Preignition in an engine is prevented by identifying engine conditions that relate to autoignition. What is the difference between knocking and detonation. Us6883497b2 method of preventing preignition for an. The most detailed numerical research of rotational detonations quality picture. 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. Theoretical and computer models of detonation in solid explosives craig m. 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.
Preignition and superknock in turbocharged sparkignition engines. 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. A detonation occurs when the flame velocity reaches supersonic speeds above 600 ms and generally in the 20002500 ms range. Detonation is an uncontrolled combustion event which occurs after the spark event. How to know whether youre experiencing preignition or. Pdf preignition and superknock in turbocharged spark. Theoretical and computer models of detonation in solid. Another stochastic phenomenon, preignition, is necessary but not sufficient to enable the pressures and temperatures that could.
The detonation of a nuclear bomb over a target such as a populated city causes immense damage. Detonation is an extreme singular mode of flame propagation in premixed gas. Detonation and preignition, often interchanged andor used to describe the same thing, are actually quite. Preignition and superknock in turbocharged sparkignition. Detonation information tech notes important information on detonation detonation is a phenomenon that can occur in any gasoline engine. The higher the specific output of the engine, the more likely it is to sustain detonation damage. 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. If youd like to comment on anything herein, or just have questions, feel free to pop in on this discussion. Neither detonation nor preignition is good for an engine.
Superknock is a manifestation of developing detonation which can be triggered by autoignition of the fuelair mixture at high pressures and temperatures. In this article we want to expand upon that foundation and look further into the real world results of preignition and detonation. These are the classic definitions of detonation and preignition. 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. Detonation detonation is the spontaneous explosion of the cylinders endgases. Preignition definition is ignition in an internal combustion engine while the inlet valve is open or before compression is completed. Damaged pistons and rings usually mean replacement. All trademarks and s on this website are property of their respective owners. Many times these terms are used interchangeably though they are technically different. Another stochastic phenomenon, preignition, is necessary but not sufficient to enable the pressures and temperatures that could cause superknock. Detonation occurs after normal combustion has already begun, that is, after ignition, and has no connection with ignition at all. 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. Pdf relationship between superknock and preignition. 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.
The control of detonation has long been a subject of in teresting. Knock onset, knock intensity, superknock and preignition. It was found that preignition most commonly initiated in the area surrounding. Ill add a couple of thoughts that come to mind when i think about knocking and detonation. Inspection of damaged pistons and rings quite often indicate which caused the damage. Potential for detonation can be reduced by reducing the. 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. Detonation is extremely damaging, evidenced by a cracked piston, failed bearings. The engine community pushes ever nearer to the limits of power output. Advances in experimental, highspeed techniques can be used to explore the processes occurring within energetic materials. 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. It is possible for heavy detonation to induce preignition. Preignition causes the engine to lose power, and produces high operating temperature. Characteristics of hazardous material releases, fires, and explosions.
There are two destructive forces that can take place within the combustion chamber. Flame initiated by ignition must in relatively short time accelerate to detonation velocity, so the transition from deflagration to. 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. Knocking should not be confused with preignitionthey are two separate events. Knocking and detonation are not what you want occurring in your engine 2. Forces and severe heat that result from the occurrence of either will usually require the complete teardown and repair of the engine. Each can lead to the other and either condition can cause extensive engine damage. Detonation or preignition is caused by the airfuel mixture igniting before the spark plug fires. The controller detects whether autoignition occurs in the engine due to the retarded spark advance. Perhaps a more fun definition of detonation would be to imagine the piston screaming up. Detonation and preignition are so closely related that it is difficult to distinguish one from the other by sound. However, severe detonation can cause engine failure in minutes. Article information, pdf download for relationship between. Cylinder pressure rises smoothly as the piston rises in the cylinder.
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. 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. Feb 24, 2017 the differences between knock, detonation, pre ignition explained and how they affect your internal combustion engine. If one or more of the engine conditions exceed a threshold, a controller retards the spark in the engine. 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. Turbo and superchargers are more likely to detonate, because of the higher pressure. Preignition definition, ignition of the charge in an internalcombustion engine earlier in the cycle than is compatible with proper operation. Schematically, the detonation wave is shown in the figure here. When knock, detonation, or preignition occurs, the airfuel mixture is ignited at an improper time in the cycle. Preignition occurs during the compression stroke, and the engine continues to fire with the ignition system switched off, although probably not all its cylinders. 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.
The octane thread got me thinking about preignition vs. 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. Present results complement those published at the seventh combustion symposium for the case without preignition. Detonation is likely to damage it, while preignition can destroy it.
Knocking in spark ignition internal combustion engines occurs when combustion of some of the. Combustion burning is a process by which energy is released. Detonation, as the name suggests, is an explosion of the fuelair mixture inside the cylinder. There is no explosion as in a detonation and the rise of temperature and pressure is much greater, probably resulting in catastrophic consequences. Detonation and preignition, often interchanged and or used to describe the same thing, are actually quite different things that lead to similar outcomes. Detonation control for propulsion pulse detonation and. The detonation was initiated at the closed tube end by means of an explosive charge.
We get asked this question a lot, and rightfully so. To evaluate the severity of an autoignition event based on the detonation diagram they proposed the equation 14, which. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Deflagration and detonation are two ways energy may be released. The regime in which a localised detonation can be generated in the hot spot. There are many ways to ruin a perfectly good engine, but today, i just want to talk about two of the most violent ones.
Our goal is to provide tools that meet the needs of explosive ordnance disposal technicians with quality and innovation. The ideal combustion process takes place without detonation or preignition. As a principle, for every 10 degrees cooler the inlet air is, it produces one percent more power. Supersonic high pressure shock front ahead of the reaction zone i. Detonation technology innovative eod and cied tools. 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. Below is an image showing normal combustion, followed by images illustrating preignition and detonation. 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. 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. All about detonation and preignition there is a difference. 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. In part one of this article we discussed the foundation and theory 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. 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. Peak overpressures can be 20100 times the initial pressure, with typical values of 20 bar. The mixture is typically ignited by a hot spot either in the head, or on some carbon deposits. Detonation and combustion the release of energy energy extremely useful for military purposes is fundamental to both these phenomena. 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. Preignition article about preignition by the free dictionary. Subsonic, typically 1 ms and 7 to 10 bar starting at ambient pressure detonation. Relationship between superknock and preignition zhi wang, hui. This is the most destructive force an engine can endure, preignition due to detonation. Pdf preignition and superknock in turbocharged sparkignition. The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites.
Detonation characteristics of hydrogen oxygen mixtures morton p. Detonation is caused by incorrect or excessive engine timing, engine temperature, cylinder pressure, fuel mixture temperature or fuel octane rating. 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. Preignition definition of preignition by the free dictionary. For a spark ignition engine, airfuel mixture is compressed in compression stroke. Knock onset, knock intensity, superknock and preignition in. Detonation of a stoichiometric mixture of acetylene and air in a oneendopen tube of diameter 0. 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. Our philosophy is that the easier your gear is to use the better your chances for success, regardless of your skill or experience level. 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 and preignition often occur simultaneously and one may cause the other. Similarly, reducing engine inlet air temperatures will greatly reduce the chance of preignition and detonation. Therefore, one should not expect from the theory any interpretations of the detonation limits, such as. Detonation definition and meaning collins english dictionary.
In the frame of the wave, the fresh mixture enters the shock at speed d, starts burning in the reaction zone until completely. 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. A typical piston engine making use of the otto cycle provides a systematic approach to the conversion of fuel energy into mechanical energy. Download pdf open epub full article content list abstract. Because of the noise that it makes, detonation is called engine knock or pinging in cars.
Detonation and preignition are two unique conditions that can severely damage an aircraft engine. Detonation is generally the result of any number of combinations of factors. 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. High boost, gasoline engine, superknock, preignition, detonation. In both detonation and combustion, energy is released when a complex molecule is broken down into simpler constituent parts. Cline introduction all high output engines are prone to destructive tendencies as a result of over boost, misfueling, mistuning and inadequate cooling. This extends the time that the burning fuel pushes on the cylinder, providing a gentle power stroke. Preignition and detonation in this discussion activity, address the following in your primary, original posting minimum of 150 250 words apa style formatting. Preignition definition of preignition by merriamwebster. This work distinguished the relationship between superknock and preignition by experimental investigation and numerical simulation.
Many engines operate in light detonation quite regularly, and some can withstand moderate detonation for extended periods of time without damage. Knock detonation and pre ignition explained youtube. However, preignitionsuperknock tends to occur at lowspeed highload. At that point, the glowing item can cause preignition and rapid destruction of the cylinder. Feb 15, 2018 your flight training copilot presents. The phenomenon of detonation was first observed and described by harry ricardo. What is the difference between preignition and detonation. Detonation of fuel before ignition or preignition due to detonation. However, preignitionsuperknock tends to occur at lowspeed. Detonation is not an optimum situation, but its not necessarily destructive. 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. This chart explains how changing a front or rear sprocket will change the gearing and over all performance of your vehicle. They are completely different but the end result can still be a wrecked engine.
These were then downloaded as tiff files where each image. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Very pertinent to direct injection and turbocharging, ecoboost, focus st and. 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. What are the various causes of preignition detonation. If the explosion moves outward at supersonic speeds faster than the speed of sound, its a detonation. Preignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark. If the combustion process propagates outward at subsonic speeds slower than the speed of sound, its a deflagration. Hydrogen has relatively high flame speed and is known to be very prone to preignition. To recap, preignition is a situation in which the fuelair mixture in a spark ignition engine ignites before the. In this mode the combustion zone follows immediately behind, and drives, a leading shock front moving into the quiescent, unburned gas mixture at supersonic velocity.
966 1498 14 338 1211 89 8 427 1463 1062 960 752 170 40 1167 1432 508 1357 765 1043 827 293 507 232 601 909 1296 87 579 1083 575 547 246 296