Combustion Dynamics Research Articles

Pointwise space–time estimates for compressible Navier–Stokes equations for a reacting mixture

AbstractIn this paper, we consider the pointwise space–time behaviors of solutions for the dynamic combustion of compressible reactive mixture. The pointwise estimates of global solutions are established in the whole space by using the Green's function method. These estimates also show the wave propagation of the solution. As a by‐product, the ‐norm decay rates of the solution are achieved.

Measurements of self-excited instabilities and nitrogen oxides emissions in a multi-element lean-premixed hydrogen/methane/air flame ensemble

Understanding the distinguishing physical properties of multi-element lean-premixed high hydrogen content flames is expected to be integral to the development of carbon-neutral, and ultimately carbon-free, gas turbine combustion systems. Despite their fundamental importance, the thermoacoustic and emission-related characteristics of such small-scale flame ensembles are not thoroughly understood, particularly for the full range of 0 to 100% hydrogen content blended with methane fuel. Here we investigate the structure and collective behavior of a multi-element lean-premixed hydrogen/methane/air flame ensemble using measurements of nitrogen oxides emissions and self-excited instability, combined with OH* and OH PLIF flame visualizations. Our results indicate that the system's responses can be classified into several distinctive stages according to their static and dynamic stability, including flame blowoff and thermoacoustically stable regions under relatively low hydrogen concentration conditions, low-frequency self-excited instabilities in intermediate hydrogen concentration, and triggering of intense pressure perturbations at about 1.7 kHz under high- or pure hydrogen combustion conditions. While the low-frequency combustion dynamics are dominated by axisymmetric translational movements of parallel flame fronts, the higher frequency response originates from significant lateral modulations accompanied by small-scale vortical rollup and flame surface annihilation due to front merging and pinch-off. Longitudinal-to-transverse dynamic transition is observed to play a mechanistic role in kinematically accommodating higher-frequency heat release rate fluctuations, and this newly identified mechanism suggests the possibility of high-frequency transverse modes, if such lateral motions are strong enough to induce inter-element flame interactions. In contrast to the substantial differences in thermoacoustic properties for different fuel compositions, the total nitrogen oxides emissions are found to depend primarily on adiabatic flame temperature; the influence of fuel composition is limited to approximately 20% under the inlet conditions considered.

Experimental investigation of transition process from LTC to ITC and HTC during diesel spray combustion at low ambient temperatures

The dynamics of low temperature combustion (LTC) and intermediate temperature combustion (ITC) dramatically affect the combustion limits and properties of high temperature combustion (HTC) and engine performance. To reveal the transition from LTC to ITC and HTC and the characteristics of heat release in spray combustion under low ambient temperatures, optical experiments were conducted in a constant volume combustion chamber (CVCC). The high-speed natural luminosity method and the high-speed schlieren method were used to obtain images of the evolution of spray ignition and vapor-phase spray combustion, respectively. The results reveal a significant increase in CVCC pressure when the flame luminosity is not captured by the high-speed natural luminosity method at a low ambient temperature (740 K), which is attributed to heat release by the LTC process. The cumulative heat release obtained from the first law of thermodynamics based on pressure attains 29.72 % of the total lower heating value of the fuel. The transition from LTC to ITC and HTC is diagnosed based on the luminosity variation of the vapor-phase spray tip region in the schlieren images. Furthermore, the transition from LTC to ITC and HTC can be monitored based on the average luminosity of the spray tip. Finally, with the decrease in ambient temperature, the end of LTC is gradually delayed by a smaller magnitude and rate of change. These results demonstrate that the transition from LTC to ITC and HTC is sensitive to ambient temperature.

Numerical and experimental study of co-combustion of refuse-derived fuels in a circulating fluidized bed during load change

This study presents a comprehensive dynamic process simulation model of a 1 MWth circulating fluidized bed test facility applied for lignite and refuse-derived fuel co-combustion. The developed dynamic process simulation model describes the circulating fluidized bed riser and the supplying system with a high level of detail considering heat transfer, gas-solid interaction, combustion, and fluid dynamics. The model was first tuned at two steady-state operation points and was then validated by the measured data from a long-term test campaign of the 1 MWth circulating fluidized bed test facility at various loads (60%–80% to 100%). During the load changes, the simulated pressure and temperature profiles along the combustor as well as the flue gas concentrations agree very well with the measurement data. Finally, increasing the proportion of waste-derived fuel in the co-combustion process was investigated to evaluate the flexibility of its use in power generation to further reduce CO2 emissions.

Investigating a deterministic yet computationally cheap combustion parameter for model predictive control of a CNG-diesel RCCI engine

This study investigates the changing deterministic features of the cycle-resolved location of maximum pressure and its correlation with combustion phasing for dynamical transitions in the combustion of a CNG-Diesel RCCI engine. The investigation is performed using nonlinear dynamical and chaotic methods such as return maps, recurrence, and cross recurrence plots. The experiments are performed on a single-cylinder automotive engine operated in RCCI mode with the aid of the development ECU. The experiments are conducted by running the engine at a fixed engine speed of 1500 rpm and a load of 3 bar BMEP. Diesel fuel is injected directly into the cylinder by following a double injection strategy using an equal amount of fuel in both the pilot and main injections. The effect of the start of main injection timing of diesel on combustion dynamics is investigated at two different masses of CNG. The predominance of deterministic periodic features is discovered in the cycle-resolved dynamics of the engine combustion during the RCCI regime. Results show that with advancement in diesel injection timing, the mode of combustion shifts from conventional dual fuel to RCCI, and this shift is coupled to the onset of noisy periodic-2 bifurcations., The periodic-2 behavior even transforms to periodic-3 and 4 with an increasing advancement in diesel injection timing for engines operating with a higher CNG mass. For most of the operating conditions, the deterministic features in the location of maximum pressure are comparable with that of combustion phasing. Recurrence and cross recurrence plots-based methodology advocates for the existence of strong correlations or at least a phase synchronization between the location of maximum pressure and combustion phasing when the engine operates in the RCCI regime, irrespective of diesel injection timing and amount of port-injected CNG fuel. The presence of similar deterministic features in the location of maximum pressure and combustion phasing and a strong relationship between these two at intermediate diesel injection timings in the RCCI regime for both the CNG masses makes this regime most suitable for using the location of maximum pressure as a feedback/controlled parameter for model predictive control of the engine.

Dynamics of Premixed Flames Near Lean and Rich Blowout

ABSTRACT Practical combustors in furnaces, industrial heaters, and gas turbine engines face a sudden loss of flame due to rich blowout (RBO) at an extremely rich fuel-air mixture or lean blowout (LBO) at an extremely lean fuel-air mixture. Thus, the stability limits of the combustion regime are governed by RBO and LBO. In the present study, we focus on the dynamics of swirl-stabilized premixed combustion near lower and higher flammability limits, where the possibilities of LBO and RBO, respectively, are observed. Near RBO and LBO, we employ metrics from statistics and dynamical systems theory to characterize the transition in flame dynamics. We observe that the range of frequencies obtained using Fourier Transform near RBO and LBO is alike. The emergence of dominantly low-frequency oscillation near those blowout limits is investigated using Hilbert Transform. The mean frequency of the combustion system gradually reduces near both blowout limits due to behavioral oscillations prominently observed. The scaling property of flame oscillation is examined using the Hurst exponent, and we observe a decreasing trend of the parameter as combustion approaches both LBO and RBO. Therefore, for the gradual reduction of the Hurst exponent near both flammability limits, we can use the parameter as a precursor for both RBO and LBO.

Mitigation of combustion instabilities by local diluent injection in a premixed swirl stabilized combustor

In this paper, we study the impact of injecting diluent gas into the outer recirculation zone of a swirl stabilized premixed methane/air flame on the flame shape and combustion dynamics. Two modes of instability were observed, a low frequency mode at 8–12 Hz which corresponds to a flame flickering mode in the outer recirculation zone and a high frequency thermo-acoustic instability at 250–275 Hz. Furthermore, air, N2 and CO2 were injected into the outer recirculation zone, at mass flow rates of at 1% and 3% compared with the main flow of premixed methane/air. The diluent addition shifts the outer recirculation zone flickering mode of instability to higher equivalence ratios and completely damps the thermo-acoustic instability for the current experimental conditions. Changing the diluent composition from air to N2 and to CO2 improved the extent of instability mitigation displaying the influence of diluent gas on the chemical kinetic in the ORZ region. Furthermore, the impact of the different diluent compositions on mitigating the combustion instability scaled according to the extinction strain rate of the diluted mixture in the outer recirculation zone.

Component-Based Reduced Order Modeling of Large-Scale Complex Systems

Large-scale engineering systems, such as propulsive engines, ship structures, and wind farms, feature complex, multi-scale interactions between multiple physical phenomena. Characterizing the operation and performance of such systems requires detailed computational models. Even with advances in modern computational capabilities, however, high-fidelity (e.g., large eddy) simulations of such a system remain out of reach. In this work, we develop a reduced‐order modeling framework to enable accurate predictions of large-scale systems. We target engineering systems which are difficult to simulate at a high-enough level of fidelity, but are decomposable into different components. These components can be modeled using a combination of strategies, such as reduced-order models (ROM) or reduced-fidelity full-order models (RF-FOM). Component-based training strategies are developed to construct ROMs for each individual component. These ROMs are then integrated to represent the full system. Notably, this approach only requires high-fidelity simulations of a much smaller computational domain. System-level responses are mimicked via external boundary forcing during training. Model reduction is accomplished using model-form preserving least-squares projections with variable transformation (MP-LSVT) (Huang et al., Journal of Computational Physics, 2022, 448: 110742). Predictive capabilities are greatly enhanced by developing adaptive bases which are locally linear in time. The trained ROMs are then coupled and integrated into the framework to model the full large-scale system. We apply the methodology to extremely complex flow physics involving combustion dynamics. With the use of the adaptive basis, the framework is demonstrated to accurately predict local pressure oscillations, time-averaged and RMS fields of target state variables, even with geometric changes.

Numerical investigation of turbulent flame-vortex interaction in premixed cavity stabilized flames

The combustion dynamics of a mixture of ethylene and air in a cavity flameholder are examined using high-resolution numerical simulations. The simulations are performed using both laminar and turbulent inflow boundary conditions to characterize the effects freestream turbulence on the flame-vortex interactions within the combustor. Experimental test results are utilized to validate the simulation's ability to capture the relevant flow and flame behavior. The turbulence intensity is shown to influence the structure of the flow field by creating a more dominant primary vortex within the combustor and decreasing the shear layer reattachment length. The integral length scales and energy spectra are calculated throughout the domain and show that the flow is driven by smaller turbulent eddies within the ramp region of the combustor. The flame-vortex interaction is further examined and revealed to cause an instability forming in the combustor under both laminar and turbulent conditions. The instability is confirmed by examining the pressure fluctuations within the combustor and it is demonstrated that the time scale of the pressure fluctuations corresponds to the frequency of the vortex shedding from the ramp wall.

Numerical Analysis of Combustion Dynamics in a Full-Scale Rotating Detonation Rocket Engine using Large Eddy Simulations

Abstract Large eddy simulations (LES) using detailed chemistry and leveraging adaptive mesh refinement (AMR) are performed to gain insights into the combustion dynamics within a full-scale methane-oxygen non-premixed rotating detonation rocket engine (RDRE) employing impinging discrete injection schemes. In particular, a comparative analysis of two operating conditions corresponding to the same global equivalence ratio but different mass flow rates is carried out to investigate the resultant impact on detonation wave characteristics and RDRE global performance. Multiple co-rotating detonation waves with spatially-distributed wave structure and preferential alignment with the inner wall of the annulus (due to asymmetry in fuel distribution) are encountered under both conditions. Both cases exhibit pre-detonation deflagrative burning in the fill region, while one of the cases shows higher susceptibility to backflow into the feed plenums due to lower plenum pressures. Heat release analysis shows that the thrust obtained from the RDRE is closely linked to the distribution of total heat release between detonative and deflagrative combustion. On the other hand, combustion efficiency is associated with the fraction of heat release occurring in fuel-rich versus fuel-lean regions within the RDRE.

Numerical analysis on the combustion characteristic of lithium-ion battery vent gases and the suppression effect

The combustion of Lithium-ion battery (LIB) vent gases plays key roles in determining LIB fire hazard. Previous studies analyze the combustion of LIB vent gases without consideration of electrolyte. This work studies the combustion characteristic of LIB vent gases with dimethyl carbonate (DMC) addition. The flammability limit, laminar burning velocity (LBV), flame temperature and heat production are explored. For different components of LIB vent gases, most of combustion parameters decrease or remain unchanged with addition of DMC. It demonstrates that the fire risk of LIB vent gases reduces with DMC addition. Moreover, the influences of H2O, C6F12O (Novec-1230) and POCH3(OCH3)2 (DMMP) on LIB vent gases flame are investigated. At Φ = 1.0, all three suppressants suppress the flame. The lowest and highest suppression efficiency are H2O and DMMP. At Φ = 0.45, Novec-1230 enhances combustion, but DMMP reduces LBV which is quite different from the enhancement effect on CH4/air flame. This is mainly because of the reducing of O free radical and heat production. The sensitivity and path reaction of DMMP indicate that phosphorus species play important roles in suppressing lean flame. This work could deepen understanding of LIB vent gases combustion dynamics and provide guidance for choosing appropriate suppressants of LIB fire.

Combustion dynamics of droplets of aqueous slurries based on coal slime and waste oil

This paper shows the analysis of burnout characteristics of droplets of the following slurry fuels: (i) based on coal slime with or without the addition of waste turbine oil; (ii) based on coal dust with or without the addition of waste turbine oil. The oil share in the mixtures varied from 0% to 15%. The solid component share varied in the range of 40–60%. Single droplets with an initial size of 1–5 mm were burned in a tubular muffle furnace at temperatures of 700–900 °C. The inertia of gas-phase and heterogeneous ignition and the combustion time of mixtures were estimated. Based on experimental data, the values of the linear and mass burnout rates of fuel droplets were calculated. At a furnace temperature of less than 800 °C, the characteristics of ignition and burnout of droplets of water-containing fuel mixtures and solid particles deteriorated significantly. The most preferred is the combustion of coal slime in the composition of aqueous slurry with the addition of high-reactive components (for example, waste oil of petroleum origin or vegetable oils). To intensify ignition and combustion, it is recommended to use no more than 50% of the solid component in the mixture. The maximum linear burnout rate was typical for droplets about 3 mm in size and reached values of 0.5–0.6 mm2/s. The mass burnout rates of droplets of the investigated fuels with a size of 5 mm varied in the range of 0.0005–0.0018 g/s.

Investigation of the chemical effect of pilot injection on main combustion in a gasoline controlled auto-ignition engine by in-cylinder measurements and numerical simulation of H2O2, HO2, and OH radicals

Compared to conventional combustion in gasoline engines, Gasoline Controlled Auto-Ignition (GCAI) has the potential to significantly reduce both fuel consumption and nitrogen oxides (NOX) raw emissions. However, GCAI combustion still has a limited operating range due to limitations in combustion stability at low loads and high rates of cylinder pressure rise at high engine loads. Previous research identified hydrogen peroxide (H2O2) decomposition as an effective means to control GCAI, which is formed among other species with pilot fuel injection during the negative valve overlap (NVO) phase. Since the chemical effect of H2O2 on the main combustion has not been experimentally confirmed so far, the aim of the experimental study described in this paper is to detect H2O2 during early compression using optical methods. This is approached by conducting Photofragmentation Laser-Induced Fluorescence (PFLIF) of H2O2 by a pump laser and simultaneous hydroxyl radical Laser-Induced Fluorescence (OH-LIF) detection in the combustion chamber of a dedicated GCAI single-cylinder research engine at low loads after NVO with pilot injection (PI). Thereto, the pilot injection strategy as well as the global air/fuel ratio (AFR) are varied. Interestingly, no H2O2, hydroxyl (OH) or hydroperoxyl (HO2) constituents were detected under the operating conditions studied, despite relatively high pilot injection fuel masses and a highly accurate H2O2 detection limit of about 1 ppm. Numerical three-dimensional computational fluid dynamics (3D-CFD) combustion simulations using a semi-detailed reaction kinetic mechanism predicted 5–8 times higher H2O2 concentrations than the detection limit, yielding an uncertainty estimate of the numerical methods. Furthermore, the 3D-CFD simulations showed a significant mixture stratification which is a possible reason for the lack of H2O2 detection under these operating conditions.

Effect of inlet flow turbulence on flame–vortex dynamics during thermo-acoustically induced flame flashback in a premixed dump combustor

The present article reports the investigation on the effect of inlet flow turbulence on flame–vortex dynamics during the thermo-acoustically induced flame flashback in a premixed dump combustor. The inlet turbulence intensity can be varied independently of the Reynolds number by using plates of different slot widths and is placed significantly upstream of the nominal flame-stabilization zone. The study aims to experimentally address the flame flashback behavior and the conventional combustion dynamics mechanisms involving flame–vortex interaction. The reacting flow-field is characterized using high-speed simultaneous measurement of dynamic pressure fluctuation with the time-resolved/phase-resolved visualization of flame and flow-field utilizing CH*/OH* chemiluminescence and particle image velocimetry. We note that higher turbulence intensity delays the onset of combustion dynamics and significantly influence the flame flashback behavior. In the present work, we observed two types of flame flashback behavior with large amplitude oscillations — (a) intermittent flame flashback, which relates to upstream flame displacement during certain phases of the acoustic pressure cycle and (b) permanent flame flashback, which results in flame quenching. The results reveals that the recirculation zone length plays a key role in determining the flame flashback. The role of enhanced turbulence is seen in two effects- (1) Dictating the length of the recirculation zone and (2) The modulation of the flame by the wake vortex, which correlates with the tendency of flame to flashback directly.

Interpretative Review of Diesel Spray Penetration Normalized by Length and Time of Breakup (Similarity Law of Diesel Spray and Its Application)

Tip penetration of diesel spray is one of the most useful parameters to evaluate diesel combustion dynamics. It has strong relationships with ignition delay, premix/diffusion combustion and engine performance, including exhaust emissions. To discuss general combustion physics in various size sprays, non-dimensional expression of spray tip penetration is reviewed. Length and time of injected fuel jet breakup can be considered as characteristic length and timescale of diesel spray. Then, normalized penetration by length and time of breakup was proposed for the scaling of various diesel sprays. Using the proposed scaling method and similarity law, tip penetrations of various size sprays are collapsed into one simple expression. It becomes a base of similarity law of diesel spray. For example, local or average A/F is uniquely expressed by the normalized length and time of breakup. Penetration of a wall impingement spray is also expressed uniquely by this normalization method and physical parameters affecting the wall impingement spray are explained. Injection rate shaping effect at an initial stage of injection is clearly demonstrated by using this scaling. Further, mixing degrees of diesel spray at an ignition timing and in a combustion phase can be reasonably explained by the equivalence ratio change with non-dimensional elapsed time after injection start.

Effects of intake charge temperature and relative air-fuel ratio on the deterministic characteristics of cyclic combustion dynamics of a HCCI engine

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios ([Formula: see text]) and intake air temperatures ([Formula: see text]) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ([Formula: see text]) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that [Formula: see text] is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in [Formula: see text] and any deviation in intermediate values of [Formula: see text]. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while [Formula: see text] at lower engine speed. Strong coupling and synchronization between [Formula: see text] and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture.

Combustion dynamics of crude and upgraded Thermal DeOxygenation oils in a compression ignition engine

Thermal DeOxygenation (TDO) is a robust thermochemical conversion scheme to produce hydrocarbons from biomass feedstock. The process targets the carbohydrate fraction of biomass to yield a broad mixture of primarily aromatic hydrocarbons within a boiling point range of 348–798 K with low oxygen content (<4 wt%). The resulting materials are amenable to traditional hydrotreating and distillation processes with approximately 70% by mass in the distillate fuel range. The simple conversion scheme combined with commercially viable upgrading routes makes TDO oils a feasible alternative fuel for transportation applications. This paper is the first systematic treatment of fit-for-purpose testing of TDO oils in a compression ignition engine. Blends of partially upgraded TDO oils (e.g. whole oil, distilled oil, hydrotreated oil and hydrotreated-distilled oil) are prepared with certified ultra-low sulfur diesel at 5%, 10%, 15% and 20% by volume. The resulting fuels are analyzed for fuel characteristics and combustion dynamics in an instrumented single-cylinder compression ignition engine. All fuel blends at 10% blend level by volume exhibited adequate engine performance. Hydrotreating of the oils is a necessary step to meet cetane number and EPA soot emissions requirements at 20% blend volume. Combined distillation and hydrotreatment meet or exceed all fuel specification and engine performance benchmarks. Partially upgraded TDO oils are suitable fuel options for compression ignition applications.

Thermal characterization of straight and curve edge blade liquid fuel swirl burner

Accurate monitoring and controlling of the temperature in the combustion chamber can raise the burner efficiency, combustion intensity, fuel consumption and reduce pollutant emission. However, except combustion is accurately monitored and controlled, high concentration of pollutant gases and products like carbon monoxide (CO) and soot can form in the combustion chamber. This paper compares the combustion thermal profiles in a liquid fuel swirl burner using developed straight edge and curve edge blade swirlers at (20, 30, 40, 50 and 60)° for 6, 8, 10 and 12 number of blades in order to optimize the temperature of the burner. Measurements were made in straight and curve blades liquid fuel swirl burner in order to study and compare the thermal characteristics of the straight and curve edge blades in optimizing the combustion dynamics. Similarly, measurements were made for burner without swirl generator and the combustion temperature assessed. Thermal profile was measured in the direction of flow via the six axial ports at distance ((d) =150, 350, 550, 750, 950 and 1150 mm) from the burner exit using Chromium-Zinc thermocouple. Results showed that the wavelength and oscillation of temperature decay in the same type of blade followed the same trend and the peak of combustion intensity is nearer the nozzle for curve edge blades than the straight edge blade. Six (6) blades performed best with the highest temperature in all the ports, while 12 blades gave the least performance. Findings further show that curve edge blade swirlers gave better performance than straight edge blade swirlers with highest temperature of (1065 and 1015) °C, respectively. Hence, it is recommended especially where high temperature and stability application is desirable

Do flame describing functions suitably represent combustion dynamics under self-sustained oscillations?

Transfer function concepts that appear in many areas and most notably in control systems have been extensively used to represent the flame response in low-order models of combustion instability. Much of the theoretical work is based on flame transfer functions (FTFs). In recent years, its nonlinear extension, namely the flame describing function (FDF), has been used to get a more accurate representation of the flame response when the level of oscillation becomes large and the system reaches a limit cycle. Despite their wide and reasonably successful use in predicting instabilities, the direct validity of using FTF/FDFs to represent the flame response still remains to be experimentally substantiated. This article is aimed at providing a direct assessment of the capacity of the FDF to suitably describe the flame behavior under self-sustained oscillations (SSOs) for a spray-swirl flame anchored by an injector that is weakly-transparent to acoustic waves. This is accomplished by making use of an experimental combustion configuration that not only exhibits unstable oscillations but also features a set of driver units to modulate the flame (namely stable flame modulation or SFM). The flame is modulated at the frequency of SSO, and the amplitude of incident velocity modulations is then progressively varied until it coincides with that found under SSO. The injector dynamics is shown to be different between SSO and SFM for an injector that is weakly-transparent to acoustic waves and imposes a certain degree of decoupling between plenum and chamber. For such injectors, the FDF built with the upstream velocity would not suitably represent SSO, as this lumps the injector and flame dynamics together. It is then important to use velocity measurement at the injector outlet, at a point where the relative velocity fluctuation matches the relative volumetric flow rate fluctuation. The describing function with velocity reference at the injector outlet is measured for various input levels and found to approximately match those measured under SSO. The best match is obtained when the amplitude of external modulation induces a level of velocity oscillations that comes closest to that prevailing under SSO. This demonstrates that the FDF may suitably capture the nonlinearity of the flame response, at least in the configuration investigated in this research.

Investigating the Effects of H2O Interaction with Rainscreen Façade ACMs During Fire Exposure

Preliminary investigations into adverse reactions between aluminum alloy sheets, used as facings for aluminum composite material rainscreen panels, and water vapor (2Al + 3H2O −> Al2O3 + 3H2) contributing to high-rise façade fire events are reported. Panels containing a PE blend (70% polyethylene 30% calcium carbonate) core were characterised and subsequently exposed to a surface irradiance of 50 kW/m2 using a cone calorimeter, in modified ISO 5660:1/ASTM 1354 procedures, involving water spray. Inverse modeling techniques were applied to determine the effects of water spray on the samples’ combustion parameters. From the current study, evidence for the liberation of diatomic hydrogen (H2) contributing to peak heat release rate during combustion was not found. Observed thermal shock and subsequent degradation led to a greater surface area exposure of combustible inner core material, contributing to an increase for both peak heat release rate (from 393 kW/m2 to 1040 kW/m2) and total energy release (97 MJ/m2 to 117 MJ/m2). Findings suggest no significant increase in the combustibility of aluminum composite panels arises through reduction–oxidation reactions between aluminum-water at 50 kW/m2 irradiance. However, thermomechanical processes, brought upon by environmental conditions and external intervention, may affect the dynamic combustion behavior of aluminum composite panels.