Low Speed Pre-Ignition: A Threat to Turbocharged Engines

As we explore the intricacies of turbocharged engines, it's essential to understand one of the lesser-known but significant threats they face: low speed pre-ignition. This phenomenon occurs when a portion of the oxygen in the air-fuel mixture is not burned completely during the combustion process, leaving behind unreacted oxygen that can react with deposits on the engine components, causing them to glow.

When this glowing deposit comes into contact with the hot cylinder walls and valves, it can cause the engine to run hotter than normal. This increased heat can lead to premature wear on the engine's components, ultimately resulting in costly repairs. To prevent low speed pre-ignition from occurring, it's crucial to identify and address the underlying causes.

One common source of low speed pre-ignition is a contaminated air filter or a dirty fuel injectors. If the air filter is clogged with debris, it can restrict airflow into the engine, causing the air-fuel mixture to become richer than intended. Similarly, dirty fuel injectors can spray fuel too richly, leading to an overabundance of oxygen in the combustion chamber. In both cases, the unburned oxygen can react with deposits on the engine components, causing them to glow.

The intake stroke is where a new batch of air and fuel enters the cylinder, which is essential for igniting the existing glowing deposit and starting the combustion process. However, if the air-fuel mixture is not properly prepared, it can lead to low speed pre-ignition. The compression stroke introduces more air and fuel into the cylinder, but if the spark does not ignite the air-fuel mixture at the optimal time, it can cause the engine to run hot.

To understand the pressure characteristics of a turbocharged engine, let's look at a graph illustrating the cylinder pressure versus crank angle. Normally, the cylinder pressure spikes up as the piston reaches top dead center and the spark ignites the air-fuel mixture. However, in the case of low speed pre-ignition, the pressure spikes occur earlier than expected, indicating that the ignition process is being triggered prematurely.

The easiest way to prevent low speed pre-ignition from occurring is to avoid flooring it when driving at low engine speeds. By downshifting into a lower gear and reducing engine RPMs, you can reduce the likelihood of excessive cylinder pressure and minimize the risk of damage to your engine. This simple yet effective strategy can help protect your turbocharged engine from the dangers of low speed pre-ignition.

A study conducted by Toyota and Denso plotted the cylinder pressure versus engine RPM to illustrate when pre-ignition occurs. The results showed that pre-ignition is more likely to occur at lower engine speeds, making it less of a concern as engine RPMs increase. However, even at higher engine speeds, pre-ignition can still occur if there are deposits present in the cylinder.

To further prevent low speed pre-ignition, tuning for a richer air-fuel mixture can be an effective solution. By using a richer air-fuel mixture, you can reduce the amount of unburned oxygen in the combustion chamber, making it less likely to react with deposits on the engine components. However, this approach comes with its own set of risks, including oil dilution and deposit formation.

Finally, using an oil catch can can be a great way to prevent low speed pre-ignition from occurring. By capturing oil droplets introduced through the PCV valve, oil catch cans can significantly reduce the risk of deposits forming on engine components. Additionally, oil catch cans can help to prevent premature wear on engine parts by reducing the amount of oil that enters the combustion chamber.

In conclusion, low speed pre-ignition is a serious threat to turbocharged engines, and understanding its causes and prevention strategies is essential for protecting your vehicle's health. By identifying and addressing underlying issues, such as contaminated air filters or dirty fuel injectors, you can minimize the risk of damage to your engine. Additionally, using techniques like downshifting into lower gears, tuning for a richer air-fuel mixture, and utilizing oil catch cans can help prevent low speed pre-ignition from occurring.

"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video we're going to be talking about why lugging your engine is a bad idea and by lugging your engine what i mean is putting your engine at a very high load for example flooring it when it's at a low engine rpm such as about you know 1500 rpm so let's say you're in 50 or 60 or something like that you're only cruising at about 40 miles an hour and your floor this is going to lug your engine and so uh the reason first of all i want to get into some logic that i actually heard from car talk and i thought it made quite a bit of sense and then i'm going to get into a study done by toyota and denso talking about low speed pre-ignition which is more prevalent for small turbocharged engines using higher boost and so first off you know putting it in a high gear and trying to accelerate is kind of counterintuitive because you're going to have less wheel torque as a result of the gearing disadvantage so obviously it makes sense to downshift if you're trying to accelerate you're putting your engine at a disadvantage because you're telling it to do more work than it can and so by putting it on these higher gears your engine has to work harder meaning it's going to be less efficient and so if it's operating in a less efficient range it's going to heat up more because efficiency of course correlates with heat so you have more heat going into the engine block itself rather than just into useful work so as you overwork that engine it overheats your temperatures inside your cylinders heats up and then once you have higher temperatures inside your cylinders you start to get unpredictable timing so you can get ping you can get knock if you have hot spots somewhere in there which can mess up your timing and so this can cause uneven combustion not only the timing but also the location if a deposit somewhere in there causes combustion to occur and so if you have that uneven combustion that's occurring in different locations or at bad times that can of course damage your piston you can have piston slap let's say you have a pressure not where it's supposed to originate well that can force the piston up against the cylinder wall and so you can start to scrape up your cylinder walls and so over time you know that seal will kind of wear out and you'll burn all kinds of oil and you won't have as good of pressure so that's kind of the you know how will this cause damage in pretty much any engine i mean this kind of gets into more of small charged engines low speed pre-ignition and so what is low speed pre-ignition well this is when you have ignition occur before your spark at a low speed a low engine speed so a low engine rpm with a high load so for example you're flooring it and it's caused by an ignition source and it occurs before the spark so this means you can't use ignition timing to get rid of it and so what this can do is it can damage and crack your pistons can damage your spark plugs thing like that so it can cause pretty detrimental impacts on your engine so what are the sources for this low speed pre-ignition well it's come down to that the ignition source has to be combustible and large enough in order to cause it some of the possible sources are oil droplets which could be introduced into your combustion chamber through the positive crankcase ventilation system deposit peelings from the cylinder walls and on top of the piston top as well as oil dilution which can occur from blow by when you get gasoline mixing in with the oil and then having that oil mist spray back up into the combustion chamber from the piston sides as they're coming up and getting some oil droplets in there and those can heat up and cause this pre-ignition so i looked at this study which was done by toyota and denso and they kind of came up with you know the process of how this occurs um inside the engine so we're gonna go over that and as i mentioned the ignition source what they found out it has to be combustible and it has to be large enough in order to cause this so here we have a piston we're kind of looking at a zoomed in view of this is the cylinder wall and this is our piston which would be moving up and down and so we've got deposits that have started to form on the cylinder wall and on the piston from wall wetting you know spraying in gasoline and so you've got these deposits that form from oil mixtures and things like that the contaminants that are introduced and they form on the piston tops now they can form fairly quickly uh on the cylinder walls up at the top of the bore as well as that crevice where the piston meets with the cylinder um and then they kind of form fairly slowly on top of the piston itself under a low engine rpm high load operations or low load operations rather so at low load operations you can have these deposits start to form up on the piston well eventually these deposits can peel off and float inside the combustion chamber and so let's say we have our compression stroke here and it peels off so we've got this combustible item this combustible deposit which is floating in the chamber we then have our power stroke so it ignites this and you have a surface flame that's on this deposit and then of course during your exhaust stroke the deposit it doesn't make it out the exhaust so it remains in the chamber um let's just say for this example it of course it could go out the exhaust and then you wouldn't have this problem uh but we're assuming that it remains within the cylinder uh which isn't all that unlikely and so the surface flame is extinguished now uh but it's still kind of glowing because there's some remaining oxygen uh in that mixture not all of it burnt completely and so that oxygen is reacting with the deposit and keeping it glowing then you have your intake stroke and of course you're bringing in all kinds of new oxygen so it really starts to glow once it's got all that oxygen around it you have your compression stroke and you've introduced that air and fuel mixture and then as a result this glowing deposit now ignites that air and fuel mixture before your spark fires and you have this low speed pre-ignition so what this looks like as far as pressure is concerned is here we've got our cylinder pressure on the left and here we've got our crank angle zero in the center that would be top dead center and so a normal combustion you'll have your pressure kind of spike up as you reach top dead center your spark fires and then you have that peak of pressure as that cylinder is moving down and as that combustion occurs and expands out that air and fuel mixture which is now burning with low speed pre-ignition however this of course occurs before the spark and so you have this peak and pressure and it's kind of this erratic pressure that occurs uh much higher than normal and so that can seriously damage your engine so that's kind of what it looks like from a pressure standpoint versus you know where your crank angle is at and so one of the last things i want to get into here is how do you prevent this from happening and the easiest scenario is to just not floor it when you're at low engine rpms so if you're at you know six gear 40 miles an hour downshift into fourth maybe or third if you need to accelerate fifth if you don't need to accelerate that hard you know things like that but point is you can downshift and it's very easy to prevent this so they actually plotted in this toyota and denso study that they did they plotted they were introducing deposits into a chamber and seeing when pre-ignition would occur and so what they plotted was the cylinder pressure uh versus the rpm the engine rpm and where you would have pre-ignition and so it's not that pre-ignition can't occur at higher engine rpms it's just that it's far less likely and that's what this graph that they figured out shows because as you get into the lower engine rpms it's a much lower pressure which pre-ignition will occur so anything above this line pre-ignition would occur anything below this line with that contaminant of course this has to be there if that's there pre-ignition still wouldn't occur even if there was that deposit floating around in there so at these lower pressures or higher pressures at a higher engine rpm you can get away with having those deposits in there and not having pre-ignition and damaging your engine um so another way of getting around it is to tune for a rich air fuel mixture so if you were to have you know this kind of scenario right here but you used a richer air fuel mixture what that does is during this exhaust stroke here you're not going to have as much air remaining oxygen remaining that wasn't burned in that air fuel mixture and so that oxygen won't be able to react with this so this will pretty much just go out completely and then when you have the intake air come in it won't be enough to restart that reaction and so you won't have all of this occur so you can use a rich air fuel mixture that however could cause oil dilution and it can cause deposits to form so it's not really the greatest solution it's just kind of something that could fix it for a very specific scenario and then also i think an oil catch can would be a great way to help prevent this for example you're not going to be introducing so you won't have oil droplets as i mentioned that was one of the things that they thought you know could be a source of it is oil droplets introduced from your pcv valve and so oil catch can of course just prevents that from occurring or helps to reduce it significantly and it can also help to reduce deposits from forming on your pistons and so that's another way of getting around it so i hope you guys have learned something from this um just know that you know you shouldn't be flooring it if you're in high gear and here's kind of the logic behind all that if you have any questions or comments feel free to leave them below thanks for watching everyone and welcome in this video we're going to be talking about five things which you should never do in your turbocharged car and as you can tell we are in my 2014 subaru sti which has a 2.5 liter turbocharged engine now the first thing i want to talk about is not running your car hard until you've let everything get up to operating temperaturehello everyone and welcome in this video we're going to be talking about why lugging your engine is a bad idea and by lugging your engine what i mean is putting your engine at a very high load for example flooring it when it's at a low engine rpm such as about you know 1500 rpm so let's say you're in 50 or 60 or something like that you're only cruising at about 40 miles an hour and your floor this is going to lug your engine and so uh the reason first of all i want to get into some logic that i actually heard from car talk and i thought it made quite a bit of sense and then i'm going to get into a study done by toyota and denso talking about low speed pre-ignition which is more prevalent for small turbocharged engines using higher boost and so first off you know putting it in a high gear and trying to accelerate is kind of counterintuitive because you're going to have less wheel torque as a result of the gearing disadvantage so obviously it makes sense to downshift if you're trying to accelerate you're putting your engine at a disadvantage because you're telling it to do more work than it can and so by putting it on these higher gears your engine has to work harder meaning it's going to be less efficient and so if it's operating in a less efficient range it's going to heat up more because efficiency of course correlates with heat so you have more heat going into the engine block itself rather than just into useful work so as you overwork that engine it overheats your temperatures inside your cylinders heats up and then once you have higher temperatures inside your cylinders you start to get unpredictable timing so you can get ping you can get knock if you have hot spots somewhere in there which can mess up your timing and so this can cause uneven combustion not only the timing but also the location if a deposit somewhere in there causes combustion to occur and so if you have that uneven combustion that's occurring in different locations or at bad times that can of course damage your piston you can have piston slap let's say you have a pressure not where it's supposed to originate well that can force the piston up against the cylinder wall and so you can start to scrape up your cylinder walls and so over time you know that seal will kind of wear out and you'll burn all kinds of oil and you won't have as good of pressure so that's kind of the you know how will this cause damage in pretty much any engine i mean this kind of gets into more of small charged engines low speed pre-ignition and so what is low speed pre-ignition well this is when you have ignition occur before your spark at a low speed a low engine speed so a low engine rpm with a high load so for example you're flooring it and it's caused by an ignition source and it occurs before the spark so this means you can't use ignition timing to get rid of it and so what this can do is it can damage and crack your pistons can damage your spark plugs thing like that so it can cause pretty detrimental impacts on your engine so what are the sources for this low speed pre-ignition well it's come down to that the ignition source has to be combustible and large enough in order to cause it some of the possible sources are oil droplets which could be introduced into your combustion chamber through the positive crankcase ventilation system deposit peelings from the cylinder walls and on top of the piston top as well as oil dilution which can occur from blow by when you get gasoline mixing in with the oil and then having that oil mist spray back up into the combustion chamber from the piston sides as they're coming up and getting some oil droplets in there and those can heat up and cause this pre-ignition so i looked at this study which was done by toyota and denso and they kind of came up with you know the process of how this occurs um inside the engine so we're gonna go over that and as i mentioned the ignition source what they found out it has to be combustible and it has to be large enough in order to cause this so here we have a piston we're kind of looking at a zoomed in view of this is the cylinder wall and this is our piston which would be moving up and down and so we've got deposits that have started to form on the cylinder wall and on the piston from wall wetting you know spraying in gasoline and so you've got these deposits that form from oil mixtures and things like that the contaminants that are introduced and they form on the piston tops now they can form fairly quickly uh on the cylinder walls up at the top of the bore as well as that crevice where the piston meets with the cylinder um and then they kind of form fairly slowly on top of the piston itself under a low engine rpm high load operations or low load operations rather so at low load operations you can have these deposits start to form up on the piston well eventually these deposits can peel off and float inside the combustion chamber and so let's say we have our compression stroke here and it peels off so we've got this combustible item this combustible deposit which is floating in the chamber we then have our power stroke so it ignites this and you have a surface flame that's on this deposit and then of course during your exhaust stroke the deposit it doesn't make it out the exhaust so it remains in the chamber um let's just say for this example it of course it could go out the exhaust and then you wouldn't have this problem uh but we're assuming that it remains within the cylinder uh which isn't all that unlikely and so the surface flame is extinguished now uh but it's still kind of glowing because there's some remaining oxygen uh in that mixture not all of it burnt completely and so that oxygen is reacting with the deposit and keeping it glowing then you have your intake stroke and of course you're bringing in all kinds of new oxygen so it really starts to glow once it's got all that oxygen around it you have your compression stroke and you've introduced that air and fuel mixture and then as a result this glowing deposit now ignites that air and fuel mixture before your spark fires and you have this low speed pre-ignition so what this looks like as far as pressure is concerned is here we've got our cylinder pressure on the left and here we've got our crank angle zero in the center that would be top dead center and so a normal combustion you'll have your pressure kind of spike up as you reach top dead center your spark fires and then you have that peak of pressure as that cylinder is moving down and as that combustion occurs and expands out that air and fuel mixture which is now burning with low speed pre-ignition however this of course occurs before the spark and so you have this peak and pressure and it's kind of this erratic pressure that occurs uh much higher than normal and so that can seriously damage your engine so that's kind of what it looks like from a pressure standpoint versus you know where your crank angle is at and so one of the last things i want to get into here is how do you prevent this from happening and the easiest scenario is to just not floor it when you're at low engine rpms so if you're at you know six gear 40 miles an hour downshift into fourth maybe or third if you need to accelerate fifth if you don't need to accelerate that hard you know things like that but point is you can downshift and it's very easy to prevent this so they actually plotted in this toyota and denso study that they did they plotted they were introducing deposits into a chamber and seeing when pre-ignition would occur and so what they plotted was the cylinder pressure uh versus the rpm the engine rpm and where you would have pre-ignition and so it's not that pre-ignition can't occur at higher engine rpms it's just that it's far less likely and that's what this graph that they figured out shows because as you get into the lower engine rpms it's a much lower pressure which pre-ignition will occur so anything above this line pre-ignition would occur anything below this line with that contaminant of course this has to be there if that's there pre-ignition still wouldn't occur even if there was that deposit floating around in there so at these lower pressures or higher pressures at a higher engine rpm you can get away with having those deposits in there and not having pre-ignition and damaging your engine um so another way of getting around it is to tune for a rich air fuel mixture so if you were to have you know this kind of scenario right here but you used a richer air fuel mixture what that does is during this exhaust stroke here you're not going to have as much air remaining oxygen remaining that wasn't burned in that air fuel mixture and so that oxygen won't be able to react with this so this will pretty much just go out completely and then when you have the intake air come in it won't be enough to restart that reaction and so you won't have all of this occur so you can use a rich air fuel mixture that however could cause oil dilution and it can cause deposits to form so it's not really the greatest solution it's just kind of something that could fix it for a very specific scenario and then also i think an oil catch can would be a great way to help prevent this for example you're not going to be introducing so you won't have oil droplets as i mentioned that was one of the things that they thought you know could be a source of it is oil droplets introduced from your pcv valve and so oil catch can of course just prevents that from occurring or helps to reduce it significantly and it can also help to reduce deposits from forming on your pistons and so that's another way of getting around it so i hope you guys have learned something from this um just know that you know you shouldn't be flooring it if you're in high gear and here's kind of the logic behind all that if you have any questions or comments feel free to leave them below thanks for watching everyone and welcome in this video we're going to be talking about five things which you should never do in your turbocharged car and as you can tell we are in my 2014 subaru sti which has a 2.5 liter turbocharged engine now the first thing i want to talk about is not running your car hard until you've let everything get up to operating temperature\n"