Abstract:Semiconductor laser ignition system has not only been widely applied in safe and reliable ignition but also possesses obvious advantaged for anti-jamming in complex electromagnetic environment ，due to its small size, light mass and energy transmission by optical fiber. To investigate the ignition characteristics of laser igniter, a new type of semiconductor laser system and laser igniter filled with micron-sized B/KNO₃/PF were designed and prepared. TG-DSC, SEM, TEM, EDS, laser reflectance and Laser induced breakdown spectroscopy were used to study the thermal behavior, morphology, distribution of element, laser absorption efficiency, and emission spectra of B/KNO₃/PF. Then the ignition characteristics of B/KNO₃/PF igniter were studied by the semiconductor laser ignition system. The results showed that the initial reaction temperature of B/KNO₃/PF decreased and the heat release increased with the higher PF mass ratio and the smaller particle size in the DSC curve. The ignition process of the laser igniter can be divided into two stages: first ignition and secondary ignition. The pulse laser had a significant effect on the ignition characteristics of the igniter. The igniter could normally ignite with the 50% ignition energy of 6.23 mJ and 12.54 mJ, respectively, when the laser pulse were 5 ms and 10 ms. The first ignition delay time of 3.50-4.69 ms, secondary ignition delay time of 7.23-8.08 ms, and flame duration of 58-83.5 ms were produced in the laser igniter by changing the laser pulse and energy. The laser ignition system cannot motivate the igniter to fire normally when the laser pulse was 2 ms. These characteristics were consistent with the energy output law of semiconductor laser.

Abstract:The ignition delay times (IDTs) of two different certified gasoline and diesel fuel blends are reported. These measurements were performed in a shock tube and in a rapid compression machine over a wide range of experimental conditions(φ= 0.5-2.0, T=700-1400 K and p=10-20 bar) relevant to internal combustion engine operation. In addition, the measured IDTs were compared with two relevant gasoline fuels: Coryton gasoline and Haltermann gasoline systematically under the same experimental conditions. Two different gasoline surrogates a primary reference fuel (PRF) and toluene PRF (TPRF) were formulated, and two different gasoline surrogate models were employed to simulate the experiments. Typical pressure and equivalence ratio effects were obtained, and the reactivity of the four different fuels diverge in the negative temperature coefficient (NTC) regime (700-900 K). Particularly at 750 K, the discrepancy is about a factor of 1.5-2.0. For the high Research Octane Number (RON) and high-octane sensitivity fuel, the simulation results obtained using the TPRF surrogate was found to be unreasonably slow compared to experimental results, due to the large quantity of toluene (77.6% by volume) present. Further investigation including reactants′concentration profile, flux and sensitivity analyses were simultaneously carried out, from which, toluene chemistry and its interaction with alkane (n-heptane and iso-octane) chemistry were explained in detail.

Abstract:In order to study the effect of dynamic shock on solid propellant during the ignition process of solid rocket motor, a simulation setup based on quenched combustion was designed. The setup is composed of an ignition bolt, a combustion chamber, and a releasing pressure bolt. The metal burst disk is installed in the shear hole of the releasing pressure bolt and controls the ignition pressure precisely during the ignition shock process. Poly(BAMO-THF)/AP/Al solid propellant samples,molded into hollow cylinder, were used to evaluate the simulation shock process in setup. The p-t curves show that the blow-out pressure of burst disk is corresponding to the measured blow-out pressure in strong ignition mode and the pressure deviation is less than ±6%. The calculated pressurization rate according to the collected p-t curves can reach 7000 MPa·s^-1 at 10 MPa ignition and 12000 MPa·s^-1 at 15 MPa ignition, which are much more than the pressurization rate for actual ignition process of solid rocket. After simulation ignition shock experiment, filler particles implanted in the end face of propellant samples are damaged, while the inside surface basically keeps an intact condition. Compressive strength generally increases after ignition shock process, while the strain value at the point decreases when the compressive strength begins to rise. It is included that propellants with unstable structure are easier to be damaged and the mechanical properties would be changed during simulation ignition shock process.

Abstract:Due to their extremely low vapor pressure, low toxicity and high thermal stability, hypergolic ionic liquids are considered to be the most potentially green fuels to replace hydrazine and its derivatives as a new generation of propellant. A better understanding of hypergolic combustion and ignition process will promote the practical application of ionic liquids-based propellant systems. In this paper, recent advances in ignition and combustion mechanism of hypergolic ionic liquids are reviewed, which include three aspects: reaction routes and mechanism, ignition and combustion process, and theoretical prediction of hypergolicity. The reaction mechanism of dicyanamide anion and nitric acid, several stages and phenomena of ignition and combustion of hypergolic ionic liquid, several methods for predicting hypergolicity are introduced and summarized. The future researches should include the reaction mechanism of other anions, the development of green oxidizer to replace those toxic ones, normalization of the ignition device and method, and the accurate prediction of ignition performance.

Abstract:Endothermic hydrocarbon fuels undergo thermal cracking before entering the combustion chamber and can produce a mixture of unreacted fuels and pyrolysis products (i.e. cracked fuels). The objective of this work is to investigate the effects of pyrolysis conversions, pyrolysis pressures, ignition pressures and free radicals on ignition characteristics of cracked n-decane over temperature of 1300-1800 K, pressure of 0.1-3.0 MPa and equivalence ratio of 1.0. Components of the thermally cracked n-decane at 3.0 and 5.0 MPa in a flow reactor were calculated theoretically using an accurately combined mechanism, which are in good agreement with the experimental results in literature. The results showed the conversion rates of n-decane cracking at 3 and 5 MPa are 46.2% and 58.8%, respectively. The distribution of cracking products is consistent, but the ethylene content decreases with the increase of pressure, while the alkane content increases with the increase of pressure. Meanwhile, the content of free radicals at 3 MPa is slightly higher than that at 5 MPa, but the content of free radicals is very low. Ignition delay time increases with the decreasing of n-decane conversion and pyrolysis pressure, while higher ignition pressure can shorten it significantly. Furthermore, the presence of free radicals in cracked n-decane could accelerate the ignition process with ignition delay time shortening more than 15% when the conversion was less than 40%, compared with that of cracked n-decane without radicals.

Abstract:Aviation kerosene is a typical endothermic hydrocarbon fuel, and its pyrolysis gas absorbs heat before entering combustion chamber, which plays an important role in the heat protection of high-speed aircraft. Auto-ignition delay time of hydrocarbon fuel and its pyrolysis gas is one of main parameters for ramjet design, and is important data to validate the combustion reaction mechanism. In this work, the reflected shock wave was used to ignite fuels. Aviation kerosene and its pyrolysis gas in a chemical shock wave tube was studied. Ignition delay time was defined as the time interval between the arrival of reflected wave indicated by the jump of pressure signal and the onset of CH* emission signal. Auto-ignition delay times of RP-3kerosene，pyrolysis gas, hydrogen, methane, ethylene and ethane were measured in the temperature range of 900-1820 K, at pressure of 1.01×10⁵ Pa and equivalence ratio of 1.0. Experimental results demonstrate that ignition delay time decreases with the increase of temperature. In the same condition, ignition delay time of methane is the longest and that of hydrogen is the shortest, and the ignition delay of pyrolysis gas is slightly longer than that of aviation kerosene. The activation energy of pyrolysis gas is very close to that of aviation kerosene, around 180 kJ·mol^-1.The lowest ignition activation energy of all single component is hydrogen, which is 127.8 kJ·mol^-1. The experimental results were compared with the simulation results of combustion kinetic mechanism, which can predict the influence of temperature on ignition delay time. Furthermore, sensitivity analysis of the mechanism was carried out, and the main elementary reactions affecting fuel ignition were obtained.

Abstract:In order to investigate the dynamic behavior and ignition mechanism of Al/polytetrafluoroethylene（PTFE） reactive material under dynamic loading, a Split Hopkinson Pressure Bar (SHPB) was used to conduct the dynamic compression experiment on reactive materials with different molding pressure. Experimental results show that the Al/PTFE reactive material exhibits typical elastic-plastic mechanical behavior under dynamic loading at strain rate ranging from 2960 s^-1 to 5150 s^-1. The yield strength and hardening modulus of Al/PTFE reactive materials do not show strain rate effect when the molding pressure is 50-150 MPa. The velocity ignition threshold increases slowly from 28.77 m·s^-1 to 29.22 m·s^-1 with the molding pressure. When the molding pressure increases to 100 MPa, the velocity ignition threshold drops significantly to 26.60 m·s^-1. With the increase of the impact velocity, the ignition delay time for reactive materials with the molding pressure of 100-150 MPa decreases from 1000-1100 μs to 600-700 μs, while that of reactive materials with the molding pressure of 30-80 MPa maintains at 600-700 μs. Combining with results of Scanning Electron Microscopy, it is found that the local larger pores inside the reactive materials with higher molding pressure is the main factor for the sudden drop of the velocity ignition threshold. Therefore, the impact ignition characteristics of Al/PTFE reactive materials are mainly related to the external loading form and the internal micro-morphology.