gas octane question for PB F150

[Snakebitten]

This is a rather interesting data point.

I did some lunchtime reading on the MX+ PIDs and your dashboards. I have the MX+, but have never done anything with the dashboards. I'm ready to go set them up so I can monitor KR, spark timing, and OAR, amongst others.

I provided the electrical PID mapping information for OBDLink app here:

https://www.f150gen14.com/forum/threads/obdlink-mx-is-on-sale-today.13217/post-340315

I will add a post this evening to provide the PID mapping for the ICE portion of the dashboard.

Note that OAR is not available in the OBDLink library of pids. So you build it yourself in the "user defined pids" library. I will include the necessary information for building that pid as well.

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[huhner5]

I've enjoyed reading this whole thread... Really wish ford would make this engine flex fuel (e85) so we could actually see what this engine (3.5) is capable of

Keep it going gentlemen

 

[amschind]

Compression ratio is a straightforward calculation: what is the change in volume of the cylinder. The fact that they manipulate things with variable valve timing and such does not change the compression ratio. The fundamental fact of the Otto cycle is that if you use high octane fuel in an engine that isn't designed for it, you don't get more power. The rest of the explanation you put forward, such as guaranteeing that BDC & etc... was inappropriate and personal. Your explanation seemed to try and lapse over into the Atkinson cycle where valve timing is used to improve MPG.

This post is not correct because it confuses mechanical compression ratio (which is absolutely fixed by the crank, rods, pistons, cylinders and combustion chamber as the poster suggests) with effective compression ratio. For a very simple engine, say a car from the 1960s or your lawnmower engine, the two values are equivalent. For a modern engine with variable timing the values are at least somewhat different, but for a modern engine with variable timing AND an computer controlled turbocharger (via the electronic wastegate), the effective compression ratio will vary dramatically from the mechanical compression ratio.

The engine can reduce effective compression by holding the intake valves open longer (as is done on modern Atkinson cycle engines) AND by keeping the wastegate open in response to the knock sensors. Conversely, the engine can also increase effective compression by closing the intake valves earlier in the compression stroke AND closing the turbo wastegate when the knock sensor indicates that raising compression isn't generating knock.

More fuel+more air=more power, generally limited by detonation in forced induction engines. Triggering the knock sensor with lower octane=less air+less fuel=less power.

I hope that helps.

 

[Gros Ventre]

This post is not correct because it confuses mechanical compression ratio (which is absolutely fixed by the crank, rods, pistons, cylinders and combustion chamber as the poster suggests) with effective compression ratio. For a very simple engine, say a car from the 1960s or your lawnmower engine, the two values are equivalent. For a modern engine with variable timing the values are at least somewhat different, but for a modern engine with variable timing AND an computer controlled turbocharger (via the electronic wastegate), the effective compression ratio will vary dramatically from the mechanical compression ratio.

The engine can reduce effective compression by holding the intake valves open longer (as is done on modern Atkinson cycle engines) AND by keeping the wastegate open in response to the knock sensors. Conversely, the engine can also increase effective compression by closing the intake valves earlier in the compression stroke AND closing the turbo wastegate when the knock sensor indicates that raising compression isn't generating knock.

More fuel+more air=more power, generally limited by detonation in forced induction engines. Triggering the knock sensor with lower octane=less air+less fuel=less power.

I hope that helps.

Oh-h-h but it is correct. You mislead people. The fact that, like in an Atkinson Cycle engine you can reduce the mass of air in cylinder by manipulation of things like valve timing, making the compression ratio effectively smaller because there's less airmass in the cylinder, does not change the compression ratio. It just means you've derated the engine either electronically or mechanically with valve timing. ...And don't forget the benefits of Gasoline Direct Injection in preventing detonation. You give yourself away when you use the word "effective." This gets directly to my point about Ford designing the engine for 91 octane and then derating it to 87 octane as a sales ploy. Note that the Powerboost compression ratio is 10.5:1, so yeah, Ford set it up as a hi-octane fuel engine........ Thus its ability to tow a pretty big load, another sales draw. Of course, once upon a time, in another galaxy far, far away, 91 octane was plain old regular gasoline... My first car was a Plymouth Duster with a 225 Slant Six engine and it ran on regular which was then 91 octane... Remember the Sunoco Dial-a-Grade gas pumps? You could get 101 octane in that galaxy, but then gas was on the order of 25-30¢/g in those days and musclecars with two four barrels ruled...

 

[Suns_PSD]

So it's your contention that running 10% Ethanol, reduces mpg more than 10%?

Maybe the Feds should just call it E-10 and just sell you 90% of a gallon of gas with no ethanol at all for the same result! LOL

No, E-10 in fact does not cost a modern engine anywhere near 10% mpg. Straight ethanol has 66% of the energy of gasoline so true E-10 would result in 96.6% of the same economy as before, assuming you experienced no gains as a result of the higher Octane, which is unlikely. Also Denaturant is added to the Ethanol and it has the same BTU's as gasoline lessening the loss a bit more.

I had a Corvette that was a flex fuel car and on E-85 it lost right at 25-30% mpg, which is right in line with the energy content of E-85. The math was pretty simple at the time, the E-85 cost 50% of what Super Unleaded cost while getting 70% of the economy, so it was a good cost value. It also absolutely hauled *ss on that stuff and it was really helpful during TX Summers where the engine lost a lot of power, particularly while idling at lights when on gasoline.

 

[Snakebitten]

E10 gallon

9/10's of the gallon is gasoline
1/10 is ethanol, so 1/10 of the gallon contains only 66% of the energy.

9/10's of the gallon contains 100% of the energy of gasoline, or 90% of the energy of a gallon of gasoline.

The 1/10th of a gallon of ethanol has 66% of the energy of 1/10th of a gallon of gasoline.

Wouldn't it mathematically be 90% + 6.6% = 96.6%?

So does a gallon of E10 gasoline contain 96.6% of the energy of a gallon of gasoline?

Just asking if the equation is even close?

 

[mnstang]

Guys, guys.....If calculus and thermodynamic engineering has taught me anything, the equation you are looking for is: WQH=1−TCTH.

However, gasoline is not an IDEAL gas, there are thermodynamic failures in efficiency with any man made gas. When you enter ethanol in the mix, it gets even worse. If you are talking in just energy usage, @FX4GUY is right, denatured ethanol has about 30 percent less energy then the same amount of gasoline does. To put it simply, ethanol reduces energy output, no matter how little of it is mixed within gasoline. Less energy=lower MPG, plain and simple.

 

[Suns_PSD]

I have tested, remember I had a Flex Fuel Corvette. On E-10 the car got 18mpg, on E-85 it got 14 mpg.

And the math is pretty basic on paper and matches nearly exactly what I've measured in real life.

I'll stick to using the ethanol free fuel for my lawnmower only as it's expensive but helps in that application as that motor sits a lot.

There is no doubt that E-10 has 3-4% less energy content, and therefore 3-4% less mpg than straight gasoline. Fortunately, the added ethanol reduces your cost of fuel by well more than 3-4%.

The ethanol is also cooling and cleaning which are real advantages in a forced induction, direct injection motor. When I pulled the heads off my flex fuel Corvette the heads and valves looked like they did when they were completed at the machine shop years earlier. Perfectly shiny and clean.

 

[amschind]

Oh-h-h but it is correct. You mislead people. The fact that, like in an Atkinson Cycle engine you can reduce the mass of air in cylinder by manipulation of things like valve timing, making the compression ratio effectively smaller because there's less airmass in the cylinder, does not change the compression ratio. It just means you've derated the engine either electronically or mechanically with valve timing. ...And don't forget the benefits of Gasoline Direct Injection in preventing detonation. You give yourself away when you use the word "effective." This gets directly to my point about Ford designing the engine for 91 octane and then derating it to 87 octane as a sales ploy. Note that the Powerboost compression ratio is 10.5:1, so yeah, Ford set it up as a hi-octane fuel engine........ Thus its ability to tow a pretty big load, another sales draw. Of course, once upon a time, in another galaxy far, far away, 91 octane was plain old regular gasoline... My first car was a Plymouth Duster with a 225 Slant Six engine and it ran on regular which was then 91 octane... Remember the Sunoco Dial-a-Grade gas pumps? You could get 101 octane in that galaxy, but then gas was on the order of 25-30¢/g in those days and musclecars with two four barrels ruled...

Effective Compression Ratio is a standard term in engineering of internal combustion engines. It appears that you are unfamiliar with it, but that's okay. We are ALL ignorant of the vast majority of the available facts in the universe. The only fault arises in failing to appreciate what we don't know.

I suggest looking at David Ricardo's work on forced induction aircraft engines in the 1920s and 1930s, as at that time your mistaken understanding of compression ratio and displacement was commonplace (because superchargers were just moving out of the laboratory at the time and even then only into very expensive military aviation engines). The relevant quote is: " The displacement of an engine is not defined by its mechanical displacement but by the amount of air that it can be made to efficiently consume." For a naturally aspirated engine, those numbers are equivalent, but for forced induction engines, they're markedly different. Not surprisingly, the increasing use of super- and turbo super-chargers spurred the development of higher and higher octane fuels, such that the octane rating for avgas in the 1940s was something like 110. Even then, the EFFECTIVE compression ratio for say a P51 at MIL power at sea level was markedly greater than at 30k feet ASL.

 

[amschind]

I think that this deserves it's own thread, as gasoline vs diesel vs ethanol is NOT straightforward, and even the definitions are confusing. For instance, gasoline is 2.5% MORE energy dense AND 11% LESS energy dense than diesel. Further, the higher efficiency of the diesel cycle over the Otto comes into play. E85 can tolerate a higher effective Compression Ratio than unleaded gasoline, but what if HCCI or SCCI gas engines become common? Real world numbers get complicated quickly.

 

[amschind]

Guys, guys.....If calculus and thermodynamic engineering has taught me anything, the equation you are looking for is: WQH=1−TCTH.

However, gasoline is not an IDEAL gas, there are thermodynamic failures in efficiency with any man made gas. When you enter ethanol in the mix, it gets even worse. If you are talking in just energy usage, @FX4GUY is right, denatured ethanol has about 30 percent less energy then the same amount of gasoline does. To put it simply, ethanol reduces energy output, no matter how little of it is mixed within gasoline. Less energy=lower MPG, plain and simple.

You're correct, but the bigger question is: Does MPG effectively measure transport efficiency? I would argue that when considering only one type of fuel yes, but when comparing different fuels, MPG falls apart as a yardstick.

 

[Gros Ventre]

Effective Compression Ratio is a standard term in engineering of internal combustion engines. It appears that you are unfamiliar with it, but that's okay. We are ALL ignorant of the vast majority of the available facts in the universe. The only fault arises in failing to appreciate what we don't know.

I suggest looking at David Ricardo's work on forced induction aircraft engines in the 1920s and 1930s, as at that time your mistaken understanding of compression ratio and displacement was commonplace (because superchargers were just moving out of the laboratory at the time and even then only into very expensive military aviation engines). The relevant quote is: " The displacement of an engine is not defined by its mechanical displacement but by the amount of air that it can be made to efficiently consume." For a naturally aspirated engine, those numbers are equivalent, but for forced induction engines, they're markedly different. Not surprisingly, the increasing use of super- and turbo super-chargers spurred the development of higher and higher octane fuels, such that the octane rating for avgas in the 1940s was something like 110. Even then, the EFFECTIVE compression ratio for say a P51 at MIL power at sea level was markedly greater than at 30k feet ASL.

I say again, you're misleading people by using sophistry. At the end of the day "compression ratio" is fact. Using the term "effective" in front of it says it all. It is not compression ratio, it is a way of accounting for a reduced mass of air in the cylinder. It also ignores the fact of the otto cycle greater efficiency if it could be run up to the same compression ratio as diesel cycles. The reality is all of the bells and whistles of things like variable cam timing that are there to improve efficiency do not override basic engine design. Compressio ratio is 10.5:1. Gasoline direct injection (curiously absent from much of this discussion) gives much ability to prevent detonation since fuel is not in the cylinder during the compression stroke (detonation only occurs during compression of a fuel air mixture to the point of self ignition prior to the spark). It has become clear that Ford designed this engine for 91 octane at full power but then derated it for 87 octane as a sales ploy since they knew that most operation of the engine would be at partial power and they could control detonation with add-ons. Octane is not a measure of energy content.

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