Enhanced Combustion Performance Research Articles

Combustion behavior of solid waste fuels in the vertical tube reactor under different oxy-fuel environments

Oxy-fuel combustion technology has been recognized as one of the promising ways for cost-effective CO2 capture. The co-combustion characteristics of flax straw biomass/bituminous coal mixture (FS/BC) and flax straw biomass/sewage sludge mixture (FS/SS) under air, oxy-fuel (21%/79% O2/CO2) and oxygen-enriched oxy-fuel (30%/70% and 40%/60% O2/CO2) conditions were investigated in the vertical tube reactor. In particular, the study focused on the burning characteristics, the effect of blending ratio, and flue gas emissions. The findings indicated that flax straw biomass exhibited superior ignition performance compared to its blends with sewage sludge and bituminous coal. A higher O2 concentration from 21% to 40 led to a reduction in ignition delay time by 4s at 850 ℃ and by up to 10s at 950 ℃. Moreover, char combustion time was reduced by 50% for FS/SS blends due to the lower fixed carbon content compared to FS/BC blends. Additionally, increasing the O2 concentration resulted in lower emissions of CO by ∽40% and N2O by ∽45% for both blends. However, this also led to a slight increase in SO2 and NO emissions by ∽15% and ∽26%, respectively. The optimal conditions for the tested samples in oxy-fuel environment were found to be 30% O2/70 CO2, which enhanced combustion performance while lowering flue gas emissions.

Enhanced combustion performance of Al–Zn alloys with property optimization inspired by “two-way tunneling” strategy

Fluorinated polymers (PVDF) are widely used due to their pre-ignition reaction with Al2O3 to improve the combustion of Al. In this study, a homogeneous PVDF coating layer was constructed on the surface of Al–Zn alloys by solvent evaporation, and Al-Zn@PVDF composites with “two-way tunneling” function during thermal decomposition and combustion were prepared. The constructed PVDF coating layer can react with Al2O3 to destroy the protective layer and promote the oxidation and combustion of Al–Zn from the outside to the inside. At the same time, the energy provided by the Al-Zn@PVDF during the ignition and combustion process also promotes the melting and vaporization of Zn, which achieves the rapid and full combustion of Al–Zn alloy from the inside to outside. The “ two-way tunneling” function of Al-Zn@PVDF composites significantly improves the combustion performance, resulting in a maximum combustion temperature of 1346.9 °C for Al-Zn@PVDF-40 % and a minimum combustion duration of 1.39 s for Al-Zn@PVDF-30 %, which is a significant improvement in combustion performance. The good chemical stability of PVDF also improves the hydrophobicity of Al–Zn and enhances its applicability. In conclusion, the construction of composites with “two-way tunneling” function first proposed in this study can significantly improve the thermal decomposition and combustion properties of Al–Zn, which is expected to further facilitate its application in propellants, explosives and pyrotechnics.

Insights into the pelletization behaviors of artificial lignocellulosic biomass based on cellulose, hemicellulose and lignin: A simplex lattice mixture design approach

The use of high quality densified pellet as an alternative to traditional fossil fuels is a promising avenue of research due to their interesting higher density, superior heating values, and enhanced combustion performance. However, little is known about the pelletization behaviors from the aspect of lignocellulosic biomass fundamental components (cellulose, hemicellulose and lignin) and their mixtures. This study presents an artificial biomass developed based on cellulose, hemicellulose and lignin using a simplex lattice design approach, aiming to understand the detailed role of major components and its effects on pellet quality. The correlation between the experimental data obtained from the simplex lattice design and the predicted response parameters were effectively explained by Scheffé's special cubic model, with a coefficient of determination beyond 90 %. Parameter estimates showed a significant synergetic effect of each components for density and Meyer hardness. Results revealed that xylan may be softened like lignin and thereby potentially act as binder. The use of a high cellulose concentration resulted in enhanced pellet strength by acting as a supporting skeleton. Xylan and cellulose played a major role in the thermal degradation of densified pellets. Based on the results obtained, the optimal components composition was determined to be 34.5 % lignin, 36.3 % cellulose, and 29.2 % xylan. Under this, the pellet exhibited the best density and Meyer hardness beyond 1500 kg/m3 and 80 N/mm2, respectively. The results provide a foundation for future efforts to be able to predict pellet properties from the perspective of biomass composition.

Catalytically ultrathin titania coating to enhance energy storage and release of aluminum hydride via atomic layer deposition

Aluminum hydride (AlH3) has attracted much attention owing to its extraordinary hydrogen storage performance, yet AlH3 is prone to hydrogen release reaction during long-term storage, leading to a decrease in energy and hindering its practical application. Herein, AlH3 particles are stabilized by catalytically ultrathin TiO2 coating via atomic layer deposition (ALD), the hydrogen content of which is controllable and reduces only 0.0026 wt% per ALD cycle of TiO2 coating. 30 cycles of TiO2 (2.4 nm) coated AlH3 exhibits a peak decomposition temperature of 203.42 ℃ and decomposition activation energy of 112.21 kJ/mol, which are 7.83 ℃ and 22.64 kJ/mol higher than those of bare AlH3. The hydrogen content loss of TiO2 coated AlH3 under hydrothermal aging conditions is much lower than that of bare AlH3 due to the passivation of defects on native Al2O3 by forming inert Al2O3 and catalytic TiO2 double-shell coating structure. TiO2 coated AlH3 exhibits enhanced combustion performance with stronger flame radiation intensity compared to bare AlH3. The density functional theory calculations indicate that the contact between AlH3 and TiO2 can weaken the strength of Al-H ion bond and promote the release of hydrogen. Our work offers a feasible method for simultaneously improving the stability and energy release of AlH3.

Chemical kinetic study of methane blended with ammonia cracked gas at elevated temperature and pressure

Ammonia (NH3) on-line cracking to produce hydrogen (H2) can avoid direct ammonia combustion and is an important method to enhance combustion performance and control nitrogen oxide (NOx) emissions. This work aims to study the effects of various ammonia energy ratios (ENH3) and cracking ratios (CNH3) on the combustion and NO emission characteristics of methane (CH4) blended with ammonia cracked gas under lean-burn condition. The results showed that methane co-combustion and ammonia cracking significantly enhance the laminar burning velocity (LBV). The chemical effect plays a dominant role in the enhancement of LBV, but its relative contribution gradually decreases with increasing ENH3 and CNH3. A linear relationship between LBV and (O+H+OH+NH2 + CH3)max was observed, with both the slope and intercept being functions of CNH3. At an ENH3 of 20 %, NO emission decrease with increasing CNH3. At an ENH3 of 80 %, NO emission first increase and then decrease. The percentage of thermal NO is less than 1 % under ambient condition and could increase to as much as 22 % under elevated condition (500 K, 10 atm). Additionally, there was a quadratic polynomial relationship between (O+H+OH+NH2)max and the final NO mole fraction within an equivalence ratio range from 0.4 to 0.8. The second-order coefficient exhibits a linear correlation with CNH3, while the first-order and constant coefficient show a quadratic polynomial correlation with CNH3.

Preparation of high-energy Al-Li alloy powders with enhanced compatibility and combustion performance by dense fluorosilane polymer composite coating

The superior combustion heat, lower ignition temperature, and enhanced combustion efficiency of aluminum–lithium (Al-Li) alloy powders have garnered significant research attention in relation to Al powders. However, the inadequate compatibility between Al-Li alloy powders (especially when Li > 3 wt%) and propellant components limits its application in the development of composite solid propellants. This study focuses on the surface-coating active Al-4.3Li (wt.%) alloy powder using a composite fluorosilane coupling agent to improve compatibility and combustion performance. A coating layer with a thickness of 30–40 nm was successfully formed on the surface of Al-4.3Li alloy powder through interactions involving Al-F, Al-O-Si, and Li-O-Si bonds, thereby achieving remarkable hydrophobicity. The heat release increased by 7.5 %, while the ignition delay time of the alloy powder decreased by nearly 200 ms, resulting in a significantly enhanced combustion performance in relation to that of the original Al-4.3Li alloy powder. Moreover, the modified Al-4.3Li alloy powder exhibited better compatibility, and no cracks or bubbles were observed in the cross-section of the propellant containing modified Al-4.3Li metal fuel. This study provides an effective approach for utilizing Al-Li alloy powders in solid propellants, which is of great significance for the development of high-energy propulsion systems.

Comparative analysis of combustion characteristics and economy between air assisted combustion and oxy-fuel combustion in glass furnaces

The oxy-fuel combustion is an effective means to improve the high energy consumption, pollution, and economic cost of glass furnaces. In this paper, the combustion characteristics in the flame spaces of traditional natural gas/air assisted combustion glass furnace (GF-NAC) and reformed natural gas/oxy-fuel combustion glass furnace (GF-NOC) are analyzed and compared by means of numerical calculation. More importantly, a systematic quantitative comparative analysis is conducted on the economic performance of the two glass furnaces from the perspectives of fixed and operating costs. The results show that enhanced combustion performance of GF-NOC over GF-NAC is found with flames being extended across the entire width of the furnace in GF-NOC. A more uniform temperature distribution within the furnace is consequently accomplished in GF-NOC. The flame center temperature, the average furnace temperature, and the average glass surface temperature in GF-NOC are increased by 7.42 %, 1.17 %, and 7.96 %, respectively, compared to GF-NAC. Furthermore, a reduction in gas velocity by 50 % at the arch in GF-NOC is observed to mitigate the erosive effects of high-temperature gas flows on the furnace crown. According to the service life of glass furnace of 15 years, the GF-NOC can save 420 M (million yuan) (12.8 %) compared to the GF-NAC. Although the fixed cost of GF-NOC is 9.82 M (5.43 %) higher than that of GF-NAC due to the expenditure on oxygen production equipment, the difference is offset by operating costs. Compared to GF-NAC, GF-NOC can save operating costs of 28.7 M (15.87 %) per year.

Computational and Chemical Kinetics Analysis of Hydrogen-Blended LPG for Domestic Cook Stove Burners

The penetration of liquefied petroleum gas (LPG) is much faster due to its wide range of applications, from industry to domestic usage. Hydrogen-blended LPG (H2-LPG) fuels offer benefits such as reduced emissions and increased fuel efficiency, and hydrogen is a promising option due to its clean-burning properties and easy transportation through pipelines. The present work investigated the combustion performance of blended fuels of hydrogen and LPG for commercial cooking burners (CCBs). SolidWorks was used to create a model of the CCB, which was then analysed using a non-premixed combustion approach with a compressible k-ε turbulent flow model in Ansys Fluent. The chemical kinetic mechanisms were employed to analyse the impact of fuel blends and combustion conditions on the burner's emissions and efficiency. The study found that blending hydrogen with LPG up to 50% can significantly enhance combustion performance, reduce CO and CO2 emissions, and increase economic viability through fuel conservation.

Plastic pyrolytic oils as renewable fuel: improving its physical properties and ignition patterns by waste renewable source-an experimental analysis.

The increase in plastic products and disposal poses a severe environmental challenge because of their poor biodegradability and undesirable disposal by landfilling. Recycling is the best possible solution to the environmental challenges implemented by the plastic industry. Pyrolysis is a process that converts waste plastics into pyrolytic oil, and it can be used as fuel in a blended form. The viscosity and lubricity of the LDWP (low-density waste polyethylene) pyrolytic oil were lower than standard diesel. Capparis spinosa methyl ester (CME) is blended and experimented with to overcome the lubricity issue of pyrolytic oil. In this investigation, 5%, 10%, and 15% CME were blended with PD20 (20% LDWP oil + 80% diesel) blend on a volume basis. Experiments were conducted to examine the effects of CME on combustion, performance, and emissions using the combination of CME and PD20 blend tested at 0%, 25%, 50%, 75%, and 100% loading conditions. All three ternary mixtures showed enhanced combustion performance and increased NOx and smoke emissions. Due to better combustion, the efficiency of the blend PCD10 (10% CME + 20% LDWP oil + 70% diesel) was higher than the PD20 blend and significantly closer to diesel. Hence, PCD10 is suggested as an alternative to diesel fuel.

Fabrication and energy release study of metastable intermolecular composite microspheres with enhanced combustion performance

Metastable intermolecular composites (MICs) are often used in military and aerospace applications because of their high energy density. However, the traditional preparation methods are either complicated and unsafe, or the prepared composites have incomplete combustion and low energy release rates. In this paper, a series of aluminum/metal oxide/nitrocellulose (AMxN) composite microspheres were prepared by spray drying technique. The field emission scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) results show that the prepared AMxN composite microspheres have regular morphology and uniform particle size, and nitrocellulose (NC) is successfully coated between fuel (Al) and oxidizers (CuO, MoO3, and Bi2O3). The thermal reactivity, energy, and combustion properties of AMxN were investigated and compared with physically mixed aluminum/metal oxide (AMx). The explosion heat of AMxN is higher than AMx, while the thermal reaction exothermic peak temperature is lower. Among them, the composite containing copper oxide has the highest explosive heat value (5034 J/g), and the composite containing bismuth oxide has the shortest burning time (2.8 ms). These results prove that NC as a binder shortens the reaction distance between the oxidizer and the fuel in the presence of spray drying. Different oxidizers can modulate the energy release rate of AMxN composites, which is beneficial for applying MICs in energetic materials.

Effect of oxidation treatment on structural characteristics and combustion behavior of residual carbon from coal gasification fine slag

Improving the combustion reactivity of residual carbon (RC) is an important prerequisite for effective combustion of coal gasification fine slag (CGFS). This study investigates the oxidation of RC using air and CO2. Compared to raw RC, the oxidation process results in a lower burnout temperature of oxidized RC, and reduced combustion time. Additionally, RC oxidized by CO2 shows better combustion performance than that oxidized by air. The enhanced combustion performance of oxidized RC primarily stems from structural modification. The combustion behavior of oxidized RC is jointly determined by its carbon microstructure, functional groups, and pore structure, with pore structure being the predominant factor. Furthermore, increasing the oxidation temperature facilitates the formation of small-sized pore structures on the surface of the oxidized RC, which promote the oxygen diffusion and the heat transfer during combustion. However, the pore collapse caused by excessive oxidation inhibits the combustion performance of the corresponding oxidized RC.

TG-MS analysis and kinetic study of co-combustion of ca-rich oil shale with biomass in air and oxy-like conditions

In this study, the combustion behavior of ca-rich oil shale, spruce biomass, and their blends under air and oxyfuel environments of 21/79 % and 30/70 % O2/CO2 like conditions were investigated. Non-isothermal thermogravimetric (TG) experiments coupled with a quadrupole mass spectrometer (MS) were conducted to study individual fuels and their blends at 1:0, 4:1, 3:2, 2:3, 1:4, and 0:1 (0, 20, 40, 60, 80 and 100 wt.% Biomass) under three different heating rates 10, 30 and 50°C/min. Co-combustion synergistic along with the kinetic analysis by the isoconversional Friedman method has been carried out to evaluate the combustion process.The results show that the addition of biomass enhanced combustion performance and reduced burnout temperatures. Under oxy conditions, the ignition temperatures stabilized with a biomass ratio > 40 %. Ash content was reduced with biomass addition and when switching from air to oxyfuel combustion, the temperature of blends’ carbonate decomposition was stable at ∼ 720 °C. A positive synergistic effect in the devolatilization and the combustion of light hydrocarbons occurred at higher biomass ratios. Yet, the char oxidation peaks were below zero indicating a negative effect under 21 % of inlet O2. With increasing the heating rate, the negative synergistic effect was weakened for the three combustion atmospheres. SO2 emissions were reduced with increasing biomass ratio and increased under oxy mode along with H2O release. The activation energy (E) was lower in oxy conditions than in air mode for individual fuel and their blends, compared to the OS sample, the reduction was higher with increasing BM ratios and for the BM fuel. Overall, this study determines the appropriate conditions for the co-combustion of oil shale and spruce biomass under air and oxy modes for future carbon-negative capture applications in industrial oil shale combustion boilers.

Preparing HNS/n-Al heat-resistant microspheres with enhanced combustion performance using droplet microfluidic technology

Reducing the formation of large carbon clusters during the combustion of energetic materials (EMs) and improving their comprehensive performance hold great significance. With fluororubber (F2604) as a binder, this study prepared HNS/n-Al microspheres with different n-Al contents (5%, 10%, and 15%) using droplet microfluidic technology. Then, it characterized and tested the morphology, particle size distribution, dispersibility, crystal structure, thermal properties, mechanical sensitivity, and combustion behavior of the microspheres. The results show that the prepared microspheres had regular shapes, uniform particle sizes, and excellent dispersibility and contained more homogeneous components than physically mixed samples. Furthermore, the microspheres retained the crystal structures of the raw materials, enjoying high safety performance. The thermal analysis shows that HNS/n-Al microspheres had high heat resistance (thermal decomposition temperature: over 354 °C) and that a higher n-Al content was associated with more thorough thermal decomposition reactions of HNS (HNS: 83%, HNS/n-Al: 84%, 86%, and 93%). The ignition experiments show that the HNS/n-Al microspheres possessed excellent and stable combustion performance, as evidenced by more complete combustion reactions and significantly elevated energy release efficiency. Therefore, it is expected to achieve high-energy and high-speed responses of carbon-rich EMs and promote their practical applications.

Ultrastable Aluminum Nanoparticles with Enhanced Combustion Performance Enabled by a Polydopamine/Polyethyleneimine Nanocoating.

In national defense, aluminum nanoparticles (Al NPs) have better combustion performance than Al microparticles but are easily oxidized during processing, especially in oxidative liquids. Although some protective coatings have been reported, it is still challenging to obtain Al NPs stable in oxidative liquids (e.g., hot liquids) without scarifying combustion performance. Here, we report ultrastable Al NPs with enhanced combustion performance enabled by the crosslinked polydopamine/polyethyleneimine (PDA/PEI) nanocoating merely ∼15 nm in thickness and ∼0.24 wt % in mass. The Al@PDA/PEI NPs are fabricated by one-step rapid graft copolymerization of dopamine and PEI on Al NPs at room temperature. The formation mechanism of the nanocoating is discussed including reactions between dopamine and PEI and interactions of the nanocoating with Al NPs. The Al@PDA/PEI NPs show excellent stability in hot water, and the mechanism is interpreted by molecular dynamics simulation. The PDA/PEI nanocoating can also enhance the combustion heat and burning rate of Al NPs.

In situ precise construction of surface-activated boron powders: A new strategy to synergistically improve the interface properties and enhance combustion performance of boron

Boron powder (B) is considered to be the most ideal fuel for fuel-rich rocket propellants due to its high calorific value. However, substances such as B2O3 and H3BO3 on the surface of B powder not only reduce the combustion efficiency of B, but also seriously deteriorate the preparation process of hydroxyl-terminated polybutadiene (HTPB)-based propellants, making it difficult for B powder to be used in fuel-rich rockets propellant. Herein, two weak polarity molecules, 1 H, 1 H, 2 H, 2 H-perfluorodecyltrichlorosilane (denoted as PT) and decyltrichlorosilane (denoted as DT), are proposed to be directly anchored on the surface of B powder by chemical bonding to change the surface of B powder. The textural and chemical properties of the B powder and the surface-activated B powders, as well their reaction and combustion performance under different conditions, were studied in detail using various experimental methods. The results show that B@PT and B@DT activated by 1 H, 1 H, 2 H, 2 H-perfluorodecyltrichlorosilane and decyltrichlorosilane respectively have better reaction and combustion performance than B powder. The perfluorodecyltrichlorosilane on the surface of B@PT can release radicals such as CnF2n+2 and CnF2n with strong oxidizing properties during the thermal decomposition process, which can corrode the oxide layer on the surface of B powder and can significantly improve the combustion performance of B powder. This research is expected to enable the large-scale application of B powder in HTPB-based fuel-rich rocket propellants.

Thermogravimetric assessment for combustion characteristic of torrefied pellet biomass from agricultural solid waste

This present paper is focused on the investigation of combustion characteristics of torrefied pellet biomass from agricultural waste. Four biomass pellet samples such as sugarcane bagasse, Napier grass, Palm Empty Fruit Bunches, and Cassava stem were torrefied in a designed cylinder tubular pyrolysis reactor. The reactor was set up under 30 min of residence time, and the temperature reaction was varied at 200, 250, and 300 °C in an inert atmosphere. The torrefied products were then characterized in terms of their psychochemical properties such as proximate, ultimate, calorific value, and combustion properties. The combustion properties of raw and torrefied biomass pellets during the combustion process were investigated by the thermogravimetric analyzer Exstar SII TG/DTA7300. The samples were heated at an ambient temperature up to 800 °C at a constant heating rate of airflow at 10 °C/min in airflow. The results showed that the moisture content and volatile matter of torrefied pellets decreased by 2 to 5% and 8 to 14%, subsequently. Otherwise, the fixed carbon content is up to three times higher than the raw material. The study conclusively that torrefaction can also able to enhance combustion performance in terms of ignition and burnout temperature, ignition and burnout index, and combustion rate. The results shows that, the ignition and burnout temperatures of torrefied pellets are higher than raw material. The ignition and combustion index of torrefied pellets are lower than raw material, and the torrefied pellets have a longer burning time and a higher combustion temperature.

Using microfluidic technology to prepare octogen high-energy microspheres containing copper–aluminum composite particles with enhanced combustion performance

Aluminized explosives are widely used in military applications. However, the easy agglomeration of aluminum (Al) powder and its high ignition temperature greatly hinder the reaction of nano aluminum (n-Al) in the process of explosion, thus affecting the combustion and explosion of aluminum-containing explosives. In the present study, copper (Cu) coated n-Al composite particles were introduced into aluminized explosives, and Cu coated n-Al composite particles and ball-milled octogen (HMX) energetic microspheres were prepared via droplet microfluidic technology using binder. The morphology, crystal form, thermal properties, combustion, and mechanical sensitivity of the microspheres were studied using a variety of techniques. The prepared microspheres had regular spherical morphology and uniform particle size, with an even distribution of particles. Using microfluidic technology will not destroy the crystal form of each particle. The introduction of Cu promoted the thermal decomposition of HMX. The mechanical sensitivity of the prepared Cu/Al microspheres was lower than that of the microspheres only containing n-Al. The Cu/Al microsphere samples exhibited excellent and stable combustion performance, and that the addition of Cu increased the combustion speed compared to the microspheres only containing n-Al. This technology represents an inexpensive and simple way to improve on existing aluminized explosives.

Capsule structured Al/FeF3/AP energetic microspheres with enhanced combustion performance and energy release efficiency by a microexplosion reaction

The agglomeration and sintering of aluminum (Al) metal fuels lead to inadequate combustion and low energy release efficiency in the solid propellant systems. Herein, we assemble Al particles with gas generator of ferric trifluoride (FeF3) into capsule structured microspheres to detonate a microexplosion reaction by the evaporation-induced self-assembly technique, with encapsulating by ammonium perchlorate (AP) oxidant. The generated ternary Al/FeF3/AP microspheres achieved superior heat of combustion (12719.75 J g−1) and combustion temperature (1639.6 °C) owing to the full contact between components, reduced reaction transport distance, and the fierce shattering microexplosion combustion. Combustion mechanism analysis indicated that Al2O3 layer that hindered the oxidation reaction of Al was etched by the hydrogen fluoride (HF) from FeF3 decomposition, which caused the rapid splashing of nano Al clusters to detonate shattering microexplosion combustion. Furthermore, the ternary Al/FeF3/AP microspheres dramatically improve the combustion performance of hydroxy-terminated polybutadiene (HTPB)-based propellants and achieve a burning rate of 2.975 mm s−1, higher than most of the published HTPB/AP/Al propellants to date. The construction of Al/FeF3/AP microspheres exhibits a huge potential for the improvement of the propulsion power of rockets and weapons.

Defective-activated-carbon-encapsulated Co as a super reactive catalyst for combustion of ammonium perchlorate

Defective-activated-carbon can serve as both fuel and combustion catalyst for ammonium perchlorate (AP) based energetic composites owing to the promoted reactivity and catalytic activity. However, the poor ability of carbon materials in accelerating the electron transfer in the secondary reaction of HClO4 decomposition hinders their applications in composite solid propellant. Herein, a hybrid with metallic Co nanoparticles encapsulated in N-doped defective activated carbon (denoted as DAC/Co) is reported to achieve bi-functional additives with simultaneously high catalytic activity and high reactivity. The DAC with high defect can not only serves as fuel due to its high reactivity, but also favors the proton transfer in the initial decomposition of AP owing to its rich defects. Moreover, the combination of the Co nanoparticles and DAC is also beneficial to electrons transfer in the secondary decomposition of AP, leading to a high catalytic activity for thermal decomposition of AP. As a result, the AP/DAC/Co-20 composite possesses a greatly enhanced combustion performance, with the combustion duration shorten by 107 ms compared to that of AP/DAC (348 ms) and pressurization rate increase by 9.8%. The present work demonstrates the feasibility of DAC/Co hybrid for practical applications in AP based solid propellant.

Flame characteristics of backward-inclined pulsating combusting jet in crossflow

The flame appearances, thermal characteristics, and combustion product concentrations of a backward-inclined pulsating combusting jet in crossflow were experimentally studied. The time-averaged and streak instantaneous flame images were acquired using a still camera and a high-speed camera, respectively. The flame extinguishment processes were captured and analysed on the basis of streak instantaneous images. The flame temperatures and combustion product concentrations were measured using a homemade fine-wire thermocouple and a gas analyser, respectively. Three characteristic flame modes (crossflow dominated, transitional, and jet-dominated) were found when the backward-inclined jet flame in crossflow was subject to acoustic excitation. These characteristic flame modes were observed in different regimes of pulsation intensity and jet backward inclination angle. Discrete flame puffs with a frequency equal to the acoustic excitation frequency appeared in the jet-dominated flame. Periodic flame puffing became unstable when the pulsation intensity was increased to values near the instability limit. When the pulsation intensity was beyond the instability limit, a strong stretching effect caused the recirculation flame, which played the role of a flame ignitor, to almost vanish (misfire). The flame extinguishment then occurred from the area around the lee side of the burner tube tip. The temperature and gas concentration measurement results showed the significant improvement of combustion performance in low inclination angle even at small pulsation intensity in the regime of the crossflow dominated flame. To enhance combustion performance at a large jet backward inclination angle, the pulsation intensity must be large enough to push the flame in the regime of the jet-dominated flame.