Ignition Delay and Ignition Modes in Zeeman Laser Gyroscope

Electrostatic discharge ignition of nanocomposite thermites prepared by Arrested Reactive Milling was investigated. The powders 2Al–3CuO and were placed in a sample holder and subjected to an electrostatic discharge from a discharging capacitor. Their optical emission was monitored. Two ignition modes were detected: immediate ignition of individual particles and delayed ignition of a cloud of aerosolized powder. Experiments addressed the effects of material composition and morphology, aging, energy input, layer thickness, and environment on the ignition mode and ignition delays. Prepared thermites were blended with pure metal powders to study ignition of such blends. Individual particle ignition was observed for samples prepared as monolayers in air and argon and for any samples in vacuum. For thicker samples in air and in argon, a delayed powder ignition mode was observed. The delays varied from to several milliseconds. Powders of 2Al–3CuO had shorter ignition delays compared with . For both materials, delays decreased for the powders prepared using longer milling times. For 2Al–3CuO, aged powders ignited after longer delays compared with the freshly prepared powders; however, shorter delays were observed for the aged . Electrostatic discharge energy and layer thickness (except for a monolayer) did not affect the ignition delay. Blending nanocomposite thermites with Al and Ti powders reduced their electrostatic discharge ignition sensitivity and caused longer ignition delays.

Numerical investigation of physicochemical effects of CO2 on coal particle ignition in O2/CO2 ambience

Analytical expressions for calculating the time characteristics of ignition of gas mixtures by a heated body are obtained for the first time with the help of the wave theory of ignition. It is shown that ignition can occur in three different modes: kinetic (one‐temperature), diffuse (two‐temperature), and transitional, which combines the properties of both diffusion and kinetic modes. The parametric region of implementation of each possible ignition mode is determined. It is found that the transition from the kinetic to the diffusion mode occurs as the temperature of the heater changes only by one characteristic interval and is accompanied by a jumplike decrease both in the ignition delay and in the amount of energy necessary for combustion initiation. A relation is established between the laws of ignition and diffusion combustion of a single particle and parameters of ignition of the gas mixture of a given sort of particles. It is shown that there is a minimum in the dependences of the time of establishing of the zero gradient of τ0 on Semenov's criterion. The value of τ0 is found to be minimum if the heater temperature is higher than the temperature of ignition of a single particle by one characteristic interval. The numerical solution of the initial system of equation confirms the validity of the basic assumptions and results of the approximate analysis. The error in determining the time characteristics of ignition with the help of approximate formulas is lower than 50%. For the kinetic mode of ignition, a transformation of the time and space scales is found, such that the time characteristics of ignition in new dimensionless variables become independent of the mass concentration of particles.

Chapter 16.5 - Chemical and Combustion Kinetics: 16.5 Ignition Delay Times

The hypergolic ignition behaviors of three ionic liquids [BMIm][DCA], [EMIm][DCA], and [EMIm][CDB] reacting with white fuming nitric acid (WFNA) were investigated using the drop test approach. Two high-speed cameras with/without a long-distance microscope and a time-resolved infrared camera were used to simultaneously record the hypergolic ignition process and the reaction region temperature evolution. Results showed two distinct hypergolic ignition modes. Specifically, for [BMIm][DCA] and [EMIm][DCA], some "vapor smoke" is generated after the fuel droplet contacts the WFNA pool, followed by sudden ejection of liquids induced by microexplosion. The measured temperature in the observation window is found to first increase, then decrease, and rise again. For [EMIm][CDB], no microexplosion is observed and the temperature monotonically increases before hypergolic ignition. It is inferred that microexplosion is caused by sufficient accumulation of gaseous intermediates or products underneath the liquid surface, and the monotonic or nonmonotonic increasing temperature is a characteristic of ignition modes. A conceptual model is proposed to illustrate the two ignition modes. In addition, the droplet impact velocity (U0) was varied from 1.1 to 2.1 m/s in the experiment. It is found that the vapor delay time (VDT), explosion delay time (EDT), and ignition delay time (IDT) are all reduced with U0 by at most 50%. For a given U0, the three time scales decrease in the order [BMIm][DCA], [EMIm][DCA], and [EMIm][CDB] (IDT as low as 14.4 ms).

Numerical simulation of ignition mode and ignition delay time of pulverized biomass particles

Experimental study of butanol/biodiesel dual-fuel combustion in intelligent charge compression ignition (ICCI) mode: A systematic analysis at low load

Analysis of the ignition induced by shock wave focusing equipped with conical and hemispherical reflectors

Identifying two ignition modes of polymer insulated wires with continuous excess current in microgravity

Effects of heat diffusion and turbulence on detonation development of hydrogen/air mixtures under engine-relevant conditions

Nanoenergetic materials have some advantages against micrometric and bulk materials. This is due to enhanced surface area and intimacy between reactive components that leads to increase in the reaction rate and decrease in the ignition delay. However, till now there is very limited understanding of fundamental physical processes that control reaction and combustion wave propagation. The heat transfer in the case of nanoparticles is characterized some specifi c features which determine the sometime unusual ignition and combustion behavior. The paper is focused on discussing the ignition and combustion of nano Al particles in conditions of a shock tube and in a plastic tube. It is shown that tiny metal particles at high temperatures and pressures become “thermally isolated” from ambient gas environment and experimentally observed ignition delays may be two order magnitudes longer of those calculated without accounting real energy accommodation and sticking coeffi cients. When going to conditions of reaction propagation in a plastic tube, some different ways for heat transfer have to be carefully analyzed. Actually, there are no evidences for unique dominant process which may provide propagation of combustion wave with observed speed through the loose Al/CuO particles mixture. It can be stated that the process comprises 2 stages with very fast ignition, releasing large amount of heat and propelling hot gas and condensed material in direction of unreacted mixture followed by more slow reaction of remaining metal with evolved in oxide decomposition oxygen. Common conclusion is that further detailed studying the fundamental properties of nanoenergetics materials and their reaction behavior may open ways for purposed control of the combustion behavior and for effective use of nanoenergetics in practical applications.

Direct numerical simulations (DNSs) of a stratified flow in a homogeneous compression charge ignition (HCCI) engine are performed to investigate the exhaust gas recirculation (EGR) and temperature/mixture stratification effects on the autoignition of synthetic dimethyl ether (DME) in the negative temperature combustion region. Detailed chemistry for a DME/air mixture is employed and solved by a hybrid multi-time scale (HMTS) algorithm to reduce the computational cost. The effect of to mimic the EGR effect on autoignition are studied. The results show that adding enhances autoignition by rapid OH radical pool formation (34–46% reduction in ignition delay time) and changes the ignition heat release rates at different ignition stages. Sensitivity analysis is performed and the important reactions pathways affecting the autoignition are specified. The DNS results show that the scales introduced by thermal and mixture stratifications have a strong effect after the low temperature chemistry (LTC) ignition especially at the locations of high scalar dissipation rates. Compared to homogenous ignition, stratified ignitions show similar first autoignition delay times, but 18% reduction in the second and third ignition delay times. The results also show that molecular transport plays an important role in stratified low temperature ignition, and that the scalar mixing time scale is strongly affected by local ignition in the stratified flow. Two ignition-kernel propagation modes are observed: a wave-like, low-speed, deflagrative mode and a spontaneous, high-speed, ignition mode. Three criteria are introduced to distinguish these modes by different characteristic time scales and Damkhöler numbers using a progress variable conditioned by an ignition kernel indicator. The low scalar dissipation rate flame front is characterized by high displacement speeds and high mixing Damkhöler number. The proposed criteria are applied successfully at the different ignition stages and approximate characteristic values are identified to delineate between the different ignition propagation modes.

A new pulse-scan-based driving method that can significantly reduce total address time delay of discharge ignition during the address period in a plasma display panel (PDP) is proposed. By applying lower negative scan-pulse voltage to the Y electrode for a short interval, the proposed scheme accelerates the ignition of the gas discharge between addressing electrode (A) and scanning electrode (Y), and then, it reduces the ignition time delay which is closely related to the addressing time. Consequently, the high-speed addressing method can be achieved by it because the width of each scan pulse or each address pulse can be reduced. Therefore, this earned addressing time can directly contribute to the implementation of a single-scan (SS) driving scheme or the improvements in brightness with more sustain pulses. Experimental results with a prototype 50-in full-high-definition SS PDP module show that the total address time delay (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> = T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> +T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) of discharge ignition with the proposed pulse-scan driving method is reduced by about 10% compared with the conventional driving method.

Effects of an injector cooling jacket on combustion characteristics of compressed-ignition sprays with a gasoline-hydrogenated catalytic biodiesel blend

Experimental and numerical study of coal dust ignition by a hot particle