Thin film-substrate systems are important in many technologies, and their performance often depends on the film-substrate interfacial adhesion. Conventional adhesion tests face significant challenges when applied to thin, compliant, or ductile film-substrate systems. In a recent computational study, we demonstrated that shock-tube bulge tests can, in principle, probe interfacial adhesion in such systems. Here, we conduct proof-of-concept experiments to validate this approach using bilayer foils composed of nanoporous gold (NPG) films on white-gold substrates. NPG films were produced by dealloying one surface of the parent alloy, generating as-dealloyed foils with fine ligaments, while annealing as-dealloyed foils generated coarsened ligaments. Both foils were subjected to shock-tube bulge tests up to the same maximum pressure. The annealed foils exhibited larger bulge deflections than the as-dealloyed foils and underwent interfacial delamination. By comparing the measured bulge deflection with finite element results obtained using known substrate properties, we inferred the yield strength of the as-dealloyed NPG film, consistent with prior measurements. By comparing measured delaminated areas with finite element predictions, we inferred a lower-bound adhesion strength for the as-dealloyed foils and estimated the adhesion strength for the annealed foils. Our results show that annealing not only coarsens the NPG ligaments and reduces the strength, but also significantly weakens the film-substrate interface. Shock-tube bulge testing coupled with finite element modeling offers a promising method for evaluating film properties and film-substrate adhesion.

The key features of the gas-phase combustion behavior of ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) can be represented by a surrogate mixture of ammonia (NH3), hydrocarbon (CH4), and chlorine precursors (CHCl3 or CCl4). New measurements of chlorinated species (HCl) and CO (Carbon Monoxide) time-history profiles were performed in shock tubes using laser absorption diagnostics. The experiments were carried out for CHCl3/CH4/NH3 and 0.1 CCl4/0.9 CH4 oxidation at an equivalence ratio (phi) of 1.0 in 99.5% He/Ar with temperatures ranging from 1460 to 2340 K, and near-atmospheric pressure. Both CHCl3 and CCl4 provided Cl radicals successfully via the reactions CHCl3 reversible arrow CCl2+HCl, 2CCl2 reversible arrow C2Cl3+Cl, and CCl4 reversible arrow CCl3+Cl. Consequently, the Cl interactions were directly observed with CH4 and NH3, such as CH4+Cl reversible arrow CH3+HCl and NH3 + Cl reversible arrow NH2 + HCl. Additionally, the 0.1 CCl4/0.9 CH4 mixture exhibited two major reaction pathways: 1) from the precursor CCl4 described as CCl4 -> CCl3 -> COCl2 -> CClO -> CO, and 2) from the CH4 submechanisms with the reaction CH3 + Cl reversible arrow CH2 + HCl. Finally, the model assembled in this study performs rather well for a preliminary version, but improvements are still necessary.

Exposure to high-temperature surfaces accelerates the deterioration of lubricants and fuels in operation, often to the point of solid coke or sludge formation. The high operation and oil-sump temperatures of gas turbines also increase the risk of undesired oil fires which is also affected by the lubricant's flammability. In addition, fuels used in jet engines that use regenerative cooling technology may also deteriorate due to high temperatures encountered before entering the combustion chamber. The present work explores the effect that thermal and oxidative degradation, caused by exposure to high-temperature surfaces, has on the ignition characteristics of a turbine lubricant, a motor oil (Castrol GTX 20W-50), and JP-5. All three hydrocarbons were exposed to high-temperature surfaces, up to 573 degrees C (and bulk fluid temperatures between 137 degrees C and 247 degrees C), under a controlled inert or oxidative environment which resulted in the formation of solid coke or sludge deposits. Oil and fuel samples collected at the end of the aging cycles were then injected into a shock tube using a custom endwall injection method to study their ignition delay time (IDT). It was found that the aging process decreased the fluids' activation energies when aged in an inert environment but appears to increase the values when aged in an oxidative environment. The resulting activation energies were in the range of 26-58.7 kcal/mol for the lubricants and 42-64.2 kcal/mol for JP-5.

A novel experimental procedure was created to study laminar flame speeds of lubrication oil and lubrication oil-methane fuel blends. Oil mist mixed with methane and ignited in a spherical flame speed rig at atmospheric conditions yields experimental flame speed data pertinent for engine applications. A similar procedure was followed for oil-air experiments. Results show some flame kernel formation, although lubrication oil ignition in atmospheric air (phi = 0.6), elevated oxygen-content air, and high-pressure air environments is limited. Flame speeds of lubrication oil methane-air blends were studied for equivalence ratios of 0.7 to 1.4. The lubrication oil mist amount ranged from 30% to 45% (1.2 to 1.3 g lubrication oil) of the fuel composition, dependent on equivalence ratio. Fuel blend flame speeds were 28% to 40% (5-15 cm/s) slower than both neat methane-air flame speeds and n-hexadecane-methane-air model predictions. To understand why the fuel blend flame speed is significantly lower, the lubrication oil's effect on gas density, adiabatic flame temperature, mixture equivalence ratio, and heat of vaporization were investigated. Addition of lubrication oil slightly lowers gas density ratio (by 0.01) and richens overall mixture equivalence ratio (0.3-0.4) compared to neat methane-air flames. Adiabatic flame temperature of the fuel blend is similar (within a 22 K difference) to that of a methane-air flame. However, a significant difference in the adiabatic flame temperature occurs between methane-air and fuel blend flames (around a 200 K decrease) when the energy required for the oil vaporization is considered, which relates to the decrease in flame speed through trendline behavior.

The pyrolysis and oxidation of propan-1-ol were investigated in this work, providing new experimental data that highlight the limitations of the most recent detailed kinetic mechanisms available in the literature. The new data, obtained near atmospheric pressure, consist of shock-tube CO time-history profiles measured behind reflected shock waves using laser absorption diagnostics near 4.6 mu m. Pyrolysis experiments were conducted with mixtures of propan-1-ol highly diluted in He/Ar (20/79.75%) within a temperature range of 1217 to 1592 K. Oxidation was studied at three different equivalence ratios, phi = 0.5, 1, and 2, using highly diluted mixtures of propan-1-ol/ O2/ He/Ar (20/79.5% He/Ar) over a temperature range of 1284 to 1696 K. Under these high-temperature conditions, accounting for the pressure dependency of the rate constants of unimolecular initiation reactions (including dehydration) is of paramount importance. Channel-specific rate constants were therefore theoretically determined using variable reaction coordinate transition state theory in the temperature and pressure ranges of interest for propan-1-ol pyrolysis and combustion. These theoretical results, together with a recent work on Habstraction reactions by H and OH, and the reactions of the successive C3H7O radicals, were incorporated into a detailed kinetic mechanism able to predict CO formation. This mechanism was also successfully tested against experimental data obtained under various conditions in the literature. Rate-of-production analyses were performed and showed that CO formation is positively sensitive to the decomposition of propan-1-ol into ethyl and hydroxymethyl radicals during the early stages of the reaction, while the formation of the beta-radical by Habstraction inhibits CO formation.

ABSTRACT Hydrogen chlorine (HCl) is an important combustion intermediate during plastic (municipal waste) and composite propellant (aerospace) combustion, but the understanding of its high‐temperature chemistry is still evolving. In this study, the pyrolysis of 0.5% HCl in Ar was investigated behind reflected shock waves in a shock tube at temperatures ranging from 2290 to 3490 K and pressures from 0.7 to 3.6 atm. A laser source was set to access the R(8) transition line of H 35 Cl in the fundamental band near 3.3 µm at the specific wavelength of 3045.06 cm −1 . Numerical predictions using chemical kinetics mechanisms from the literature did not capture well the decomposition behavior of HCl in our conditions. According to these models, the most sensitive reaction HCl + M H + Cl + M (M = Ar) could be isolated, and its rate constant was retrieved from the experimental measurements. A pressure dependence was observed over the range of pressures covered. The present study measured the bimolecular reaction rate of the title reaction ( k 1.5 atm in cm 3 ·mol −1 ·s −1 , T in K, R = 1.987 cal·mol −1 ·K −1 ) as: valid near 1.5 atm, as well as ( k <1 atm in cm 3 ·mol −1 ·s −1 ): and ( k >2 atm in cm 3 ·mol −1 ·s −1 ): suitable for conditions below 1 atm and above 2 atm, respectively. A generalized overall equation for the unimolecular reaction HCl H + Cl was obtained and is described as k all in (s −1 ). Finally, the results indicate that the measurements at pressures up to 3.6 atm in the present study were sufficient to determine that the title reaction is in its high‐pressure limit.

Ammonia is an important molecule in aeronautical and aerospace applications. Current models for ammonia are mostly tuned against ignition delay time, laminar flame speed, and speciation data, yet, there are few data available such as species time histories of intermediates such as NH2. To assist in resolving ammonia kinetics pathways, an NH2 diagnostic has been developed at 597.375 nm, based on the known spectroscopy of NH2. The new diagnostic is utilized with an NH3 laser stationed at 10440.17 nm to measure species concentration time histories behind reflected shock waves. Using both systems, a 0.008/0.992 NH3/Ar mixture was tested at 2089 K, 1.27 atm. This paper presents results that demonstrate the successful set up of the absorption diagnostic and its application to a reacting flow field in a shock tube. From the results, an absorption coefficient of 0.8751 cm(-1)-atm(-1) was obtained. This method will be applied to acquire a full temperature-dependent absorption coefficient curve for NH2 and ultimately for monitoring NH2 in ammonia-based mixtures.

The objective of this work is to use an economical diagnostic tool - chemiluminescence of NH2* - to give direct information on the H-2 preferential diffusion effects in premixed ammonia-air flames. Abundant quantities of NH2* are produced in ammonia-air flames which makes it an interesting tracer of heat release, as stated in a previous study. Evidence of preferential diffusion was observed using a Bunsen-type burner and attributed to ammonia decomposition into hydrogen leading to preferential diffusion. In this study, new analyses based on additional experiments and simulations are proposed to support and quantify this hypothesis. Mixtures of equivalence ratios 0.9-1.4 have been investigated. With a Bunsen burner, we were unable to stabilize flames leaner than 0.9. The flow velocities required to stabilize these flames are very low (<0.2 m/s) due to the low flame speed of ammonia/air mixtures. Spectroscopic and local chemiluminescence measurements of the flames were calibrated against a quartz-tungsten halogen lamp. The unique spectrum of each equivalence ratio depicting the reactivity of the flame was studied, and the ratio of two excited species: NH2*/OH* was used to provide a rough estimate of the equivalence ratio. This NH2*/OH* ratio was later applied to estimate the local equivalence ratio along the flame contour. Analysis of the NH2* profiles along the flame contour for various cases revealed changes in intensity and profile thickness, indicating the effects of H-2 preferential diffusion. Relative lower intensities and thicker profiles of NH2* indicated a low reactivity and vice-versa. Since NH2* can be used as a good indicator, a sub-mechanism to predict these profiles has been proposed. The rate constants of pure collision reactions were determined using the collision theory, and the rate constant of the chemiluminescence reaction was determined experimentally. Other involved reactions and species were identified using a sensitivity analysis on NH2 and NH2*. The proposed sub-mechanism was compared with the experimental profiles, and the impact of the base mechanism has been stated.

Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a fire suppressant candidate for the use of lithium-ion batteries (LIBs). It is known that the electrolyte components in LIBs are highly flammable, making them susceptible to igniting, whether this is due to a manufacturing fault or an abuse of the LIB itself. To address this risk, the efficiency of BtFEC as a fire suppressant was investigated experimentally in a high-temperature combustion environment, allowing for further refinement and validation of the model. Using a shock tube, BtFEC combustion properties were measured experimentally behind a reflected shock wave, capturing OH* chemiluminescence to assess ignition delay times (IDT) as well as CO time-history profiles through the implementation of laser absorption spectroscopy. Both pyrolysis and oxidation conditions were captured with three equivalence ratios (phi = 0.5, 1.0, and 1.5) for a temperature range of similar to 1200-1650 K at near-atmospheric pressures. In addition, key species measurements were taken using a microflow reactor (MFR) with a controlled temperature profile associated with Fourier transform infrared spectroscopy (FTIR). Key species investigated were BtFEC, CO, CO2, CHF3, CF2O, C2F6, and HF for the temperatures range of 800-1300 K. MFR measurements allowed for a new set of measurements by which to validate the model compared to the previous study [Mathieu et al. Proc. Combust. Inst. 2023, 39, 499] where the first assembly of the model used CO time-history, IDT, and laminar flame speed measurements. Refinement of the model was carried out with new high-level calculations as well as sensitivity, rate-of-production, and reaction pathway analyses using recent reaction rate updates from the literature. The modifications led to improvements in the level of agreement between the kinetic modeling and the new experimental data.

This study briefly reviews available literature on key combustion properties of traditional Jet A and sustainable aviation fuels (SAFs). New experiments were conducted using a hightemperature, high-pressure stainless-steel constant-volume vessel equipped with a Z-type schlieren imaging system for flame visualization. Laminar flame speeds of Jet A and Syntroleum S-8 were measured at 400 K and 1 atm, and the results are compared to existing literature and chemical kinetic simulations using the CRECK PolliMi and HyChem mechanism in Chemkin Pro. The peak laminar flame speeds for Jet A and S-8 were observed to be 56.38 and 58.73 cm/s at equivalence ratios of 1.09 and 1.05, respectively, with S-8 exhibiting better overall agreement with literature values. Markstein lengths were also analyzed, revealing higher flame stability for S-8 under rich conditions compared to Jet A.

Physical and chemical processes of ammonium perchlorate and hydroxyl-terminated polybutadiene (AP/HTPB) composite propellant combustion have been studied for several decades, and more than 50 years of model development can be reported. Computational methods focus on the heterogeneous aspects—the solid-phase and its decomposition—whereas AP self-deflagration and burning characteristics should be seen as a multi-step, physiochemical process. There has been a lack of systematic studies on the gas-phase chemical kinetics mechanisms for AP combustion, with emphasis on the starting gas-phase species NH3 and HClO4. Only three recent detailed gas-phase mechanisms with sufficient detail in terms of the number of chemical reactions and number of species are currently available in the literature prior to 2023, and simulations are carried out within the present review to assess the state of their current performance and to highlight potential knowledge gaps that should be filled. Given the importance and prevalence of AP in modern propellants, it is surprising that the chemical kinetics of AP combustion are very much understudied. The authors highlight the fact that the few existing AP mechanisms have never been fully vetted against an applicable database of experimental results, certainly not in the manner that mechanisms are typically validated within the combustion science community for fuels such as hydrogen and various hydrocarbons. This review does not put forward such a mechanism, but rather 1) brings to light the limitations of current AP kinetics mechanisms in predicting some limited, available kinetics data, and 2) underlines the need for additional, fundamental data that can be used to calibrate an AP kinetics model. A limited gas-phase experimental database was identified from currently available sources for two main compound families: ammonia (NH3) and perchloric acid (HClO4). The decomposition of AP is initiated by NH4ClO4 → NH3 + HClO4 and leads to these two rather complex molecules that differ strongly in their nature and consequently in their reaction schemes for combustion processes. On the one hand, existing measurements of ignition delay times, laminar flame speeds, and speciation were collected for NH3, N2O, and NO2, and on the other hand, a similar albeit much smaller body of experimental results was assembled for HClO4, ClO2, and Cl2. These global kinetics data were used to evaluate modern AP/HTPB propellant models. We observe that there is much room for improvement regarding models' performance. Significant improvements in our ability to model the gas-phase chemical kinetics of AP combustion can be made by taking advantage of recent developments in ammonia oxidation chemistry modeling. However, additional, fundamental data are needed before similar strengthening of the perchlorate-related chemical kinetics as well as for cross-system reactions involving both N- and Cl-based species can be made.

The study investigated the impact of a novel, iron-based metal-organic framework (FeMOF) additive on the burning rate of AP/HTPB-based composite solid rocket propellants. This FeMOF possesses a unique composition that combines catalytic iron and oxidizing perchlorate components, which were evaluated through a constant-volume strand burner. The study systematically varied additive concentrations, ammonium perchlorate particle size distributions, and additive particle processing methods to improve burning rate performance. Results demonstrated that the FeMOF enhances burning rates compared to the baseline formulations, with finer particle distributions and bimodal oxidizer sizes further enhancing the burning rate. The findings in this paper highlight the FeMOF's potential as a high-performance, tunable additive for advanced propellant formulations, paving the way for future material property analyses and thermal performance optimization.

Operational, efficiency, safety, and economic issues may arise from the formation and accumulation of sludge, varnish, and coke deposits that result from the degradation of engine lubricants through oxidation or thermal breakdown processes. Having a good understanding of the limits of lubricant performance may be useful in determining the best way to protect the engines. To this end, experiments were conducted using Mobil DTE 732, a turbine lubricant, that is aerated using a coarse gas dispersion tube. The oil then flows through a heated test section with a known axial temperature distribution. The inlet and outlet bulk oil temperature measurements are collected and used to determine the amount of time required for deposit formation and buildup. The induction times were determined for various surface temperatures, up to 236 degrees C. It was found that increased temperatures shortened induction times, and exposure to oxygen increased the rate at which deposits accumulate, but the nature of the deposits, soft and easily removed, was different from those formed during higher-temperature experiments completed in an inert environment in previous studies. Oil samples collected during the test were analyzed with Fourier transform infrared (FTIR) spectroscopy, with no significant changes detected.

The interpretation of fuel/air ignition delay times measured in shock-tube experiments becomes challenging at low temperatures and low dilution levels due to inhomogeneous ignition phenomena across the test gas. The rapid growth of a turbulent boundary layer at the wall of the shock tube introduces non-ideal, gas-dynamic effects that can disturb the conditions behind the reflected shock wave, especially at longer test times, potentially causing localized ignition. The magnitude of such effects may vary between shock-tube facilities, but their influence on ignition may not necessarily be facility-dependent. To better understand this phenomenon, ignition delay time and high-speed chemiluminescence imaging measurements for lean and stoichiometric C3H8/O2/ diluent mixtures have been performed in two different shock-tube facilities at two different laboratories that differ in geometry. C3H8/O2 mixtures were diluted in both N2 and Ar with diluent/O2 volume ratios maintained at 3.76/1. Temperatures behind the reflected shock wave ranged from 900 to 1400 K at reflected-shock pressures of 6 to 8 bar. Mixture-averaged dp/dt values are reported at 0.5 to 2.0 %/ms in the N2-diluted mixtures and up to 4.0 %/ms in the Ar-diluted mixtures. The ignition delay time results are compared to simulations based on the NUIGMech 1.3 mechanism under both constant-volume conditions and incorporating facility-dependent dp/dt. Measured ignition delay times begin to depart from model predictions at 1050 K, forming a 'roll-off' region, where inhomogeneities accelerate ignition. These non-uniformities were first observed in both facilities at UDE and TAMU using pressure and chemiluminescence diagnostics and later confirmed at TAMU with endwall highspeed imaging during ignition. The measurements reveal that flame kernels appear up to 3 ms before the main ignition event, ultimately leading to shorter ignition delay times when compared to model predictions. Additionally, localized ignition appears to occur at the sidewall first, where larger temperature non-uniformities may exist due to interactions between the shock-heated gas and the turbulent boundary layer. This work extends inhomogeneous ignition studies in shock tubes by showing that such nonideal behavior is reproducible at similar conditions in two different shock-tube facilities from two different laboratories. Our results indicate that fluidmechanic instabilities considerably influence the ignition process for post-reflected-shock temperatures below 1225-1326 K, depending on the criteria imposed on the definition of a bifurcation timescale. Experiments conducted in Ar-diluted mixtures containing 10 and 20 percent helium by volume were generally inconclusive, and it was determined that greater quantities of helium may be necessary to promote homogeneous ignition at the conditions of interest.

During a thermal runaway, Lithium-ion battery cells are subjected to a large increase in temperature, which will vaporize and potentially thermally degrade their liquid electrolyte. The formation of gas in the battery cell will increase the pressure until the flammable gases vent and potentially lead to a fire incident. While the pyrolysis chemistry of the electrolyte components has been studied near atmospheric pressure, the effect of pressure has not been investigated. This study was undertaken to better understand the effect of pressure on the thermal dissociation of two common linear electrolyte components, diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). The pyrolysis of DEC and EMC was studied in the gas phase, in 99.75% He/Ar, and was carried out at high temperatures and for pressures near 5.5 atm. The time-resolved CO formation was measured using a quantum cascade laser, providing a unique experimental dataset. A detailed chemical kinetics analysis was performed to understand the effect of pressure on DEC and EMC, with CO time-history results obtained in similar conditions at near-atmospheric pressure for DEC and EMC serving as baselines for comparison. Numerical predictions using detailed chemical kinetics mechanisms from the literature were carried out, and reaction pathways at different pressures were highlighted to emphasize the effect of pressure on the pyrolysis chemistry.