Ignition Reaction Research Articles

Oxidation and ignition of aluminum nanomaterials

The oxidation and ignition of aluminum nanoparticles with a mean diameter of 150 nm are investigated with the help of simultaneous thermal analysis, X-ray powder diffraction, energy dispersive X-ray spectra analysis (EDS) and scanning and transmission electron microscopy at heating rates of 2-30 K min(-1). A unique early ignition reaction is observed when the heating rate is ≥8 K min(-1) and there is a co-existence of various polymorphs of alumina (γ-, δ-, θ-, and α-Al2O3) below the melting temperature of aluminum nanoparticles. It is proposed that such an early ignition reaction is due to a combined effect of solid phase transformation of the alumina shell and the early melting of the aluminum core, and is responsible for the co-existence of various polymorphs of alumina at the low temperature. The ignition temperature increases approximately with the increase of the heating rate. Regardless of the heating rate, the oxidation scenario can be described by a three-stage reaction with the main reaction occurring before the melting of aluminum nanoparticles.

Ignition reactor and pump pulse parameters in a reactor–laser system

The experience gained in operating a demonstration nuclear-pumped laser in stand B (Physics and Power- Engineering Institute (FEI)) with a pulsed ignition reactor based on the 235U BARS-6 reactor is analyzed. It is shown that laser block → ignition reactor neutron feedback coupling greatly limits the parameters of the pump pulse from the amplifier. A method is proposed for decreasing the feedback by replacing 235U with the threshold fissile element 237 Np in the ignition reactor. Such a reactor will increase by approximately 15-fold the energy and power of the pump pulse in the laser block of the demonstration reactor of the nuclear-pumped laser in stand B.

Combustion enhancement in a supersonic flow by simultaneous operation of DBD and plasma jet

A new strong ignition system combining a plasma jet (PJ) torch and a Dielectric Barrier Discharge (DBD) device in a supersonic flow was developed in this study. The DBD device, which generates nonequilibrium plasma and the PJ torch, which injects equilibrium plasma jet were installed straight on the bottom wall of the combustor. Nonequilibrium plasma was successfully generated in a supersonic flow by DBD. Discharge power of DBD was at most 10W, and it was considerably smaller than that for the PJ. Ignition test of hydrogen fuel perpendicularly injected into a supersonic airflow was conducted under simultaneous operation of the DBD device and the PJ torch. Although ignition never occurred by single operation of the DBD device in a non-heated supersonic flow, combustion enhancement effect by DBD on relatively weak and unstable flame was detected by simultaneous operation of it with the PJ torch. However, the combustion enhancement did not occur in a flow field where strong combustion occurred with only the PJ. The main mechanism of combustion enhancement by the DBD plasma was considered to be existence of O3. The O3 has a much longer lifetime than the other species and it accelerates ignition reaction of a H2/air mixture as almost the same as O radical.

Lift-off and stabilization of n-heptane combustion in a diesel engine with a multiple-nozzle injection

This paper presents a joint numerical and experimental investigation of flame lift-off and stabilization mechanisms in heavy-duty diesel engines. The injection strategy, employing different nozzle configurations, allows for quantification of the impact of varying inter-jet angle spacing in the presence of swirl. For this purpose, three different inter-jet angles are chosen in this study; 45°, 90° and 135°. Large-eddy simulations are performed utilizing a detailed chemical kinetic mechanism for n-heptane to resolve the turbulent fuel and air mixing and to capture the important species surrounding the ignition and flame-fronts to describe the flame stabilization process. Measurements are carried out for OH chemiluminescence to identify the flame lift-off position in an optical accessible engine. In general, the swirl flow in the ambient air shows a great impact on the lift-off, with a 15% difference in the lift-off lengths on the upwind and downwind side of the jet. The LES results show that important ignition reactions undergo in a broad region in front of the lift-off position. With decreasing inter-jet angle, it is shown that the impact of transportation of hot products from adjacent jets becomes more prominent. Hot reservoirs surrounding the lift-off length increase the local ambient temperature and augment the auto-ignition process by mixing of the cold injected fuel and hot air.

Inverse Hysteresis Phenomena During CO and C3H6 Oxidation over a Pt/Al2O3 Catalyst

It is well known that conversion as a function of temperature hysteresis can occur during ignition and extinction exothermic reaction experiments, such as CO oxidation over Pt/Al2O3, with the activity during the ignition process not matching that during the extinction process. Conversions being higher during extinction than that during ignition are often observed. Several explanations have been proposed in which heat effects, different catalyst surface states, and different Pt oxidation states are the most common. In this work CO oxidation hysteresis behavior, when in a mixture with C3H6, was investigated. The results show that when C3H6 was absent, CO oxidation followed normal hysteresis behavior; however, when C3H6 was added to the mixture, the catalytic activity during the extinction phase decreased. As the C3H6 concentration in the mixture increased, the hysteresis loop became smaller and ultimately reverse hysteresis was observed. The decrease in catalytic activity during extinction was due to the formation of C3H6 oxidation intermediate species. These species competed with CO for active sites, thus inhibiting CO oxidation, and were not present during ignition as CO was the dominant adsorbed species when starting at low temperature.

Controlling Gasoline Low Temperature Combustion by Diesel Micro Pilot Injection

The simultaneous reduction of fuel consumption and pollutant emissions, namely NOx and soot, is the predominant goal in modern engine development. In this context, low temperature combustion concepts are believed to be the most promising approaches to resolve the above mentioned conflict of goals. Disadvantageously these combustion concepts show high peak pressures or high rates of pressure rise due to early ignition and high reaction rates especially at high loads. Furthermore, there are still challenges in controlling combustion phasing. In this context using a small amount of pilot diesel injected directly into the combustion chamber to ignite a highly diluted gasoline air mixture can overcome the aforementioned difficulties. As the gasoline does not ignite without the diesel, the pilot injection timing can be used to control combustion phasing. By increasing dilution even high loads with low rates of pressure rise and without knocking are possible. This paper shows the results of experimental investigations carried out on a heavy duty boosted single cylinder diesel engine. Based on the indicated cylinder pressure, the combustion process is characterized by performing knock analyses as well as thermodynamic analyses. Furthermore, an optically accessible engine has been set up to investigate both the diesel injection and the combustion process by means of digital high speed imaging. Together with the thermodynamic analyses the results of these optical investigations make up the base for the presented theoretical model of this combined diesel-gasoline combustion process. To show the load potential of this Dual-Fuel-CAI concept, the engine was operated at 2100 1/min with an IMEP of 19 bar. NOx emissions did not exceed 0.027 g/kWh.

Kinetic Parameters of Binary Iron/Oxidant Pyrolants

The thermal properties of pyrotechnic mixtures containing iron powder as fuel and KNO3, KClO3, and KClO4 as oxidants are reported. The thermogravimetry–differential thermal analysis results for pure components and corresponding pyrotechnic mixtures revealed that the melting point, decomposition temperature, and rate of oxygen releasing of the oxidants have dominant effects on ignition reaction of the pyrotechnic mixtures. The apparent activation energy and activation parameters for the combustion processes were evaluated from the differential scanning calorimetry experiments. Based on the ignition temperatures obtained and the resulting kinetic data, the thermal reactivity of the pyrotechnic mixtures was found to decrease as in the order Fe + KClO3 > Fe + KNO3 > Fe + KClO4.

Critical Initiating State and 2D Lagrangian Analysis of Pressed TNT

Shock initiation experiments on the explosives pressed TNT was performed to obtain in-situ pressure/radial displacement gauge data for the purpose of determining the Ignition and Growth reaction flow model with proper modeling parameters. The pressure and radial displacement were got by manganin-constantan composite 2-D Lagrange sensor. The particle velocity, relative volume, internal energy and fraction reacted of shock initiation process has been calculated by 2-D Lagrangian analysis method.

Hypergolic Reaction of Dicyanamide-Based Fuels with Nitric Acid

Understanding the ignition reactions for hypergolic propellants is an important step in developing a complete reaction model that can be used in engine design and optimizing the composition of the fuel−oxidizer pair. To that end, an experimental study of the hypergolic reaction of sodium dicyanamide with nitric acid was conducted to investigate a recently proposed reaction mechanism for ignition of this family of ionic liquids. Sodium dicyanamide was used to simplify contributions to products from the cation of the fuel. Gas-phase reaction products were studied using microprobe sampling and mass spectrometric analysis. In addition, a chemical assay was used to test for the presence of dinitrobiuret, the key intermediate in the proposed mechanism. Most of the results from the study support the proposed mechanism, with the only exception being the lack of direct evidence for dinitrobiuret. Additional reactions for the ignition reaction scheme are proposed.

Effect of compact density and preheating temperature of the Al–Ti–C preform on the fabrication of in situ Mg–TiC composites

Magnesium reinforced in situ TiC particulates was successfully synthesized by utilizing the self-propagating high temperature synthesis (SHS) process. The result showed that preform temperature and compact density have effects on the SHS reaction. It is observed that when the compact density was below 68% of the theoretical density, no SHS reaction occurred. However, with an increase in density from 68 to 72%, the successful thermal explosion reaction was observed in the Mg melt. Besides this, the effect of preheat temperature on the fabrication of Mg/TiC composite was extensively studied and found that the preheat temperature below 300 °C failed to give rise to SHS reaction. However, the preheat temperature of 450, 500, and 550 °C favors the reaction inside the liquid melt, but the temperature of 600 °C leads to the ignition reaction in the preheating furnace itself. SEM and EDX study confirms fine distribution of TiC in the matrix.

Studies on the ignition behaviour of boron powder

The ignition behaviour of boron powder, prepared through electrowinning process, was studied by using thermogravimetry coupled with simultaneous differential thermal analysis (TG-SDTA). The dependence of the inception of the ignition reaction on the partial pressure of oxygen, particle size of the boron powder and heating rate was investigated. It was observed that all these factors affect the ignition temperature. Boron powder with a mean particle size of about 10 mu m was found to be susceptible to ignition in oxygen even at 783K. In general, the susceptibility to ignition was found to vary inversely with the degree of crystallinity. Presence of carbon was found to retard the oxidation of boron and raise the ignition temperature. These results are useful in safe handling and storage of finely divided boron powder and in the subsequent production of boron carbide from it. (C) 2009 Elsevier B.V. All rights reserved.

Influence of pH on nanosized Mn–Zn ferrite synthesized by sol–gel auto combustion process

Sol-gel auto combustion process was employed to synthesize nanosized Mn-Zn ferrite at different pH values (\1, 5, 6, 7, 8 and 10). Although self propagating combustion behavior of gel was noted at pH 5 but more effective com- bustion was observed at pH 6. The smoldering effect was observed in gel prepared at pH 7, 8 and 10, whereas pH \ 1 showed localized burning. Thermogravimetric (TG) and X-ray diffraction (XRD) analyses were done to investigate the effect of pH on the combustion behavior, particle size and the formation of desired magnetic (spinel) phase. From TG curves of burnt powders, activation energy of ignition reaction at each pH value was calculated. The results showed that fuel to oxidant ratio and the amount of gel residuals decided the value of activation energy required to further purify the burnt powders. Calcination parameters (time and temperature in air) of powders P1 and P6 synthesized at pH \ 1 and pH 6 were also determined. B-H loop results showed that calcined powder C6 was more ferromagnetic than C1 due to fully developed spinel phase and larger par- ticle size.

Numerical study of ignition mechanism of n-heptane direct injection compression-ignition engine

A detailed chemical dynamical mechanism of oxidation of n-heptane was implemented into kiva-3 code to study the ignition mechanism of a high-temperature, high-pressure, three-dimensional-space, transient turbulent, non-homogeneous, mono-component fuel in the engine. By testing the quantity of the heat released by the chemical reaction within the cylinder cell, the elementary reaction showing an obvious increase in the cell temperature was defined as ignition reaction and the corresponding cell as ignition position. The main pathway of the ignition reaction was studied by using the reverse deducing method. The result shows that the ignition in the engine can be divided into low-temperature ignition and high-temperature ignition, both of which follow the same rule in releasing heat, called the impulse heat releasing feature. Low-temperature ignition reaction, whose ignition reaction is c5h9o1-4 = ch3cho + c3h5-a, follows the oxidation mechanism, while high-temperature ignition reaction, whose ignition reaction is c2h3o1-2 = ch3co, follows the decomposition mechanism. No matter which ignition it is in, the chemical reaction that restrains the ignition reaction from lasting is the deoxidization reaction of alkylperoxy radicals.

Performance and Combustion Characteristics Analysis of HCCI Engine Operation with Diesel Like Fuels

HCCI is considered a very promising solution to reduce engine pollutant emissions, however so far only experimental prototypes have been inspired by this concept. HCCI combustion of both DME and n -heptane fuels display a distinct two-stage ignition reaction with the first stage taking place at fairly low temperatures and the second stage taking place at high temperatures. The second stage is responsible for the main stage of the heat release process. In this study, a single-zone, zero-dimensional, thermo-kinetic combustion model has been developed. MATLAB software is used to predict engine performance characteristics of HCCI engines using two types of diesel fuel: Dimethyl ether and n -heptane. The effects of intake temperature and pressure, fuel loading and addition of EGR gases on auto-ignition characteristics, optimum combustion phasing, and performance of the HCCI engines are considered in this study.

Ignition of n-heptane pool by heated stagnating oxidizing flow

The ignition temperature of a liquid pool of n-heptane by heated oxidizer in a stagnation flow was experimentally determined for system pressures of 0.61–3 atm and pressure-weighted strain rates of 60–350 s −1. The surface of the liquid pool was maintained at a fixed location through continuous replenishment. The state of ignition was brought about, and monitored, by gradually increasing the oxidizer temperature. The strain rate was determined by seeding and measuring the oxidizer flow velocity using laser Doppler velocimetry (LDV). Computational simulation of the ignition event with detailed chemistry and transport was conducted by using a stagnation-flow code. The kinetic mechanisms utilized are a high-temperature n-heptane oxidation model, with 130 species and 955 reactions, and a reduced one of 58 species derived from a detailed mechanism of 561 species and 2539 reactions. The former mechanism yielded better agreement with the experimental measurements in general over the conditions examined. It was also found that the mole fraction of n-heptane at the interface changed only slightly with pressure and strain rate, and can be considered to have minimal effect on the ignition responses studies herein. A recently developed explosive mode analysis (EMA) was conducted to identify the controlling radicals and reactions in the non-premixed ignition of n-heptane.

Nanosecond laser induced ignition thresholds and reaction velocities of energetic bimetallic nanolaminates

Thresholds for optically igniting self-propagating reactions are quantified for energetic Ni/Ti, Co/Al, and Al/Pt nanolaminates, where smaller enthalpy material pairs required larger laser ignition fluences. The threshold fluences (J/cm2) for ignition by 30 ns laser pulses focused to ∼8 μm spot size varied from 720 to 15 000 J/cm2 for Ni/Ti, 8.6 to 380 J/cm2 for Co/Al, and 3.2 to 27 J/cm2 for Al/Pt. Conversely, smaller enthalpy nanolaminates exhibited reduced steady-state propagation speeds ranging from 0.05 to 0.9 m/s for Ni/Ti, 0.6 to 8.5 m/s for Co/Al, and 24 to 73 m/s for Al/Pt. Increasing the laser spot diameter tenfold reduced the ignition threshold fluence by as much as two orders of magnitude.

Fundamental Combustion Properties of H2/CO Mixtures: Ignition and Flame Propagation at Elevated Pressures

Because of the current interest in the use of syngas in gas turbine applications, this article provides an overview of the fundamental combustion characteristics of H2/CO mixtures, with emphasis on ignition and flame propagation at high pressures. Specifically, the effects of pressure on the fundamental combustion properties, including auto-ignition delays, forced ignition limits, and laminar flame speeds, are demonstrated and discussed through several recent high-pressure experiments. The controlling reactions in ignition and flame propagation are identified. Through comparison of the newly obtained high-pressure experimental data and the computational results based on existing kinetic models, discrepancies in the rate parameters for the sensitive reactions are also discussed.

Shock initiation of composition B and C-4 explosives: Experiments and modeling

Shock initiation experiments with composition B and C-4 HE were performed to obtain in situ pressure gauge data for the purpose of providing the ignition and growth reactive flow model with proper modeling parameters. A 100-mm-bore propellant-driven gas gun was utilized to initiate the explosive charges containing manganin piezoresistive pressure gauge packages embedded in the explosive sample. Experimental data provided new information on the shock velocity-particle velocity relationship for each of the investigated material in their respective pressure range. The run-to-detonation distance points in the pop plot for these experiments showed agreement with previously published data, and ignition and growth modeling calculations resulted in a good fit to the experimental data. Identical ignition and growth reaction rate parameters were used for C-4 and composition B, and the composition B model also included a third reaction rate to simulate the completion of reaction by the TNT component. This model can be applied to shock initiation scenarios that have not or cannot be tested experimentally with a high level of confidence in its predictions.

Thermal investigation of fabricating porous NiTi SMA by SHS

In this paper, the porous NiTi shape memory alloy (SMA) fabricated by self-propagating high-temperature synthesis (SHS) has been investigated experimentally and numerically. The mathematical models about the ignition and the sintering were constructed to investigate the effect of the preheating temperature and the coil temperature on the combustion. The results showed that the temperature difference between the ignition face and the bottom face was large due to low heat transfer conductivity. The ignition time would increase with the decrease of the coil temperature and the preheating temperature. The temperatures for different locations showed a strong dependence on the combustion time for lower preheating temperature, for the preheating temperature 1173 K, this mode of the combustion has transferred from SHS to thermal explosion. The transient partial molten phenomenon occurred during the process of combustion, which was more homogenous for preheating temperature 873 K. The mean velocity of the combustion wave was investigated systematically. An experiment was also carried out to investigate the ignition and SHS reaction for porous NiTi alloy in this paper. It was found that the results of experiment and numerical simulation were shown in good consistence.

MS2-2: Large Eddy Simulation of Diesel Spray Flame using KIVA-LES with Flamelet Model and CIP Scheme(MS: Modeling and Simulation,General Session Papers)

LES of Diesel spray flame has been conducted using KIVA-LES code where flamelet model is incorporated to improve the modeling of the diesel spray flame. To reduce the computational cost, the ignition reaction is simulated with Shell model, while the combustion is modeled using FTS model with one-step reaction. The results show that the unsteady process of diesel spray flame was predicted with flamelet approach, although the 333 hour is needed to simulate 5.0 ms after start of injection. Furthermore the mixture fraction and temperature map shows that the combustion phase is complicated significantly compared to the jet flame, because the droplet evaporation is affected on the fuel vapor supply and cooling locally in the diesel spray flame.