Bad mpg?

[Antonm]

AntonM’s law: where smaller engines make same power as larger engines, because pressure goes up at bdc.

Again, talking out of your ass (again, its recurring thing with you), I've never said, or anything even close to that.

And your feeble attempt where you tried to point it it out didn't say that either .

You're like a CNN reporter, they find something that's wilding untrue, then just keep repeating hoping that someone will believe you.

And we've gone over the actual truth, with evidence from your own equations, multiple times (maybe repetition isn't the way to get through your comprehension issues).
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[Antonm]

Next up: Charles law. Overheat your engine so, it's displacement goes up!

Charles law is also a law that absolutely does affect the way all engines operate.

Doesn't increase displacement, but it does change the amount of available oxygen for combustion use. Charles law is the driving reason we use intercoolers on forced induction applications actually.

Another place Charles law jumps into naturally aspirated gasoline engines is explaining why some carbureted engine can make more peak power than EFI. Has to do with the latent heat of vaporization cooling affect that gasoline gives the intake charge below the carburetor. This basically cools the intake charge so that, in accordance with Charles law, more air molecules can fit in the same space at the same pressure. And as we all know is, if you've got more air, you can therefore burn more fuel, and make more power.

So now both Boyle from the 1600's, and Charles from 1700's, are both wrong somehow,,, talk about advancing science , if you're disproving not one, but two laws, that have both been established for hundreds of years, then you are on your way to being a bigger household name that Einstein,,,, or,,, maybe ,,,, just maybe,,,,you're just a clueless internet troll.
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[Antonm]

I'm almost regretting reading it.......

It appears there was something lost in translation that has become a pea under a mattress.

Why,,,



or at least amused a little?

Personally I find this hilarious ,,,some internet troll thinks that two basic scientific laws don't work/ don't matter.

Reminds me of the old skit Jay Leno used to do when he still hosted the tonight show, it was called "Jay walking", he'd go out of the streets of LA/ Burbank and ask people silly easy questions, of course he only showed the videos of the really dumb ones that got the questions horribly wrong,,, kinda like this guy

If you haven't seen these Jay Leno bits, see youtube link below.

Jay Leno Jay Walking Videos

Share your videos with friends, family, and the world

www.youtube.com

Can't make comedy gold like that anymore, someone's feelings might get hurt.
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[B-train]

Is this a statement you are willing to stand behind? Its totally wrong, but that hasn't stopped you before.

If you put 10cc of fuel (or really any given amount of fuel within the range each engine can efficiently burn) in either engine (part throttle stuff where talking here) and mix in air to the same AFR, then guess what,,,,, both engines will be making the same power.

The only slight difference would be any difference in efficiency between the engines (which a 5.3 and 6.2 having the same design, they have pretty similar efficiencies).

So that statement ,yet again, demonstrates a gross conceptual error in your part.

And now you go blathering on about transmission downshifts and other crap. The facts are a 5.3 and 6.2 will get very similar (talking second significant digit differences) in fuel milage if driven under the same conditions, moving the same mass. Even the stupid EPA fuel milage test they put on the window sticker shows this.
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In this instance, a ratio of 14.7:1 will never be the same amount of fuel in each cylinder just due to geometry (volume). If you put 10cc as your total fuel amount, then the 6.2L will always have a leaner mix due to the volume constraints of "the delivered " amount of fuel at 10cc and in theory the 5.3L would have a full cylinder at 14.7:1.

However, a leaner mixture on light throttle applications will generally burn cleaner, and hotter, pushing down the piston more efficiently based on the fuel consumed.

If we just look at a piston cylinder volume as a whole with only compressed air in it, you will automatically have more force exerted on the connecting rod and crankshaft (assuming same rod lengths, cylinder length - only variable of cylinder diameter changing) with a 6.2L vs a 5.3L. Again, only speaking of downward force here based off cylinder pressure vs diameter.

Think of how a brake system works with a master cylinder and caliper pistons (just in reverse essentially). The brake line feeding 2 different size caliper pistons will have different force multipliers based off initial line pressure. An engine cylinder at the same pressure with 2 different piston diameters will have more force with the larger diameter piston.

This is why a 6.2L can work less hard doing the exact same thing as a 5.3L. THIS ASSUMES EQUAL/SAME CONDITIONS. Apples to apples.......apples to oranges is a different calculation (ie: different throttle positions for each engine).

 

[Antonm]

In this instance, a ratio of 14.7:1 will never be the same amount of fuel in each cylinder just due to geometry (volume). If you put 10cc as your total fuel amount, then the 6.2L will always have a leaner mix due to the volume constraints of "the delivered " amount of fuel at 10cc and in theory the 5.3L would have a full cylinder at 14.7:1.

This is simply not true. You can certainly add air until you get to your desired AFR.

Think about it a little more in this part throttle cruising scenario.

Both engines have a throttle body, and both have a mass airflow sensor. If you set both throttle bodies at whatever position yields the same mass air flow rate on their respective meters (yes the throttle body positions will be slightly different between the two engines) then would both both engine not be taking in the same amount of air?

And if they're taking in the same amount of air, can the injectors not deliver the same amount of fuel to both engines such that they'd be running at the same afr?

And this is true up until the point the smaller engine is at wide open throttle.
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[Pressureangle]

You do realize that if you put the same quantity of air in two different volume cylinders, the pressures will be different right?

For a given set amount of air ,,,, say that amount of air needed to perfectly burn a given amount of fuel at stoichiometric ratio, if you put that amount of air in a smaller engine then;

View attachment 447886


But if you take that same amount of air (the amount needed to burn a given amount of fuel at stochiometric), and put it in a larger engine, then you get;

View attachment 447887

Maybe I should have mentioned this earlier, but I just kinda assumed this was a common sense thing.

So burning the same amount of fuel, at the same afr (which requires the same amount of air) in two different displacements engines makes the same power ( assuming the engine efficiencies are the same of course).

That lecture you keep referring to even alludes to that later on when talking about ways to raise power, see Pressure (adding boost) at BDC statement below.

View attachment 447891

I think that maybe you've not be seeing the forest for the trees and focusing on just the equation as symbols, and not what the equation is actually doing/ telling you. Which happens even in the adult / professional world every now and then.
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Man you love to step in it.

Piston area, man, piston area. Lower pressure + larger area =.... equal.

 

[Antonm]

Man you love to step in it.

Piston area, man, piston area. Lower pressure + larger area =.... equal.

Feel free to step in, that's kinda the whole purpose of these forums isn't it?

Tell me the specific of what you think is wrong, and we'll discuss it.
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[B-train]

This is simply not true. You can certainly add air until you get to your desired AFR.

Think about it a little more in this part throttle cruising scenario.

Both engines have a throttle body, and both have a mass airflow sensor. If you set both throttle bodies at whatever position yields the same mass air flow rate on their respective meters (yes the throttle body positions will be slightly different between the two engines) then would both both engine not be taking in the same amount of air?

And if they're taking in the same amount of air, can the injectors not deliver the same amount of fuel to both engines such that they'd be running at the same afr?

And this is true up until the point the smaller engine is at wide open throttle.
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My reply was based on you saying that 10 cc of fuel in either engine would make the same power. The AFR can't be the same with 10cc of fuel. Basic math says that a larger cylinder will be less full at 14.7:1 than a smaller one. My response was purely basic principles. Yes, there are variables. Yes, to keep the same AFR the 6.2L will need more fuel because it's a larger volume than the 5.3L. These are facts based on basic math principles of cylinders.

This whole discussion has gone off the rails. I think a lot of people are thinking similar things here, maybe just not conveying them via words in the way that others interpret them correctly (?)

Long story short: larger diameter piston = more force for same AFR ratio than a smaller diameter piston. More force = more twisting power (aka: torque). Greater torque on a flat road will mean that the driver of a 6.2L will have to pull back on the throttle to go the same speed as the identical weight vehicle with a 5.3L resulting in the same, or possibly better, MPG at the end of an identical test run.

 

[B-train]

It feels like I'm living in a real life episode of MYTH BUSTERS......we just need a lab to hash this out. LOL

 

[Antonm]

My reply was based on you saying that 10 cc of fuel in either engine would make the same power. The AFR can't be the same with 10cc of fuel. Basic math says that a larger cylinder will be less full at 14.7:1 than a smaller one. My response was purely basic principles. Yes, there are variables. Yes, to keep the same AFR the 6.2L will need more fuel because it's a larger volume than the 5.3L. These are facts based on basic math principles of cylinders.

This whole discussion has gone off the rails. I think a lot of people are thinking similar things here, maybe just not conveying them via words in the way that others interpret them correctly (?)

Long story short: larger diameter piston = more force for same AFR ratio than a smaller diameter piston. More force = more twisting power (aka: torque). Greater torque on a flat road will mean that the driver of a 6.2L will have to pull back on the throttle to go the same speed as the identical weight vehicle with a 5.3L resulting in the same, or possibly better, MPG at the end of an identical test run.

What you said above is just not correct.

Before you start typing out your angry reply, take a few moments to read below and think about it for just a second.

You most likely think the AFR can't be same when mixing 10cc of fuel into two different size engines because you assume each of those engine is full of air , two different quantities of air (5.3 and 6.2 L respectively), and as such, it could never make the same ratio.

But,,, unless the engine is at wide open throttle, neither engine is full of air. While driving around a manifold vacuum of 15 in-hg is pretty normal. 15in Hg converts over to about 7.3 psia (pounds per square inch absolute).

At sea level atmospheric pressure it typically around 14.7 psia, this pressure is also referred to as 0 psig (pounds per square inch gauge) or one atmosphere.

So driving around at that 7.3 psia in the manifold, each cylinder is only getting filled with about half of the air it could hold.

Now assuming you believe Boyles law (unlike someone else here) we can easily see what pressure another displacement engine would be at if it was ingesting that same amount of air.

Lets use this example,,,say you're driving down the road at steady throttle cruising with a manifold vacuum of 15 in-hg or 7.3 psia in a 6.2L Tahoe, burning however much fuel that amount of air can burn at stochiometric ratio (14.1 for 10% ethanol gasoline or 14.7 for pure gasoline). What manifold pressure (which will still be less that atmospheric pressure) would be required to fit that same amount of air in a 5.3L?

Using Boyles law and rearranging the equation to solve for P2, that makes the pressure in a 5.3's cylinders (that's holding the exact same amount of air as the 6.2 cylinder is at 7.3 psia), come out to 8.5 psia, or about 17.3 in-hg vacuum.

So for the 5.3 ingest the exact same amount of air, it would need to open its throttle body a little further than the 6.2 and allow 8.5 psia (of the 14.7 psia available in the atmosphere) to come in. Its still running at vacuum, but it's at higher pressure (closer to atmospheric) than the 6.2, but its holding the exact same amount of air.

Now that both engines have the same amount of air in them (just one at a slightly higher pressure at bottom dead center to hold it), if you inject the same amount of fuel, you'll end up with the same afr for both engines, even though they have different displacements. And if you burn the same amount of fuel, at the same afr, in two engines with the same efficiencies,,, then they make the same power at those manifold vacuum points ( 7.3 psia and 8.5 psia for the 6.2 and 5.3 respectively in this example).

This is the whole argument above about different cylinder pressures for displacements. All the pressures talked about so far in this thread are in vacuum/ below atmospheric pressure, just some are higher (closer to atmospheric) than others.

What I described above can happen for all power levels below whatever the power level is when the smaller engine reaches wide open throttle (355hp in the case of a 5.3).

We can also find the manifold vacuum the 6.2 would be at with the 5.3 at wide open throttle using the same method. I'll skip stepping through the work because its described above, the answer is 12.56 psia.

So when the 5.3 is tapped out at wide open making its max horsepower, the 6.2 is still throttling back and only using 12.56 psia of the 14.7 psia available to it, at that same engine RPM. So it can open its throttle body a little more (because its still running at a manifold vacuum), take in more air, inject more fuel ,and make more power.

Maybe the whole psia thing and one pressure being higher, but still a vacuum / below atmospheric pressure is what confused the last guy. Hadn't thought to explain that a higher pressure in a naturally aspirated engine just meant less vacuum/ closer to atmospheric and not a positive pressure.

Long post, but its hard to get across the entire point/ explain everything, without leaving out details that could cause arguments, and still keep the post lengths short at the same time.

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