Detonation wave is a shock wave in a reactive medium that is sustained by energy released in chemical reactions that the shock itself triggers and sustains. Detonation is the spontaneous combustion of the endgas remaining fuelair mixture in the chamber. Definition of detonation the sudden and violent release of mechanical, chemical or nuclear energy from a confined space which creates a shock wave that travels at supersonic speeds. This is the most destructive force an engine can endure, preignition due to detonation. Compared to a pulsed detonation engine, this design allows an easier operation in reducedpressure environment and an increase in engine mass flow rate and. An explosive is a chemical material that is capable of extremely rapid combustion resulting in an explosion or detonation. Potential for detonation can be reduced by reducing the. The mixture is ignited by the spark, normally in the centre of the cylinder, and a flame front moves from the spark towards the outside of the cylinder in a controlled burn. The sudden and violent release of mechanical, chemical or nuclear energy from a confined space which creates a shock wave that travels at supersonic speeds.
If there is still no indication of gun detonation following step 7. Relationship between superknock and preignition article pdf available in international journal of engine research 162. There are many ways to ruin a perfectly good engine, but today, i just want to talk about two of the most violent ones. Under normal operation, the spark plugs each ignite a point in the fuelair charge, which then propagate through the cylinder and provides a consistent, regulated burn in a process called deflagration. Prediction of detonation pressure and velocity of explosives. Classical theory of detonation archive ouverte hal. Kasimov, theory of detonation with an embedded sonic locus, siam journal of applied mathematics, 66, no. For a spark ignition engine, airfuel mixture is compressed in compression stroke. When knock, detonation, or preignition occurs, the airfuel mixture is ignited at an improper time in the cycle. If you dont understand exactly what each of these events are and how they occur, you wont know how to prevent them from happening, or possibly even recognizing when it happens. For some reason, likely heat and pressure, the end gas in the chamber.
A detonation velocity depends on a mixture composition, pressure and temperature. Detonation is an uncontrolled combustion event which occurs after the spark event. Neither detonation nor pre ignition is good for an engine. As they often learn cylinder chamber combustion processes can quickly gravitate to engine failure. It always occurs after normal combustion is initiated by the spark plug. In the frame of the wave, the fresh mixture enters the shock at speed d, starts burning in the reaction zone until completely. Pre ignition is very likely to be destructive due to the very high cylinder pressure that occurs before the piston has reached top dead center. Simulations of detonation wave propagation in rectangular ducts using a threedimensional weno scheme huashu dou1, her mann tsai1, boo cheong khoo,2 jianxian qiu2 1temasek laboratories, national university of singapore, singapore 117508 2department of mechanical engineering, national university of singapore, singapore 119260. Detonation and combustion stanford university computer. Detonation and preignition, often interchanged andor used to describe the same thing, are actually quite different things that lead to similar outcomes. Supersonic high pressure shock front ahead of the reaction zone i. What is the difference between knocking and detonation in ic.
The initial combustion at the spark plug is followed by a normal combustion burn. This early before the spark plug fires ignition of fuel creates a shock wave throughout the cylinder as the burning and expanding fuelair mixture collides with the piston that is. Calculation of combustion, explosion and detonation characteristics. Safety measures must be taken to ensure that the mechanism for signal transmission is disabled until the pulse from the logging unit is required to be sent. A pulse detonation engine is a propulsion system which uses detonation waves for combustion of mixture of fuel and oxidizer. The detonation phenomenon cambridge university press, 2008. Feb 15, 2018 would you like to support this channel and help us grow. For the case of detonation occurring in rectangular ducts, studies show the presence of a rectangular mode, diagonal mode and spinning mode 47 of the detonation front. Roeske lawrence livermore national laboratory livermore, ca 94551 a new detonation profile test dpt was developed to measure.
Detonation of explosives is often achieved by the transmission of an electrical signal, from a logging unit via the logging cable, to the blasting cap detonator. The engine is pumped because the fuel in the engine is renewed after every detonation cycle. In a different article, well look more closely at the normal combustion event, and explore how our use of the engine controls throttle, mixture and prop affect what. A new detonation profile test dpt was developed to measure simultaneously the detonation wave breakout profile and the average detonation velocity at the breakout surface. Ill add a couple of thoughts that come to mind when i think about knocking and detonation. Knock pinging is the actual noise that can be audibly heard if detonation is bad enough. The detonation is characterised by the existence of a shock wave in the front of which the reactions start. The reactivity is characterized by the detonation cell size, the flame velocity and the expansion ratio. Detonation, or engine knock, occurs simply when fuel preignites before the piston reaches scheduled spark ignition. Upon teardown, forensic analysis would reveal the telltale signs of both detonation and pre ignition damage, although its the pre ignition that ultimately did the engine in.
In both detonation and combustion, energy is released when a complex molecule is broken down into simpler constituent parts. This is a detailed description of how our theory of weaklycurved slowlyvarying detonations can be used to predict critical conditions for direct initiation of detonation in various. This condition can damage or destory pistons, rings, bearings, crankshafts, and head gaskets. Experiments have shown that these waves have a complex transverse structure, and have puzzled scientists by yielding some results that are at odds with. Many times these terms are used interchangeably though they are technically different. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Detonation and combustion stanford computer science. If there is no indication of gun detonation, repeat steps 7. Detonations synonyms, detonations pronunciation, detonations translation, english dictionary definition of detonations. Preignition is very likely to be destructive due to the very high cylinder pressure that occurs before the piston has reached top dead center. Detonation definition and meaning collins english dictionary. It is able to exposeand clear routes of trip and command detonation wires while on the move. Detonation always comes after normal combustion has been started by the spark plug.
Detonation, or engine knock, occurs simply when fuel pre ignites before the piston reaches scheduled spark ignition. Subsonic, typically 1 ms and 7 to 10 bar starting at ambient pressure detonation. Structure of a detonation from high speed photography and soot tubes 3d cellular structure, constantly changing cell width. A shock wave can be transmitted from detonating high explosive into materials that cause them to shatter. The most detailed numerical research of rotational detonations quality picture. The test evaluated small cylindrical samples with diameter up to 19.
May 06, 2015 preignition and detonation mnosko2011. Detonation characteristics of hydrogen oxygen mixtures morton p. Detonation, as the name suggests, is an explosion of the fuelair mixture inside the cylinder. A sketch of an envisioned twophase steady detonation structure is shown in figure 1. Calculation of combustion, explosion and detonation.
Pdf autoignitions and detonations in engines and ducts. Pdf in this paper we introduce a general definition of a selfsustained detonation wave as a structure composed of a lead shock front and a following unsteady transonic flow. Pre ignition is an uncontrolled combustion event which occurs before the spark event. Detonation definition is the action or process of detonating. Detonation of fuel before ignition or preignition due to detonation. The engine community pushes ever nearer to the limits of power output. Jul 22, 2019 detonation generally caused by fuel with a low octane rating is the tendency for the fuel to preignite or autoignite in an engines combustion chamber. Under purely axial injection of a combustible mixture from the head end of a toroidal section of coaxial cylinders, the rotating detonation is proven to give no average angular momentum at any cross section, giving an axial flow. Jan 01, 2000 detonation, as the authors point out, differs from other forms of combustion in that all the important energy transfer is by mass flow in strong compression waves, with negligible contributions from other processes like heat conduction. Density is an important consideration when choosing an explosive. We are only beginning to understand the nonlinear interaction between chemistry and fluid mechanics that produces the rapid energy release known as detonation.
The science of high explosives is basically a coupling of chemistry and fluid mechanics. Knocking also knock, detonation, spark knock, pinging or pinking in spark ignition internal combustion engines occurs when combustion of some of the airfuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of airfuel mixture explode outside the envelope of the normal combustion front. A shock wave can be transmitted from detonating high explosive into materials that cause them. In this study the term structure refers to the spatial details of the detonation wave. If we consider an ideal pde it has more efficiency than. A defaut, il faut eliminer les sources d inflammation et. This extends the time that the burning fuel pushes on the cylinder, providing a gentle power stroke.
The third capability is the full widthexplosive hazardroller, able to. Knocking and detonation are not what you want occurring in your engine 2. The origins of autoignition at hot spots are analysed and the pressure pulses that arise from them are related to knock in gasoline engines and to developing detonations in ducts. The second capability is the vehiclemounted trip and command detonation wire neutralization system wns capability. Normal combustion expands out, but the gasses on the edge of the flame front compress and begin combusting spontaneously. What is the difference between knocking and detonation in. Pdf relationship between superknock and preignition. Spontaneous combustion of the endgas, or remaining airfuel mixture in the chamber. Combustion, flame, explosion, detonation linkoping university. An introduction 3 2 stoenavt214 the output of an explosive can be defined in terms of two factors. The realistic representation of chemistry poses a major challenge to.
Would you like to support this channel and help us grow. Under normal conditions, the combusting air and fuel mixture inside the combustion chamber ignites in a controlled manner. Cline introduction all high output engines are prone to destructive tendencies as a result of over boost, misfueling, mistuning and inadequate cooling. Prediction of detonation pressure and velocity of xplosives 83 can be obtained when p emaxi is known. What is the difference between preignition and detonation. Detonation generally caused by fuel with a low octane rating is the tendency for the fuel to preignite or autoignite in an engines combustion chamber. This means that a powerful explosion is trying to expand a cylinder chamber that is shrinking in size, attempting to reverse the direction of the piston and the engine. The plane was equipped with a snazzy avidyne entegra multifunction display. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign. Flame acceleration and deflagrationtodetonation transition in.
Neither detonation nor preignition is good for an engine. For free running explosives, the density is often specified as the pounds of explosives per foot of charge length in a given size borehole. The detonation velocity for the mixed explosives can be estimated by a similar pathway to the detonation pressure. We get asked this question a lot, and rightfully so. This paper is aimed to assess the role of boundary layer effect on modifying the detonation cell width of the test gas mixture in the narrow channel. Detonation cell size dcs characteristic size of the cellular structure. What is the difference between knocking and detonation in ic engine. The engine is rotating clockwise and the piston tries to turn the. In handbook of petroleum exploration and production, 2000. Simulations of detonation wave propagation in rectangular. What is the difference between knocking and detonation. Detonation and combustion the release of energy energy extremely useful for military purposes is fundamental to both these phenomena.