Ignition Behavior Research Articles

Experiments and modeling of forced ignition in methane/air mixtures with added NO

Ignition of fuel/oxidizer mixtures containing combustion products is important to the operation of advanced combustors. Previous work indicates that the presence of NO can reduce ignition delay times, yet the influence of NO on forced ignition is not clear. This work examines ignition kernels generated by spark discharges in CH4/air flows diluted with a mixture of NO and N2. Differences in chemistry initiated by the presence of NO are examined by comparing mixtures diluted with only N2 to mixtures diluted with both NO and N2. Ignition probability and kernel growth rates are determined using measurements of infrared radiation emissions from the developing ignition kernels. The presence of NO in the unburned mixture does not affect ignition probability. However, the addition of small quantities of NO on the order of 300–1200 parts per million increases the size of ignition kernels relative to those generated in mixtures diluted with pure N2 by up to 20%. Numerical modeling is performed to examine the role of low temperature chemistry on ignition behavior. The sensitivity of ignition kernel growth to the presence of NO is attributed to increased CH4 oxidation rates caused by low-temperature chemistry activated in the early stages of kernel development.

Explosion Mechanism of Lubricating Oil Droplets in High-Temperature and High-Pressure Combustion Environments

Lubricating oil-induced pre-ignition is a critical issue that requires attention in downsized gasoline engines and marine low-speed two-stroke natural gas engines. As a result, the ignition behavior of lubricating oil at high temperatures and pressures has been extensively studied. In some cases, when studying the ignition of oil droplets using a rapid compression machine, an explosion-like behavior of the oil droplets is observed, producing a soot cloud that can spread throughout the combustion chamber, especially when the ignition delay time of the ambient gas is short. To gain detailed insights into the mechanism of oil droplet explosion, the explosion process under initial pressures from 13 to 31 bar and temperatures from 700 to 1600 K was visualized using high-speed photography and microphotography on a rapid compression machine. The effects of temperature and shock waves were experimentally investigated, and droplet deformation after shock wave impact was calculated using a simple model. The results demonstrated that high temperature does not have a significant effect on droplet explosion under the conditions studied in this paper. The shock wave impact is the primary cause of the droplet’s explosion.

Numerical and experimental analysis of detonation induced by shock wave focusing

Previous studies have demonstrated that shock wave focusing is an efficient method for detonation initiation by creating hot spots in the interaction of shock-shock or the collision of shock with the boundary layer. The velocity of the incident shock wave and the shape of the reflector are both crucial to the self-ignition process and the flame propagation mode. This study adopts both numerical and experimental methods to investigate the ignition modes and detonation propagation induced by shock wave focusing. Two reflectors, a 60° wedge reflector and a 90° wedge reflector, and four incident shock wave velocities are employed as parametric variables, and their effects on the detonation initiation behavior are systematically investigated. The results show that three ignition modes, namely, deflagration, quasi-detonation, and direct detonation, occur with increasing intensity of the incident shock wave. The comparison between different cases suggests that the formation of new hot spots and transverse waves is of great importance to the initiation and maintenance of detonation waves. The Richtmyer-Meshkov instability (RMI) is demonstrated to be the reason for the generation of a mushroom-shaped jet, which can be observed both in simulations and experiments and represents the successful formation of detonation. This study offers new insight into the ignition behavior in wedge reflectors, supporting the crucial role of shock wave focusing in self-ignition and detonation initiation.

On tert-butyl hydroperoxide in ignition intensification of n-heptane under engine-relevant condition

The higher reactivity of hydrocarbon fuels is necessary to match supersonic airflow in scramjet engines and micro-scale effect in micro-internal combustion engines. Tert-butyl hydroperoxide (TBHP) was selected in this study as an additive reactively enhancer to explore its capacity to intensify the auto-ignition of a typical hydrocarbon (n-heptane). Ignition delay times (IDTs) of n-heptane doped with TBHP were thus measured at engine-relevant conditions covering pressure of 20 atm, temperatures of 650 – 1250 K, and equivalence ratios of 0.5 and 1.0. A nonlinear promotion effect of TBHP on the auto-ignition of n-heptane was observed. Detonation caused by TBHP in region 2 has an impact on actual reflected shock temperature and pressure at high beginning temperatures (> 1000 K). With the addition of TBHP, the negative temperature coefficient (NTC) behavior of first-stage ignition eventually vanishes accompanied with a weakened main NTC of IDT. Analyses of exothermic reactions, reaction pathways, and species evolution indicated that the quick production of ȮH and ĊH3 radicals from TBHP enhances the reactivity of n-heptane and affects the main exothermic reaction in the early period. This study reveals the potential of TBHP to be used in the ignition regulation of the combustion of hydrocarbon fuels and provides a methodological approach for the efficient utilization of hydrocarbon fuel in scramjet engines and micro internal combustion engines.

A Novel Approach on Dielectric Barrier Discharge Using Printed Circuit Boards

Drug-resistant bacteria, prions, and nosocomial infections underline the need of more effective sterilizing technologies. The cold plasma technology is expected to bring a benefit in this context. Six different plasma sources, based on printed circuit boards, were evaluated fourfold. This includes measurements of the power consumption, the ignition behavior by an ICCD-camera, and ozone formation by absorption spectroscopy at 254nm. To evaluate the biocidal effect, four bacterial test series were performed with Escherichia coli. The entirety of the tests analyzes the plasma inactivation process from the input parameters to the desired biocidal effect. The discharge current and time-resolved ignition behaviors indicated a simultaneous formation of filaments at the beginning of the negative half-cycle. The dynamics of the ozone production showed a saturated exponential growth upon a maximum value of 435ppm. Additionally, the microbiological test series unveiled differences between the plasma source concepts. A total reduction rate of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {10^{-4}}$ </tex-math></inline-formula> within a minute was achievable. An air flow through slits within the plasma sources destabilized the plasma. Minor changes of the electrode geometry changed all measured parameters. Hence, to develop a pathogen inactivating plasma source, these results recommend a comb-shaped electrode design, which is laminated on a dielectric.

Peridynamic modeling of damage and non-shock ignition behavior of confined polymer bonded explosives under impact loading

A mechanical-thermal-chemical coupled peridynamic (PD) modeling for analyzing the damage and non-shock ignition behavior of polymer bonded explosives (PBXs) subject to impact loading has been presented. The friction and heat conduction and Arrenhenius law are embedded into the PD theory, ensuring that the simulation model is capable of capturing major features of dynamic damage response of PBX. A PD material model considering plasticity and the asymmetric behaviors of PBX under tensile and compressive loadings is proposed in this study. For a ring-shaped PBX 9501 sample confined by the steel structures, the simulation results indicate that the PBX 9501 in the regions towards the impact face and support face suffers from the serious damage. Meanwhile, the corresponding average temperatures in these two regions are also higher than their counterparts in other regions due to the more intense interaction between PBX 9501 and the steel confinement structures. The ignition time decreases with the increasing impact velocity within the range of 40–120 m s−1. The internal steel shell response is analyzed according to its velocity history within a representative box. It is found that the deformation process of internal steel shell is closely related to the complicated flow behaviors of PBX 9501.

The role of HMX particle size in the combustion and agglomeration of HTPB-based propellant

Cyclotetramethylene tetranitramine (HMX) is usually added to solid propellants, but the inclusion of HMX significantly affects the propellant combustion characteristics, especially by yielding more condensed combustion products (CCPs). The effect of HMX size on aluminum agglomeration and CCPs of hydroxyl-terminated polybutadiene (HTPB)-based propellant is evaluated experimentally in this paper. Using a thermogravimetry–differential scanning calorimeter, laser ignition setup, and high-pressure combustion bomb, we have examined the propellants' thermal reactivity, ignition behavior, combustion characteristics, agglomeration, and CCPs with 10–200 μm virgin HMX particles. The results indicate that HMX in propellant suppresses the pyrolysis reaction of ammonium perchlorate. Meanwhile, the exothermic peak temperature of 200 μm HMX increases by 17.8°C compared to 10 μm HMX. With the increase of HMX size from 10 μm to 200 μm, the combustion intensity of the propellant increases, and the ignition delay time of aluminum particles decreases from 580.6 ms to 498.3 ms. Increasing HMX size leads to an increased burning rate, while the pressure exponent decreases from 0.34 to 0.23. Including HMX in propellants also promotes aluminum agglomeration during propellant combustion. With HMX size expanding from 10 μm to 200 μm, the mean agglomerate size in the CCPs decreases from 221.9 μm to 124.5 μm, and the fraction of aluminum involved in agglomeration decreases from 0.206 to 0.104. The unburned aluminum content in agglomerated particles increases monotonically with increasing agglomerates size. Overall, HMX size has a significant impact on the ignition, combustion, and agglomeration characteristics of aluminized propellant. The conclusions of the paper can be used as a guidance for optimizing the propellant formulation

Cenosphere Formation and Combustion Characteristics of Single Droplets of Vacuum Residual Oils

ABSTRACT The ignition, combustion characteristics, and cenosphere formation of single droplets combustion of four vacuum residues (VRs) from different refineries with various asphaltene contents were studied experimentally. The single droplets of VRs were suspended at the tip of a silicon carbide fiber and heated in air at temperatures of 973 and 1023 K, respectively, in an electrically heated tube furnace. The ignition and combustion behavior of the VRs were recorded using a CCD camera, which enabled the determination of droplet size, ignition delay time, flame duration, and cenosphere size. The effect of initial droplet size, gas temperature, and asphaltene content on the ignition delay time, flame duration, cenosphere morphology, and particle size were investigated. The whole ignition and combustion process of single droplets of the VRs consisted of five stages in succession: (1) pre-ignition, mainly involving the evaporation of highly volatile components from the droplet surface; (2) steady combustion of fuel vapors evaporated from the droplet surface; (3) splashing combustion of fuel vapors evaporated from droplet interior; (4) disruptive combustion due to thermal decomposition of asphaltene; and (5) solid residue ignition and combustion. A visible and sooty flame was formed upon ignition and lasted during stages 2–4. The droplet size increased sharply in the stage 4 due to the thermal decomposition of asphaltene, which was more profound for VRs with higher asphaltene content and at higher gas temperatures. The ignition delay time increased with increasing initial droplet size and gas temperature but varied little as the asphaltene content in the VRs increased, suggesting that the ignition process of VRs was controlled by the vaporization of high volatile components on the droplet surface. The thermal decomposition of asphaltene produced solid residue, which was in the form of a cenosphere with the shell thickness being ca. 20 μm and a number of blowholes presented in the shell. The VRs with higher asphaltene content had more and bigger blowholes. The ratio of cenosphere particle size to initial droplet size is independent of the initial droplet size but almost increased linearly with the asphaltene content in the VRs.

Ignition and vapor transfer behavior of liquid fuel ignited by radiation from neighbouring liquid pool fire

Ignition of liquid fuel by neighbouring fire occurs occasionally in the oil storage farm. The ignition behavior is simultaneously affected by heat transfer and liquid evaporation of the unburned pool. The thermal exchange and vapor transfer involving ignition of extremely flammable liquids by neighbouring pool fire are investigated. The mean radiative heat flux of the pool to be ignited is calculated by implementing the double integration of the horizontal viewing angle coefficient of cylinder flame model. The threshold value of the incident heat flow for ignition of heptane pool decreases from 1.3 to 0.7 kW/m2 as the non-dimensional interval distance increases from d/D = 0.4 to d/D = 1.35. The radiation heat transfer by the neighbouring pool fire plays the principal role in the ignition of liquid fuel while the convection heat transfer plays the secondary role. The evaporation rate model of liquid fuel to be ignited by nearby pool fire is established according to heat transfer analysis of the unburned pool. The relative error of the experimental and theoretical value of evaporation rate of liquid fuel is within 20%. The critical vapor concentration on liquid level of ignition of n-heptane and ethanol fuel is 12.2% and 10.94% respectively.

Recent Progress on Combustion Characteristics of Ammonia-Based Fuel Blends and Their Potential in Internal Combustion Engines

Review Recent Progress on Combustion Characteristics of Ammonia-Based Fuel Blends and Their Potential in Internal Combustion Engines Denghao Zhu , and Bo Shu * Department of Physical Chemistry, Physikalisch-Technische Bundesanstalt, Bundesallee 100, DE-38116 Braunschweig, Germany * Correspondence: bo.shu@ptb.de Received: 21 November 2022 Accepted: 22 December 2022 Published: 18 January 2023 Abstract: Ammonia has recently attracted numerous attentions from researchers and policy makers as promising energy and hydrogen carrier for mitigating the carbon footprints in the energy sector. The mature infrastructure for the production, storage, and transportation of ammonia allows a quick role of ammonia in energy systems. By applying green hydrogen and renewable energies, green ammonia can be produced, which makes ammonia even more attractive. Prior to the commercial use of ammonia for large-scale energy systems, e.g., internal combustion engines and stationary gas turbines, a fundamental understanding of the ignition and combustion behaviors of ammonia is essential. In the past decades, a lot of studies on ammonia combustion have been published. Those studies covered broad topics including experimental and numerical investigations which were either fundamental or practical oriented. To continuously follow state-of-the-art and to provide a brief overview of the most recent research on ammonia combustion so that others can easily identify the most relevant work, this review summarizes the recent progress on combustion characteristics of ammonia and ammonia fuel blends as well as their potential use in internal combustion engines. Combining the advantages and drawbacks identified in both fundamental and practical studies, a clearer road map for ammonia application is given.

Effect of aluminum-based additives on the ignition performance of ammonium perchlorate-based composite solid propellants

The addition of aluminum particles in composite propellants has a positive effect on the performance of solid rocket motor, while it also brings some changes in the ignition behaviors. To clarify the ignition process and performance of aluminized propellants, a visualization experimental system was built. It is found that the ignition process of aluminized propellants mainly includes heating and melting of the solid phase, evaporation, mixing and ignition of decomposed gas. Besides, few aluminum particles agglomerate together and they are not ignited during the ignition process of propellants. According to the process of ignition, the ignition delay time can be described as the sum of pyrolysis time, mixing time and chemical reaction time. After the propellants is ignited and the stable flame is formed, the aluminum particles on the burning surface mainly undergo exposure – accumulation – fusion – separation – ignition – combustion. And the structure of the agglomerate transitions from a coral-like to an oxidized cap. At the same time, the ignition of agglomerated products occurs in the stable flame. With the increase of aluminum content and initial aluminum particle size, the ignition delay time also increases, but the proportion of these three times in the ignition delay is not very much related to the formulation of propellants. With the increase of power density of ignition, the ignition delay time decreased markedly, but the decreasing trends continuously became more gradual and eventually flattened out. As the power density of ignition increases, the percentage of pyrolysis time in the ignition delay time decreases rapidly and gradually stabilizes, while the percentage of mixing time gradually increases and the chemical reaction time does not change much. A sufficiently large and reasonable ignition energy power can reduce the ignition delay time and also reduce the impact of the differences between formulations on ignition performance.

Arc bead ignition of a cellulose fuel bed derived from experimental and simulated data

Cellulose is the most abundant material and widely used fuel in the world, and on the other hand, it is also the risk of forest potential fire hazards. Fires caused by electrical arc beads, which are detrimental to the environment, occur in wildland-urban interface (WUI) areas. This study experimentally and numerically examined the ignition behavior of the cellulose fuel bed by focusing on arc beads. Experiments were conducted using authentic arc fault beads, and the effects of the bead temperature and implantation depth on ignition phenomena were investigated. Three ignition categories were determined: no, smoldering, and flaming ignition. Ignition temperature limits were determined by performing a statistical analysis, and experimental observations were used to develop a mathematical model. The two-step reaction leading to cellulose ignition was discussed, and natural convection, diffusion, and thermal radiation were all identified as influential parameters. Four ignition mechanisms were identified using the model: no ignition, smoldering or charring inside the fuel bed, smoldering leading to volatiles ignited, and flaming ignition. The ignition phenomenon was limited by the conduction and accumulation of heat, presence of volatile substances, and concentration of atmospheric oxygen. The model reasonably predicted the ignition phenomenon and described the ignition mechanism. These results can be used to reduce the risk of fire hazards related to arc beads, particularly in WUI areas.

Optimization of methane simplified chemical kinetic mechanism based on uncertainty quantitation analysis by sparse polynomial chaos expansions

A robust and compact simplified chemical kinetics mechanism for methane oxidation is newly developed based on the Directed Relation Graph with Error Propagation method (DRGEP) and the Full Species Sensitivity Analysis method (FSSA). It is constructed by adaptive self-tuning of reaction rates with a non-dominated sorting genetic algorithm II (NSGA-II) approach to satisfy ignition behaviors under varied engine conditions. Its high fidelity is achieved by uncertainty quantitative (UQ) analysis to retain the uncertainties caused by updated reaction rates. In UQ analysis, the sparse polynomial chaos expansions (SPCE) model based on the Least Angle regression (LAR) method is applied to the adaptive selection of significant polynomial bases, and the accuracy of the SPCE model is tested using a statistical methodology (e.g. leave-one-out cross-validation). Consequently, compared with the full PCE approximations, the UQ analysis scheme reduces the computational cost by more than one order of magnitude and effectively alleviates the “dimension disaster” dilemma of the classical PCE scheme. Therefore, the application of the adaptive SPCE scheme allows more reactions to be involved in quantifying the uncertainty propagation. Finally, the aforementioned new simplified methane mechanism is widely verified under engine-relevant conditions, and good auto-ignition performance is highlighted, especially in fuel-lean combustion.

Aluminum Particle Ignition Studies with Focus on Effect of Oxide Barrier

Aluminum particle ignition behavior in open atmosphere rocket propellants fires is of particular interest for preventing accidents for rockets carrying high-value payloads. For nominal motor pressures, aluminum particles oxidize to aluminum oxide in the gas phase and release significant combustion energy while minimizing motor instability. During rocket abort or launch pad malfunction which occur under atmospheric or low pressure, behavior of aluminum particle combustion becomes complex and aluminum appears to melt, agglomerate or form a skeletal structure. Furthermore, an oxide shell of alumina instantly forms on any fresh aluminum surface which is exposed to an oxidizing environment. Aluminum combustion then strongly depends on the oxide layer growth, which is influenced by causative factors, including particle size, environmental gas composition, and heating rate. This work focuses on the effect of the oxide barrier which forms on the surface of aluminum that is recognized to impede combustion of aluminum in solid rocket propellants. Understanding the mechanism for breach of this barrier is deemed to be an important consideration in the overall process. In this discussion, results of various experiments will be discussed which have a bearing on this process. Basically, a recognized criterion is the melting of the oxide layer at 2350 K is sufficient. However, in other situations, depending on the mechanism of oxide formation, there will occur defects in the oxide shell which provide for aluminum ignition at lower temperatures. For slow heating in an oxidizing environment, where the oxide layer can grow thick, then ignition is more difficult. Because there is no uniform model to establish an ignition criterion due to the unknown history of an aluminum particle, this paper reports experimental findings involving oxyacetylene torch, thermogravimetric analysis with differential scanning calorimeter, aluminum particle heating, electric ignition and aluminum powder heating, to address the influence of the oxide layer on the aluminum particle ignition.

Igniting volume of four ignition sources

Several standardized ignition sources are used to determine the safety characteristics of gases, vapours and dusts. Standards indicate the source of ignition but vary in specifying other features such as the burning duration, energy or the volume in which the energy is released. Since heat is not visible under normal conditions, a schlieren technique was used to visualize the entire igniting volume and not just the flames. This article focuses on the igniting volume, compares it among the four standardized ignition sources and displays its relationship to the size of the test vessel. Differences in the ignition behaviour of the ignition sources might lead to the determination of erroneous safety characteristics and with that to the unsafe operation of processes.

HYPERGOLIC IGNITION OF SOLID FUELS WITH REACTIVE ADDITIVES USING HYDROGEN PEROXIDE

Hypergolic ignition offers significant benefits for hybrid rockets since it eliminates the need for external ignition devices or catalyst beds. Numerous studies have demonstrated promising results when utilizing various reactive additives and oxidizers. Nevertheless, the impact of fuel temperature and particle size on ignition performance, which is critical in practical applications, is often overlooked. In this study, we explored the ignition behavior of a metal hydride-based hypergolic fuel with rocketgrade hydrogen peroxide (RGHP) as the oxidizer. The solid fuel was composed of low-density polyethylene as the binder and sodium borohydride as the reactive additive. Through image processing, we analyzed the ignition behavior by measuring the ignition delay time in droplet tests using different concentrations of the additives, particle sizes, and initial fuel surface temperatures. Three types of ignitions were observed, and all of the droplet tests were successfully ignited. To examine the initial fuel temperature and powder particle size effects on the ignition, we varied the initial temperature of the fuel pellet and composition percentage of two different particle sizes in the powder. Our experimental findings suggest that both the initial fuel surface temperature and powder particle size play a crucial role in the hypergolic ignition delay time.

Control-Oriented Combustion Modeling for Compression-Ignition Engines Operating With Low Cetane Fuels

To support the transition toward sustainable alternative fuels in the transportation sector, advanced statistical modeling techniques are needed to characterize and control combustion at low cetane fueling conditions. In this work, a novel control-oriented combustion phasing model is presented that simulates asymmetrical phasing distributions as a function of fuel cetane, fuel injection timing, and electrical power supplied to a thermal ignition assist device. The model was regressed using experimental data from a commercial compression-ignition (CI) engine operating with four fuel blends of cetane number ranging from 25 to 48. The model estimates the mode and median of phasing distributions within 2.4 and 2.6 crank angle degrees (CAD), respectively, over a range of 52 CAD. Additionally, kernel density estimation (KDE) is proposed for nonparametric modeling of torque as a function of phasing. A set of KDE-driven extremum seeking algorithms for learning torque-optimal phasing ranges and probabilistic misfire limits is validated across the multi-fuel data. By using a probabilistic criteria, this approach can permit an acceptable proportion of undesired events to occur before classifying a limit. This feature better suits it for engine operation with low cetane fuels, where late burns and misfires may not be entirely avoidable. This work will facilitate online learning-based control strategies that can enable CI engines to adapt to fuels with a wide range of ignition behaviors.

Exploring the reaction kinetics of methyl formate + NO2: implication for ignition behavior of methyl formate/NO2 mixtures.

The reaction pathways and potential energy profiles are theoretically explored for H-abstraction, addition and addition-dissociation reactions of methyl formate (MF, HC(O)OCH3) + NO2 using the high level quantum chemical compound method CCSD(T)/cc-pVxZ(x = T, Q)//M062X/6-311+G(2df,2p). Notably, three different HNO2 isomers (cis-HONO, trans-HONO and HNO2) are all considered in each reaction pathway. The corresponding temperature- and pressure-dependent rate constants are then computed by RRKM/ME simulations with one-dimensional hindered rotor approximation and asymmetric Eckart tunneling corrections. The calculations show that the rate constants are pressure independent. Although trans-HONO is the most stable HNO2 isomer, the results reveal that the dominant channels are cis-HONO + HC(O)OCH2/C(O)OCH3 and cis-HC(O)(ONO)OCH3 for the H-abstraction and addition, respectively. Moreover, the lowest energy barrier for the H-abstraction channel (cis-abs) is 11.2 kcal mol-1 lower than the addition channel (cis-add), and thus the addition channel is less kinetically favored. The computed rate constants for the MF + NO2 reaction are then incorporated into a kinetic model and the importance of the title reaction in predicting the ignition behavior of MF/NO2 mixtures is demonstrated by kinetic modeling. The detailed reaction kinetics in this work will be helpful for kinetic model development of other ester-based fuels.

Hypergolic ignition behaviors of green propellants with hydrogen peroxide: The TMEDA/DMEA system

For nearly-six decades, hydrazine and its derivatives have been the standard fuels for rockets and spacecrafts. However, their attractive features are offset by their toxicity and associated high handling and storage costs. This work presents a novel green fuel system based on N,N,N’N’-Tetramethylethylenediamine (TMEDA), dimethylaminoethanol (DMEA) and methanol or ethanol with high test peroxide (HTP). Drop tests were performed with 27 samples using both high speed photography and transient infrared imaging. Results have shown that neither pure TMEDA nor pure DMEA is hypergolic with high test peroxide (HTP) even with copper chloride (anhydrous or hydrated) as the catalyst. Interestingly, their combination provided a synergistic effect achieving hypergolic behavior with a consistently low ignition delay time (IDT) using only half a percent of catalyst, and the near-optimal hypergolic ignition behavior was achieved with a volume ratio of TMEDA to DMEA of 50:50. In addition, in order to adjust some properties of this blend, TMEDA/DMEA (50:50) was further mixed with methanol or ethanol with different ratios and they showed even better hypergolic ignition performance with IDT as low as 10 ms. Besides their good hypergolic ignition performance characteristics, these new fuel systems based on two propagators (TMEDA/DMEA) and a solvent (methanol or ethanol) also present low viscosity and comparable theoretical specific impulses compared to the conventional hydrazine-based systems. It is believed that this catalytically promoted hypergolic systems with HTP open up a new avenue to the replacement of conventional highly toxic hypergolic propellants.

Development of green‐colour‐emitting pyrotechnics as a core for 3D temperature imaging sensors inside coal boilers

AbstractEfficiency in the control operation of the boilers for coal and coal with biomass can be further improved if the flue gas temperature distribution can be better characterized. This is very difficult in these harsh environmental systems, where spatially resolved measurements are nearly impossible with solid‐state sensors. In this work, we evaluate the development of pyrotechnic compounds that would serve as the basis for a novel optical mapping of the temperature inside coal boilers. For this purpose, various green‐colour‐emitting pyrotechnics using BaCl2 · 2H2O and Ba(NO3)2 as the green light source were prepared, as this colour offers a distinct signal from the combustion‐based background in the boiler. These pyrotechnics were characterized using thermogravimetric analysis (TGA) and X‐ray diffraction (XRD) and tested using a flat‐flame burner. Furthermore, the composition was varied to evaluate the effect of different metal fuels such as Sn, Co, and Mg, as well as various binders such as ethylcellulose, shellac, parlon, and PVC on green light emission. The emission intensity and the apparent ignition temperature were strongly dependent on the metal type, with Mg showing higher intensities. On the other hand, the effect of the binder showed that the ignition behaviour, emission intensity, and spectral purity were influenced by the nature and exothermicity of the binder. The addition of other potential green light‐producing materials, such as boric acid, increased the intensity of emission by 17% for a BaCl2 · 2H2O‐based composition. This study identified prospective compositions with intense and bright green‐colour emissions that have high spectral purities.