Where does power come from?

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Troy Patterson
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Where does power come from?

Post by Troy Patterson »

Something to consider when thinking about combustion, air / fuel ratios, and heating / exciting nitrogen molecules:

"Molecular proximity" (as I refer to it) has to do with how uniformly the nitrogen molecules in the combustion space are heated / excited by / during the combustion process. Keep in mind the induction charge (atmosphere + air / fuel mixture) in the combustion chamber is in constant motion so we have to think about what is happening in there as fluid, or ever changing.

Despite the fluid nature of the combustion process, it is still possible to achieve significant uniformity in the heating of the nitrogen molecules. Increased compression tolerance; engine efficiency; horsepower and torque gains by way of improved combustion chamber design demonstrate this point.

Also, bear in mind the underlying assumption is that the nitrogen molecules are most responsible for the conversion of heat into a working force - against the piston. Our successful use of Nitrous Oxide supports this - which leads me to burn, which speaks to air / fuel ratio and "molecular proximity."

As someone else pointed out earlier in this thread, nitrogen controls the burn (rate), moderating and absorbing heat (protecting our fragile engine). Slightly leaner air / fuel ratios generate more heat, and therefore have the "potential" to make more power as a result.

The extra of lean air / fuel ratio's creates a cascading effect accelerating the combustion process in a generally localized area of the combustion chamber. This is the downside to lean a/f ratios for high performance / racing engines is the heat - at this stage of understanding and development of the internal combustion engine.

"Super exciting" the nitrogen molecules by way of a lean a/f ratio produces a destructive pressure spike, detonation, - by burning off the more volatile elements in the fuel very rapidly. The fuel most people burn isn't formulated to handle this sort of super rapid oxidation process, nor are most engines. Top fuel, for example, is an exception.

What's left are the heavier elements of the fuel which continue to burn for an extended period of time after the exhaust valve opens. After the exhaust valve opens, the heat of the oxidation process is no longer controlled nor is the heat meaningfully absorbed by the presence of nitrogen molecules with the combustion process under pressure. The absence of pressure exerted on the oxidation process means we've lost "molecular proximity" with the stabilizing and heat absorbing nitrogen molecules. At this point, any heat produced can be absorbed by the combustion chamber, piston, exhaust port and exhaust system.

I see this as the "shape of the burn", but I'm real curious to hear from Mark.

Poor a/f ratios, bad combustion, improper ignition timing, poor combustion chamber design, etc., etc., can all result in a disruption in "molecular proximity."

How do I make a half second reduction in 1/4 times by running my outrageously large carburetors? Do you still need to ask?

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Last edited by Troy Patterson on Mon Oct 15, 2007 12:49 pm, edited 1 time in total.
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Post by tommurphy73 »

In a high boost turbo charge application water injection is used to limit the detonation tendencies of the fuel by slowing the burn rate of the air fuel mixture and cooling the intake charge. I have wondered if for high compression N/A engines if water injection would also offer the same advantages without the use of high octance fuel. Also if water entered the combustion chamber in liquid form it has an expansion rate of approximately 1600 its original volume so rather than just using heated nitrogen to act against the piston we would also have the additional pressure from the expansion of water. Once water has turned into steam it has the same expansion rate as any other gas.

Feel free to disagee with any or all of this

http://galileo.phys.virginia.edu/classe ... mProps.htm

Any thoughts on this?

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Tom
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Post by maxc »

Hi all,
23 years ago i met a combustion reseacher. He talked about 'the 4 or 5 fingers of flame fronts' they propagate outwords and downwords along the edge of chamber\cylinder walls. They travel much higher speed than the average speed of combustion. Why? Simple the fuel is better atomized the edge of the clylinder because of the heat radiating from the cly. I found web site 2 years ago that had a thermo photo of it. Can't find the site. :cry:
So there is more that one shockwave propagating making the center\bottom end gases compress or maybe ignite. More details later.

I'm slow typer bad speller.
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Post by maxc »

Here's some basic combustion science.

From: Robert Harris <bob@bobthecomputerguy.com>
To: DIY_EFI@lists.diy-efi.org
Subject: Water and its effect on combustion.
Date: Mon, 10 Jul 2000 10:24:08 -0700
Message-ID: <9ptjms0uu4oe292mpk6a6vhm2hn8bu9h1j@4ax.com>

Let us take a quick look at ignition. Those who have a Heywood can look it up - mines on loan so going by memory. The first thing that happens is a plasma cloud is formed by the arc consisting of super heated electron stripped atoms. When this cloud "explodes" a ball of high energy particles is shot outward.

The highest energy particles are the hydrogen atoms - and they penetrate the charge about 5 times as far as the rest of the particles. As they lose energy and return to normal temps - about 5000 k - they begin to react chemically with any surrounding fuel and oxygen particles. The effectiveness of spark ignition is directly related to the availability of free hydrogen. Molecules containing tightly bound hydrogen such as methanol, nitromethane, and methane are far more difficult to ignite than those with less bonds.

During combustion - water - H2O ( present and formed ) is extremely active in the oxidation of the hydrocarbon. The predominate reaction is the following:

OH + H ==> H2O
H2O + O ==> H2O2
H2O2 ==> OH + OH
Loop to top and repeat.

The OH radical is the most effective at stripping hydrogen from the HC molecule in most ranges of combustion temperature.

Another predominate process is the HOO radical. It is more active at lower temperatures and is competitive with the H2O2 at higher temps.

OO + H ==> HOO
HOO + H ==> H2O2
H2O2 ==> OH + OH

This mechanism is very active at both stripping hydrogen from the HC and for getting O2 into usable combustion reactions.

Next consider the combustion of CO. Virtually no C ==> CO2. Its a two step process. C+O ==> CO. CO virtually drops out of early mid combustion as the O H reactions are significantly faster and effectively compete for the available oxygen.

Then consider that pure CO and pure O2 burns very slowly if at all. Virtually the only mechanism to complete the oxidization ( Glassman - Combustion Third Edition ) of CO ==> CO2 is the "water method".

CO + OH ==> CO2 + H
H + OH ==> H20
H2O + O ==> H2O2
H2O2 ==> OH + OH
goto to top and repeat.

This simple reaction accounts for 99% + of the conversion of CO to CO2. It is important in that fully two thirds of the energy of carbon combustion is released in the CO ==> CO2 process and that this process occurs slow and late in the combustion of the fuel. Excess water can and does speed this conversion - by actively entering into the conversion process thru the above mechanism.

The peak flame temperature is determined by three factors alone - the energy present and released, the total atomic mass, and the atomic ratio - commonly called CHON for Carbon, Hydrogen, Oxygen, and Nitrogen. The chemical reactions in combustion leading to peak temperature are supremely indifferent to pressure. The temperatures and rates of normal IC combustion are sufficient to cause most of the fuel and water present to be dissociated and enter into the flame.

As can be seen above, water is most definitily not only not inert but is a very active and important player in the combustion of hydrocarbon fuel. Ricardo and others have documented that under certain conditions (normally supercharged) water can replace fuel up to about 50% and develop the same power output, or that the power output can be increased by up to 50% addition of water. This conditions were investigated by NACA and others for piston aircraft engines. It is important to note that these improvements came at the upper end of the power range where sufficient fuel and air was available to have an excess of energy that could not be converted to usable pressure in a timely manner.

As a side note - Volvo recently released some SAE papers documenting the use of cooled EGR to both reduce detonation and return to a stoic mixture under boost in the 15 psi range - while maintaining approximately the same power output. Notice - they reduced fuel and still get the same power output.

When you consider that EGR consists primarily of nitrogen, CO2, and water (to the tune of about two gallons formed from each gallon of fuel burned), you might draw the conclusion that it also was not "inert". They peaked their tests at about 18% cooled EGR - which would work out to about 36% water injection and got about the same results under similar conditions that the early NACA research got.

quote" The effectiveness of spark ignition is directly related to the availability of free hydrogen".
humidity chart. http://www.aquamist.co.uk/rescr/faq/airmass/humid.GIF

Standard burn speed info. http://members.cox.net/dnaquin/burn%20rate.jpg I don't think this was posted here before.
Last edited by maxc on Sat Jan 19, 2008 6:39 pm, edited 3 times in total.
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Where does power come from?

Post by Troy Patterson »

Very interesting stuff Mark. It's slightly different in focus. It'll take me a little time (as I've very little time) to absorb this and comment.

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Post by SchmidtMotorWorks »

water can replace fuel up to about 50% and develop the same
power output,
Do you mean to say that water is acting as a fuel or that water is seperated by another fuel and burned?

As far as I know the seperation of water consumes more energy than the resulting Hydrogen provides.
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Post by tommurphy73 »

Some more information on the topic of water and combustion

http://www.freepatentsonline.com/4158551.html

Quote from patent
The presence of limited quantities of water in the combustion chamber of an internal combustion engine is known to improve the engine operation in several respects. First, the water lowers the temperature of the combustion to minimize predetonation and thus effectively decreases the octane requirement of the fuel for a given engine compression ratio. The cooler burning also enhances the completeness of the combustion process, producing an emission with fewer pollutants. Finally, the water addition in the combustion process increases the fuel efficiency of the engine to substantially reduce the hydrocarbon fuel required for operation.

Water injection has long been used with jet engines to increase power during take-off and a variety of schemes have been proposed for the injection of water vapor directly into the combustion chambers of reciprocating and other engines and other fuel burners.

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Post by maxc »

SchmidtMotorWorks wrote:Do you mean to say that water is acting as a fuel or that water is seperated by another fuel and burned?

As far as I know the seperation of water consumes more energy than the resulting Hydrogen provides.
Some of what is happening is that the high volume EGR flow is helping in the atomization of the fuel charge. Witch in turn creates a stronger spark kernel the MOST IMPORTANT PART of combustion. Maybe a little hydrogen is released but most of energy is coming form a better flame front. By the way Robert Harris was not my teacher.
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Post by Troy Patterson »

maxc wrote:Some of what is happening is that the high volume EGR flow is helping in the atomization of the fuel charge. Witch in turn creates a stronger spark kernel the MOST IMPORTANT PART of combustion. Maybe a little hydrogen is released but most of energy is coming form a better flame front. By the way Robert Harris was not my teacher.
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Mark
So, if I understand you correctly, the EGR is being used (by Audi?) at WOT? It's a high flow EGR valve?

If this is correct, is it aiding in atomizing the fuel delivered via an injector? Is this a racing application with a very high fuel pressure or a commuter car with lower fuel pump pressure / fuel injection?

Just want to understand.

The comments on cooling or cooled EGR - gases?

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Post by Larry Morgan Jr. »

tommurphy73 wrote:In a high boost turbo charge application water injection is used to limit the detonation tendencies of the fuel by slowing the burn rate of the air fuel mixture and cooling the intake charge. I have wondered if for high compression N/A engines if water injection would also offer the same advantages without the use of high octance fuel. Also if water entered the combustion chamber in liquid form it has an expansion rate of approximately 1600 its original volume so rather than just using heated nitrogen to act against the piston we would also have the additional pressure from the expansion of water. Once water has turned into steam it has the same expansion rate as any other gas.

Feel free to disagee with any or all of this

http://galileo.phys.virginia.edu/classe ... mProps.htm

Any thoughts on this?

Regards
Tom
Dunno if you have heard about this yet, or if anyone has mentioned it, but Bruce Crower has developed a six stroke engine on that principle. First four strokes are as usual, then the fifth stroke, it injects water. The residual heat turns the water to steam and creates another power stroke. The six stroke, it pushes the steam out, and is ready for the start of a gas intake stroke.

http://www.autoweek.com/apps/pbcs.dll/a ... WEEKSISSUE
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Post by maxc »

There is not to much new detailed information on what the car company's are doing with egr controls. But cooling the exhaust gasses for example to 700F. Makes it easier to use a smaller tube to the intake manifold for denser flow. And that heated intake charge helps the fuel injected in the engine atomize better for better spark kernel. Ever though the mixture density is less, the atomization and more powerful kernel make up the difference for stronger combustion.
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maxc wrote:There is not to much new detailed information on what the car company's are doing with egr controls. But cooling the exhaust gasses for example to 700F. Makes it easier to use a smaller tube to the intake manifold for denser flow. And that heated intake charge helps the fuel injected in the engine atomize better for better spark kernel. Ever though the mixture density is less, the atomization and more powerful kernel make up the difference for stronger combustion.
Sounds now like you are talking about Smokey's engine with regard to heated induction atomizing fuel!

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Post by Troy Patterson »

Tommy, I am a total advocate of water injection, and for that matter, EGR on high performance / racing engines. Because my Research and Development was cut short by California's Bureau of Auto Repair, I have yet to document and quantify results.

As with any of these concepts, misapplication can / will likely produce bad results.
Larry Morgan Jr. wrote:Dunno if you have heard about this yet, or if anyone has mentioned it, but Bruce Crower has developed a six stroke engine on that principle. First four strokes are as usual, then the fifth stroke, it injects water. The residual heat turns the water to steam and creates another power stroke. The six stroke, it pushes the steam out, and is ready for the start of a gas intake stroke.

http://www.autoweek.com/apps/pbcs.dll/a ... WEEKSISSUE
Very interesting Larry.

My gut feeling, although it may offer an advantage with diesel engines at this stage of development, I don't like it as it complicates the engine. If it incorporated the water injection process in some manner into the normal 4 stroke cycle, that'd be really cool.

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Last edited by Troy Patterson on Tue Oct 16, 2007 1:06 am, edited 1 time in total.
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Post by Troy Patterson »

Although, I haven't tried adding hydrogen to the combustion process, my brother has on a dually - without any data acquisition equipment. His "butt-o-meter" and subjective evaluation of gas mileage suggested it improved engine performance and efficiency a small, but perceptible amount.

I don't offer that as proof, but thought I'd put it out there. There are some stanch skeptics I will add.

Free Hydrogen improving the flame kernel is very interesting. I see this as reducing the likelihood of generally localized combustion caused by the added heat of lean air / fuel ratios and the resultant destructive pressure spike as well as the late burn off of remaining fuel elements prior to and after EVO by igniting more of the air / fuel mixture early in the combustion cycle.

To the "increased" degree the air / fuel mixture is ignited more uniformly and completely by the exploding flame kernel, we are able to lean the mixture, increase compression and / or reduce timing.

Cold air, reduced inlet temperatures by way of thermal barrier coating(s), EGR gases and water injection, etc., all serve to increase charge density in the combustion chamber as well as buy compression tolerance and / or air fuel mixture leaning (to a small degree) also. It also increases dynamic compression improving "molecular proximity" (as I see it).

I'd point out that diesel engine's running significantly higher compression ratios are also more thermally efficient by a small yet meaningful margin.

Increased dynamic compression equals increased "molecular proximity," but there's more to it than that.

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Last edited by Troy Patterson on Tue Oct 16, 2007 1:09 am, edited 1 time in total.
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Re: Where does power comes from?

Post by Larry Morgan Jr. »

Troy Patterson wrote: My gut feeling, although it may offer an advantage with diesel engines at this stage of development, I don't like it as it complicates the engine. If it incorporated the water injection process in some manner into the normal 4 stroke cycle, that'd be really cool.

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Hehe, yeah, especially when the water injection leaks and starts flash rusting the internals of your engine. :shock:

I'm not really sure how you could incorporate it into a standard 4 stroke cycle...

Anyway, don't wanna be getting this thread too side-tracked..

So, uh, power, it comes from, uh, heat, and stuff... please continue...
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