Detonation FAQ
10-29-2002, 01:24 AM
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Detonation FAQ
Does anyone know of any books or online Guides/FAQ's that I can read up on that explain what detonation is, and the many reasons of what causes it, and how to cure the basic problems of it? I already have a basic understanding of it, but I want to learn more. Thanks. 
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10-29-2002, 01:32 AM
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Detonation - A condition in which, after the spark plug fires, some of the unburned air-fuel mixture in the combustion chamber explodes spontaneously, set off only by the heat and pressure of air-fuel mixture that has already been ignited. Detonation, or "knock," greatly increases the mechanical and thermal stresses on the engine. It is an unwanted explosion of the air/fuel mixture in the combustion chamber caused by excess heat and compression, advanced timing, or an overly lean mixture. Also referred to as "ping". The pinging or knocking noise is the result of intense pressure waves in the charge which cause the cylinder walls to vibrate. Also called "fuel knock."
10-29-2002, 01:34 AM
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Brendan..thanks man. I've seen that definition before, but I was wondering if there was more to it or not. tongue.gif 
I've seen that definition before, but I was wondering if there was more to it or not. tongue.gif
10-29-2002, 04:42 AM
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Vehicle: 2008 Toyota Prius 2006 Suzuki SV650S
Hyundai's definition for ya....
ECM Misfire Detection Method
It can be tough to hear or feel a misfire, which is one reason why new emissions-control standards require the on-board diagnostics (OBD-II) of the engine control module (ECM) to monitor each cylinder for misfire.
Engine misfire detection is based on the difference of engine rotational speed between the firing cylinders and the missing cylinder. When a cylinder is misfiring, it takes a "longer time" for the crankshaft to rotate to the next cylinder in the firing order. This "time" is measured by the crankshaft angle sensor (CAS) which measures the actual rotational travel of the crankshaft in real time. This information is evaluated by the ECM. If the misfiring cylinder took "longer" to rotate the crankshaft than the other cylinders, the ECM will set the appropriate diagnostic trouble code (DTC) for that cylinder. As an example; an inline 4 cylinder engine's crankshaft rotates 180° as each cylinder fires through the firing order. In a properly running engine with a firing order of 1-3-4-2, the time between the firing of 1-3 will be the same as 3-4, 4-2, and 2-1. In an engine that has a misfire in cylinder #2; it takes the crankshaft longer to travel through the 2-1 firing rotation.
The repair of today's misfire is more difficult than pre-OBD-II vehicles because the ECM is programmed to detect the slightest change of crankshaft rotational speed. The criteria for detecting a misfire is set by the Federal Government and all vehicles sold in the U.S. must comply with these requirements. The engine management system must be able to perform three critical elements of misfire detection:
Monitor, identify and if severe enough, illuminate the "check engine" light for a misfiring cylinder;
Set separate diagnostic trouble codes for multiple cylinders;
During a misfire great enough to damage the catalyst, the "check engine" light must blink.
Diagnostic Trouble Code Definition
P0300 - Misfiring in more than one cylinder, but unable to detect the specific cylinder because the misfire is random.
P0301 - Misfire in cylinder number 1 is very likely.
P0302 - Misfire in cylinder number 2 is very likely.
P0303 - Misfire in cylinder number 3 is very likely.
P0304 - Misfire in cylinder number 4 is very likely.
P0305 - Misfire in cylinder number 5 is very likely.
P0306 - Misfire in cylinder number 6 is very likely.
[ October 29, 2002, 12:28 PM: Message edited by: Random ]
QUOTE
ECM Misfire Detection Method
It can be tough to hear or feel a misfire, which is one reason why new emissions-control standards require the on-board diagnostics (OBD-II) of the engine control module (ECM) to monitor each cylinder for misfire.
Engine misfire detection is based on the difference of engine rotational speed between the firing cylinders and the missing cylinder. When a cylinder is misfiring, it takes a "longer time" for the crankshaft to rotate to the next cylinder in the firing order. This "time" is measured by the crankshaft angle sensor (CAS) which measures the actual rotational travel of the crankshaft in real time. This information is evaluated by the ECM. If the misfiring cylinder took "longer" to rotate the crankshaft than the other cylinders, the ECM will set the appropriate diagnostic trouble code (DTC) for that cylinder. As an example; an inline 4 cylinder engine's crankshaft rotates 180° as each cylinder fires through the firing order. In a properly running engine with a firing order of 1-3-4-2, the time between the firing of 1-3 will be the same as 3-4, 4-2, and 2-1. In an engine that has a misfire in cylinder #2; it takes the crankshaft longer to travel through the 2-1 firing rotation.
The repair of today's misfire is more difficult than pre-OBD-II vehicles because the ECM is programmed to detect the slightest change of crankshaft rotational speed. The criteria for detecting a misfire is set by the Federal Government and all vehicles sold in the U.S. must comply with these requirements. The engine management system must be able to perform three critical elements of misfire detection:
Monitor, identify and if severe enough, illuminate the "check engine" light for a misfiring cylinder;
Set separate diagnostic trouble codes for multiple cylinders;
During a misfire great enough to damage the catalyst, the "check engine" light must blink.
Diagnostic Trouble Code Definition
P0300 - Misfiring in more than one cylinder, but unable to detect the specific cylinder because the misfire is random.
P0301 - Misfire in cylinder number 1 is very likely.
P0302 - Misfire in cylinder number 2 is very likely.
P0303 - Misfire in cylinder number 3 is very likely.
P0304 - Misfire in cylinder number 4 is very likely.
P0305 - Misfire in cylinder number 5 is very likely.
P0306 - Misfire in cylinder number 6 is very likely.
[ October 29, 2002, 12:28 PM: Message edited by: Random ]
10-29-2002, 05:07 AM
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I saved this from FXtreme by tom1192:
This is something we have not discussed much at all or in great detail. I found this slice of info off a website that sells the J&S Safeguard and thought some of you going with force induction might want to read. I took out the gratuitus plugs for the device itself.
Here goes:
Detonation
Engine Knock-that annoying rattling sound that sometimes comes from under the hood of your pride and joy, is a killer. We have all heard the stories of blown head gaskets and broken pistons. Maybe it has already happened to you, too. But just what is knock, sometimes also referred to as detonation?
The knocking sounds you hear are the cylinder walls set into oscillation by intense pressure waves, caused by abnormal combustion. Normal combustion is a controlled burn that starts from the spark plug and spreads outward, causing a pressure rise in the combustion chamber. This pressure is then converted into torque on the crankshaft. Ideally, the peak pressures will occur about ten to fifteen degrees after top dead center (TDC), as the piston is on its way down.
Detonation is a form of abnormal combustion that starts off right, but at the last millisecond, something goes wrong. The remaining air-fuel mixture, called the "end gas", explodes all at once, instead of burning in a controlled way. Resultant engine damage is caused by an instantaneous pressure rise that can excede 1500 psi. This is more than double the normal peak combustion pressure, and will blow head gaskets, break piston ring lands and hammer the rod bearings. Another form of damage seen is that the tops of the pistons will be eroded and can even melt.
High octane fuels are resistant to detonation because they contain compounds that slow down the chemical chain reaction we call combustion. If left unchecked, these chain reactions would quickly escalate, resulting in increasing damage to the piston and other engine components. All fuels, regardless of octane, have a knock limit. This is reached when the temperature of the "end gas" reaches an autoignition point. Combustion chamber designers use high swirl inlets and large "quench areas" to fight this "autoignition" problem. There are other factors beyond these mechanical design features which influence "end gas" temperatures. Some of these are: (1) Intake charge temperature, (2) Coolant temperature, (3) Compression Ratio, (4) Boost pressure, (5) Spark timing, (6) Air-fuel ratio, and (6) Humidity.
An increase in compression ratio, boost pressure, or spark timing will increase peak cylinder pressure, which in turn raises the "end gas" temperature. Higher inlet and coolant temperatures also increase the "end gas" temperature. Richer mixtures can be used to cool the charge. At some point beyond about 10:1, however, will again increase the tendency to detonate. A decrease in humidity will also tend to increase detonation.
Solutions
Some things you can change, and some you are stuck with. Obvious things to do are get cold, fresh air to your air cleaner, use the best form of charge cooling (intercoolers) you can afford, and work on your cooling system to bring the temperatures down. Get an Air-fuel meter (O2 meter), and if necessary, install a fuel enrichment device. For turbo/supercharged engines water-alcohol injection can be very effective, but the volumes required mean constant refilling and maintenance, so in the long term it is a specialized solution that has a lot of drawbacks.
Spark retard, within limits is the most powerful means of controlling detonation. Traditionally, this has been a manual affair by simply cranking the distributor back "x" degrees, Some electronic devices can retard timing in relation to manifold or boost pressure and other devices offer simple manual knobs you can alter the timing with if an audible "ping" is heard. Many newer cars are quipped with knock sensors that retard the timing when detonation occurs. This form of closed loop spark control where the vehicle's ecu automatically retards all cylinders when detonation occurs, a situation we call "retard all". On a select few modern engine controllers (Porsche, Corvette) the microprocessor is programmed to retard individual cylinders as knock or detonation occurs. The problem with either of these approaches is twofold: First, the OEM carefully maps a complex set of spark curves and only allows a small degree of retard to take place, typically 4 degrees; Secondly, these ecus are highly specific and are not readily adaptable or programmable for other applications.
*********************************************
Preignition
Preignition and detonation are two separate and distinct events. It was first pointed out as far back as 1906 that the two phenomena were not only quite distinct but were in fact not related to each other. In the first place, preignition in itself does not produce an audible "knock" and if it is audible at all it could be described as a "dull thud". Because preignition is frequently brought about as a result of persistent detonation, the distinct "knock or ping" of the latter came quite erroneously to be associated with it.
It is by no means uncommon for preignition, or in this case it would be more correct to describe it as autoignition, to occur at the same phase as the timed spark. In this case the ignition can be switched off, and the engine could continue to run perfectly steadily without the slightest observable change in performance, sound, or any other characteristic. The danger, however, lies in the fact that all control of timing can be lost and ignition may creep in earlier in the cycle.
The danger of preignition lies not so much in the development of high pressures but rather in the very greatincrease in heat flow to the piston and cylinder walls when the ignition occurs too early in the cycle. This increase in heat flow, in turn, raises still further the temperature of the hot spot or surface which is causing the preignition resulting in even earlier ignition. At some point the temperatures are elevated to the point where the incoming charge is ignited, causing backfiring in the inlet tract. The belief, still widely held, that preignition can give rise to dangerously high cylinder pressures is totally false. Under no circumstances is the peak pressure resulting from preignition appreciably higher than from a spark-initiated ignition and, in both cases, the peak is reached when the maximum pressure is attained at or just after top dead center, that is to say, about 10 degrees earlier than the normal optimum. As the time of ignition is further advanced by either advancing the time of the spark or by earlier preignition, the maximum cylinder pressure falls again due to the excessive heat loss, for the piston is then compressing gas at or about its maximum temperature, and the intensity of heat flow is increased many times. The danger lies not in the production of excessive pressures but of excessive heat fow. The intense heat flow in the affected cylinder can result in piston seizure followed by the breaking-up of the piston with catastrophic results to the whole engine.
In nine cases out of ten, preignition is initiated by overheating of the sparkplug electrodes or some sharp point or edge that has gone "critical". We are accustomed these days to focus all our attention on the subject of detonation for it is the limiting factor controlling the performance of a spark-ignition engine. We are apt to forget that the real danger is that it leads on to preignition. In itself, detonation is not dangerous... It is the preignition it gives rise to that can so easily wreck an engine.
This is something we have not discussed much at all or in great detail. I found this slice of info off a website that sells the J&S Safeguard and thought some of you going with force induction might want to read. I took out the gratuitus plugs for the device itself.
Here goes:
Detonation
Engine Knock-that annoying rattling sound that sometimes comes from under the hood of your pride and joy, is a killer. We have all heard the stories of blown head gaskets and broken pistons. Maybe it has already happened to you, too. But just what is knock, sometimes also referred to as detonation?
The knocking sounds you hear are the cylinder walls set into oscillation by intense pressure waves, caused by abnormal combustion. Normal combustion is a controlled burn that starts from the spark plug and spreads outward, causing a pressure rise in the combustion chamber. This pressure is then converted into torque on the crankshaft. Ideally, the peak pressures will occur about ten to fifteen degrees after top dead center (TDC), as the piston is on its way down.
Detonation is a form of abnormal combustion that starts off right, but at the last millisecond, something goes wrong. The remaining air-fuel mixture, called the "end gas", explodes all at once, instead of burning in a controlled way. Resultant engine damage is caused by an instantaneous pressure rise that can excede 1500 psi. This is more than double the normal peak combustion pressure, and will blow head gaskets, break piston ring lands and hammer the rod bearings. Another form of damage seen is that the tops of the pistons will be eroded and can even melt.
High octane fuels are resistant to detonation because they contain compounds that slow down the chemical chain reaction we call combustion. If left unchecked, these chain reactions would quickly escalate, resulting in increasing damage to the piston and other engine components. All fuels, regardless of octane, have a knock limit. This is reached when the temperature of the "end gas" reaches an autoignition point. Combustion chamber designers use high swirl inlets and large "quench areas" to fight this "autoignition" problem. There are other factors beyond these mechanical design features which influence "end gas" temperatures. Some of these are: (1) Intake charge temperature, (2) Coolant temperature, (3) Compression Ratio, (4) Boost pressure, (5) Spark timing, (6) Air-fuel ratio, and (6) Humidity.
An increase in compression ratio, boost pressure, or spark timing will increase peak cylinder pressure, which in turn raises the "end gas" temperature. Higher inlet and coolant temperatures also increase the "end gas" temperature. Richer mixtures can be used to cool the charge. At some point beyond about 10:1, however, will again increase the tendency to detonate. A decrease in humidity will also tend to increase detonation.
Solutions
Some things you can change, and some you are stuck with. Obvious things to do are get cold, fresh air to your air cleaner, use the best form of charge cooling (intercoolers) you can afford, and work on your cooling system to bring the temperatures down. Get an Air-fuel meter (O2 meter), and if necessary, install a fuel enrichment device. For turbo/supercharged engines water-alcohol injection can be very effective, but the volumes required mean constant refilling and maintenance, so in the long term it is a specialized solution that has a lot of drawbacks.
Spark retard, within limits is the most powerful means of controlling detonation. Traditionally, this has been a manual affair by simply cranking the distributor back "x" degrees, Some electronic devices can retard timing in relation to manifold or boost pressure and other devices offer simple manual knobs you can alter the timing with if an audible "ping" is heard. Many newer cars are quipped with knock sensors that retard the timing when detonation occurs. This form of closed loop spark control where the vehicle's ecu automatically retards all cylinders when detonation occurs, a situation we call "retard all". On a select few modern engine controllers (Porsche, Corvette) the microprocessor is programmed to retard individual cylinders as knock or detonation occurs. The problem with either of these approaches is twofold: First, the OEM carefully maps a complex set of spark curves and only allows a small degree of retard to take place, typically 4 degrees; Secondly, these ecus are highly specific and are not readily adaptable or programmable for other applications.
*********************************************
Preignition
Preignition and detonation are two separate and distinct events. It was first pointed out as far back as 1906 that the two phenomena were not only quite distinct but were in fact not related to each other. In the first place, preignition in itself does not produce an audible "knock" and if it is audible at all it could be described as a "dull thud". Because preignition is frequently brought about as a result of persistent detonation, the distinct "knock or ping" of the latter came quite erroneously to be associated with it.
It is by no means uncommon for preignition, or in this case it would be more correct to describe it as autoignition, to occur at the same phase as the timed spark. In this case the ignition can be switched off, and the engine could continue to run perfectly steadily without the slightest observable change in performance, sound, or any other characteristic. The danger, however, lies in the fact that all control of timing can be lost and ignition may creep in earlier in the cycle.
The danger of preignition lies not so much in the development of high pressures but rather in the very greatincrease in heat flow to the piston and cylinder walls when the ignition occurs too early in the cycle. This increase in heat flow, in turn, raises still further the temperature of the hot spot or surface which is causing the preignition resulting in even earlier ignition. At some point the temperatures are elevated to the point where the incoming charge is ignited, causing backfiring in the inlet tract. The belief, still widely held, that preignition can give rise to dangerously high cylinder pressures is totally false. Under no circumstances is the peak pressure resulting from preignition appreciably higher than from a spark-initiated ignition and, in both cases, the peak is reached when the maximum pressure is attained at or just after top dead center, that is to say, about 10 degrees earlier than the normal optimum. As the time of ignition is further advanced by either advancing the time of the spark or by earlier preignition, the maximum cylinder pressure falls again due to the excessive heat loss, for the piston is then compressing gas at or about its maximum temperature, and the intensity of heat flow is increased many times. The danger lies not in the production of excessive pressures but of excessive heat fow. The intense heat flow in the affected cylinder can result in piston seizure followed by the breaking-up of the piston with catastrophic results to the whole engine.
In nine cases out of ten, preignition is initiated by overheating of the sparkplug electrodes or some sharp point or edge that has gone "critical". We are accustomed these days to focus all our attention on the subject of detonation for it is the limiting factor controlling the performance of a spark-ignition engine. We are apt to forget that the real danger is that it leads on to preignition. In itself, detonation is not dangerous... It is the preignition it gives rise to that can so easily wreck an engine.