Detonation and combustion the release of energy energy extremely useful for military purposes is fundamental to both these phenomena. High boost, gasoline engine, superknock, preignition, detonation. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Damaged pistons and rings usually mean replacement. Detonation and preignition, often interchanged and or used to describe the same thing, are actually quite different things that lead to similar outcomes. Preignition and detonation in this discussion activity, address the following in your primary, original posting minimum of 150 250 words apa style formatting. Cline introduction all high output engines are prone to destructive tendencies as a result of over boost, misfueling, mistuning and inadequate cooling. They are completely different but the end result can still be a wrecked engine.
It was found that preignition most commonly initiated in the area surrounding. Detonation and preignition often occur simultaneously and one may cause the other. Detonation, as the name suggests, is an explosion of the fuelair mixture inside the cylinder. Preignition definition of preignition by merriamwebster. The regime in which a localised detonation can be generated in the hot spot. If the explosion moves outward at supersonic speeds faster than the speed of sound, its a detonation. A typical piston engine making use of the otto cycle provides a systematic approach to the conversion of fuel energy into mechanical energy. The detonation of a nuclear bomb over a target such as a populated city causes immense damage. Jul 22, 2019 switching to a higher octane fuel in order to reduce the heat of the firing chamber and burn fuel more slowly is the best way to combat false firing. Detonation is not an optimum situation, but its not necessarily destructive. In part one of this article we discussed the foundation and theory of detonation and preignition. Preignition or preignition in a sparkignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the airfuel mixture in the cylinder ignites before the spark plug fires.
These are the classic definitions of detonation and preignition. Churchill the university of michigan, ann arbor, michigan detonation velocities were measured in mixtures of hydrogen and oxygen containing 25 to 75. Present results complement those published at the seventh combustion symposium for the case without preignition. Detonationpre ignition and the outboard motor one of the most common causes of major internal engine damage results from the abnormal combustion conditions that have plagued the internal combustion engine since its beginning, namely detonation and preignition, or surface ignition. Similarly, reducing engine inlet air temperatures will greatly reduce the chance of preignition and detonation. Very pertinent to direct injection and turbocharging, ecoboost, focus st and. Therefore, one should not expect from the theory any interpretations of the detonation limits, such as. Detonation is extremely damaging, evidenced by a cracked piston, failed bearings. Ill add a couple of thoughts that come to mind when i think about knocking and detonation.
Detonation and preignition, often interchanged andor used to describe the same thing, are actually quite. Our goal is to provide tools that meet the needs of explosive ordnance disposal technicians with quality and innovation. Theoretical and computer models of detonation in solid explosives craig m. Schematically, the detonation wave is shown in the figure here. Detonation is caused by incorrect or excessive engine timing, engine temperature, cylinder pressure, fuel mixture temperature or fuel octane rating. It is known that the chapmanjouguet theory of detonation is based on the assumption of an instantaneous and complete transformation of explosives into detonation products in the wave front. Our philosophy is that the easier your gear is to use the better your chances for success, regardless of your skill or experience level. What is the difference between preignition and detonation. Preignition and superknock in turbocharged sparkignition. This chart explains how changing a front or rear sprocket will change the gearing and over all performance of your vehicle. Article information, pdf download for relationship between. The engine community pushes ever nearer to the limits of power output.
This is the most destructive force an engine can endure, preignition due to detonation. We get asked this question a lot, and rightfully so. Pdf preignition and superknock in turbocharged spark. Detonation or preignition is caused by the airfuel mixture igniting before the spark plug fires. Preignition occurs during the compression stroke, and the engine continues to fire with the ignition system switched off, although probably not all its cylinders. However, preignitionsuperknock tends to occur at lowspeed. Knock onset, knock intensity, superknock and preignition in.
A detonation occurs when the flame velocity reaches supersonic speeds above 600 ms and generally in the 20002500 ms range. Advances in experimental, highspeed techniques can be used to explore the processes occurring within energetic materials. The higher the specific output of the engine, the more likely it is to sustain detonation damage. The phenomenon of detonation was first observed and described by harry ricardo. If the combustion process propagates outward at subsonic speeds slower than the speed of sound, its a deflagration. Page 1 detonationpreignition and the outboard motor one of the most common causes of major internal engine damage results from the abnormal combustion download detonationpreignition and the outboard document.
Us6883497b2 method of preventing preignition for an. Knocking in spark ignition internal combustion engines occurs when combustion of some of the. Preignition definition is ignition in an internal combustion engine while the inlet valve is open or before compression is completed. When an internal combustion engine is torn down for rebuilding and badly burned and distorted pistons and valves are found, it is very likely caused by extremely high combustion chamber temperatures and. However, severe detonation can cause engine failure in minutes. Flame initiated by ignition must in relatively short time accelerate to detonation velocity, so the transition from deflagration to. It is possible for heavy detonation to induce preignition. Preignition in an engine is prevented by identifying engine conditions that relate to autoignition.
Switching to a higher octane fuel in order to reduce the heat of the firing chamber and burn fuel more slowly is the best way to combat false firing. The octane thread got me thinking about preignition vs. Detonation control for propulsion pulse detonation and. Peak overpressures can be 20100 times the initial pressure, with typical values of 20 bar. Detonation technology innovative eod and cied tools. Subsonic, typically 1 ms and 7 to 10 bar starting at ambient pressure detonation. 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. Knock onset, knock intensity, superknock and preignition.
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. Characteristics of hazardous material releases, fires, and explosions. Putting aside the debate about what is the most appropriate fuel mixture setting, and engine operation leanofpeak, having a modern multichannel engine monitor fitted enhances the safety of your aircraft. Relationship between superknock and preignition zhi wang, hui. Also known as ping or spark knock, detonation takes place after the spark plug has fired and a portion of the airfuel mixture has been consumed in. Pulse detonation and rotating detonation engines provides, with its comprehensive coverage from fundamental detonation science to practical research engineering techniques, a wealth of information for scientists in the field of combustion and propulsion. Inspection of damaged pistons and rings quite often indicate which caused the damage. All trademarks and s on this website are property of their respective owners. In the frame of the wave, the fresh mixture enters the shock at speed d, starts burning in the reaction zone until completely. The control of detonation has long been a subject of in teresting. Because of the noise that it makes, detonation is called engine knock or pinging in cars. There are two destructive forces that can take place within the combustion chamber. The controller detects whether autoignition occurs in the engine due to the retarded spark advance.
Detonation is generally the result of any number of combinations of factors. 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. When knock, detonation, or preignition occurs, the airfuel mixture is ignited at an improper time in the cycle. Indias detonation of a nuclear device was a cause of celebration in india, and it is difficult to imagine that any national leader would ever sign a prohibition until the public agrees with the leader. Urtiew lawrence livermore national laboratory livermore, ca 94550 abstract recent experimental and theoretical advances in understanding energy transfer and chemical kinetics have led to improved models of detonation waves in solid explosives. Hydrogen has relatively high flame speed and is known to be very prone to preignition. Consistent and precise movements of the piston heads, with the help of expanding gases, provide power for aircraft piston engines such as those commonly used in the cessna 172 and other similar planes. In this article we want to expand upon that foundation and look further into the real world results of preignition and detonation. Preignition definition of preignition by the free dictionary.
Knock detonation and pre ignition explained youtube. Neither detonation nor preignition is good for an engine. These were then downloaded as tiff files where each image. As a principle, for every 10 degrees cooler the inlet air is, it produces one percent more power. Perhaps a more fun definition of detonation would be to imagine the piston screaming up. Detonation and preignition are not good for an engine and can be caused by a number of things, carbon build up within the combustion chamber being one of. 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. If youd like to comment on anything herein, or just have questions, feel free to pop in on this discussion.
Preignition definition, ignition of the charge in an internalcombustion engine earlier in the cycle than is compatible with proper operation. Preignition causes the engine to lose power, and produces high operating temperature. Detonation is an uncontrolled combustion event which occurs after the spark event. How to know whether youre experiencing preignition or. All about detonation and preignition there is a difference.
Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Pdf relationship between superknock and preignition. Forces and severe heat that result from the occurrence of either will usually require the complete teardown and repair of the engine. First, lets get into what happens when detonation occurs and then we can get into why it happens and then the difference between detonation and preignition. For a spark ignition engine, airfuel mixture is compressed in compression stroke. 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. Detonation information tech notes important information on detonation detonation is a phenomenon that can occur in any gasoline engine. Another stochastic phenomenon, preignition, is necessary but not sufficient to enable the pressures and temperatures that could.
Many engines operate in light detonation quite regularly, and some can withstand moderate detonation for extended periods of time without damage. Detonation detonation is the spontaneous explosion of the cylinders endgases. Detonation is likely to damage it, while preignition can destroy it. Detonation and preignition are so closely related that it is difficult to distinguish one from the other by sound. Potential for detonation can be reduced by reducing the. To evaluate the severity of an autoignition event based on the detonation diagram they proposed the equation 14, which. Detonation and preignition are two unique conditions that can severely damage an aircraft engine. Superknock is a manifestation of developing detonation which can be triggered by autoignition of the fuelair mixture at high pressures and temperatures. Another stochastic phenomenon, preignition, is necessary but not sufficient to enable the pressures and temperatures that could cause superknock. Preignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark. Diagnostic techniques in deflagration and detonation studies. Knocking and detonation are not what you want occurring in your engine 2.
Turbo and superchargers are more likely to detonate, because of the higher pressure. Faa phak, page 618 detonation can be caused by a number of factors, but generally they relate to a situation outside of the engines design. Knocking should not be confused with preignitionthey are two separate events. The simplest way we remember, is the closer your sprockets are to being the same size, the slower it accelerates but the higher the top speed. Cylinder pressure rises smoothly as the piston rises in the cylinder. The ideal combustion process takes place without detonation or preignition. Detonation definition and meaning collins english dictionary. What are the various causes of preignition detonation.
As nouns the difference between detonation and preignition is that detonation is an explosion or sudden report made by the nearinstantaneous decomposition or combustion of unstable substances as, the detonation of gun cotton specifically, combustion that spreads supersonically via shock compression while preignition is automotive the premature detonation of a fuel charge in. As with detonation, preignition may also cause severe engine damage, because the expanding gases exert excessive pressure on the piston while still on its compression stroke. If one or more of the engine conditions exceed a threshold, a controller retards the spark in the engine. Detonation and twophase flow compiles technical papers presented at the ars propellants, combustion, and liquid rockets conference held in palm beach, florida on april 2628, 1961. Theoretical and computer models of detonation in solid.
The most detailed numerical research of rotational detonations quality picture. Combustion burning is a process by which energy is released. 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. Download pdf open epub full article content list abstract. However, preignitionsuperknock tends to occur at lowspeed highload. In both detonation and combustion, energy is released when a complex molecule is broken down into simpler constituent parts. Detonation characteristics of hydrogen oxygen mixtures morton p. Preignition and superknock in turbocharged sparkignition engines. Deflagration and detonation are two ways energy may be released. Upon teardown, forensic analysis would reveal the telltale signs of both detonation and preignition damage, although its the preignition that ultimately did the engine in. What is the difference between knocking and detonation. Below is an image showing normal combustion, followed by images illustrating preignition and detonation.
Feb 24, 2017 the differences between knock, detonation, pre ignition explained and how they affect your internal combustion engine. Detonation of fuel before ignition or preignition due to detonation. Supersonic high pressure shock front ahead of the reaction zone i. At that point, the glowing item can cause preignition and rapid destruction of the cylinder. Importance of preignition to the development of detonation is examined on the basis of a wavedynamic analysis of schlieren photographs obtained by schmidt, steinicke and neubert. This work distinguished the relationship between superknock and preignition by experimental investigation and numerical simulation. The mixture is typically ignited by a hot spot either in the head, or on some carbon deposits. This extends the time that the burning fuel pushes on the cylinder, providing a gentle power stroke. Many times these terms are used interchangeably though they are technically different. Detonation is an extreme singular mode of flame propagation in premixed gas.
There are many ways to ruin a perfectly good engine, but today, i just want to talk about two of the most violent ones. Each can lead to the other and either condition can cause extensive engine damage. Pdf preignition and superknock in turbocharged sparkignition. My truck, a 93 toyota with the 22re engine with 192k miles on it, pings under what i would consider a higher load condition in 5th gear climbing grades while trying to accellerate under mid to full throttle situations. The detonation was initiated at the closed tube end by means of an explosive charge.
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