100 MPG

[Anonymous]

...

Thanks for the stimulating input. I guess

I was responding to crashbox455's idiotic posts on page 1 and then I realized that they were from 2005.

Why? Technically he is right... Heat and temperature are two different thigns...

the compression stroke doesn't increase heat- it moves the heat from the mixture into the cylinder- your engine's water temp goes up, but the mixture actually loses heat. the increased pressure causes some of the HC's to re-condense into liquids. so don't go crazy with the compression.

Technically he is wrong. This is compounded by the fact that he uses the ideal gas law in another post to try and prove his point when, in fact, he only disproves it.

First,
PV=nRT

This tells us that as pressure goes up, temperature goes up in a closed system (compression stroke).

What he complete neglects is the fact that Q (heat) = m (mass of charge) x cp (specific heats or air and fuel) x DeltaT (temperature difference from compressing from BDC to TDC)

Since no real world system is adiabatic, yes some heat of compression is lost to the cylinder block, piston and head and thus wasted. But in no way does the mixture have a net lose of heat in this process.

If he somehow discovered how to do work on a fluid without increasing its heat, I’d love to hear about it. That is totally absurd.

Didn’t you guys pay attention in Thermodynamics, Combustion Theory, and IC Engines in college?

Heat: added or external energy that causes a rise in temperature, expansion, evaporation, or other physical change

Temperature: a measure of the warmth or coldness of an object or substance with reference to some standard value. The temperature of two systems is the same when the systems are in thermal equilibrium

Heat causes the temperature change. The reason they're not the same is because different substances can absorb different amounts of heat (joules) before their temperature (degrees) will change (specific heat, anyone?). In other words, dump a certain amount of heat into water, and dump that same amount of heat into metal, and tell me which substance's temperature rises more quickly. Water has a much higher "specific heat" than metal.

Thanks. I gathered that much back in high school chemistry. Those realities only prove my point. Please see aforementioned.

Also, there is another fallacy that is being spread on numerous forums, including this one. It's the old "lean mixtures burn hotter" argument. THIS IS NOT TRUE. Gasoline burns "hottest" (puts out the most thermal energy) at 14.7:1. The reason the engine runs hotter when it's running lean is because the air/fuel burns more slowly. There is more time for the thermal energy to be transfered into the engine. This is also why your horsepower drops so quickly when running lean (you don't take away X amount of chemical energy in your fuel for the same amount of energy loss at the crankshaft). This is because more energy is being lost into the engine instead of pushing down on the pistons.

That is absolutely wrong. It is not a fallacy. The stoichometric ratio is only used to balance the reaction equation. Lean mixtures (to a degree, not excessively lean ones) burn hotter because the chemical reaction takes place in excess oxygen, thus bringing combustion efficiency much closer to 100%. This is quantifiable and measurable in how much N2 (which is normally an inert gas) is consumed due to the higher combustion temps. N2 doesn’t do jack until reaction temps of around 1600º F.

An engine that is overly rich will run cooler only because it takes some amount of energy to evaporate the cool liquid fuel before it will burn (but this not only makes it run cooler, it slows the burn). This is a complete waste of energy, though with most cylinder head designs is completely warranted to keep from burning exhaust valves, etc. This again is due to the "slow burn" nature of the cylinder heads, along with relatively low compression ratio (and thus expansion ratio).

I have no idea who promulgated the idea on here that fuel some how needs or even is cooled before it burns. The exact opposite occurs. Fuel is heated up in steps from the time it enters the fuel pump and is injected into the intake runner and then compressed in the cylinder. All of these processes add heat to the fuel. At no time (unless someone is using a ghetto draw through turbo turbocharger with intercooler) is the fuel cooled.

This is what I was responding to which I “…â€￾ out after the fact when I realized how old the post was.

 

[StrangeRanger]

If he somehow discovered how to do work on a fluid without increasing its heat, I’d love to hear about it. That is totally absurd.

Didn’t you guys pay attention in Thermodynamics, Combustion Theory, and IC Engines in college?

They've simply perfected the Carnot engine. And somehow bypassed the Second Law. :roll:

 

[Anonymous]

If he somehow discovered how to do work on a fluid without increasing its heat, I’d love to hear about it. That is totally absurd.

Didn’t you guys pay attention in Thermodynamics, Combustion Theory, and IC Engines in college?

They've simply perfected the Carnot engine. And somehow bypassed the Second Law. :roll:

LOL. That's kind of what I wonder when I read many of these treads.

I probably came off as an a-hole in the previous post, which was not my intent. I think it's great that people want to think outside of the box, but one can only go so far as thermodynamics will allow.

 

[Lazy JW]

That is absolutely wrong. It is not a fallacy. The stoichometric ratio is only used to balance the reaction equation. Lean mixtures (to a degree, not excessively lean ones) burn hotter because the chemical reaction takes place in excess oxygen, thus bringing combustion efficiency much closer to 100%....

In real-world practice I know of snowmobile tuners who use EGT to get maximum power. This happens to occur right near max temperature and their exhaust sensors show almighty close to stoich. When they lean out further, temperature drops and also power.
Joe

 

[StrangeRanger]

Leaner is hotter. That's one of the principle conundrums of tuning for power, economy and efficiency. As the A/F ratio increases i.e. more air therefore leaner, the combustion temperatures rise and the NOX emissions skyrocket. If the A/F ratio is richened to the point where combustion temperatures are too low to form NOX, the HC emissions rise although not as dramatically as NOX does under lean conditions. It is not entirely serendipitous that these two A/F vs. emissions curves cross one another at a point very close to stoichiometric.

 

[BamaPaul]

Ok this post is 2 years old and it has taken me 3 days to read through the 4 pages plus all of the external links. Has anyone come up with anything good? I searched the web for Fuel Vaporizer and found this link on EBAY for a $15 Info auction Ebay. Guess what Vehicle it was used on, a 1994 F150 w/ a 300. Maybe he should join this post.

I would also like to know how to refresh my NiCad Batteries (one of his other auctions)-Paul

 

[Pinhead]

That is absolutely wrong. It is not a fallacy. The stoichometric ratio is only used to balance the reaction equation. Lean mixtures (to a degree, not excessively lean ones) burn hotter because the chemical reaction takes place in excess oxygen, thus bringing combustion efficiency much closer to 100%.

Bringing combustion efficiency closer to 100% will increase burn temps. This can be done by increasing mixture motion and turbulence, etc. In a "perfect" situation, stoich will burn hotter than leaner than stoich will. That's all I was saying.

BUT... If running lean brings the burn efficiency closer to 100% why don't you get more power when running slightly lean?...

Read my compound/crossbow analogy again.

This is quantifiable and measurable in how much N2 (which is normally an inert gas) is consumed due to the higher combustion temps. N2 doesn’t do jack until reaction temps of around 1600º F.

You forget the other part of the equation, TIME. Yet again, crossbow/compound bow.

I have no idea who promulgated the idea on here that fuel some how needs or even is cooled before it burns. The exact opposite occurs. Fuel is heated up in steps from the time it enters the fuel pump and is injected into the intake runner and then compressed in the cylinder. All of these processes add heat to the fuel. At no time (unless someone is using a ghetto draw through turbo turbocharger with intercooler) is the fuel cooled.

This was simply a misunderstanding. I didn't mean that the fuel will cool off. I meant that the unburned fuel that is left in the chamber after the initial flame front takes place will absorb the heat, change phase from liquid to gas (thus absorbing more heat from the already burnt air/fuel) and then burn later in the cycle, being completely wasted usually in the catalytic converter. The act of absorbing the heat/energy by the "excess" liquid fuel makes the "burn" within the chamber cooler. This is one of the reasons running lean can burn exhaust valves.

HOWEVER

Looking again to the compound bow/crossbow analogy...

If more energy is changed from thermal energy into kinetic energy, the overall temperature will drop much more quickly and therefore running "lean" won't hurt a thing. This is the final point I have been trying to get to.

Take these two engines as an example.

Engine 1 runs a typical "slow burn" design.
Engine 2 employs a "fast burn" design.
"Proper" tuning puts peak cylinder pressure around 13 degrees ATDC

Engine 1 requires 30 degrees of ignition advance to be properly tuned.
Engine 2 requires 5 degrees of ignition advance to be properly tuned.

This means that the chamber in engine 1 is in contact with the burn for 43 degrees before the thermal energy is really turned into kinetic energy. Engine 2's chamber is in contact with the burn for 18 degrees.

It should be pretty easy to spot which engine will run hotter simply by looking at how long the chamber "sits in the fire."

Taking the compound bow/crossbow analogy into consideration, the results are even more dramatic. When thermal energy is turned into kinetic energy within the engine, the temperature of the gases drops (simple physics, right? energy is transformed, not consumed). If you can get the air/fuel to burn within a much smaller time frame, even if peak temperature is higher, the duration is much smaller, the thermal energy is changed to kinetic energy much more efficiently, and less heat is dumped into the engine.

This is assuming both engines are running the same air/fuel ratio.

Even if Engine 1 was running 14.7:1 ratio and engine 2 was running 20:1 ratio, engine 2 would still run cooler and have much more power per unit of fuel.

This is why I say you can't make a blanket statement like "running lean makes it burn hotter." This ignores too many variables.

 

[Pinhead]

If you think I'm crazy, read some of David Vizard's articles:

The 100 mpg carb - Does it really exist?
Turbulence and Combustion Dynamics
In Cylinder Turbulence and Combustion Dynamics- Part 2

 

[Pinhead]

1HP per CC, or 1HP per CU IN?

If I can get 250HP from a 250cc bike, I will have some fun. 8)

Yes, per CC.

If the combustion chamber and piston are correctly configured, the amount of static compression is almost without limit and the detonation resistance can be almost limitless as well. The quality of the inlet charge is admittedly important, but if an engine running a manifolded 4 bbl. carb can run 20-1 CR, it's safe to think that a port injected engine could be even more efficient. If we run 16-1 to 18-1 in street engines without detonation, it must be luck. We don't even measure the mechanical compression ratios of most engines we build, as the chamber / piston dictate detonation tolerance, and the CR numbers are next to useless. Our typical blown engines have CR'S over 12-1, and they still tolerate over 20 psi and love it. How can it be? Perhaps, had you all ever read about, or worked with engines producing 1hp / cc of displacement dependably on gasoline, you wouldn’t be so reluctant to look to "other" sources of information.

From It's Difficult To Make Hard Heads "Soft"

 

[XPC66]

Any of you guys actually measured EGT, CHT and power with different fuel mixtures?

I have and I'm bloody confused after reading most of the posts.

 

[StrangeRanger]

Current F1 engines get somewhere around 0.3 HP per cc (about 725 HP from 2.4 litres.) They are generally considered the state of the art in normally aspirated Otto-cycle engines. So this guy Widmer has found a way to produce more than 3 times the specific HP that any of the F1 constructors have managed to produce with their collective billions of dollars in R&D?

Show me the dyno sheets, and not from his dyno.

 

[Pinhead]

That's like saying "if it were possible the manufacturers would be doing it." They spend millions on R&D, too. Tell every cylinder head porter and engine builder that the millions in R&D over at Ford makes our engines perfect and therefore un-improvable, and that they haven't actually been seeing increases in horsepower...

 

[Anonymous]

Hi all,
It will take me some time to read this entire thread, in the mean time here's
some relevant information on combustion temperatures. Flame temperatures
are highest at stoichiometric air fuel ratios, as the mixtures lean further
flame temperatures decline. I developed this chart for a quick reference.
These are estimated, actual flame temperatures depend on many variables.

air:fuel | E ratio | flame temp.
11.7:1 | 1.26 | 1968
12.7:1 | 1.16 | 2047
13.7:1 | 1.07 | 2114
14.7:1 | 1.00 | 2122
15.7:1 | 0.94 | 2071
16.7:1 | 0.88 | 1996
17.7:1 | 0.83 | 1926

 

[Lazy JW]

Any of you guys actually measured EGT, CHT and power with different fuel mixtures?

I have and I'm bloody confused after reading most of the posts.

I have not, but the snowmobile tuners in Idaho/Montana put their sleds on the dyno and let 'er rip. They report peak power just to the lean side of stoich but typically back off to barely on the rich side to keep from melting them down. I suspect that any discrepancies between theoretical and actual observed temps are due to mechanical inefficiencies and also variations in fuel droplet size. They make pretty amazing power but nowhere near 1 hp/cc. Lots of them burn those engines down every year too.

If a Top Fueler dragster made 1 hp/cc wouldn't that be around 8000+ hp? (I dunno how many cubes they run nowadays)

I'd like to see someone do that on 87 octane
Joe

 

[lyonsy]

its just in f1 if they could get that kind of an advantage they whould take it since they will spend millions to gain 5 hp in any part of the rev range.
same for moto gp.
only thing is it could be banned.
iam not sure if you could call an f1 n/a with the revs they do they are actully supercharging them selfs in the region of 2 to 4 psi then get an extra 1-2psi from there air intake system.
but then when somthing idles at 6000rpm.

 

[StrangeRanger]

If a Top Fueler dragster made 1 hp/cc wouldn't that be around 8000+ hp? (I dunno how many cubes they run nowadays)

I'd like to see someone do that on 87 octane

500 CID = 8194 cc

At 8000 HP they make roughly 1 HP/cc but they are supercharged and supercharged and run 85% nitromethane, 15% methanol. They also rebuild the engine after every pass, some people might find that an unacceptable level of maintenancein a daily driver

 

[Pinhead]

This chart should demonstrate the advantage of the "soft head" concept of ultra high compression for a fast burn.

The elimination of the pressure spike should also be a good indication of why these engines are so detonation tolerant even with the super-high compression.

 

[wsa111]

On a naturally aspired engine, peak power is at 12.9-13.2, any leaner & you will fry pistons & possibly other componets.

Ideal mixture at cruising is 14.7-15.0.

Pinhead in the real world if you don't stay within these parameters you will toast the engine.

If the engine is supercharged you will need a richer mixture so you don't fry the internal componets from detionation & or heat.

Thoery is great but in the real world you go or blow up. William

 

[Anonymous]

On a naturally aspired engine, peak power is at 12.9-13.2, any leaner & you will fry pistons & possibly other componets.

Ideal mixture at cruising is 14.7-15.0.

Pinhead in the real world if you don't stay within these parameters you will toast the engine.

If the engine is supercharged you will need a richer mixture so you don't fry the internal componets from detionation & or heat.

Thoery is great but in the real world you go or blow up. William

Actually after a certain point the leaner you go the more the temp will drop.

And if you are boosted the leaner you can go and actually still fire the cyl. I'm talking 15-16-17-18:1 a/f ratio. But you need lots of boost.

with good tuning you wont melt anything simply because there will not be enough heat at extreem lean.

 

[Anonymous]

Saying there is a perfect air fuel ratio for power and cruse would mean that
every engine is created equal. I might need 12:1 A/F for power on my
inefficient engine where your more efferent engine would make maximum
power with a much leaner mixture.

Same holds true for lean cruse A/F ratios, a fast burn engine might get best
mileage at 17:1 where an engine with poor burn characteristics would
overheat from the slow flame speed.