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Highlights • Combustion and emission characteristics of a dual-fuel aero-engine were simulated. • Emission characteristics of a dual-fuel aero-engine were analyzed. • Emissions of CO 2 decreased by 12% with burning dual fuel compared with single fuel. • Emissions of CO decreased by 33% with burning dual fuel compared with single fuel. Abstract Compared with aviation kerosene, liquefied natural gas (LNG) has the characteristics of higher energy density, wider flammability limits, better cooling potential, better thermal stability, and lower cost. Using LNG as an alternative fuel to aviation kerosene will be an effective mean to solve the depletion of aviation kerosene and the environmental problems caused by this fuel. However, there are many technical difficulties for LNG used as a sole fuel for aero-engine. One possible way is mixing LNG with kerosene, as a mixed fuel for the aero-engine. In this paper, the characteristics of combustion and emissions of an aero-engine which respectively burning sole aviation kerosene and 50% aviation kerosene/50% methane mixed fuel were reaction kinetic simulated by adopting the reduced reaction mechanism of n -decane which was chosen as a surrogate fuel for aviation kerosene. The results show that, the flow distribution characteristics in a flame tube of the combustor under the condition that the aero-engine burning 50% aviation kerosene/50% methane mixed fuel is the same as the condition that the aero-engine burning aviation kerosene. However, the high temperature area in the main combustion zone is shorted, and the maximum temperature in the flame tube and the average temperature at the outlet of this flame tube are decreased by 15 K and 11 K, respectively. Moreover, the concentration field distribution characteristics of fuel under the condition that the aero-engine burning 50% aviation kerosene/50% methane mixed fuel is the same as the condition that the aero-engine burning aviation kerosene. However, the maximum concentration of fuel is increased, the maximum concentrations of C 2 H 2 , C 2 H 4 , C 4 H 4 are decreased greatly in the flame tube, and the average concentrations of CO 2 and CO at the outlet of this flame tube are decreased by 12% and 33%, respectively, but the average concentration of H 2 O is increased by 13%. [ABSTRACT FROM AUTHOR]

• The oxidation and laminar combustion characteristics of natural gas were experimental tested. • A new construction method of the reduced mechanism of natural gas was proposed. • A reduced mechanism containing 40 species and 189 reactions of natural gas was formed. • The reduced mechanism can predict well the characteristics of oxidation, ignition delay and laminar combustion of natural gas. The oxidation process in the flow tube reactor and the laminar combustion process in the constant volume combustion bomb of natural gas (0.9 methane/0.07 ethane/0.03 propane, mole fraction) were experimental tested. Furthermore, a reduced reaction mechanism (including 40 species and 189 reactions) of natural gas was developed based on the Aramco 2.0 mechanism by combining the path sensitivity analysis, rate of production analysis, reaction path analysis and the decoupling method. The results show that, in the oxidation process of natural gas, with the equivalence ratio increasing, the starting and ending temperatures for oxidation reaction of natural gas are increased, the reaction temperatures corresponding to CO generation and consumption are higher, and the amount of NO production is decreased. In the the laminar combustion process of natural gas, with the initial temperature and oxygen content increasing or the initial pressure, CO 2 and H 2 O contents decreasing, the laminar flame speed is increased. Through comparing with the calculated results by the Aramco 2.0 mechanism and the corresponding test data, the reduced reaction mechanism can well predict the oxidation, ignition delay and laminar combustion characteristics of natural gas under various conditions. [ABSTRACT FROM AUTHOR]

• Combustion and emission characteristics of a heavy-duty gas turbine combustor fueled with natural gas were simulated. • Simulated NO x concentration at the outlet of the flame tube is only higher than the experimental value by 5.08%. • Fuel ratios in the duty, uniform, and annular zones of the flame tube were twice redistributed. • After fuel modified redistributed, NO x emission decreases from 157.1 mg/m3 to 139.51 mg/m3. In this paper, the ignition delay and laminar combustion characteristics of natural gas were tested in a chemical shock tube and a constant volume combustion reactor, respectively, and simulated with the Gri_3.0, USC_2.0 and NUI_Galway models, respectively. It is proved that the ignition delay and laminar combustion characteristics of natural gas simulated with the Gri_3.0 model are in better agreement with the experiment than the USC_2.0 and NUI_Galway models. Furthermore, the simulated variation trends of the mole fractions of main species, especially NO and NO 2 with temperature by the Gri_3.0 model are in better agreement with the experimental data in the oxidation of natural gas. The combustion process and pollutants generation characteristics in a single flame tube of a heavy-duty gas turbine burning natural gas were simulated by coupling the Gri_3.0 model with the computational fluid dynamics. It is shown that the simulated average temperature and the NO x concentration at the outlet of the flame tube are slightly higher than the experimental value by 8.06% and 5.08%, respectively. Because the NO x emission is higher than the designed value, fuel flows in the annular, main, and pilot combustion zones of the flame tube were reassigned and effects of the fuel redistributions on the NO x emission characteristics were investigated. It is shown that the NO x concentration at the outlet of the flame tube increases from 157.1 mg/m3 to 175.5 mg/m3 when the fuel flow in the pilot combustion zone is redistributed to the main combustion zone, and decreases from 157.1 mg/m3 to 139.51 mg/m3 when the fuel flow in the pilot combustion zone is redistributed to the annular combustion zone. The research results will provide theoretical basis and technical support for the optimization of this gas turbine operation. [ABSTRACT FROM AUTHOR]

• 3D LES simulation is conducted on spherical expanding flame of premixed natural gas/air mixture. • 3D flame front is decomposed into 36 2D flame fronts by rotation of the ZOX cross-section. • Flame morphology, flame propagation speed, cellular instability and disturbance are analyzed. • Disturbance amplitude and wave number of the flame perturbation are extracted by FFT. • Effects of spark energy, spark radius and time step on the simulation results are discussed. The flame dynamic and cellular instability of spherically expanding flame for premixed natural gas/air mixture were studied by numerically solve the 3D, transient, reactive Navier-Stokes equations. The computational methodology uses large eddy simulation and premixed combustion model with adaptive mesh refinement. The 3D flame front is decomposed into 36 2D flame fronts by every 5° rotation of the ZOX cross-section during post-processing. Fast Fourier Transform (FFT) with Hanning window is adopted to extract the disturbance amplitude and wave number of the flame perturbation. The effects of spark energy, spark radius and time step on the simulation results are also discussed. The computational methodology is first validated by experimental data at atmospheric condition and then applied to premixed natural gas/air mixtures under elevated temperature and pressure. The results showed that the initial temperature has little effect on the flame morphology, while the crack splitting on the flame front intensifies from the initial stage of flame propagation and the number of cells on the flame surface obviously increases as the initial pressure increases. The initial pressure has a more significant effect on the critical flame radius than the initial temperature. This is because increasing the initial pressure leads to the reduction of flame thickness while both the flame thickness and the density ratio decrease with the increase of initial temperature. Moreover, disturbance energy within the wavenumber range of 4–15 increases significantly with the increase of initial pressure, especially at stoichiometry condition. This is because the restriction effect of flame stretch on flame inherent instability reduces with the increase of initial pressure. [ABSTRACT FROM AUTHOR]

• A new surrogate fuel of RP-3 kerosene was developed. • Ignition and laminar combustion characteristics of the surrogate fuel were experimental studied. • The surrogate fuel emulated all of the selected property targets of RP-3 kerosene. • The ignition and laminar combustion characteristics of the surrogate fuel were agreed with RP-3 kerosene. A new surrogate fuel was developed to emulate both the physical and chemical properties of RP-3 kerosene. Six property targets were chosen for the new surrogate fuel formulation, which are hydrogen/carbon ratio, average molecular weight, cetane number, low calorific value, density and viscosity. The surrogate fuel was developed with only those species readily available in existing kinetic mechanisms, that are n-decane, n-dodecane, iso-cetane, methylcyclohexane and toluene. The mole fractions of the above components are 14%, 10%, 30%, 36%, 10%, respectively, which determined by an optimizer based on the error of the property targets between the surrogate fuel and RP-3 kerosene. Comparisons with RP-3 kerosene show that the newly developed surrogate fuel reproduces the six property targets of RP-3 kerosene. Further experimental investigations were performed in a chemical shock tube and constant volume bomb to obtain the ignition delay and laminar combustion characteristics of the new surrogate fuel and RP-3 kerosene. The results show that the ignition delay times and laminar combustion velocities of the surrogate fuel are in good agreement with that of RP-3 kerosene. [ABSTRACT FROM AUTHOR]

• A new method for assisted atomization with plasma jets is proposed. • Independently designed experiments demonstrate that this new approach is feasible. • With the new method, the SMD is reduced by 6.31%–31.91%. In order to explore the critical technology of plasma application to assist fuel atomization, a jet discharge plasma excitation atomization device was independently designed. And the test of fuel atomization characteristics were carried out. The effects of Ar volumetric flow and peak voltage on Sauter mean diameter (SMD) and penetration depth were investigated. The experimental results show that the introduction of plasma can significantly improve atomization characteristics. The introduction of plasma has significantly improved the atomization characteristics, and the SMD is reduced by 6.31%–31.91%. Plasma-assisted regulation can be achieved by changing the peak voltage and Ar volumetric flow. Ar jet plasma excitation inhibits the penetration of single-hole fuel jets in lateral airflow. The regulation of the longitudinal upper and lower boundaries of the single-hole fuel jet can be achieved by changing the peak voltage and Ar volumetric flow. Compared with the traditional atomization device, the new plasma excitation atomization device can produce a better atomization effect. The better the atomization effect, the more thoroughly the fuel particles can be mixed with the air, which can not only considerably shorten the combustion time, but also the more complete the combustion. In addition, it can promote energy saving and emission reduction and prolong the engine's life. In general, the new plasma atomization device provides a new idea for the future direction of atomization. [ABSTRACT FROM AUTHOR]

• This paper focused on the instability of RP-3 aviation kerosene/air premixed flame. • Experiments were carried out in a constant volume chamber to study the unstable flame propagation processes of RP-3/air premixed flame over wide initial conditions. • The transition acceleration onset was measured and the effects of diffusional-thermal, hydrodynamic instability and stretch rate in spherically expanding flames on R cr were analyzed. • The acceleration exponent α was obtaind and with the increase of equivalence ratio, the changes in α and its corresponding flame radius were analyzed. In the present work, experiments were carried out in a constant volume chamber to study the unstable flame propagation processes of RP-3/air premixed flame at initial pressures of 0.1, 0.2 and 0.3 MPa, initial temperatures of 420, 450 and 480 K and over a wide equivalence ratio range from 1.0 to 1.7. Results show that the RP-3/air premixed flame tends to be unstable with increased equivalence ratio and initial pressure. The measured transition acceleration onset and calculated critical flame radius R cr agree well with each other. The effects of diffusional- thermal, hydrodynamic instability and stretch rate in spherically expanding flames on α show that α of RP-3/air premixed flame strongly depends on effective Lewis number L e eff and Markstein number Ma. With the increase of equivalence ratio, acceleration exponent α tends to increase and the flame radius corresponding to the onset of similarity acceleration decreases. [ABSTRACT FROM AUTHOR]

By combining the reaction class-based global sensitivity analysis (RC-GSA) methodology, species sensitivity analysis (SSA) methodology, decoupling method and genetic algorithm (GA), a reduced reaction mechanism of the surrogate fuel (10% n -dodecane/14% n -decane/30% isohexadecane/36% methylcyclohexane/10% toluene, in mole fraction) for RP-3 kerosene was constructed. As an example, the detailed construction process of skeleton mechanism of methylcyclohexane (MCH) was presented, and the skeleton mechanism constructions of other components in the surrogate fuel were similar to that of MCH. First, the dominant reaction classes in the fuel-relevant mechanism of MCH were recognized by the RC-GSA, the representative species in each retained reaction classes were selected by the SSA, and the skeleton fuel-relevant mechanism of MCH was developed. Second, through combining the skeleton fuel-relevant mechanism of MCH with the reduced reaction mechanism of C 0 -C 3 by the decoupling method, the initial skeleton mechanism of MCH was obtained. Third, based on the GA, the rate constants of fuel-relevant reactions in the initial skeleton mechanism of MCH were optimized to enhance the prediction performance. Finally, by coupling the skeleton reaction mechanisms of n -dodecane, n -decane, toluene, isohexadecane, MCH, and the reduced reaction mechanism of C0-C3, a reduced mechanism (containing 121 species and 469 reactions) of the surrogate fuel for RP-3 kerosene was formed. The predicted main species concentrations during the oxidation process in the jet-stirred reactor, the ignition delay times in the shock tube and laminar flame speeds in the constant volume bomb by this reduced mechanism are in good agreement with the corresponding experimental data of RP-3 kerosene. [ABSTRACT FROM AUTHOR]

• The studied combustor has the structure characteristics which has no head swirler structure, it relies on vortex plates, primary combustion holes and a head circular structure to organize the flow field in the primary combustion zone. • The function of vortex plates, primary combustion holes and the cooperation between them have been studied to understand the flow and combustion characteristics in the combustor. • The circumferential flame propagation mainly relies on the vortex plates according the results. The number of vortex plates has effect on the shape of the combustor head recirculation zone, and there is an optimal value to optimize the combustion performance. In this paper, a combustor using vortex plates instead of swirler as the head swirl device has been studied. The flow and combustion characteristics in the combustor mainly depend on the combustor structural characteristics, therefore, the study of combustor structural parameters on combustion characteristics is a key means for the improvement of combustor performance. Numerical simulation method was used to study the flow and combustion characteristics in the primary combustion zone of a small aero-gas turbine engine annular reverse-flow combustor. The results show that the nozzle mounted on the flame tube outer wall is better than on the head considering the benefit to fuel/air mixing and combustion performance for this type combustor. The cooperation between vortex plates and primary combustion holes is the method of organizing flow in the primary combustion zone, and the cooperation is effective than simply relying on the vortex plates or the primary combustion holes. The circumferential flame propagation mainly relies on the vortex plates according the results. The number of vortex plates has effect on the shape of the combustor head reverse-flow zone, and there is an optimal value to optimize the combustion performance. [ABSTRACT FROM AUTHOR]

• DBD is used to explore a new way to optimize fuel atomization. • He-assisting DBD can reduce droplets size and increase spray angle. • Active-particle types in the atomization field are obtained. In order to study the influence law of active particles on atomization characteristics of aviation kerosene and explore the key technologies of plasma application in fuel atomization auxiliary, the dielectric barrier discharge plasma nozzle was independently designed, and the experiments of He plasma jet spectrum diagnosis and fuel atomization characteristic were carried out. The active particle composition of He plasma jet was explored, and the influence of He volume flow rate and peak voltage on electron excitation temperature, SMD and spray cone angle were studied. The results show that He plasma ionizes the air in the surrounding space to produce active particles such as OH, O and He Ⅰ atoms. The electron excitation temperature varies between 3100 and 7300 K and reaches the maximum when the peak voltage is 11 kV. The influence of electric field application and He volume flow changes on the atomization characteristics are very obvious, specifically, as the peak voltage increases, the SMD decreases and the spray cone angle increases. Under the high peak voltage (12–13 kV), the increasing trend of the spray cone angle gradually slows down and stabilizes. As the volume flow of He increases, the SMD decreases and the spray cone angle increases. The difference in oil supply pressure will affect the atomization effect of plasma excited fuel. The specific realization is that under △P inj = 0.05 MPa, the increase of He volume flow has little effect on the atomization effect. When △P inj = 0.15–0.35 MPa, the change of peak voltage has a greater impact on SMD, while at a lower △P inj (0.05–0.25 MPa), the change of peak voltage has a greater impact on the growth trend of the spray cone angle. [ABSTRACT FROM AUTHOR]

• A biocrude was collected from the hydrothermal liquefaction of algae slurry. • LBV of microalgae oil/RP-3/air mixtures were obtained in a constant volume chamber. • The effects of temperature, pressure, microalgae oil addition on LBV were analyzed. • By fitting experimental data, an empirical formula of LBV with factors was obtained. In the present work, algae-derived biocrude was collected from the hydrothermal liquefaction of algae slurry, and the mixtures of algae-derived biocrude and RP-3 aviation kerosene was used as aviation substitute fuel named as microalgae oil/RP-3 blend. In order to understand the laminar burning velocity (LBV) of microalgae oil/RP-3, experiments have been carried out in a constant volume chamber (CVC) to investigate the effects of initial temperature, initial pressure and microalgae oil addition on the LBV of microalgae oil/RP-3 blend over a wide equivalence ratio range from 0.8 to 1.4. Experimental result shows that with the increase of initial temperature and microalgae oil addition, the LBV of microalgae oil/RP-3 mixture increases, while with the increase of initial pressure the LBV of microalgae oil/RP-3 mixture decreases. According to the method of Metghachi, the relationship between the LBV and its influence factors was obtained, the exponents of α T (ϕ) , β P (ϕ) and γ R (ϕ) indicate that the change of initial temperature and pressure have less effect on LBV around equivalence ratio of 1.1 compared with other equivalence ratio conditions, while the change of microalgae oil addition has more significant effect to improve LBV at equivalence ratio of 1.1. [ABSTRACT FROM AUTHOR]

• We focus on laminar flame characteristics of BFG with various CH 4 additions. • CH 4 addition exhibits opposite effects on S L and L b at ϕ = 0.8–1.2 and ϕ = 1.4. • Thermal effect plays a major role at ϕ = 0.8–1.2 instead of chemical effect at ϕ = 1.4. • R38 and R52 are the main chain branching and chain termination reactions. • OH and H concentrations evidently increase with methane addition. As a typical low heating value fuel, blast furnace gas (BFG) is used as an alternative fuel for gas turbine combustion. Due to its high concentration of inert gas components, natural gas is usually added to improve ignition and stable combustion in the combustion chamber. In this paper, laminar flame characteristics of BFG/CH 4 /air mixtures were investigated using constant volume combustion chamber and CHEMKIN package using the Gri-Mech 3.0 model. Experiments and numerical simulations were conducted at an elevated pressure and temperature of 0.2 MPa and 453 K, equivalence ratios of 0.8–1.4, and mixing ratios of methane of 0, 5, 10, 15%. The results show that the laminar burning velocity decreases rapidly from 24.19 cm/s to 13.90 cm/s at ϕ = 1.4 with the increase of methane addition from 0% to 15%, but obviously increases from 16.49 cm/s to 28.68 cm/s at ϕ = 0.8, from 21.05 cm/s to 35.65 cm/s at ϕ = 1.0, from 23.52 cm/s to 32.09 cm/s at ϕ = 1.2 with the increase of methane addition from 0% to 15%. Meanwhile, methane addition has an opposite effect on the Markstein length at ϕ = 0.8–1.2 and ϕ = 1.4. The thermal, transport and chemical effects were examined, exhibiting a major role of the thermal effect in the range of ϕ = 0.8–1.2 and a significant contribution of the chemical effect at ϕ = 1.4 to the laminar flame propagation of BFG/CH 4 /air mixtures. Further sensitivity analysis shows that R38 (H + O 2 ↔ O + OH) and R52 (H + CH 3 (+M) ↔ CH 4 (+M)) are the main chain branching and chain termination reactions, respectively. Analysis on flame structure indicates that concentrations free radicals, especially OH and H evidently increase with methane addition. The maximum mole fraction of OH increases almost linearly from 1.02 × 10 - 3 to 3.82 × 10 - 3 with the increase of methane addition from 0% to 15%. The maximum mole fraction of H increases with a lower gradient than that of OH from 1.31 × 10 - 3 to 2.89 × 10 - 3 with the increase of methane addition from 0% to 15%. [ABSTRACT FROM AUTHOR]

• We focus on laminar burning velocity of blast furnace gas with very low heat value. • Effects of initial pressure, initial temperature and fuel composition were studied. • Gri-Mech 3.0 mechanism gives the best predications among six kinetic mechanisms. • Chemical kinetic effect is more dominant than thermal and transport effects. • R99 and R45 are the main chain branching and chain termination reactions. Laminar burning velocities of blast furnace gas with low heat value were investigated using constant volume combustion chamber and CHEMKIN package. Experiments and numerical simulations using Li, Davis, Gri-Mech 3.0, San Diego Mech, USC Mech II, NUI Galway Mech models were conducted at initial pressures of 0.1–0.2 MPa, initial temperatures of 303–453 K, and equivalence ratios of 0.8–1.6. Fuel composition was changed considering the volume fraction variation in blast furnace gas with calorific values of 3.27–4.03 MJ/m3. The effects of initial pressure and temperature on laminar burning velocities were correlated with high-order polynomials dependent on the equivalence ratio. The thermal and transport effects were examined and sensitivity analyses were further conducted to study the chemical kinetic effect. The results show that the laminar burning velocities increase with the decrease of initial pressure and the increase of initial temperature, and the Gri-Mech 3.0 mechanism gives very good predications among the six kinetic mechanisms. In addition, the laminar burning velocities increase with the increase of H 2 /CO ratio and the decrease of CO 2 /N 2 ratio under the same low heat value. The chemical kinetic effect plays a major part during the laminar flame propagation under all the operation conditions considered. Due to the high CO content and low H 2 content in blast furnace gas, R99 and R45 are the main chain branching and chain termination reactions, respectively. The effects of initial condition and fuel composition on laminar burning velocities are closely related to the concentrations of H, O and OH radicals. [ABSTRACT FROM AUTHOR]

• This paper focused on the use of LNG in aircraft engine. • Experiments have been done in a constant volume chamber for CH 4 /RP-3/air mixtures at various initial conditions. • Experimental data agree well with previous literature and mechanism of Zeng. • The effects of CH 4 mixing on the laminar burning velocity of CH 4 /RP-3/air premixed have been analyzed. • The effects of CH 4 mixing on the Markstein length of CH 4 /RP-3/air premixed flames have also been analyzed. Experiments have been carried out in a constant volume combustion bomb to investigate the effects of initial temperature (450 and 480 K), initial pressure (0.1 and 0.3 MPa) and CH 4 mixing ratio (0, 0.2, 0.4, 0.6, 0.8, 0.85, 0.9 and 0.95) on the laminar burning velocity and Markstein length of homogeneous, quiescent CH 4 /RP-3/air mixture over wide equivalence ratio from 0.7 to 1.4. Results show that with the increase of initial temperature from 450 to 480 K, no cellular structure in flame is observed, but obvious cellular structure is observed when initial pressure increases to 0.3 MPa at equivalence ratio of 1.2. The laminar burning velocity reaches its maximum in slightly rich mixture (ϕ = 1.1) and with the increase of initial temperature and decrease of initial pressure the peak laminar burning velocity of CH 4 /RP-3/air mixture increases. It is found that the laminar burning velocity of CH 4 /RP-3/air mixture decreases slowly when methane mixing rate increase from 0 to 0.8, but decreases rapidly from 0.8 to 0.95. Analysis results show that at equivalence ratio of 1.1, the Arrhenius factor exp - T a / 2 T ad has greater effect on the laminar burning velocity of CH 4 /RP-3/air mixtures when the methane mixing ratio is larger than 0.8. At equivalence ratio of 0.8 (lean mixture), with the increase of CH 4 mixing ratio the Le - 1 decreases, which leads to the decrease of Markstein length and make the premixed flame tends to be unstable, while at equivalence ratio of 1.4 (rich mixture), with the increase of CH 4 mixing ratio the Ze and δ increase, which stabilizes the premixed flame. [ABSTRACT FROM AUTHOR]

Biogas is a byproduct from the decomposition of organic matter and consists primarily of CH 4 , CO 2 and N 2. Combustion of biogas in land-based gas turbines for power generation is a promising approach to reducing greenhouse gases and dependence on fossil fuels. The focus of this research was to investigate the effects of fuel compositions, fuel injectors position and pilot split on combustion performance on a DLE combustor designed for a micro-gas turbine. The lean ignition and extinction performance were tested for different fuel composition in an atmospheric condition, the combustion performance were tested in the engine working condition. For the combustion performance test, the emissions of CO and NOx were the main focus of the combustion products. The results showed a noticeable benefit of the reduction in NOx emissions with the reduction of fuel Wobbe Index (WI). The combustor also shows good combustion characteristics considering pollutant emission for the 50%–100% engine load as the fuel WI is besides the designed range. Mixing distance, jet direction and jet depth of fuel have significant effect on the reduction of NOx emissions since the increase of the mixing distance, fuel momentum and jet depth are conducive to improving the mixing uniformity of fuel and air. Pilot split has a significant impact on NOx emissions, the NOx emission has a lowest value for a certain pilot split. The experimental testing results confirmed the feasibility of the utilizing the biogas as an alternative fuel for the micro gas turbine, the results also provide general guidance for the challenge of micro gas turbine burner design for fuel flexibility. [ABSTRACT FROM AUTHOR]