Direct Ignition Research Articles

Direct near-infrared laser ignition of CL-20 by introducing DATNBI as a bi-functional additive: Energetic photosensitizer and self-assembly stimulator

The ignition strategy of energetic materials using low-energy near-infrared (NIR) laser has garnered significant attention due to its enhanced safety and reliability. This study explores the use of a relatively photosensitive but mechanical insensitive energetic material, DATNBI, to facilitate the self-assembly of nano-CL-20 crystals into polycrystalline particles though solvothermal induction, yielding a rough structure conducive to NIR laser ignition. The findings demonstrate that by adjusting the content of DATNBI, it is possible to achieve micro-nano controllable spherical CL-20/DATNBI (C/D) particles, with CL-20 as the primary component and DATNBI as the auxiliary component. The incorporation of DATNBI and the rough surface structure enhance the light absorption of C/D particles in the NIR band. Additionally, the unique synergistic effect between CL-20 and DATNBI during thermal decomposition further promotes NIR laser ignition. As expected, the C/D particles achieved self-sustained combustion and exhibited excellent combustion performance under a 1064 nm laser, which is challenging to be achieved with raw CL-20 or raw DATNBI. Furthermore, the relatively insensitive DATNBI and spherical structure reduced the impact sensitivity of the C/D particles. This multifunctional material strategy, integrating energy, safety environment-friendliness, and laser ignition performance, offers a novel approach for laser ignition of energetic materials.

Laser ablation ignition modes in a cavity-based supersonic combustor

A numerical and experimental study was conducted to investigate the Laser Ablation (LA) ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder. The experiments were operated under a Mach number 2.92 supersonic inflow, with stagnation pressure of 2.4 MPa and stagnation temperature of 1600 K. Reynolds-averaged Navier-Stokes simulations were conducted to characterize the mixing process and flow field structure. This study identified four distinct LA ignition modes. Under the specified condition, laser ablation in zero and negative defocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition (LADI) mode and Laser Ablation Re-Ignition (LARI) mode, correspondingly. LA ignition in a local small cavity, created by depressing the flow field regulator, could facilitate the ignition mode transforming from LARI mode to Laser Ablation Transition Ignition (LATI) mode. On the other hand, the elevation of the flow field regulator effectively inhibited the forward propagation of the initial flame kernel and reduced the dissipation of LA plasma, further enhancing the LADI mode. Based on these characteristics, the LADI mode was subdivided into strong (LADI-S) and weak (LADI-W) modes. Facilitating the transition of ignition modes through alterations in the local flow field could contribute to attaining a more effective and stable LA ignition.

Effect of Injection Timing on Performance and Emission of a Diesel Engine using Fuelled by Hydrogen Gas

The injection timing of pilot fuel in diesel engine working on dual fuel mode with gaseous fuel is a very important parameter at the start of ignition which affects performance and emissions of the engine. In this regard, the experiments were conducted on single cylinder 4-stroke, direct ignition diesel engine with a power of 3.50 kW at a constant speed of 1500 RPM. Kirloskar model TV1 with diesel as pilot fuel and hydrogen as gaseous fuel was employed. Experiments were conducted with the aim to determine the effect of advancing (21o bTDC) and retarding (17o bTDC) diesel fuel injection timing on the engine performance and emissions at various load conditions with the standard injection timing of 19o bTDC. The brake thermal efficiency (BTE) and exhaust emissions like NO­x, carbon monoxide (CO), carbon dioxide (CO­2) and hydrocarbon (HC) were analyzed with hydrogen (H2) as gaseous fuel. The results showed that dual mode (diesel and H2 gas) retards injection timing (17o bTDC) and gives a net increase in BTE efficiency at all load conditions with lower (20%) hydrogen substitution. At higher H2 substitution (40%), BTE is better for dual standard (19o bTDC) injection timing at all load conditions. Further NOx (ppm), HC (ppm), CO (%) and CO2 (%) emissions are significantly reduced with dual retard (17o bTDC) injection timing of the pilot fuel.

Phased transition from methane to hydrogen in internal combustion engines: Utilizing hythane and direct injection jet ignition for enhanced efficiency and reduced emissions

A strategic pathway to decarbonizing internal combustion engines and advancing toward sustainable energy includes the transition from conventional fuels to methane combustion, followed by methane-hydrogen mixtures, and ultimately to hydrogen-only combustion. This progression leverages the miscibility of hydrogen and methane, enabling the use of Hythane, a fuel blend that combines the advantages of both gases. Methane's widespread availability and existing infrastructure facilitate a cost-effective transition, while its combustion produces lower emissions compared to gasoline and diesel. Hydrogen's high reactivity and clean combustion properties enhance engine efficiency and reduce emissions, making it a crucial component in this phased transition. Challenges in homogeneous charge compression ignition (HCCI) combustion of CH₄-H₂ mixtures, such as controlling ignition timing and managing stable combustion, are addressed by the direct injection jet ignition (DIJI) technique. DIJI creates stratified air-fuel mixtures that ensure rapid and complete combustion, minimizing quenching and reducing heat losses. This study presents a comprehensive analysis of the combustion properties of methane and hydrogen, the benefits of phasing the transition with the availability of green hydrogen, and the technical challenges and solutions in developing HCCI and DIJI combustion systems for Hythane. The research underscores the potential of DIJI to enhance engine performance, efficiency, and emissions control, paving the way for a sustainable energy future in transportation.

Fundamental study on the factors influencing the stability of ammonia combustion and the effects of pre-chamber on the combustion characteristics

Ammonia is gaining attention as a carbon-free alternative fuel for internal combustion engines. However, its poor combustion characteristics hinder its development, especially the combustion instability at low equivalence ratios. At present, most literature has not studied the factors affecting ammonia flame propagation stability under high ambient temperature and pressure. Therefore, this paper focuses on this issue, as well as the promotion of jet ignition combined with blending methane, and the prediction method of the flame propagation state under different conditions is proposed. The experimental results demonstrate that the main reason for the difficulty of stable propagation of ammonia flame at low equivalence ratios in top direct ignition mode is the buoyancy effect. The relationship between the flame propagation state and the corresponding Froude number with the flame radius of 20 mm (Fr20) is established. The flame propagation of the mixture can be stable in top ignition mode when its Fr20 is larger than 0.89, and the flame propagation of the mixture is unable in top ignition mode when its Fr20 is less than 0.50. The Fr20 increases with temperature, decreases with pressure, and first increases and then decreases with the increase of the equivalence ratio. Among the three parameters, the equivalence ratio has the greatest correlation with the Fr20. The prediction results show that under engine conditions, blending 20 % methane can expand the stable combustion limit of ammonia, but the effect is less compared with increasing the equivalence ratio to 0.55 and 0.6. In jet ignition mode, a higher equivalence ratio of the mixture in the pre-chamber can expand the low equivalence ratio limit of stable combustion of the mixture in the main chamber due to the acceleration of the longitudinal propagation of the flame by the jet. The combustion characteristics of the mixture in the main chamber are closely related to its properties, so at a too-low equivalence ratio, the jet has a limited promotion, in addition, the effect of blending 10 % methane is also little.

Study on ignition mode transition of methanol pre-chamber jet ignition system controlled by boundary condition parameters

Optimizing boundary condition parameters is an effective means to substantially improve the combustion performance of methanol pre-chamber turbulent jet ignition systems. In this study, an optically accessible constant-volume combustion chamber was employed to delve deeply into the impacts of critical boundary condition parameters on the combustion performance of the pre-chamber jet ignition system. The findings suggest that adjusting the pre-chamber boundary condition parameters can lead to various jet ignition modes, including jet flame ignition, jet direct ignition, jet delayed ignition, jet wake ignition, and dual jet ignition. Different jet ignition modes result in variations in ignition timing, ignition location, combustion rate, and lean burn limits. Under identical initial temperature and pressure conditions, compared to jet flame ignition with the lowest combustion velocity and jet wake ignition with almost no lean burn capability, dual jet ignition can reduce the combustion duration by about 50% and elevate the lean burn limit by more than double. Unlike the patterns observed in traditional spark ignition systems, within the range of experimental tests, lowering the temperature and increasing the pressure significantly improved the lean combustion limit of the pre-chamber system and reduced the probability of jet wake ignition. This performance enhancement is attributed to the increase in the density of the mixture in the main combustion chamber.

Laser induced spark ignition of a gaseous methane–oxygen model rocket combustor

The spatio-temporal evolution of laser induced spark ignition of non-premixed gaseous methane and oxygen is investigated. The reactants are injected into an optically accessible combustion chamber from an oxidizer centered shear-coaxial injector. High-speed schlieren imaging and measurements of laser energy deposited are used to characterize ignition behavior at various spark locations throughout the chamber. A spatial map of ignition probability is generated from tests at multiple axial and radial locations from the point of propellant injection. The rate of pressure rise from successful tests reveals two modes of ignition dependent on the location of the laser-induced breakdown, direct and indirect, based on laser-induced breakdown occurring within reactant jet or in the recirculation region, respectively. Physical processes occurring over multiple timescales throughout the direct ignition method are first discussed. Ignition outcomes associated with the indirect method are determined by the hydrodynamic ejection protruding from the laser spark, the behavior of which is explored in detail using flow statistics extracted from images taken at a single spark location. The spatial–temporal progression of this jet is found to be dependent on deposited laser energy, leading to a relationship between the amount of energy added to the flow and ignition outcome. General bounds for spark location, deposited laser energy, and ejection behavior are identified to predict ignition outcomes. Cases that are an exception from these bounds are investigated in detail to understand the cause of unique behavior. These cases lie within regions of the variable space that are susceptible to stochastic elements of the flow.Novelty and Significance Statement: This work investigates laser induced spark ignition of O2 and CH4 issuing from a shear-coaxial injector in a model rocket combustor. Probability of ignition as a function of deposited energy and spatial location is studied with high-speed schlieren imaging and pressure measurements. Two distinct ignition modes that have previously not been identified, direct and indirect, are dependent on the laser deposition location with respect to the reactant jet. For indirect cases, where laser deposition is at a distance from the reactants, the hydrodynamic jet ejection generated from the breakdown of the plasma plays a critical role on ignition probability. The behavior of the ejection jet is characterized to provide a phenomenological description of the ignition process. The results of this research show the important interaction between chemical, fluid dynamic, and thermodynamic processes and their impact on laser ignition.

Near-infrared laser induced direct ignition of 4,4′,5,5′-tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine by constructing diverse crystal structures

Although laser ignition is considered to be one of the most promising ways to detonate energetic materials due to its high safety and reliability, it is still a challenge to achieve direct ignition of energetic materials by a laser with low-power and near-infrared (NIR) band. In this paper, a molecular self-assembly strategy based on recrystallization was utilized to prepare 4,4′,5,5′-tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine (DATNBI) crystals with various micro-nano structures. The characterization results suggest that DATNBI crystals with different degrees of roughness and defects by the induction of solvents and surfactants. The crystal defects can not only bring about the enhancement of light absorption of DATNBI in NIR band, but also advance its thermal decomposition, providing reliable support for direct laser ignition of DATNBI profit from the hot spot ignition theory. Combined with density functional theory, it is speculated that electrons of defect states achieve electron-hole recombination by laser radiation, thereby enhancing photothermal conversion. Compared with raw DATNBI, DATNBI crystals with rough surface and abundant defects can be directly ignited by a NIR laser and exhibits self-sustainable combustion. In summary, a direct NIR laser-ignitable energetic material has been prepared via appropriate crystal structure design.

A novel approach to enhance the combustion quality of C5 alcohol with 2-Ethylhexyl nitrate as a cetane enhancer in common rail direct ignition diesel engine

The purpose of this investigation is to explore the effect of 1-Pentanol and 2-Ethylhexyl nitrate (2-EHN), on the characteristics of a common rail direct injection (CRDI) diesel engine. The major feedstock for the production of 1-pentanol (bio-alcohol) is non food biomass waste. The conversion of waste biomass into useful energy contributes to the cleaner production of fuel and its utilization. The trial was conducted in a 2-cylinder CRDI test rig. The engine was fuelled with diesel, 40P60D (40% 1-Pentanol & 60% diesel v/v) and then 500, 1000 and 2000 ppm of 2-EHN was doped to 40P60D. The addition of 1-Pentnaol showed a slight negative effect on combustion at low and medium loads. Furthermore, an extension in the delay period (DP) and combustion duration (CD) was seen for 1-Pentanol blend. The doping of 2-EHN, enhances the cetane count and leads to improvement in the combustion parameters and a reduction in DP and CD was noted. The 1000 ppm of 2-EHN doped blend showed 8.7% of higher BTE and 8.61% lower BSEC compared to 40P60D, also 1.89% and 50% lower HC and CO at 80% load and 36.9% lower NO at 60% load in contrast to diesel. Among all the concentrations 1000 ppm of 2-EHN showed satisfactory results. It is concluded that 40% of 1-Pentanol with 1000 ppm of 2-EHN can be used as an alternative fuel to pure diesel without compromising in performance of the engine.

Effect of Fuel Injection Strategies on Performance, Regulated and Unregulated Emissions of a Gasoline Compression Ignition Engine

Abstract Gasoline compression ignition (GCI) mode engines are characterized by partially premixed charge combustion, leading to significant and simultaneous reductions of nitrogen oxides and particulate matter emissions. However, gasoline compression ignition engine operation suffers from a limited operating window. Air preheating and low-research octane number fuels are required to improve the engine performance. This experimental study used a blend of 70% (v/v) gasoline and 30% diesel as test fuel in a direct injection medium-duty compression ignition engine. Experiments were carried out at 5- and 10-bar brake mean effective pressure (BMEP) engine loads at 1500–2500 rpm engine speeds using a triple injection strategy (two pilots and one main injection) for all test conditions. The combustion phasing was kept constant with respect to crank angle to produce a high power output. The investigations examined engine performance and regulated and unregulated emissions. The test engine was initially operated in conventional diesel combustion mode with diesel for baseline data generation. Gasoline compression ignition mode operation demonstrated a remarkable 16% increase in the brake thermal efficiency and a substantial reduction of 65% in nitrogen oxide emissions compared to the baseline conventional diesel combustion mode. The GCI engine exhaust showed higher concentrations of regulated emissions, namely hydrocarbons and carbon monoxide, and unregulated trace emissions, such as methane, acetylene, toluene, inorganic gaseous species, and unsaturated hydrocarbons.

Forensic Investigation of Electrical Conduct Copper Bead Microstructure as an Effort to Identify Causes of Fire

The purpose of this study was to evaluate the characteristics of the bead formed due to short circuit, overload and direct flame treatment on NYM 3x1.5 copper power cable. Handling of short circuit and overload is carried out at a current load of 800% of the current carrying capacity (144 Amperes) and direct flame treatment is carried out at a temperature of 960 degrees Celsius. The bead specimens formed from each treatment were examined and tested in the laboratory: chemical composition examination, visual inspection, macro and micro structural examination, hardness testing, and SEM-EDS examination. The difference in the characteristics of the arc bead that is formed under short circuit conditions and overload is that in short circuit conditions the damage point is localized at a certain point, namely at the short circuit contact point, while under overload conditions the point damage is localized at one or several specific locations along the wire. The macro characteristic of arc beads formed under short-circuit and overload conditions is that they contain many cavities and a clear transition boundary between the melted/ re-solidified material and the non-melted material. While the characteristics of the granules in the form of globular formed in the direct flame treatment, do not show sharp transitions between melting/ re-solidified materials. The micro structure of NYM 3x1.5 beads of electrically conducting copper wire material under the treatment conditions: short circuit, overload and direct ignition, is an alpha (α) phase dendritic structure.

Experimental observation of the TJI-initiated HPDI gas combustion: Vertically crossed flame jet and methane jet

In the field of natural gas marine engines, the high-pressure direct injection (HPDI) technology is widely used to achieve emission reduction while maintaining equivalent thermal efficiency and power output compared to diesel engines. In these engines, the in-cylinder combustion is primarily initiated by the diesel spray flame near the top dead center (TDC). In the present work, pre-chamber turbulent jet ignition (TJI) is employed to substitute diesel injection to initiate the combustion of HPDI methane jets. The optical experiments of ignition and flame development in the TJI-HPDI system with various injector configurations and injection/ignition control parameters are conducted in a constant-volume combustion chamber (CVCC). It is revealed that with the increase of injection-ignition delay(ti), three ignition modes are observed sequentially: methane jet suppresses ignition, methane jet first suppresses ignition then promotes flame propagation, and direct ignition and promoted flame propagation. The effect of various injection-ignition delays and injection pulse width were explored. The injection-ignition delay significantly influences the combustion characteristics such as heat release rate, while the injection pulse width influences the duration of the lifted jet flame. The flame lift-off length first decreases and then increases due to variations in thermodynamic conditions and oxygen concentration. With a larger-nozzle injector, the critical injection-ignition delay to initiate the main chamber combustion is significantly reduced. Moreover, the use of different nozzle diameters leads to varying levels of turbulent intensity in the methane jet, which in turn affects the combustion behavior.

An analytical approach to converting vibration signal to combustion characteristics of homogeneous charge compression ignition engines

Homogeneous charge compression ignition (HCCI) is a promising low-temperature combustion technique for low-emission internal combustion engines. Unlike conventional engines, HCCI lacks a direct ignition control mechanism, necessitating closed-loop combustion control. This study proposes a phenomenological-based, cost-effective, and non-intrusive approach using vibration data analysis to determine essential combustion parameters. Experiments were conducted on a single-cylinder research engine with an accelerometer attached to the engine head. The engine operation envelope covered the whole engine’s operating area in naturally aspirated HCCI mode. Wavelet analysis revealed that combustion-related frequencies centered around 500 Hz, independent of operating conditions. The correlation-seeking analysis included peak acceleration amplitude and its crank angle with peak heat release rate (HRR) data. The peak HRR location was accurately identified within one degree when vibration amplitude exceeded the 100 m/s2 threshold. This encompassed 98.5% of the analyzed combustion cycles. The peak HRR prediction accuracy had a maximum error below 21% and was suitable to monitor reaction rates, especially in incomplete combustion and high ringing cycles.

Type Ia supernovae induced by primordial black holes from dark first-order phase transition

A primordial black hole (PBH) with mass 10−15≤MPBH/M⊙≤10−10 is currently beyond the sensitivity of both microlensing and black hole (BH) evaporation methods. A novel scenario has been proposed: When a PBH with mass 10−14≤MPBH/M⊙≤10−11 transits through a white dwarf (WD) made up of carbon and oxygen, Bondi-Hoyle-Lyttleton (BHL) accretion in a reactive medium creates a shock wave, which generates direct detonation ignition in the WD core and then leads to thermonuclear supernovae (SNe Ia). The aim of this study is to impose constraints on the PBH to dark matter (DM) abundance fraction, fPBH, via comparing the SN Ia event rates between PBH hypotheses and observational data. For PBH fraction less than unity, we found the observed event rate prefers PBH mass region, 7.6×10−13≤MPBH/M⊙≤6.1×10−12, under the Navarro–Frenk–White (NFW) profile. Meanwhile, the aforementioned PBH mass and abundance can be efficiently produced via a cosmological first-order phase transition (FOPT) in dark sector which associates with O(MeV) energy scale and thus gives rise to complementary signals of stochastic gravitational waves (GWs) with peak frequencies from 10−6 Hz to 10−5 Hz which can be probed by future μAres GW interferometer.

Deflagration and detonation induced by shock wave focusing at different Mach numbers

Shock wave focusing is an effective way to create a hot spot or a high-pressure and high-temperature region at a certain place, showing its unique usage in detonation initiation, which is beneficial for the development of detonation-based engines. The flame propagation behavior after the autoignition induced by shock wave focusing is crucial to the formation and self-sustaining of the detonation wave. In this study, wedge reflectors with two different angles (60° and 90°) and a planar reflector are employed, and the Mach number of incident shock waves ranging from 2.0 to 2.8 is utilized to trigger different flame propagation modes. Dynamic pressure transducers and the high-speed schlieren imaging system are both employed to investigate the shock-shock collision and ignition procedure. The results reveal a total of four flame propagation modes: deflagration, DDT (Deflagration-to-Detonation Transition), unsteady detonation, and direct detonation. The detonation wave formed in the DDT and unsteady detonation mode is only approximately 75%−85% of the Chapman-Jouguet (C-J) speed; meanwhile, the directly induced detonation wave speed is close to the C-J speed. Transverse waves, which are strong evidence for the existence of detonation waves, are discovered in experiments. The usage of wedge reflectors significantly reduces the initial pressure difference ratio needed for direct detonation ignition. We also provide a practical method for differentiating between detonation and deflagration modes, which involves contrasting the speed of the reflected shock wave with the speed of the theoretically nonreactive reflected shock wave. These findings should serve as a reference for the detonation initiation technique in advanced detonation propulsion engines.

Comparative study on the influence of incident heat flux on thermal runaway fire development of large-format lithium-ion batteries

In response to the growing demand for higher energy density in various applications, large-format batteries have gained popularity. However, the larger size of these batteries also increases their exposed area, which may lead to more severe thermal events. This study aims to understand the influence of incident heat flux on the occurrence and progression patterns of fires in large-format lithium-ion batteries. Two representative large-format lithium-ion batteries, 38 Ah LiNi0.3Co0.3Mn0.3O2 prismatic cell and 78 Ah LiNi0.8Co0.1Mn0.1O2 pouch cell, were investigated. To evaluate the thermal hazard to the environment, the heat release rates (HRR) of the lithium-ion battery fire were measured under incident heat fluxes ranging from 10 to 50 kW∙m−2, using the oxygen consumption principle. The results highlight significant differences in thermal runaway and fire development between the 38 Ah and 78 Ah cells, attributable to variations in structure and materials, and scale effect. The 38 Ah cell exhibited an evident venting stage, characterized by an unignited jet on the verge of ignition, followed by a transition from momentum-driven jet fire to buoyancy-driven jet fire. In contrast, the 78 Ah cell experienced direct ignition, accompanied by strong air entrainment, overflow flame, and flame sinking phenomena as the fire progressed. Notably, unlike the 38 Ah cell, the peak HRR, THR, and burning time of the 78 Ah cell were minimally sensitivity to the incident heat flux. Furthermore, a generalized relationship model between the incident heat flux and the ignition time was established and validated based on the energy conservation equation during the ignition stage of the cell. This model enhances our understanding of the interplay between incident heat flux and ignition time, contributing to the development of strategies for fire prevention and mitigation in large-format lithium-ion batteries.

Performance and emission characteristics of safflower oil biodiesel blended with nanoparticles and hydrogen on diesel engines of road and bridge machinery

Due to high usage and demand of fossil fuels, the search of alternative fuels is necessary to safeguard the natural resources. In this study, safflower oil, CeO2 nanoparticles and hydrogen blends are used in a direct ignition engine of road and bridge machinery to study the performance and emission properties of test fuels. Hydrogen was added along with nanoparticles on biofuel while conducting the tests. Hydrogen was supplied at a mass flow rate of 10 L per minute throughout the testing of road and bridge machineryignition engine. The results of the tests were used to compute the road and bridge machinery ignition engine performance and emission properties. In order to compare the various biodiesel blends all the tests were carried out between 1800 rpm and 2800 rpm. In addition to the pure diesel and biodiesel blends, these nanoparticles and hydrogen blended fuels enhances the performance. Brake-specific fuel consumption was reduced while power, torque, and thermal efficiency were all increased. Road and bridge machinery ignition engine torque increased by 6% and 5% for S10NH and S20NH test fuels due to addition of hydrogen and nanoparticles to the normal blend, respectively, as compared to blend without nanoparticles and hydrogen. Pure C100 had a BTE of 24%, while S10 and S20 had a BTE of 21.9 %and 21.3%, respectively at lower engine speed. Enriched biodiesel with nanoparticles and hydrogen reduces CO and CO2 emissions, as compared with pure diesel. The primary goal of lowering CO and CO2 emissions was achieved, although the NOx emission level increased marginally.

Ammonia energy storage for hybrid electric aircraft

This work considers the development of a hybrid electric vertical takeoff and landing aircraft with an NH3 engine. An NH3 cracker with an external heat supply from the engine and a high-temperature catalytic reactor is needed to crack part of the NH3 in H2 and N2. The engine has two turbochargers in cascade, an intercooler, and an SCR catalyst with additional NH3 injection before the catalyst to control emissions. The H2 is used to ignite an NH3 mixture which may also be enriched with hydrogen to address particularly slow-burning points. The proposed learn burn engine which features direct injection and jet ignition of H2 may have power densities above 100 kW per liter and fuel conversion efficiencies approaching 50%. This engine can be further specialized to work on a narrow range of speeds and loads, ideally, one single point, to produce electricity on board the aircraft. The energy storage per unit mass of the complete system is expected to reduce vs. diesel but not dramatically. Importantly, it is much better than the storage of energy in a battery.

Powerful H2 Engines with Direct Ignition for Medium-/Heavy-Duty Applications

Powerful H2 Engines with Direct Ignition for Medium-/Heavy-Duty Applications

Design and fabrication of energetic Al/Ni exploding foil with enhanced energy efficiency and plasma density for direct ignition

In order to lower the firing voltage, an energetic Al/Ni exploding foil (Al/Ni-EF) with enhanced energy efficiency and plasma density was prepared in this study, to realize the direct ignition of pyrotechnics. An Al/Ni reactive multilayer foil (Al/Ni-RMF) was firstly synthesized by magnetron sputtering and wet etch method, and its structure and exothermic behavior were investigated. Scanning Electron Microscopy, Atomic Force Microscope and X-ray Diffraction characterizations confirmed the periodic layer structure of Al/Ni-RMF with a total thickness of 4 μm. The highest heat release in Al/Ni-RMF could be achieved theoretically when the ratio of Al and Ni was 1.5, and thus the thickness of single Al and Ni layer was determined to be 300 nm and 200 nm, respectively. The obtained Al/Ni-RMF was subsequently fabricated to be an exploding foil, and its electric explosion performance was further studied. Energy efficiency of the Al/Ni-EF was measured to be 85.9% during the electric explosion process, which was 30.9% higher than that of Cu exploding foil (Cu-EF). The plasma generated at Al/Ni-EF had larger volume, longer duration time and higher temperature than Cu-EF due to the intermetallic reaction between Al and Ni, which was beneficial for the direct ignition of Boron/Potassium Nitrate composition (B/KNO3, BPN). Afterwards, a special Al/Ni-EF ignitor without slapper was constructed, and the fierce ignition of BPN at the minimum discharge voltage of 800 V was observed. Above results confirmed the feasibility of direct ignition, such a unique strategy was beneficial for the development of low-energy, low-cost and miniaturized ignitor.