Peripheral Port Renesis dyno's
12-27-2007, 01:28 PM
#77
BDC Motorsports
Glenmorangie 
thats just not correct.
octane is not a measure of how fast or slow any given gasoline will burn. it is only a measure of the fuel's resistance to pre-ignition. pre-ignition is defined as the fuel igniting on its own due to pressure and heat before the arrival of the flame front.
thats just not correct.
octane is not a measure of how fast or slow any given gasoline will burn. it is only a measure of the fuel's resistance to pre-ignition. pre-ignition is defined as the fuel igniting on its own due to pressure and heat before the arrival of the flame front.
I disagree. I never said that octane was a measure of how fast or slow it burned although it's been my experience that it's implicitly related. I said it was a fuel's resiliency to knock. It seems however that a higher octane fuel is less volatile and burns more slowly with a more controlled and stable flame-front depending upon what it is. Alcohol is one example.
Also on pre-ignition, it strikes me that it's defined as the occurrence of any type of knock that fires the charge prior to and outside the confines of a well-timed spark event. I can think of a few things -- heat and pressure as you've mentioned, any kind of glow-plug effect from an external source, just plain firing the plug too early because of poor tuning, and the biggie auto-ignition of the fuel in the charge.
I'll give the URL you've linked a read and see what it has to say. Thanks for it.
http://www.faqs.org/faqs/autos/gasoline-faq/part3/ importantly 6.2 and 6.3 as well as 6.13 6.16 and 6.17
on modern engine management systems you will only get the most power out of a given engine by using the octane that limits knock effectively. if you go lower than that number the PCM will hear the knock and adjust your timing to reduce power.
on modern engine management systems you will only get the most power out of a given engine by using the octane that limits knock effectively. if you go lower than that number the PCM will hear the knock and adjust your timing to reduce power.
On the contrary, there's two major things I can think of just off the top of my head that effect burn rate -- charge density and fuel type (even though there's a host of other factors). When using a higher octane fuel, such as leaded race gas or perhaps an alcohol, I can keep everything else remaining as close as possible to the same (turbo, engine, boost pressure, whatever) and can get away with firing the plug lots earlier than I would with a more volatile pump fuel. I've done it more times than I can count.
Example: http://www.youtube.com/watch?v=_9o5T0PIWVA On this setup, I was running 65-70% fuel (I reduced the load on the EFI system) and replaced the other 30-35% missing fuel with methyl alcohol (enough to bring the mixture back into low 11's:1) at 25psi of boost. Here's the kicker -- normally I wouldn't tune a car on pump gas past 14-15psi as I fear it's instability for not only what you've eluded to (bad tank of gas) but also for other factors that ultimately boil down to its untrustworthiness. At that boost, I fire the plug at 13-14* with a split of 9-11* depending on the CR of the motor and its port work. On the setup linked to the video above, at 25psi (10psi more boost), I was firing the plug at 16*BTDC with a split of 6* and I beat the crap out of that thing like that for months!
If the aspect of the speed of the flame front isn't related to the overall octane rating of the fuel or atleast implicitly factored in, then why do you suppose that I and others can repeatedly get away with this kind of fairly radical timing advance without killing the motor by way of manually inducing pre-ignition? What's your thoughts on that? Is there something else I am not thinking of that's perhaps related?
If you're using a standalone and doing your own tuning you may be able to tune for a lower octane than originally called for by the manufacturer - since they always leave a margin of error- but by doing so you leave yourself at the mercy of one bad tank of gas.
B
12-27-2007, 02:09 PM
#78
Administrator
ive always considered the differences between the two to be putting to fine an edge on it. but for purposes of this discussion we need to set the defintions as charles said so
Detonation
Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.
Pre-ignition
Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. This can happen so far ahead of spark that it is happening during compression. so the fuel my be trying to expand while the engine is trying to compress.
deferring to your terminolgy then when i previously wrote pre-ignition i was talking about detonation. the difference being that pre-ignition literally happens BEFORE spark plug fire while the other happens after.
controlling the timing of spark fire allows the engine to ramp down the heat as well as try to eliminate the offset of the seperate pressure waves by controlling the one that it can. if the engine managment is firing the plugs too early this can ramp up the pressure too soon contributing to the detonation
more to write later- for now i have to clean up Henry and get him some lunch
Detonation
Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.
Pre-ignition
Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. This can happen so far ahead of spark that it is happening during compression. so the fuel my be trying to expand while the engine is trying to compress.
deferring to your terminolgy then when i previously wrote pre-ignition i was talking about detonation. the difference being that pre-ignition literally happens BEFORE spark plug fire while the other happens after.
controlling the timing of spark fire allows the engine to ramp down the heat as well as try to eliminate the offset of the seperate pressure waves by controlling the one that it can. if the engine managment is firing the plugs too early this can ramp up the pressure too soon contributing to the detonation
more to write later- for now i have to clean up Henry and get him some lunch
12-27-2007, 03:37 PM
#80
Administrator
but i agree with Jeff as well- the two are only seperated by the spark event. that is the only thing that distinguishes them. either can cause the other. they are both combustion events when you dont want them which cause pressure rises when you dont want them. to me , as i said before, it puts to fine a point on it to seperate them. you could just as easily say that pre-ignition is a form of detonation.
detonation - in the context of the definitions above- can be fatal to an engine. pre-ignition is nearly always fatal. the times its not it causes more detonation and more heat leading to another pre-ignition event that is fatal.
but as with a different thread where it was tried- I agree to these definitions so we can talk about the POINT of the discussion.
detonation - in the context of the definitions above- can be fatal to an engine. pre-ignition is nearly always fatal. the times its not it causes more detonation and more heat leading to another pre-ignition event that is fatal.
but as with a different thread where it was tried- I agree to these definitions so we can talk about the POINT of the discussion.
12-27-2007, 04:07 PM
#81
Registered
Thread Starter
Jeff is correct from the standpoint that each is bad for the engine. I disagree that you can say that pre-ignition is a form of detonation. It isn't. It is however accurate to say that pre-ignition can lead to detonation. That is accurate. You can have detonation without preignition. You can have preignition without detonation. You can also have both. They are still two separate but closely related phenomenon.
12-27-2007, 04:36 PM
#83
The video of the motor on the dyno clearly shows a mismatch combination of parts. That has to be one of the worse cases of reversion I've seen in modern times. That setup is either never going to show the true potential of the combination or it's allready showing the limits.
12-27-2007, 04:43 PM
#84
Registered
Thread Starter
Charlie, I spoke to Brian on the phone at length about this today. He'll get on here and post later. He did get a bit confused while he typed his response. After I threw out a few scenarios he realized it. It is coincidental that the types of fuels that he has used all just so happen to both burn slower and have higher octane ratings. Specifically Methanol and leaded gas in relation to standard pump gas. If only these fuels are compared it is easy to see draw the conclusion that higher octane must mean slower burn.
As you pointed out it doesn't and you are correct that octane rating is merely a numerical representation of resistance to pre-ignition. It is not indicitive of rate of burn. There are 2 prime examples. Hydrogen and Diesel fuel. Diesel fuel has a very low octane rating of somewhere between 20 and 40 yet burns very slowly. Hydrogen has a higher octane rating than gasoline yet burns much faster. You can make great power with diesel but can't with hydrogen. What further throws more confusion into all of this is that based on the known information of octane and flame front travel, you still can't draw a conclusion as to how auto ignition temperature fits in. It's all pretty complex. It's easy to draw conclusions when you only see a small aspect of the available information. In Brian's case, the fuels he used do have slower flame travel and higher octane. When that's the only info you see it's very easy to draw conclusions from it. When more info is made available however it becomes apparent that some things just happen to be coincidental.
As you pointed out it doesn't and you are correct that octane rating is merely a numerical representation of resistance to pre-ignition. It is not indicitive of rate of burn. There are 2 prime examples. Hydrogen and Diesel fuel. Diesel fuel has a very low octane rating of somewhere between 20 and 40 yet burns very slowly. Hydrogen has a higher octane rating than gasoline yet burns much faster. You can make great power with diesel but can't with hydrogen. What further throws more confusion into all of this is that based on the known information of octane and flame front travel, you still can't draw a conclusion as to how auto ignition temperature fits in. It's all pretty complex. It's easy to draw conclusions when you only see a small aspect of the available information. In Brian's case, the fuels he used do have slower flame travel and higher octane. When that's the only info you see it's very easy to draw conclusions from it. When more info is made available however it becomes apparent that some things just happen to be coincidental.
12-27-2007, 04:55 PM
#85
From my experience when dealing with different fuel types when appiled to a rotary motor, octane numbers are the least important.
The burn rate, specific gravity and most important cooling effects are what affects the rotary motor the most. Not all fuel types no matter what octane will have the cooling affects that a rotary loves be it NA or FI. I've yet to see a pure NA rotary make more useable/reliable power with high octane fuel.
The burn rate, specific gravity and most important cooling effects are what affects the rotary motor the most. Not all fuel types no matter what octane will have the cooling affects that a rotary loves be it NA or FI. I've yet to see a pure NA rotary make more useable/reliable power with high octane fuel.
Last edited by crispeed; 12-27-2007 at 04:58 PM.
12-27-2007, 04:59 PM
#86
Registered
Thread Starter
I agree with that entirely. If we are only talking about gasoline and nothing else, it's perfectly fine to look at only octane number. Of course I am speaking in terms of forced induction. However if alternative fuels come into play my foremost concern is not the octane number unless it absolutely sucks!
You do also bring up another good point regarding fuels that wasn't mentioned and that is cooling ability.
You do also bring up another good point regarding fuels that wasn't mentioned and that is cooling ability.
12-27-2007, 05:27 PM
#87
Administrator
thats because the octane of the fuel doesnt make a bit of difference how much power an engine can make on it as long as there is no detonation/knock/pre-ignition
Maximum Best Torque (MBT) by a given fuel is mainly determined by WHEN the ingition occurs and Flame Front speed. Flame front speed is determined by the shape of the chamber and how much turbulence is created(turbulence i.e. swirling increase flame front propagation) by that shape , and by the burn speed of the fuel.
the OCTANE of the fuel has no bearing on what the speed is. Only what is mixed in the fuel does.The specific mixture of paraffins, olefins , aromatics oxygenates are what determine the flame speed. some octane boosters may lead to lower flame speeds while others can increase it. and the pressures can effect how much the given chemical will increase or decrease the speed.
some other links in no particular order of importance
http://www.daytona-sensors.com/tech_tuning.html
http://72.14.205.104/search?q=cache:...ient=firefox-a
http://www.sacskyranch.com/deton.htm
http://72.14.205.104/search?q=cache:...ient=firefox-a
alcohol is actually a good example. high octane because of its cooling properties and high energy due to high flame speed. it works well in the injected scenario above because it is cooling AND fuel
Maximum Best Torque (MBT) by a given fuel is mainly determined by WHEN the ingition occurs and Flame Front speed. Flame front speed is determined by the shape of the chamber and how much turbulence is created(turbulence i.e. swirling increase flame front propagation) by that shape , and by the burn speed of the fuel.
the OCTANE of the fuel has no bearing on what the speed is. Only what is mixed in the fuel does.The specific mixture of paraffins, olefins , aromatics oxygenates are what determine the flame speed. some octane boosters may lead to lower flame speeds while others can increase it. and the pressures can effect how much the given chemical will increase or decrease the speed.
some other links in no particular order of importance
http://www.daytona-sensors.com/tech_tuning.html
http://72.14.205.104/search?q=cache:...ient=firefox-a
http://www.sacskyranch.com/deton.htm
http://72.14.205.104/search?q=cache:...ient=firefox-a
alcohol is actually a good example. high octane because of its cooling properties and high energy due to high flame speed. it works well in the injected scenario above because it is cooling AND fuel
12-27-2007, 05:53 PM
#88
You do agree that there is difference between maximum power and torque?
The requirement for high rpm vs low rpm use on the same application is sometime different and that's where burn speed plays an important role.
The requirement for high rpm vs low rpm use on the same application is sometime different and that's where burn speed plays an important role.
Last edited by crispeed; 12-27-2007 at 05:57 PM.
12-27-2007, 07:08 PM
#89
Administrator
welll.. power is torque times work so no, not really the way you pose the question. when you are tuning you are trying to find MBT. your looking for the timing that gives you the best power without knock + a safety margin.
OEMs are going to have a bigger safety margin than racers. Drag Racers can have an even smaller safety margin because the limited amount of time the car is doing its thing leaves less chance for detonation or pre-ignition. circuit or road racers have different margins dependant on their need to balance against fuel consumption and when you are tuning for specific fuels then burn speed is very important.
most however are tuning street cars for a wide variety of fuels. fuels that change formulation throughout the year, from area to area some with more olefins,some with more oxygenates etc
OEMs are going to have a bigger safety margin than racers. Drag Racers can have an even smaller safety margin because the limited amount of time the car is doing its thing leaves less chance for detonation or pre-ignition. circuit or road racers have different margins dependant on their need to balance against fuel consumption and when you are tuning for specific fuels then burn speed is very important.
most however are tuning street cars for a wide variety of fuels. fuels that change formulation throughout the year, from area to area some with more olefins,some with more oxygenates etc
12-27-2007, 08:01 PM
#93
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Power = Torque multiplied by rpm and a constant at any given rpm, so if you've tuned for best power, you have got best torque, you can't possibly have a different afr for one and another for the other with breaking the universe.
Last edited by PhillipM; 12-27-2007 at 08:26 PM.
12-27-2007, 08:18 PM
#94
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oh boy, MM is gonna rip you a new one, as you are wrong on both counts. I don't know all the details about the tuning and the math etc,
hp= (torque x rpm)/5252
hp= (torque x rpm)/5252
12-27-2007, 08:23 PM
#97
The Professor
the only reason they intersect is because they are part of an engine function, if it was a constantly defined function like you are implying, then all engines would have the same powerband, they dont 
12-27-2007, 08:26 PM
#99
The Professor
example:
okay, you have to torque your lug nuts to 100 ft/lbs so the momentary force applied is 100ft/lbs at any given tangent.
Now your muscles have to use X amount of ENERGY to get your arm to apply this 100ft/lbs of torque. Uh, this is horsepower.
Yes they intersect and are related in this one application: engines.
No they are not always related.
okay, you have to torque your lug nuts to 100 ft/lbs so the momentary force applied is 100ft/lbs at any given tangent.
Now your muscles have to use X amount of ENERGY to get your arm to apply this 100ft/lbs of torque. Uh, this is horsepower.
Yes they intersect and are related in this one application: engines.
No they are not always related.
12-27-2007, 08:27 PM
#100
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Well unfortunately that is the application we are talking about, or hadn't you noticed?
Bit difficult to change the afr of your arm muscles, and you can still manipulate the engine function to fit the muscle scenario, if you couldn't then there would be a problem with your physics model.
Bit difficult to change the afr of your arm muscles, and you can still manipulate the engine function to fit the muscle scenario, if you couldn't then there would be a problem with your physics model.
Last edited by PhillipM; 12-27-2007 at 08:29 PM.