Average Heat Release Rate Research Articles

Fire parameters of recycled plastic pellets

AbstractDuring the recycling process, waste plastic undergoes various processes that change its geometry. The thermal properties and fire behaviour of plastic in different geometries has not been widely studied. This paper aims to determine critical thermal properties of plastic pellets made of recycled plastic. For this paper, cone calorimeter tests of various volumes of recycled plastic pellets of low‐ and high‐density polyethylene and polypropylene were conducted. During these tests, the heat release rate (HRR), mass loss rate and time‐to‐ignition were measured, thereafter the heat of combustion (HOC) was calculated. A calibration of suitable time‐to‐ignition equations is carried out. The average HRR is between 353 and 581 kW/m2 with an external heat flux of 50 kW/m2. The measured time‐to‐ignition values ranged between 27 s at 50 kW/m2 and just more than 90 s at 25 kW/m2. Values obtained analytically from the thermally thin time‐to‐ignition equations for these materials describe ignition well, which appears to be due to the particulate nature of the samples. The HOC (40–41 MJ/kg) shows good agreement with the HOC for virgin plastic found in literature. These properties can be used as a basis for material characterisation, and further testing will be done before using this as simulation inputs to determine how bulk stored plastic pellets will behave in the event of a fire.

Hierarchical Nano/Micro-Array Structured CuMgAl-LDH/rGO Hybrids for Remarkably Improved Flame Retardancy and Smoke Suppression Performance of Flexible Polyvinyl Chloride.

In this study, we explored the rational integration of layered double hydroxides (LDHs) with reduced graphene oxide (rGO) to create a hierarchical nano/microarray structured CuMgAl-LDH/rGO hybrid aimed at enhancing the flame retardancy and smoke suppression properties of polymer nanocomposites. The results indicated that the limiting oxygen index (LOI) value of the G-CuMgAl/polyvinyl chloride (PVC) composite reached 35.8%, reflecting a 6.4% increase compared to pristine PVC (29.4%), and achieved a UL-94 V-0 rating. Furthermore, in comparison to pristine PVC, the peak heat release rate (PHRR) of the G-CuMgAl/PVC composite was significantly reduced by 40.2%; the total heat release rate (THR) decreased by 24.3%; the maximum average heat release rate (MARHE) diminished by 41.6%; the peak smoke production (PSPR) decreased by 37.8%; the total smoke production (TSP) was reduced by 31.3%; and the average effective heat of combustion (av-EHC) decreased by 15.2%. The enhanced flame retardancy and reduced smoke production can primarily be attributed to the multiple synergistic interactions among the highly dispersed constituents and the nano/microstructures, which effectively impede the transfer of heat, mass, and O2 from various directions while preventing further combustion of the underlying matrix by creating a tortuous path in the condensed phase. Additionally, this study provides a novel perspective on the design and synthesis of structured LDHs/rGO hybrids, with the potential to enhance flame retardancy and smoke suppression properties across a broad spectrum of polymer materials.

Numerical investigation on combustion performance optimization with strut/wall combined-staged injection strategy within an axisymmetric variable geometry combustor at Mach 3

Numerical simulations were conducted on the strut/wall multistage injection strategy to optimize the combustion performance at Mach 3. Two kinds of the combustion models were used: The Eddy-Dissipation Model (EDM) was used first to highlight the effects of mixing performance on the combustion performance; then the Finite-Rate/Eddy-Dissipation Model (FR/EDM) was used to modify the influence mechanism of wall injection positions by incorporating with finite-rate reaction effects. The combustion process was divided into three stages to analyze the average heat release rate and the contribution of average total temperature change of each stage to identify the key influencing factor of each stage. The results indicated that under low flight Mach number conditions, the finite-rate reaction effects exerted a more pronounced influence on the combustion. The strut/wall multistage injection strategy was found to be an effective means of enhancing combustion, with the positive feedback between the strut flame and the wall flame being particularly influential. Additionally, apart from the mixing efficiency, the distribution of heat release length of each stage also emerged as a critical factor in determining combustion performance. By adjusting the wall injection positions, the better combustion performance and the bigger working stability of the combustor could be achieved. The study elucidated the regulatory strategy of wall injection positions on combustion performance, offering value insights for optimizing combustion performance under low Mach number conditions.

Fire Properties of Paper Sheets Made of Cellulose Fibers Treated with Various Retardants.

This article presents the results of flame-retardancy tests conducted on cellulose sheets produced using a Rapid Köthen apparatus treated with retardants. The agents used were potassium carbonate (PC) K2CO3 (concentrations of 20; 33.3; and 50% wt/wt), monoammonium phosphate (MAP) NH4H2PO4 (concentrations of 35% wt/wt), diammonium phosphate (DAP) (NH4)2HPO4 (concentrations of 42.9% wt/wt), and bisguanidal phosphate (FOS) C2H10N6 (concentrations of 22.5% wt/wt). The agents were used to improve Kraft cellulose-based sheets' flame-retardant properties and compare their performances. As part of the study, the flammability of the materials was determined by the following methods: an oxygen index (OI) test, a mass loss calorimeter (MLC) test, and a mini fire tube (MFT) test. All formulations showed an increase in flame retardancy compared to the control test. All protected samples were non-flammable for OI determinations, and DAP-protected samples showed the highest OI index. For the MLC test, DAP-protected and MAP-protected samples showed the best heat-release rate (HRR), total heat release (THR), and average heat-release rate (ARHE) (samples did not ignite for 600 s). In the MFT test, all treated samples had comparably reduced weight loss. The best parameter was achieved for MAP and DAP (15% weight loss).

Optimal design on fin-metal foam hybrid structure for melting and solidification phase change storage: An experimental and numerical study

A fin-metal foam composite structure is employed in the phase change energy storage coupled Organic Rankine Cycle system to enhance thermal performance. The 3-D numerical model is validated through an experimental system to analyze the impact of metal foam parameters and fluctuating heat source parameters (amplitude and half-period) on the system's storage-release process during heat source fluctuation. According to the Taguchi method, metal foam porosity significantly influences the total storage-release time. An increase in porosity leads to a continuous increase in the total storage-release time, while an increase in PPI and a decrease in heat source amplitude initially increase and then decrease the total storage-release time. Under constant metal foam PPI (10) and porosity (0.97), Case T (half period = 60 and amplitude = 1.0) demonstrates a 2.04 % increase in average heat transfer rate and a 1.78 % reduction in total storage-release time compared to Case 0 (constant heat source). The average heat release rate sees a 4.23 % increase, while total heat storage and heat release rise by 0.96 % and 1.87 %. The research has specific technical significance for the photothermal application of phase change energy storage technology to the variability and unpredictability of solar energy.

Research on the synergistic flame retardation of epoxy resin through surface-modified aluminum diethylphosphinate in conjunction with DOPO and CFA

Surface modification of aluminum diethylphosphinate (ADP) was successfully achieved through the utilization of silane coupling agent KH-560. Simultaneously, the modified aluminum diethylphosphinate (K-ADP) served as the primary flame retardant, with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as the phosphorus-based flame retardant and charring‐forming agent (CFA) as the nitrogen-based synergistic flame retardant. This approach was employed to investigate the flame-retardant modification of epoxy resin. The optimal dosage of the surface modifier was investigated through moisture absorption test and viscosity measurements. Synergistic flame-retardant interactions among K-ADP, DOPO, and CFA were examined using techniques such as cone calorimetry test, thermogravimetric analysis, and residual char infrared analysis. The results indicated that the optimal dosage of KH-560 is 5%, resulting in a significant reduction in moisture absorption to 0.195%. At 80 °C, the addition of K-ADP leaded to only a 22.7% increase in system viscosity, demonstrating a notable viscosity reduction effect. When the addition of K-ADP is 14%, the Limiting Oxygen Index (LOI) value reached 30.5%, achieving a V-0 rating. Moreover, by maintaining the total addition at 14% and introducing DOPO and CFA, it is evident that most of samples meet UL-94 V-0 rating, with the LOI elevated to 32.2%. CCT results indicated a significant decrease in both average heat release rate and total smoke production, reduced by 24.1% and 7.0%, respectively. This notably enhanced the flame-retardant and smoke-suppressant properties of the EP composite material. The addition of K-ADP, DOPO, and CFA improved the mechanical performance of the EP composite material, surpassing the effectiveness of adding ADP individually.

Solar photothermal utilization of coupled latent heat storage: A numerical and optimization study

The combination of Organic Rankine Cycle (ORC) and Latent Heat Thermal Energy Storage (LHTES) is a novel approach for effectively utilizing solar energy. However, the influence of solar energy fluctuations on the heat transfer process of LHTES systems is not yet clear. In this study, a sinusoidal heat source is applied to a rotating triple-tube LHTES system, and numerical analysis and model verification are conducted. The parameters of the sinusoidal heat source are optimized using the response surface method. The effects of heat source amplitude, half period, and rotation speed on the heat release time and heat release rate of LHTES are investigated, and corresponding quadratic regression equations are fitted. The optimized structure (rotation speed = 0.5 rpm, amplitude = 7.5 K, half-cycle = 100) obtained through the response surface method reduced the solidification time by 12.45% compared to the initial structure (rotation speed = 0.3 rpm, amplitude = 7.5 K, half-cycle = 100). The average temperature response and heat release rate increased by 28.34% and 16.25%, respectively. The sensible heat and total heat release within one solidification cycle increased by 12.17% and 1.87%, respectively. This study lays the foundation for the optimization design of LHTES systems and the integrated application of Organic Rankine Cycle.

Characteristic parameter evolutions and fire smoke patterns of the wall fire plume: Experimental and theoretical analysis

In the fire investigation field, fire smoke patterns are studied as one of the most important indicators for fire accident investigation and scene reconstruction. This paper studies the evolutions of wall fire plume characteristic parameter and the smoke patterns considering five oil pan sizes and three fuel types, with a wall fire plume experimental platform inside a large-scale laboratory. The mass loss rate (or heat release rate), flame height and near-wall centerline temperature are measured and analyzed quantitatively, and smoke patterns are extracted based on the image analysis. Results show that: (1) The heat release rate in the stable stage and the average heat release rate over the whole burning process are in linear relationship for various fuels. The relation of the near-wall temperature profile and dimensionless height is obtained, and the wall fire is divided into four regions. (2) Various fuels produce different smoke pattern characteristics due to the different composition and property. The wall fire plume smoke patterns considering the near-wall temperature profile can be divided into several conditions. In each condition, with the increase of oil pan size, the opening of fitting curve increases and the vertex height decreases. (3) The boundary of the smoke pattern increases with oil pan size. The non-dimensional wall fire plume smoke pattern model with the corresponding temperature profile is obtained. These can increase the data reserve of the wall fire plume smoke patterns produced by different fuels and enrich the experiment and numerical calculation basis of building fire.

A 2D biobased P/N-containing aggregate for boosting fire retardancy of PA6/aluminum diethylphosphinate via synergy

Engineering polyamide 6 (PA6) is preferred for its superior mechanical properties, yet the intrinsic flammability restricts its industrial applications. As one of the biomass phosphorus-containing chemicals, phytic acid (PA) is favorable for its high phosphorus content and aggregation ability, making it expected to enhance the fire retardancy of PA6. Herein, a melamine-phytate aggregate (MPA) is prepared by electrostatic interaction in aqueous solution, and applied as a synergist for aluminum diethylphosphinate (ADP) in PA6. The strong synergistic effect exists between ADP and MPA towards PA6, especially when their mass ratio is 3:1 and the total loading is 18 wt%. Compared to the neat PA6, this formula allows for remarkable decreases in peak heat release rate (PHRR), total heat release (THR), and maximum average heat release rate (MARHE) by ∼ 48 %, ∼ 27 %, and ∼ 30 %, respectively, as well as a high synergistic efficiency of ∼ 43 % in PHRR. This PA6 composite also presents a V-0 rating in the vertical burning (UL-94) test and a high limiting oxygen index (LOI) of 29.7 %. This work offers an eco-friendly strategy for developing bio-based P/N fire-retardant aggregates for fabricating PA6 materials with high fire safety.

Burning characteristics of power cables with cone calorimeter

Power cables consist of insulation, padding and sheathing, which are highly susceptible to ignition. Power cables are an important factor affecting fire risk in urban utility tunnels (UUTs). In this paper, the combustion characteristics of four types of power cables (YJV, ZR-YJV, ZR-VV, and ZR-PE) in UUTs were investigated using a cone calorimeter. In this paper, laboratory experiments were conducted to investigate the combustion characteristics of power cables with two different parameters including two heat fluxes (35 kW/m2 and 75 kW/m2) and two sheath thicknesses (3 mm and 5 mm). The effects of heat release rate (HRR), effective heat combustion (EHC), optical density index (ODI) and smoke production rate (SPR) on ignition and combustion were investigated. The results showed that ZR-VV power cables have lower TTI, lower average HRR, lower EHC, higher MLR, and lower SEA than YJV and ZR-YJV power cables.With a conical calorimeter and heat flux of 35 kW/m2, the HRR of the power cables increased within 200 s, while for ODI, the total smoke output of ZR-YJV cables was minimized. Heat flux has a significant effect on HRR, SPR and EHC of ZR-PE cable. Sheath thickness has little effect on HRR, SPR and EHC of ZR-PE cables. In addition, one of the most important parameters, the ignition time, which depends on the composition and structure of the cable, was identified. Finally, the effect of external heat flux is complex and depends on the combustion characteristics of the power cable. Laboratory tests provide useful information for understanding the combustion behavior of power cables, including heat release rate, effective thermal burn, optical density index, and smoke production.

A novel P/N/Si/Zn-containing hybrid flame retardant for enhancing flame retardancy and smoke suppression of epoxy resins.

Currently, additively efficient flame retardants are being developed to enhance the smoke suppression, flame retardancy, and thermal properties of composite materials. To this end, the current study designed and prepared a novel P/N/Si/Zn-containing organic-inorganic hybrid denoted as APHZ. Its inorganic part was 2-methylimidazole zinc salt (ZIF-8), which improved its smoke suppression and catalytic carbonization. The organic part (P/N/Si-containing compound) promoted its flame retardancy and interfacial compatibility between APHZ and epoxy resin (EP). The test results revealed that EP/APHZ-3 composites achieved a V-0 rating and a notable LOI value of 30.7% when introducing 3 wt% APHZ into the EP matrix. Cone calorimetry tests (CCT) further demonstrated that the average heat release rate (av-HRR), total smoke production (TSP), and CO production (COP) of EP/APHZ-3 were reduced by 23.3%, 14.0%, and 21.1%, respectively. Meanwhile, the char residual was increased by 60.6%, as compared to pure EP. Furthermore, the flame-retardant mechanism of EP/APHZ composites was investigated by the XPS, TG-FTIR, and Raman spectroscopy techniques. The observed synergistic effect of the imidazole skeleton ZIF-8 and P/N/Si-containing compound in APHZ facilitated the generation of a dense multi-element char layer, with the condensed phase flame-retardant mechanism playing a dominant role. These findings contribute to developing and designing high-performance flame-retardant EP.

Experimental study on the combustion characteristics of carbon fiber composite materials coated in different coatings

The special environment in which the aircraft operates in terms of flight and safety assurance has special requirements for coating performance. Based on the combustion characteristics of four kinds of high-performance aviation coatings coated with carbon fiber composites, for parameters such as average ignition time and heat release rate of the composite, the results show that the carbon fiber composite has the longest average ignition time, Minimum heat release rate, while the 2-ethyl-4-Mylimidazole cured epoxy coated fiber composite had the shortest average ignition time. The maximum heat release rate was observed.

Improvement of heat release methodologies using mass loss calorimeter and oxygen consumption hood to assess flammability of wood plastic composites

The mass loss calorimeter provides a robust method for evaluating flammability of very sooty materials such as wood plastic composites as a lower cost and rugged alternative to the reliable and effective cone calorimeter. The high amounts of smoke and carbon monoxide associated with these materials resulted in a much-reduced heat release rate, resulting in incomplete combustion of the diffusion flame, which required modifications to the standards in measuring heat release rate via oxygen consumption or carbon dioxide production or thermopiles. In addition to liquid fuels of ethylene glycol and methanol, the solids polystyrene and polymethyl methacrylate were used as calibration materials for the mass loss calorimeter and the instrumented heat release rate hood. Because of concerns about the flue gas thermopile methodology for heat release rate measurements, a second thermopile was attached to the exterior of the metal pipe chimney typically used for heat release rate calculations in the mass loss calorimeter. A heat balance analysis indicated that this is an effective design compared with alternative designs. Estimates of flaming heat release rate are reported using both signals from the thermopiles for calculation of heat release rates and confirmed with the updated oxygen consumption analysis under an instrumented hood. This special fire test arrangement was used to assess the flammability of four different wood plastic composites, some with fire-retardant treatments, such as ammonium polyphosphate and brominated, all of which tended to have high smoke production leading to high-radiant energy losses. The reduction of heat release rate with 10% by content of fire-retardant treatment was confirmed by both heat release rate measures. The average heat release rate decreased 19% to 39% when fire retardants were added, relative to this wood flour–polyethylene composite.

Thermal Stability, Flame Retardancy and Flame Retardant Mechanisms of Hollow Glass Microspheres/Montmorillonite/Epoxy Sheet Molding Compound Composites

Epoxy sheet molding compound (ESMC) composites have excellent mechanical properties, dimensional stability and electrical insulation, and are widely used in the automotive industry. In our previous work silane coupling agent modified, hollow glass microspheres (SiHGM) and montmorillonite (MMT) were incorporated to enhance the mechanical properties of the ESMC composites. It was found that the ESMC composites containing MMT (EP/SiHGM/MMT-1) exhibited excellent mechanical strength. However, the flammability of the epoxy resin (EP) limits the use of ESMC composites for applications that require good flame retardancy. In this paper we describe our research in which MMT was used to increase the flame retardancy of ESMC composites. The results showed that the addition of MMT made the ESMC composites have excellent flame retardancy. The limiting oxygen index (LOI) of the ESMC composites containing 1 phr MMT (EP/SiHGM/MMT-1) was 26.8%, which was 8.94% higher than that of the ESMC composites without MMT (EP/SiHGM/MMT-0). In addition, the peak heat release rate (PHRR), average heat release rate (AHRR) and total heat release (THR) of the EP/SiHGM/MMT-1 were 322.8 kW/m2, 95.3 kW/m2 and 38.6 MJ/m2, respectively, which were 22.6%, 8.2% and 8.0% lower than those of EP/SiHGM/MMT-0. The carbon monoxide production (COP) and carbon dioxide production (CO2P) of EP/SiHGM/MMT-1 were 0.0092 g/s and 0.2071 g/s, respectively, which were 34.3% and 22.8% lower than those of EP/SiHGM/MMT-0. The fire growth index (FGI) of EP/SiHGM/MMT-1 was 2.4, which was a decrease by 29.4% compared to EP/SiHGM/MMT-0. In addition, the flame retardant mechanisms were revealed. We suggest that MMT promoted dehydration and charring of the epoxy resin and helped construct an intact physical barrier, which had good blocking effects. The prepared composite has great application prospects for those occasions that require high flame retardancy. Thus, this work provides an innovative strategy for preparing low density epoxy composites with excellent flame retardancy and high mechanical properties.

A Multi-Material Flame-Retarding System Based on Expandable Graphite for Glass-Fiber-Reinforced PA6.

A synergistic multi-material flame retardant system based on expandable graphite (EG), aluminum diethylphosphinate (AlPi), melamine polyphosphate (MPP), and montmorillonite (MMT) has been studied in glass-fiber-reinforced polyamide 6 (PA6). Analytical evaluations and fire performances were evaluated using coupled thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR) as well as cone calorimetry, UL-94 fire testing, and limiting oxygen index (LOI). A combination of EG/AlPi/MPP/MMT has been shown to provide superior flame-retarding properties when integrated at 20 wt.% into glass-fiber-reinforced PA6 (25 wt.%), achieving UL-94 V0 classification and an oxygen index of 32%. Strong residue formation resulted in low heat development overall, with a peak heat release rate (pHRR) of 103 kW/m2, a maximum of average heat release rate (MAHRE) of 33 kW/m2, and deficient total smoke production (TSP) of 3.8 m2. Particularly remarkable was the structural stability of the char residue. The char residue could easily withstand an areal weight of 35 g/cm2, showing no visible deformation.

Design of Experiments-Based Fire Performance Optimization of Epoxy and Carbon-Fiber-Reinforced Epoxy Polymer Composites.

The fire performance of epoxy and carbon-fiber-reinforced polymer (CFRP) composites with and without fire retardants (FR) (i.e., ammonium polyphosphate (APP), aluminum trihydroxide (ATH), melamine (MEL), expandable graphite (EG)) was investigated. A design of experiment (DoE) approach was applied to study the single- and multifactorial effects of FR. The fire performance of epoxy and CFRP was evaluated by limiting the oxygen index (LOI) and heat release, which were obtained by limiting the oxygen index test and cone calorimetry. It was found that mixtures of 70 wt.-% epoxy, 24.6 wt.-% of APP, and 5.4 wt.-% MEL resulted in the highest LOI level of 45 within tested groups for epoxy resin and also for CFRP specimens (LOI level of 39). This mixture also resulted in the lowest average heat release rate (HRR180s) of 104 kW·m-2 and a spec. total heat release (THR600s) of 1.14 MJ·m-2·g-1, indicating the importance of balancing spumific and charring agents in intumescent systems and synergy thereof.

Synthesis of multi‐element hybrid polyphosphonitrile microspheres and their flame retardant application in epoxy resins

AbstractIn this paper, Salen‐Ni basis polyphosphazene microsphere (Salen‐PZN‐Ni), boric acid (BA), and 3‐aminopropyltriethoxysilane (KH‐550) were used as raw materials to prepare a new flame retardant Salen‐PZN‐Ni@BA@KH‐550 by surface modification. The thermal and flame retardant properties of epoxy resin (EP) composites were studied. The introduction of Salen‐PZN‐Ni@BA@KH‐550 refined the thermal stability of EP composites, as well as the amount of carbon residue at 800°C. At 5 wt% of Salen‐PZN‐Ni@BA@KH‐550, the limiting oxygen index (LOI) of EP composites is increased from 25.4% to 30.5% and UL‐94 has been achieved with a V‐1 rating. Meanwhile, the mechanical properties of Salen‐PZN‐Ni@BA@KH‐550/EP composites were also improved. In addition, the good char formation ability of Salen‐PZN‐Ni@BA@KH‐550 caused the reduction of peak heat release rate, total heat release rate, maximum average heat release rate and total smoke generation of the EP composites. All these results indicate that Salen‐PZN‐Ni@BA@KH‐550/EP composites have a wider range of applications.

Fire Risk of Polyethylene (PE)-Based Foam Blocks Used as Interior Building Materials and Fire Suppression through a Simple Surface Coating: Analysis of Vulnerability, Propagation, and Flame Retardancy

Building fires can spread through surface combustion of both combustible and interior finishing materials. Recently, the use of foam blocks as interior materials for high-rise residential buildings has increased. However, as foam blocks are primarily composed of polyethylene, they are not flame-retardant and can readily burn and the fire can spread, leading to large-scale damage. Herein, the fire hazard and diffusion characteristics of foam blocks were compared with those of flame-retardant and general wallpapers to confirm the risk of fire. The fire risk of the foam blocks was confirmed using flammability, cone calorimetry, and spread-of-flame analyses. Based on a comparative analysis of the fire risk of foam blocks, the average total heat release was 11.2 MJ/m. This is approximately three times higher than the average heat release rate of the flame-retardant wallpaper and approximately two times higher than that of the general wallpaper. The foam blocks ignited rapidly owing to fire and generated large amounts of combustion gas and heat. To prevent such a fire, 5 wt% montmorillonite (MMT) was simply coated after surface modification to suppress the occurrence of fire. Various flame-retardant materials, surface modifications, and fire safety systems must be developed to prevent fire hazards.

Large eddy simulations of pilot-stage equivalence ratio effects on combustion instabilities in a coaxial staged model combustor

In this paper, the effects of pilot-stage equivalence ratio on combustion instabilities in a coaxial staged model combustor are investigated using the Wall-Modeled Large Eddy Simulation. The global equivalence ratio is maintained constant, and the Stratification Ratio of the first main-stage and the second main-stage is set to 1; the dynamic mode decomposition and system identification methods are employed to analyze the flame dynamics, velocity, heat release rate modes, and flame transfer function (FTF) of the model combustor under different pilot-stage equivalence ratios. The results show that when the pilot-stage equivalence ratio is 0.6, the oscillation amplitude of heat release rate (HRR) exceeds 7.5% of the global average HRR, and the velocity oscillation and the global HRR oscillation in the combustor are coupled. As the pilot-stage equivalence ratio increases to 0.8, the oscillation amplitude of HRR decreases to 2.5%, and the oscillation of velocity and global HRR in the combustor are decoupled. Furthermore, the maximum value of FTF decreases from 3.5 to below 1 with the increase in the pilot-stage equivalence ratio.

Numerical study on rotating detonation combustion with the discrete distribution of partially pre-vaporized n-heptane sprays

The rotating detonation engine (RDE) is a novel aerospace propulsion device, with liquid fuel playing a pivotal role in enabling the practical implementation of the RDE. The Eulerian-Lagrangian simulation is used to analyze a two-dimensional rotating detonation combustion with partially pre-vaporized n-heptane sprays. The investigation aims to examine the influence of various inlet area ratios (ψ) on both the droplet evaporation and rotating detonation combustion within the combustion chamber. The findings indicate that a smaller ψ is advantageous for droplet evaporation within the fuel filling area, and the droplet traverses sequentially through the acceleration layer, the deceleration layer, and the re-acceleration layer within this region. With a relatively large ψ, a burned gas bump becomes evident on the deflagration surface, augmenting the evaporation rate of droplets within its proximity. The droplet continues to accelerate within the fuel filling area, while its velocity remains low at the burned gas bump. Furthermore, spot-like diffused flames emerge subsequent to the RDW, with their area expanding to the increase in ψ. Meanwhile, the average heat release rate (HRR) and thrust within the combustor of the rotating detonation engine (RDE) demonstrates diverse oscillation patterns in response to changes in ψ. In this study, when the inlet area ratio is around 0.6, the RDE obtains the most stable average HRR and thrust.