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Combustion chambers and processes
Published in M.J. Nunney, Light and Heavy Vehicle Technology, 2007
For high-efficiency engines operating at high speeds, it will be evident that a very fast rate of burning of the combustible charge is required. As with any mixture of gases, however, there must be a limit to which the rate of burning may be increased, beyond which the combustion process undergoes a sudden and dramatic change that results in detonation. In normal combustion, the burning progresses in a steady and uniform flame front that travels across the chamber at about 20–40 m/s (65–130 ft/s), this being known as the combustion speed. With detonation the flame front similarly advances across the chamber, but about ten times faster, and before it can complete its journey the unburnt gases ahead of it – or end gases as they are usually termed – become heated to such an extent by the overall pressure rise in the chamber that their self-ignition temperature is exceeded (Figure 3.2). When this occurs a condition of spontaneous combustion is created, resulting in a high-pressure detonation wave travelling through the chamber at a speed comparable to that of sound. Quite understandably, this produces a shock loading on the engine structure and components sufficient to generate a clearly audible knocking or pinking noise. If this abnormal combustion is allowed to persist, it can cause serious damage to the engine, such as blowing a hole in the piston crown (Figure 3.3).
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
Imprints of a soot-blackened wall from a reflected detonation, as in Figure 8.2, can be used to investigate the cellular nature of the detonation wave. Specially designed pressure transducers have been used to measure the pressure spikes in a detonation wave front, and pressures more than twice that predicted by normal shock theory have been observed.
DDT limits of ethanol–air in an obstacles-filled tube
Published in Combustion Science and Technology, 2023
Andrés Armando Mendiburu Zevallos, Gabriel Ciccarelli, João A. Carvalho Jr.
A detonation wave is a multidimensional front consisting of shock waves moving in the forward direction, as well as in the transverse direction (Ciccarelli and Dorofeev, 2008). Chemical reaction is initiated by the adiabatic compression of the mixture processed by the strongest parts of the corrugated lead shock wave. The points where the weaker transverse shocks intersect the lead shock front are commonly referred to as triple-points. There are two “families” of triple-points, where alternating triple-points travel in opposite directions, transversely along the detonation front. When a detonation wave propagates in a tube, the triple-points trace out a cellular pattern on the inner-wall of the tube. This so-called “fish-scale” pattern is captured on a foil that is pre-coated with carbon soot. The average dimension of the cells formed on the foil, , is known as the detonation cell size. Note, the cell size is equivalent to the average spacing between triple-points of the same family. The detonation cell size is an important parameter used to characterize the detonability of a fuel. Specifically, the smaller the detonation cell size, the more easily the fuel–oxygen mixture is detonated, e.g., less energy is required for direct initiation (Ciccarelli and Dorofeev, 2008).
Numerical Study of the Influence of Inlet Mass Flow Rate on Rotating Detonation Flow Field Characteristics and Pressure Gain Performance
Published in Combustion Science and Technology, 2022
Detonation and deflagration differ in the way of flame propagation (Li et al. 2018; Wang et al. 2022). Detonation can be approximately considered as isovolumetric combustion, which has many advantages such as low-entropy increase, self-pressurization, and high thermal cycle efficiency. The detonation wave is a hypersonic combustion wave formed by the coupling of chemical reaction and shock wave, which can bring total pressure gain to the propulsion system. Under the compression of the shock wave, the pressure and temperature of the combustible mixture increase rapidly before the reaction, so that the high-enthalpy reaction product has greater energy to extract useful work. The Rotating Detonation Engine (RDE) is a new concept engine that uses detonation combustion as propulsion power (Schwer and Kailasanath 2011). Rotating Detonation Wave (RDW) propagates continuously in the circumferential direction in the annular combustion chamber, the fresh combustible mixture undergoes a detonation reaction, and the high-enthalpy products are discharged along the axial direction of the engine to generate thrust. Compared with the Pulse Detonation Engine (PDE), the RDE can work continuously with ignition once and have the advantages of high frequency, simple structure, stable thrust, operation under a wide range of Mach number, etc. The RDE has become a research hotspot in the propulsion system currently (Liu et al. 2010; Ma et al. 2012; Qi et al. 2018; Sun et al. 2016).
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].