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Detonation of Gaseous Mixtures
Published in Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong, Combustion Engineering, 2022
Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong
A detonation is a combustion wave that travels at supersonic speeds producing high temperatures and pressures for short periods of time. Detonation is an important combustion topic, because, given sufficient volume and time, a propagating flame (deflagration) can change into a detonation. Detonations often create dangerous situations, such as an explosion due to leakage of natural gas in a building, a coalmine explosion due to the presence of methane, or a hydrogen–oxygen explosion in an overheated nuclear reactor. The study of detonations can lead to ways to prevent such accidents.
Power unit – engine
Published in Andrew Livesey, Motorcycle Engineering, 2021
Pre-ignition, post-ignition, pinking, and detonation are often confused, as their symptoms and effects are almost identical; that is, the air and fuel are burned in a noisy manner, usually a knocking noise, and there is a loss of power or uneven running. Running-on is associated with these symptoms too. Pre-ignition is when the fuel is ignited before the spark occurs; this is usually by something burning or becoming overheated in the combustion chamber. Often this is the spark plug insulator, a carbon deposit, or a section of damaged cylinder head gasket. Post-ignition is when the fuel burns late, or more likely, combustion continues after the engine is switched off. When the engine continues to run for a while when the ignition is switched off, this is called running-on. Pinking, also called knock, is the noise made by the mixture burning too quickly or on two flame fronts and is caused by the ignition timing being too advanced or too low-octane-rated fuel being used. Detonation is when pockets of fuel burn in an irregular way, usually because of poor air–fuel mixing, incorrect ignition timing, or poor combustion chamber design.
A Generic Overview of Severe Accident Phenomena
Published in J. T. Rogers, Fission Product Transport Processes in Reactor Accidents, 2020
The detonation sensitivity of hydrogen/air/steam mixtures, and factors affecting the transition from a deflagration to a detonation, are important questions with respect to containment performance. Detonations occur when flame speeds are sufficiently high to produce strong shock waves that ignite the gas ahead of the flame front by compression. This results in high local peak pressures that greatly exceed constant-volume combustion pressures. However, the direct initiation of detonations requires relatively high-energy ignition sources, which are not likely to be found in containment. A more plausible mechanism is the possible transition of a deflagration to a detonation, which is dependant on geometry and thermodynamic conditions. The thermodynamic conditions (composition, pressure, temperature) determine the detonation cell size, which must be compatible with the local propagation volume for a transition to occur, and for detonation to be sustained. Geometry conditions (e.g., obstacles and vents) determine whether transitions can occur for given thermodynamic conditions.
Analytical and numerical study of the expansion effect on the velocity deficit of rotating detonation waves
Published in Combustion Theory and Modelling, 2020
Mingyi Luan, Shujie Zhang, Zhijie Xia, Songbai Yao, J.-P. Wang
Detonation is a premixed combustion mode; the shock wave and following reaction zone form the detonation wave. Compared with deflagration, detonation generates lower entropy and thus has higher efficiency. One way to use detonation for propulsion is with the rotating detonation engine (RDE). The potential thermodynamic advantages of detonation make RDEs one of the most promising propulsion systems for use in aircraft and rocket engines. The basic concept of RDEs was first introduced by Voitsekhovskii [1] and research on RDEs are now being conducted in several laboratories around the world, including in Russia [2,3], Poland [4], the US [5,6], France [7,8], Japan[9] and China [10,11]. Furthermore, many initial numerical studies have been performed on topics such as the basic physics [12–14], detailed mechanism [15–17], thermodynamic analysis [18,19], and performance [16]. Moreover, theoretical studies have been performed to investigate RDEs, including some basic characteristics of detonation [20] and models to evaluate the flow field [21,22].
Experimental Investigations on the Propagation Characteristics of Rotating Detonations Utilizing the Ethylene-Air Mixture
Published in Combustion Science and Technology, 2023
Minghao Zhao, Ke Wang, Yiyuan Zhu, Qibin Zhang, Wei Fan
Distribution of the pressure transducers is shown in Figure 3. Seven high-frequency piezoelectric pressure transducers are utilized in this study. Two piezoelectric pressure transducers (ppt1 and ppt2) with a distance of 100 mm are installed near the outlet of the pre-detonation tube, which are used to monitor the pressure of the detonation wave. By analyzing the pressure and velocity measured, it can be determined whether a fully-developed detonation wave is generated in the pre-detonation tube. The other five pressure transducers (p1-p5) are installed in the outer cylinder of the rotating detonation chamber to measure the pressure of the rotating detonation wave. Three pressure transducers (p1, p2, and p3) are installed at an interval of 120° in the circumferential direction, and the distances from the head end of the combustion chamber are 30 mm, 35 mm, and 30 mm, respectively. The pressure transducers (p3, p4, and p5) are installed in the same circumferential direction, and the distances between each other are 25 mm and 30 mm. In order to avoid damage to the pressure transducers, a water cooling channel is adopted in the outer cylinder to reduce the heat load on the transducers. In addition, three piezoresistive transducers are utilized. Two transducers (pf and po) are installed in the fuel and oxidizer plenums to measure the supply pressures, respectively. The other one (pN) is installed in the outer cylinder of the rotating detonation chamber to measure the chamber pressure. The transducers pN and p1 are in the same circumferential direction, and the distances between each other are 25 mm. All measured signals are collected by a data acquisition system with a sampling rate of 1 MHz.