Ignition Characteristics Research Articles

Ethanol stratified ultra-lean combustion with hydrogen enrichment in a constant volume vessel

An experimental study was conducted to determine the effects of ignition timings, injection pressures, and hydrogen enrichment on ethanol stratified ultra-lean combustion. The combustion chamber was a constant volume vessel with an injection and ignition system. The ignition and combustion characteristics of ethanol spray with different ignition timings (0–50 ms after start of injection), injection pressures (5, 15, and 25 MPa), and hydrogen premixed equivalence ratios (0.05, 0.1, and 0.2) under ambient temperature 353 K and 1 atm. The direct injection of ethanol and hydrogen enrichment results in an increase in the stable ignition limit to an extremely lean condition: a global equivalence ratio of 0.15 (67% ethanol/33% H2). Furthermore, the probability of ignition first increased then decreased with the delay in ignition timings; rose with an increase in the injection pressure and hydrogen ratio. However, the delay in ignition timings and high injection pressures resulting in extremely lean zone in the constant volume vessel, which led to incomplete combustion. The addition of hydrogen not only stabilized ignition process but also improved the combustion characteristics. Stable ignition and combustion were achieved at early ignition timing (2–3 ms), moderate injection pressure (15 MPa), and a minimum global equivalence ratio of 0.2 (50% ethanol/ 50% H2).

Evaluation of dibutyl maleate/diesel blends on combustion, performance and emissions in a DI diesel engine

Ignition characteristics of diesel are weak due to higher viscosity and density especially at cold start conditions. So, it is seen that the usage of dibutyl maleate having high content of oxygen as an additive to improve the bad properties of pure diesel is essential and sensible. In this research, a single cylinder DI diesel engine was operated at four different engine loads including 4.12, 9.61, 15.10 and 20.60 Nm to observe and see the influences of dibutyl maleate on performance and combustion characteristics such as heat release rate, in-cylinder pressure, ignition delay etc. and thermal efficiency. It was found that in-cylinder pressure decreased with the addition of dibutyl maleate whereas remarkable increase was observed on pressure rise rate and ringing intensity with fuel blends. ID (Ignition delay) period increased with dibutyl maleate addition into diesel due to lower cetane number while combustion duration shortened with fuel blends compared to diesel. Besides, indicated thermal efficiency decreased about 20.18% and 24.25% with D90DBM10 and D90DBM20 respectively according to neat diesel at 15.10 Nm. Specific fuel consumption increased 5.08% and 8.13% with D90DBM10 and D90DBM20 respectively compared that neat diesel. It was also seen that cyclic variations increased in case of usage dibutyl maleate addition. Test results also demonstrated that HC (Hydrocarbon) and soot reduced while CO (carbon monoxide), CO2 (carbon dioxide) and NOx (nitrogen oxides) raised with the usage of dibutyl maleate compared to neat diesel.

Determination of ignition and smoldering propagation of coal based industrial raw materials caused by embedding local hot spot

Embedded local hot spot (EHP) poses a huge threat to the energy production of combustible coal-based industrial raw materials (CCIM), but it is also a source of good utilization of smoldering energy for waste removal. The characteristics of ignition and smoldering propagation of CCIMs by EHPs are studied based on two–step parallel reaction. The effects of temperature, buried depth (lp) and size of EHPs on the ignition characteristics of CCIMs are investigated. The temperature, chemical species and heat release evolution of the smoldering process of CCIMs are explained. The results show that the computational model is reliable. As the temperature and size of the EHPs increases, the ignition delay time (IDT) decreases. The IDT corresponding to the lp = 0 mm is greater than that of lp = 20 mm. Besides, the IDT is proportional to the reciprocal of the heat energy carried by EHPs. The critical temperature of EHPs increases with the increase of lp except in the case of lp = 0 mm. As the radius of the EHPs increases, the critical temperature decreases. The movement of hot spots shows four characteristics, namely, surface movement, movement to the surface, up–down–upward movement and decay.

Effects of temperature and composition inhomogeneity on the ignition characteristics of NH3/H2 co-firing fuels under HCCI operating conditions

The application of ammonia (NH3) in combustion devices, such as internal combustion engines (ICEs), is expected to largely reduce the greenhouse gas (CO2) emission. NH3/H2 cofiring fuels in homogeneous charge compression ignition (HCCI) engines may provide a potential way to deal with zero carbon requirements. However, in HCCI engines, the ignition process needs to be moderated since the ignition is only controlled by the chemical kinetics of the fuel. Therefore, this study investigates the effects of temperature and composition stratification strategies on the auto-ignition characteristics of NH3/H2/air mixtures under HCCI engine operating conditions with direct numerical simulation (DNS). 12 cases with different stratification strategies have been set under turbulent conditions. The chemical kinetics of NH3/H2/air was verified with the laminar flame speeds and ignition delay times. Results show that the temperature stratification can reduce the peak value of heat release rate (HRR), advance the ignition time and extend the combustion duration. In this case, the chemical reaction front is dominated by the deflagration or flame propagation mode. However, in contrast, composition stratification shows very limited effect on the overall combustion process, which is similar to homogeneous ignition and denoted as the spontaneous ignition mode. When increasing the hydrogen content in the fuel, the ignition time is obviously advanced and the peak of HRR is slightly increased. Higher NO emission is also observed which is mainly due to the increase of O, H, and OH intermediates to enhance the fuel NO production. Temperature stratification degree can improve the ignition process under both negatively correlated or unrelated T-Φ fields. However, the improvement is more evident for unrelated T-Φ condition when increasing the stratification degree.

Analysis of Ignition Characteristics and Influencing Factors of Combustible Fly Ash in Boiler Start-Up Stage Flue Gas

In order to realize the full-time denitration of a boiler, high-temperature flue gas needs to be introduced when SCR is conducted during the boiler start-up stage, and there is a fire risk due to the presence of combustible fly ash at this time. Therefore, research on reburning and the explosion risk of tail flue gas encountering high-temperature flue gas during start-up and shutdown was carried out. A small testbed was designed to record the temperature of the flue gas and the composition of the flue gas before and after the test, and the ignition characteristics of combustible fly ash in the flue gas were systematically studied. The ignition temperature of combustible fly ash in various conditions was obtained, the ignition characteristics of combustible fly ash in the airflow were analyzed, and the effects of combustible gas, high-temperature flue gas temperature, and fly ash composition on ignition were also analyzed. The results show that the flue gas temperature in the test section was about 400 °C, the low-temperature flue gas temperature increased from 650 °C to 813 °C, and the combustible fly ash did not ignite regardless of whether alcohol was added as a combustible gas component. When the volatile content of combustible fly ash was 10~26.7%, the ignition temperature was 660~760 °C. The lower the volatile content of combustible fly ash was, the higher the ignition point was. When alcohol was added as a combustible component of gas, the ignition point decreased by about 50 °C. The critical ignition temperature of combustible fly ash in this test was lower than that under actual power plant operation conditions.

Investigation of the injection pressure impact on non-monotonic two-stage ignition delay of diesel engines under cold-start

Poor startability under cold-start conditions is a long-term obstacle of the compression ignition engine and adjustment of the injection pressure is an effective way to improve the startability. Therefore, a detailed investigation of the effect of injection pressure (Pi) on the ignition characteristics of the fuel spray under cold-start conditions is needed. Though numerous studies have been conducted on the effect of Pi on the ignition characteristics of the fuel spray, the two-stage ignition process of the fuel spray under cold-start conditions is still an unknown field. In this paper, the effect of Pi on the two-stage ignition process of the fuel spray under cold-start conditions is investigated in a constant volume combustion chamber through simultaneous Shadowgraphy and high-speed natural luminosity method an analytical model for two-stage ignition delay is established accordingly for further investigation. Based on the experiment results, a monotonic decreasing trend on low-temperature ignition delay time LTI (i.e., form 4.5 ms to 2.5 ms under the ambient temperature of 760 K) and an increasing trend on the cool flame propagation time τ (i.e., form 0.4 ms to 1.6 ms under the ambient temperature of 760 K) are found and finally results in a non-monotonic trend of high-temperature ignition delay (HTI) as the injection pressure raises from 40 MPa to 160 MPa. According to the established model, increased Pi leads to promoted atomization and intensified dilution effect of the fuel spray, which is concluded as the reason for decreased LTI and increased τ, respectively. In this way, the non-monotonic trend of HTI under engine cold-start as Pi increases is quantitatively explained through the promoted model.

Experimental Study on the Ignition Characteristics of Scramjet Combustor with Tandem Cavities Using Micro-Pulse Detonation Engine

This experimental investigation focused on the ignition and combustion characteristics of a tandem cavity-based scramjet combustor with side-by-side identical cavities. This study utilized the Pusan National University-direct connect scramjet combustor (PNU-DCSC), which was capable of simulating flight conditions at Mach number 4.0–5.0 and altitudes of 20–25 km using the vitiated air heater (VAH). The combustion tests were conducted under off-design point conditions corresponding to low inlet enthalpy. It is a condition in which self-ignition does not occur, and a micro pulse detonation engine (μPDE) ignitor is used. The results revealed that as the injection pressure of the gaseous hydrogen fuel (GH2) and the corresponding equivalence ratio increased, the combustion mode transitioned from the cavity-shear layer flame to the jet-wake flame. Furthermore, the measured wall static pressure profiles along the isolator and scramjet combustor indicated that the region of elevated pressure distribution caused by the shock train expanded upstream with higher equivalence ratios. When ignited from the secondary cavity, the combustion area did not extend to the primary cavity at lower equivalence ratios, while it expanded upstream faster with higher equivalence ratios. Therefore, the combustion characteristics of the tandem cavity were found to vary based on the overall equivalence ratio of the main fuel (GH2) and ignition position.

Thermodynamic analysis of employing argon as the diluent and adding hydrogen in an HCCI ammonia engine: Ignition characteristics and performances of combustion and NO emissions

Ammonia is an efficient hydrogen energy carrier and a potential zero-carbon fuel for internal combustion engines. However, the poor ignition and combustion performances of ammonia limit its further application in homogeneous charge compression ignition engines. This study proposes to employ an inert gas argon as a diluent to improve ammonia's ignition and combustion performances. Furthermore, the effect of adding hydrogen is also investigated under a wide calculation range of compression ratio, excess oxygen ratio, and argon ratio through thermodynamic analysis. The calculation results indicate that replacing nitrogen with argon can significantly shorten the ignition delay time and promote the thermal conversion efficiency and power density. Under a specific condition (compression ratio = 19 and excess oxygen ratio = 3.0), when replacing air with an argon-oxygen mixture of argon/oxygen ratio = 79: 21, the ignition delay time of pure ammonia reduces from 700 ms to 0.31 ms, the thermal conversion efficiency increases from 65.1% to 78.2%, and the power density raises by approximately 20%. Nevertheless, the NO volume fraction grows by 1179 × 10−6 VOL due to the high temperature. The ignition delay time drops with the increase of hydrogen blend ratio. With an initial condition of 1250 K and 3.0 MPa, the ignition delay time decreases by 81%–95% when the hydrogen blend ratio is elevated from 5% to 20%. However, adding hydrogen also falls the thermal conversion efficiency and elevates the NO volume fraction. A hydrogen blend ratio of 5% is an excellent tradeoff value.

Spray combustion of fast-pyrolysis bio-oils under engine-like conditions

In the EU funded SmartCHP project, biomass derived fast-pyrolysis bio-oil (FPBO) is used to fuel modified stationary diesel engines for combined heat and power applications. In this study, the spray combustion characteristics of fast-pyrolysis bio-oil and FPBO/ethanol blends are experimentally investigated in a combustion research unit. Due to the special physicochemical properties of fast-pyrolysis bio-oil, major modifications are made to the combustion research unit to facilitate testing this fuel, including the installation of a high-temperature chamber and a heavy-fuel oil injection system. Experimental tests are carried out at a chamber wall temperature of 750 °C and an ambient pressure of 50 bar. The pressure-based heat release analysis is used to evaluate fuel ignition and combustion characteristics, while a high-speed imaging technique is adopted to visualize natural luminosity of spray flames through a borescope.Results show that fast-pyrolysis bio-oil has lower sooting tendency than diesel, and it significantly alleviates the fuel dribble phenomenon. At injection pressure of 300 bar, the poor atomization of fast-pyrolysis bio-oil leads to rather grainy-looking spray flame images, and nozzle orifices becoming clogged within couple of injections. The increase of injection pressure to 900 bar results in an obvious improvement of the atomization quality and nozzle durability for fast-pyrolysis bio-oil. Adding ethanol into fast-pyrolysis bio-oil could improve fuel atomization and further reduce the natural luminosity. The ignition delay of fast-pyrolysis bio-oil is slightly retarded by 10% ethanol addition, while it is advanced by 30% ethanol addition.

Critical ignition conditions for propane/air premixtures impinging on electric heated surfaces: An experimental study

To contribute to exact predictions of the ignition of flammable mixture by a hot surface and ensure safety against fire, this study aims to clarify the critical ignition condition of a propane/air premixture impinging on a hot surface with external heating. The ignition threshold of heat flux depends on the flow velocity, but that of temperature hardly depends on flow velocity and equivalence ratio. The ignition occurred at the position where the residence time of species was the longest. It corresponds to the position of the lowest heat transfer coefficient. The temperature boundary layer thickness played a significant role in the ignition process as only the heat flux from the top, bottom, and back surfaces of the heater contributed to ignition in the presence of forced convection. The prediction model of the ignition threshold of heat flux and temperature was derived through dimensional analysis. This model effectively explains the ignition characteristics, regardless of the differences in thermal convection mode, dimensions, and geometric arrangements of a heater, as confirmed by comparison with reference data. Additionally, the ignition threshold of temperature can be predicted if the external heating power is known, and it is useful to assess the fire risk.

A comparison of mechanistic models for the combustion of iron microparticles and their application to polydisperse iron-air suspensions

Metals can serve as carbon-free energy carriers, e.g., in innovative metal-metal oxide cycles as proposed by Bergthorson (Prog. Energy Combust. Sci., 2018). For this purpose, iron powder is a suitable candidate since it can be oxidized with air, exhibits a high energy density, is non-toxic and abundant. Nevertheless, the combustion of iron powder in air is challenging especially with respect to flame stabilization which depends on the particle size distribution and the morphology of the iron microparticles among other factors. Models for the prediction of reaction front speed in iron-air suspensions can contribute to overcoming this challenge. To this end, three different models for iron particle oxidation are integrated into a laminar flame solver for simulating such reaction fronts. The scientific objective of this work is to elucidate the influence of polydispersity of the iron particles on the reaction front speed, which is still not satisfactorily understood. In a systematic approach, cases with successively increasing complexity are considered: The investigation starts with single particle combustion and then proceeds with iron-air suspensions prescribing binary particle size distributions (PSDs), parametrized generic PSDs, and an exemplary PSD measured for a real iron powder sample. The simulations show that, dependent on the kinetic particle model, the particles’ thermal inertia, and the PSD, particles undergo thermochemical conversion in a sequential manner according to their size and every particle fraction exhibits an individual combustion environment (surrounding gas phase temperature and oxygen concentration). The local environment can be leaner or richer than the overall iron-to-air ratio would suggest and can be very different from single particle experiments. The contribution of individual particle fractions to the overall reaction front speed depends on its ranking within the PSD. The study further demonstrates, that although the three particle models show good agreement for single particle combustion, they lead to very different reaction front speeds. This is due to the different ignition behavior predicted by the particle models, which is shown to strongly influence the reaction front characteristics. Overall, the present work illustrates the complex relationship between characteristics of single particle ignition and combustion, polydispersity, and properties of reaction fronts in iron-air suspensions.

Shock tube experiments and kinetic modeling of ignition of unsaturated [formula omitted] methyl esters

Ignition delay times (IDTs) of methyl crotonate (MC), methyl 3-butanoate (MB3D), and methyl methacrylate (MMA), were systematically measured to explore the influences of the position of unsaturated CC double bond and the structure of alkyl chain on ignition characteristics of unsaturated C5 methyl esters. Experiments were performed at 1108–1783 K and 4–16 atm with the equivalance ratio ranging from 0.25 to 2 in a shock tube. Reactivities of three unsaturated esters are similar: their IDTs increase with decreasing temperature and increasing equivalence ratio but are less sensitive to pressure. To gain the insight into differences in kinetics during fuel ignition, the literature MC, MB3D and MMA models were evaluated and the MMA model was updated. Sensitivity and reaction pathway analyses show that the hydrogen-abstraction, unimolecular decomposition, and radical addition reactions are important in controlling MC ignition. However, only hydrogen-abstraction and radical addition reactions show the significance during MB3D and MMA ignitions. Furthermore, the impact of saturation was also explored. The saturated methyl esters have slightly longer IDTs than MC, MB3D, and MMA under fuel-lean conditions with T> 1350 K, because the unsaturated methyl esters are the key intermediates and the hydrogen-abstraction reactions dominate the consumption of saturated esters.

Direct numerical simulation of NH3/air combustion with H2 addition under HCCI relevant conditions

In the present work, two-dimensional direct numerical simulations (DNS) of NH3/air turbulent combustion with H2 addition under homogeneous-charge compression ignition (HCCI) relevant conditions were performed to explore the ignition and combustion characteristics. Three hydrogen addition levels in the fuel were considered with molar fractions of 0.0 (pure ammonia), 0.1 and 0.8. The corresponding one-dimensional laminar flames were also simulated to provide reference solutions. The general combustion characteristics were first presented. It was found that turbulence and thermal stratification facilitate the ignition process. The ignition occurs earlier with increasing hydrogen addition levels and temperature fluctuations. After ignition, high heat release rate (HRR) occurs simultaneously over the entire domain with low temperature fluctuations while significant HRR occurs in narrow sheets with high temperature fluctuations. HRR is significantly enhanced in positive curvature regions of the cases with high hydrogen addition levels due to the preferential diffusion of H and other radicals. The combustion mode was examined based on the analysis of the displacement speed and species transport equation budget. The mean displacement speed is decreased with increasing temperature fluctuations and the budget analysis suggests that high temperature gradient facilitates deflagration. The reaction fronts are thinner with increasing H2 addition levels, and the combustion mode of deflagration is promoted. The effects of turbulence intensity on the flame structure and combustion mode were evaluated. The ignition occurs earlier and the area of the reaction front increases with increasing turbulence intensity. The magnitude of the temperature gradient also increases with increasing turbulence intensity, which facilitates the occurrence of deflagration. The turbulent flame structures were compared with the corresponding 0D ignition and 1D thermally stratified flame results, and it was found that the mean turbulent flame structure can be well approximated by 1D thermally stratified flames.

Features of Ignition of Mixtures of Hydrogen With Hydrocarbons (C2, C3, C5) Over Rhodium and Palladium at Pressures of 1–2 atm

Features of Ignition of Mixtures of Hydrogen With Hydrocarbons (C2, C3, C5) Over Rhodium and Palladium at Pressures of 1–2 atm

Numerical Simulation of Plasma Igniter Efflux Characteristics Based on Multi-Physical Field Coupling

To explore the chamber plasma jet ignition effect, the establishment of pre-chamber plasma jet ignition based on a 3D model using the method of numerical simulation was carried out on the working process of the plasma ignition numerical calculation. The analysis of firearms in the combustion chamber ignition characteristics provided a reference for the ignition performance boost. The results show that the jet velocity at the igniter outlet can reach 78 m/s and the jet temperature can reach 2300 K, which makes the hot jet spread far enough in the reflux area and ensures that the jet can achieve the effect of heating and igniting in a larger area. The mixture in the air reacts with the kerosene position along the border, ignition in the igniter fine channel before export, igniter speeding up the export position of flow velocity, the jet core region of the temperature of 2400 K, the igniter export position of kerosene component concentration was 45%, the concentration of O2 was 20%, the H2O concentration was 15%, and the CO2 concentration was 7%. The ratio of air to kerosene should be such that the two flow at similar speeds in the mixing area.

Chemical insights into the two-stage ignition behavior of NH3/H2 mixtures in an RCM

This study investigated the two-stage ignition behavior of NH3/H2 mixtures using a rapid compression machine (RCM). The ignition delay times and first-stage ignition delay times of NH3/H2 blends were measured at temperatures ranging from 881 to 1127 K, pressures of 15 and 25 bar, and equivalence ratios (ϕ) of 1.0 and 1.5. Experimental results showed that H2 had a significant promotional effect on the ignition of NH3, and two-stage ignition behavior was observed in some test mixtures. Time-resolved species concentrations were recorded using the gas chromatography (GC) method during the single- and two-stage ignition process. Species evolution suggested that the consumption of NH3 and H2 separated during the two-stage ignition process. The oxidation of H2 primarily occurred at the first-stage ignition point, while NH3 oxidation occurred at the total ignition point. A kinetic model was developed to predict the two-stage ignition behavior of NH3/H2 and the species profiles. Model analysis showed that H2 played a key role in initiating the oxidation process and contributed to the early heat release. When H2 content was high (e.g. 50%), its oxidation led to the simultaneous total oxidation of NH3, resulting in single-stage ignition characteristics. However, when a small amount of H2 was present (e.g. 10%), its oxidation only partially consumed NH3, leading to the two-stage ignition behavior. Sensitivity analyses indicated that the co-oxidation of fuels during the first-stage ignition was primarily dominated by H2 oxidation chemistry, while NH3 oxidation became dominant during the following total ignition stage as H2 was completely consumed. Additional model simulations revealed that the ignition behavior of NH3/H2 mixtures is strongly influenced by temperature and pressure. A distinct threshold for temperature and pressure was identified, demarcating the transition between single-stage and two-stage ignition phenomena. Moreover, the fraction of H2 in the mixture had a significant impact on the ignition behavior, with higher fractions leading to increased intensity of the first-stage ignition and closer proximity to the total ignition point. However, when the H2 fraction exceeds a certain threshold, two-stage ignition behavior disappears.

Effect of AlH3 on the energy performance and combustion agglomeration characteristics of solid propellants

Increasing the performance of an energetic material can be achieved by changing its composition or using additives, such as metal powders. Aluminum hydride (AlH3) exhibits attractive properties, such as high hydrogen/energy storage, relatively good stability, and low dehydrogenation temperature. AlH3 has excellent prospects for use as a component in solid propellants for increasing the specific impulse of rocket engines and effectively reducing the erosion of engine nozzles. In this work, the effect of AlH3 on the energy performance, ignition characteristics, and combustion characteristics of solid propellants, as well as the agglomeration characteristics of metal particles was investigated. It was found that with increasing AlH3 content, the theoretical mass heat of combustion and the theoretical volumetric heat of combustion of the propellants increased, and the combustion efficiency also gradually improved. When the content of AlH3 in the propellant increased from 0.00% to 17.00%, the temperature of the propellant combustion chamber was reduced from 3314.59 to 2957.49 K and the theoretical specific impulse increased from 2584.2 to 2641.7 N‧s/kg. The average molecular mass of the gas was reduced from 25.54 to 21.54 due to the large amount of hydrogen gas released by the combustion of AlH3. The maximum combustion temperature decreased and the burning rate increased with the gradual replacement of aluminum (Al) in the propellant with AlH3. The maximum combustion temperatures of the pure Al propellant and the pure AlH3 propellant were 2510.5 and 2232.5 K, respectively. The linear burning rates were 0.29 and 0.46 cm/s at 1.0 MPa, respectively. The agglomeration process of AlH3 included three main stages, namely accumulation, aggregation, and agglomeration. With the increase in the AlH3 content, the number of agglomerated particles in the propellant gas-phase flame region decreased continuously.

Investigation of the effects of flame surface development on the ignition mechanism of aero-engine combustors

Large eddy simulation was employed to simulate the effects of different vane angles of the primary and pilot stages on the ignition process of a combustor under normal temperature and pressure conditions. The simulation results of different vane angles of the pilot stage were then verified experimentally. Kernel initiation and flame propagation in the cases of ignition success and failure were analysed. It was found that in the ignition failure case, the flame kernels are confined to the downstream zones of the venturi and cannot propagate radially, and almost no negative displacement exists in the axial direction. However, in the ignition success case, sub-fire kernels are always present outside the radial boundary of the primary stage. Five ignition modes were finally proposed: (I1) typical ignition, (I2) relatively high-speed ignition, (I3) single-kernel alternating dominant, (I4) main kernel dominant, and (I5) dual-kernel dominant modes. Using high-speed photography, the flame shape changes and ignition characteristics in the cases of successful and failed ignition with different pilot-stage vane angles were investigated.

The enhancement of heterobimetallic MOFs on the pyrolysis and laser ignition of FOX-7

The hydrothermal approach had been used to synthesize two new heterobimetallic Metal Organic Frameworks (MOFs), Ba4Pb4(CH3CO2)8[(CH6CO2)4Pb](CH3CO2)4 (PbBa-MOF) and Ba2Ni(CO2H)6(OH2)4 (NiBa-MOF), their structure and surface topography were then examined with XRD and SEM. By using the TG-DSC and TG-FTIR-MS methods, the pyrolytic decomposition properties of MOFs and their catalytic activities on the 1,1-diamino-2,2-dintroethene (FOX-7) pyrolysis were investigated. The PbBa-MOF has a single thermal decomposition process with a high thermal decomposition temperature, while NiBa-MOF has a three-stage thermal decomposition process initiated from a lower temperature. Furthermore, the thermolysis peak temperature of the FOX-7/PbBa-MOF and FOX-7/NiBa-MOF mixture has a great decrease by 24.2 °C and 27.4 °C compared with the FOX-7. However, the low pyrolysis peak temperature and the pyrolysis activation energy (Ea) are almost unchanged. The selective high temperature catalytic effect of the MOFs on FOX-7 results from the activation of -NH2 in the high temperature pyrolytic decomposition of FOX-7 by the metallic ions of the MOFs. This thermal catalytic property indicates that MOFs can promote the pyrolytic decomposition of FOX-7 while ensuring the safety requirements for the compatibility of energetic mixtures in the preparation of propellants. The relationship between the features of pyrolytic decomposition and laser ignition was finally covered and defined. The two MOFs decreased the minimum ignition energy and ignition delay time of the FOX-7. Novel MOFs combustion catalyst may strengthen ignition and combustion features of the high-energy and low-sensitivity solid propellants containing FOX-7.

Numerical Modeling and Analysis of Energy-Assisted Compression Ignition of Varying Cetane Number Jet Fuels for High-Altitude Operation

Abstract Computational fluid dynamics (CFD) simulations are performed to study the potential of energy-assisted compression ignition (EACI) strategy for enabling ignition and enhancing combustion of different cetane number jet fuels during high-altitude operation. EACI employs an ignition assistant (IA), which is an advanced glow-plug design with the ability to sustain higher temperatures for prolonged periods, to provide the necessary ignition energy for precise ignition control and enhanced combustion. In the numerical simulations, the combustion chemistry solver is coupled with a multicomponent wide distillation fuel mechanism, energy source modeling, and a turbulence-chemistry interaction model to accurately capture the ignition assisted-combustion. The simulation is first validated against optical engine measurements for cetane number (CN) 48 jet fuel and then transferred to another single-cylinder test engine to study the ignition and combustion characteristics of EACI with CN 35 jet fuel at varying IA temperatures. Simulation results show that EACI significantly improves fuel ignitability. Ignition delay reductions for CN 48 fuel of 57% and CN 35 fuel of 25% are noted at IA temperatures of 1550 K and 1405 K compared to when the IA is switched off. Furthermore, EACI improved the combustion efficiency to 99.7% compared to the 90% estimated for the IA off case in the optical engine.