lower CO emissions (confirmed experimentally). In the non-premixed mode, fuel injection port is either placed on the exit/air port side (named as RS configuration) or on the opposite side of the exit/air port (named as RO configuration). The combustor operating in RO configuration displayed wider lean operational limit, and lower CO emissions as compared to the RS configuration, while NOx emissions were almost same in both the cases.

Hydrogen addition effects on methane–air colorless distributed combustion flames

In this investigation the role of hydrogen addition in a reverse flow configuration, consisting of both non-premixed and premixed combustion modes, have been examined for the CDC flames. In the non-premixed configuration the air injection port is positioned at combustor exit end while the fuel injection port is positioned on the side so that the fuel is injected in cross-flow with respect to air injection. The thermal intensity of the flames investigated is 85 MW/m 3 atm to simulate high thermal intensity gas turbine combustion conditions. The results are presented on the global flame signatures, exhaust emissions, and radical emissions using experiments and flowfield using numerical simulations. Ultra low NO x emissions are found for both the premixed and non-premixed combustion modes. Addition of hydrogen to methane fuel resulted in only a slight increase of NO emission, significant decrease of CO emission and extended the lean operational limit of the combustor.

Investigation of reverse flow distributed combustion for gas turbine application

In this paper reverse flow modes of colorless distributed combustion (CDC) have been investigated for application to gas turbine combustors. Rapid mixing between the injected fuel and hot oxidizer has been carefully explored for spontaneous ignition of the mixture to achieve distributed combustion reactions. Distributed reactions can be achieved in premixed, partially premixed or non-premixed modes of combustor operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation reverse flow modes consisting of three configurations at thermal intensity of 28 MW/m 3-atm and five configurations at thermal intensity of 57 MW/m 3-atm have been investigated and these high thermal loadings represent characteristic gas turbine combustion conditions. In all the configurations the air injection port is positioned at the combustor exit end, whereas the location of fuel injection ports is changed to give different configurations. The results are presented on the exhaust emissions and radical emissions using experiments, and evaluation of flowfield using numerical simulations. Ultra-low NO x emissions were found for both the premixed and non-premixed combustion modes investigated here. Cross-flow configuration, wherein the fuel is injected at high velocity cross stream to the air jet resulted in characteristics closest to premixed combustion mode. Change in fuel injection location resulted in changing the combustion characteristics from closer to diffusion mode to distributed regime. This feature is beneficial for part load operation where higher stability limit is desirable.

Investigation of forward flow distributed combustion for gas turbine application

New innovative advanced combustion design methodology for gas turbine applications is presented that is focused on the quest towards zero emissions. The new design methodology is called colorless distributed combustion (CDC) and is significantly different from the currently used methodology. In this paper forward flow modes of CDC have been investigated for application to gas turbine combustors. The CDC provides significant improvement in pattern factor, reduced NO x emission and uniform thermal field in the entire combustion zone for it to be called as an isothermal reactor. Basic requirement for CDC is carefully tailored mixture preparation through good mixing between the combustion air and product gases prior to rapid mixing with fuel so that the reactants are at much higher temperature to result in hot and diluted oxidant stream at temperatures that are high enough to autoignite the fuel and oxidant mixture. With desirable conditions one can achieve spontaneous ignition of the fuel with distributed combustion reactions. Distributed reactions can also be achieved in premixed mode of operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation forward flow modes consisting of two non-premixed combustion modes and one premixed combustion mode have been examined that provide potential for CDC. In all the configurations the air injection port is positioned at the opposite side of the combustor exit, whereas the location of fuel injection ports is changed to give different configurations. Two combustion geometries resulting in thermal intensity of 5 MW/m 3-atm and 28 MW/m 3-atm are investigated. Increase in thermal intensity (lower combustion volume) presents many challenges, such as, lower residence time, lower recirculation of gases and effect of confinement on jet characteristics. The results are presented on the global flame signatures, exhaust emissions, and radical emissions using experiments and flowfield using numerical simulations. Ultra-low NO x emissions are found for both the premixed and non-premixed combustion modes at the two thermal intensities investigated here. Almost colorless flames (no visible flame signatures) have been observed for the premixed combustion mode. The reaction zone is observed to be significantly different in the two non-premixed modes. Higher thermal intensity case resulted in lower recirculation of gases within the combustion chamber and higher CO levels, possibly due to lower associated residence time. The characteristics at the two thermal intensity combustors investigated here were found to be similar.

Experimental and numerical studies of mixing and flame stability in a micro-cyclone combustor

A 30-W-class micro-cyclone combustor was developed as a heat source for a 1-W thermoelectric power generator (TPG). Methane gas was used as a fuel instead of liquefied fuel in this feasibility study for convenience. The combustion stability of the combustor was measured, and the flame shapes were visualized experimentally. Numerical simulations were performed to examine the details of the flame structure and flame stabilization mechanism inside the micro-cyclone combustor. The micro-cyclone combustor burned the supplied fuel stably inside the combustion chamber in the range where the combustor generated 30 W of heat energy. The mixing and flow characteristics of non-reacting and reacting flows in the combustor were examined using the simulation results. The mixing of the fuel with air in a non-reacting flow field was enhanced by increasing the equivalence ratio for a fixed fuel flow rate. For non-reacting flow, a recirculation region and a small negative axial velocity region near the injection ports were formed. The recirculation region became wider with decreasing equivalence ratios. For reacting flows, however, the recirculation region disappeared and the only small negative axial velocity region was formed near the fuel injection ports. The flame was stabilized inside the combustor because the flame base was anchored near the negative axial velocity region near the fuel injection ports.

마이크로 사이클론 연소기의 혼합 및 유동특성에 관한 수치해석 연구

A micro cyclone combustor was developed to be used as a heat source of thermoelectric power generator (TPG). The cyclone combustor was designed so that fuel and air were supplied to the combustion chamber separately. The mixing and flow characteristics in the combustor were investigated numerically. The global equivalence ratio (Φ), defined using the fuel and air flow rates, was introduced to examine the flow features of the combustor. The mixing of fuel and air inside the combustor could be well understood using the fuel concentration distribution. It was found that the weak recirculating zone was formed upper the fuel-supplying tube in case of Φ ＜ 1.0. In addition, it was found that small regions that have a negative axial velocity exist near the fuel injection ports. It is assumed that these negative axial velocity regions can stabilize a flame inside the micro cyclone combustor.

Stability of Nickel-based Cermet Anode for Carbon Deposition during Cell Operation with Slightly Humidified Gaseous Hydrocarbon Fuels

Stability of nickel-based cermet anode for carbon deposition had been investigated with little humidified gaseous hydrocarbon fuels (methane, ethane, and propane) as functions of operation temperature and fuel utilization rate. High operation temperature and/or low fuel utilization rate caused severe carbon deposition on the anode in the vicinity of the fuel injection port. The amount of deposited carbon decreased with decreasing the operation temperature and/or increasing the fuel utilization rate. Ni-ScSZ anode-supported cells had been stably operated without severe carbon deposition for 80 to 150 hours; for methane at T = 973 K and Uf = 50 %, for ethane at 823 K and Uf = 50 %, for propane at 773 K Uf = 75 %, respectively.

Feasibility of Ni-based cermet anode for direct HC SOFCs: Fueling ethane at a low S/C condition to Ni–ScSZ anode-supported cell

The feasibility of a Ni-based cermet anode for direct hydrocarbon (HC) SOFCs was investigated with ethane fuel as a step towards utilizing higher HCs such as propane and butane. The possibility of stable operation of SOFCs with ethane fuel at a low steam/carbon (S/C) ratio of 1.2 mol% H 2O–98.8 mol% C 2H 6 was investigated with anode-supported SOFCs utilizing a scandia stabilized zirconia (ScSZ) electrolyte and a Ni–ScSZ anode. Severe carbon deposition was observed around the anode especially at the fuel injection port during the cell tests at T = 973 K. The amount of deposited carbon became smaller with decreasing operation temperature, and a stable cell operation was achieved at T ≈ 823 K without severe carbon deposition over a week. However, at a low fuel utilization rate ( U f) around 20%, nickel was heavily disintegrated accompanied by severe carbon deposition even at T ≈ 823 K. With increasing U f, the disintegration became less, and a stable cell operations were achieved only with a small amount of deposited carbon for over a week at high U f > 46%.

Effect of Flame-Holding Cavities on Supersonic-Combustion Performance

An experimental study was performed to evaluate the e ame-holding and mixing enhancement characteristics of supersonic reacting e ow over acoustically open cavities. Several cone gurations of acoustically open cavities were placed inside a supersonic-combustion duct just downstream of the fuel injection ports. The resulting changes in e ame behavior and combustion characteristics were assessed using schlieren visualization of the uncone ned e ow and wall pressure measurements of the cone ned e ow along the duct. The results were then compared with the baselinecase, which used no cavity. Although thecavitiesimproved thecombustion performancefrom thebaseline, the amount of enhancement was dependent on the particular shape of the cavity as well as the e ow conditions. Certain cavity cone gurations that were strategically placed inside the combustion duct led to a faster increase in the axial pressure force. The data showed that the recovery temperature was higher and the total pressure proe le was more uniform at the exit plane, suggesting enhanced volumetric heat release and faster mixing associated with the cavity- ine uenced e owe eld.

Numerical Analysis of Non-Combustion and Combustion Fields Accompanied with Swirl Flows

Numerical and experimental analyses were carried out with respect to the relationships among the change of diffusion and combustion processes, the location of fuel injection port and the distribution profiles of surrounding air flows. With the object of simulating the complex flow field, a calculation was made under the conditions of three inlets using velocity profiles measured at respective inlets. Effective viscosity expressed in a similar formula to Prandtl one and numerical analyzing procedures of effective difference, finite reaction rate and of combustion efficiency were introduced to improve the applicability and the convergence characteristics of the calculation. The calculation results agreed qualitatively with the experimental ones, and it was concluded that the diffusion rate of fuel is significantly influenced by the fuel supplying position and the surrounding air flows.

Numerical Analysis of Non-Combustion and Combustion Fields Accompanied with Swirl Flows

Numerical and experimental analyses were carried out with respect to the relationships among the change of diffusion and combustion processes, the location of fuel injection port and the distribution profiles of surrounding air flows. With the object of simulating the complex flow field, a calculation was made under the conditions of three inlets using velocity profiles measured at respective inlets. Effective viscosity expressed in a similar formula to Prandtl one and numerical analyzing procedures of effective difference, finite reaction rate and of combustion efficiency were introduced to improve the applicability and the convergence characteristics of the calculation. The calculation results agreed qualitatively with the experimental ones, and it was concluded that the diffusion rate of fuel is significantly influenced by the fuel supplying position and the surrounding air flows.