I just looked over the link provided,and the O2 percentages look awfully familiar.So do some of the others.So I guess that proves the military gave me some bad numbers.I'm new to computers and the net also,so I don't have the greatest luck trying to research info alot of the time.Thanks Jim for the info.I doubt if I could have found anything like it any time soon.
Don't know what kind of math formula to use with that to figure out percentages.You'd have to know intake cfm also to complete the formula.But it seems like there's no more then maybe 5% max unburned fuel at operating temp.

Okay.This leaves me confused with some of my own personal experiences.Craig,you seem to know the most on these formulas and their applications.But anyone else who knows or has good ideas on the subject,please feel free to help out here.

Here's my personal experience in building a vapor carb from plans for someone else.First the car.1978 Pinto 2.3L,4 speed manual trans.stock gearing with 185/75R14 tires replacing the stock 155/80R13's.Vapor carb on stock intake.Timing set back to only 2 degrees advance.More caused preignition.Spark plugs 2 steps cooler then stock.The engine compression tested at 112lbs lowest,and 119lbs highest before being changed.We ended up getting an average of 60mpg during the 4,000 miles it was driven before it died from tarry residues gumming up the valves and rings.
I don't know many spacifics on the others I mentioned before,like I do with this car.

But it now seems pretty obvious that combustion efficiency isn't the major factor here I thought it was.I know the tire change could have gained us about 5 mpg better then stock.But the rest now has me confused.I'm going to try figuring some of this out.With the cooler plugs nessacary,we obviously had higher combustion temps.Being limited to 2 degrees advance leads me to believe we had both better and faster combustion.And with less advance required,we had less power loss on the compression stroke.Because the early spark starts trying to force the piston back down sooner.But could these changes have made that much of a difference?Or is there something here I'm missing yet.Stock mpg on these Pintos was 25.I got 35 mpg on mine with larger tires and better ignition.So you can use these for baseline comparison.

I should probably explain that all my books and manuals I used to have,military and otherwise were stolen 10 years ago.And my educated guesses and beliefs are based on what I remember studying,and my 24 years experience as a mechanic.Sorry,but it's the best I can do for now.

If we are talking about overall efficiency, I think the numbers you quoted (around 30%) look reasonable, except for the 90% jet engine. The 90% value may actually be a combustion efficiency number, it is much to high for the overall efficiency. There are lots of different types of "jet engines" and I'm not an expert on any of them. I don't have a source to verify the efficiencies of current engines, but I wouldn't be too surprised if the latest high efficiency engines (gas and diesel) were doing a little better. Maybe someone else knows.

Getting back to basics for a minute, someone pointed out that in an internal combustion engine about 1/3 of the energy is lost to the environment as heat (mostly though the cooling system), about 1/3 is lost out the exhaust (as hot gasses), and about 1/3 is turned into useful (shaft) power. These are round numbers, but close enough. Obviously, our goal is to minimize the lost energy.

If we look at the 1/3 that is lost as heat to the environment, we can theoretically get rid of the cooling system and operating the engine at higher temperatures, except it will melt . This is where the proposed ceramic (and ceramic coated engines) come in. The idea is to design an engine that will operate reliably at higher temperatures. I don't have any problem with this concept, but (as far as I know) no-one has developed a practical, cost effective design. I think a lot of the issues have to due with trying to manufacture complex ceramic parts (e.g., space shuttle tile problem). As materials improve and engines can be reliably operated at higher temperatures (for reasonable costs), this loss should inch down.

The 1/3 that is lost out the exhaust (as hot gasses) is pretty much a given. The second law of thermodynamics limits the maximum efficiency between a high temperature source (combustion temperatures) and a low temperature sink (ambient temperature). As we discussed earlier, this maximum efficiency is about 70% based on assumed temperatures of about 1300F and 70F. That means we are going to lose at least 30% no matter how well we design the engine (no free lunch there).

If we consider the 1/3 that is lost to cooling (material limits) and the 1/3 that is lost through the exhaust (thermodynamic limit), we don't have a lot left to work with. All modern engines are designed to provide maximum combustion efficiency (while still meeting emission and temperature limits). Current fuel injection control systems are very complex and are designed to continuously optimize the combustion process.

If we go back to the 50s and 60s there was clearly room for improvement in the carburetors. At that time, I can believe that someone could design a carburetor that would be a significant improvement over the stock designs. I also understand that a carburetor could be designed/adjusted to operate very lean, resulting in higher operating temperatures and an improvement in efficiency. However, if the engine was not designed for those operating conditions it would not be reliable. In addition, there are emissions consequences (i.e., high NOX) associated with high combustion temperatures that would have to be addressed.

With regard to the "vapor carburetor" design, I'm not sure I understand what it was trying to do. I suspect it was designed to operate the engine under very lean conditions, minimizing incomplete combustion and increasing operating temperatures. I expect this would result is an increase in efficiency (I don't know how much), but I also expect it would be very hard on the engine and would adversely affect some emissions. If that was the goal, the same thing could be accomplished today by reprogramming the fuel injection system on a modern engine.

If I understood your earlier posts correctly, you were attributing the increased efficiency of the "vapor carburetor" design to minimizing incomplete combustion. I doubt that was the major effect because stock engines should have very small loses due to that. If this design was causing the engine to run very lean (and hot) it could have increased efficiency in the short term. If that is the case, this design concept has been superseded by modern fuel injection (and engine management) systems that allow all these variables to be continuously monitored and controlled.

Personally, I think internal combustion engines have reached the point where improvements in efficiency will come very gradually, because all the easy stuff was done years ago. Engine management systems and materials will continue to improve, but I would be surprised to see a sudden leap in efficiency. I suspect we will see bigger improvements in the remainder of the vehicle (lighter weight, improved drive-trains, etc.), but that's a whole other subject.

What do you think?

me too. heh heh.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I think we are now all on the same page.

A gasoline engine is, after all, only one form of a "heat engine."

http://www.taftan.com/thermodynamics/HENGINE.HTM

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heaeng.html

No matter what cycle it uses, Carnot, Otto, Rankin, etc. a heat engine must conform to the laws of physics and thermodynamics.

It is tough to convert heat into mechanical energy. The early attempts used external combustion.

http://inventors.about.com/library/inventors/blsteamengine.htm

Then came internal combustion.

http://inventors.about.com/library/weekly/aacarsgasa.htm

I see a promising future for the fuel cell, which converts the energy contained in hydrogen atoms directly into electricity, which can be used to produce mechanical energy using electric motors. The hydrogen combines with oxygen, and the exhaust is mostly warm water.

http://science.howstuffworks.com/fuel-cell1.htm

Best Regards,
Jim

Somebody's been doing their homework .

Fuel cells have LOTS of potential, but everyone has to remember that obtaining H2 requires extracting it from water, which requires at least as much energy as is obtained when it is recombined with O2 to form energy and water again. H2 is not really an energy source, it is a way to transport and store energy. From an environmental and energy conservation point of view, it really only helps if the energy used to originally extract the H2 is "clean."

Two things.
First, you'll never be able to extract enough H2 to equal the energy spent in the extraction. You'll always lose.
Second, the most common source for H2 currently is natural gas, not water.

As with the hybrids, fuel cell vehicles are decades away from standing on their own merits.

Not that I'm against the research...it's just that, by the time they sort any of this out, my biggest concern will be whether my nursing home requires hybrid or fuel-cell wheelchairs.

__________________
1989 300 SEL that mostly works, but needs TLC

I agree, using H2O as a source for H2 requires too much energy.

For your consideration is the Proton Exchange Membrane (PEM) fuel cell, which can use ethanol or methanol directly as a fuel source.

http://en.wikipedia.org/wiki/Direct-methanol_fuel_cell

Use of ethanol/methanol fuels would require very little modification to the infrastructure we know of today, the 'gas' station would become a fuel station and pump ethanol or methanol.

I see promise, and a lot of difficult development.

Today and for the immediate future, the gasoline fueled, internal combustion, Otto cycle engine seems to be the most cost-effective power source we have for automobiles.

There is, of course, human power, such as walking and bicyling, but that is best left for another discussion thread...


Best Regards,
Jim

Interesting, but the problem with all these types of processes is that the (total system) emissions are no longer limited to water. Now we are back to putting CO2 in the environment. That kind of defeats the point of having "clean" fuel cells that are independent from fossil fuel (which is how these are being sold politically). Why don't we just burn the natural gas, ethanol, or methanol in a conventional engine?

I have heard these processes proposed as "stopgap" measures because they use the existing infrastructure. The idea (I think) is that this will get enough fuel cells in service to justify the development of a "real" H2 infrastructure. We may live long enough to see this happen?

I respectfully disagree. I believe Diesel cycle engines are a better bet than Otto as far as efficiency goes, and, if gas prices keep moving up, we are going to see a lot more of them. Today's Diesels are a new breed and very close in performance to gas engines. In terms of efficiency they easily beat gas engines. Despite the fact that the Otto cycle is more efficient than the Diesel one, because Diesels operate at much higher pressure ratios (from 16 to 24:1) their efficiency is higher. The maximum possible efficiency for an Otto engine at a 10:1 compression ratio is about 45%. Typical efficiencies for cars are 18 to 20% city and 26 to 28% highway, where is the other 17 to 27% going? Well, friction (valves, piston rings etc), combustion loss (small usually) and more importantly the losses associated with letting the air into the cylinders. These are particularly high at light engine loads. We have reduced them by going to 3,4 and 5 valves per cylinder, using variable inlet geometry and variable valve timing and a number of other things. We can go to lighter pistons, fewer rings, leaner burning and so on at increased complexity and cost but I do not think gas engines could even then match diesel efficiency.
That's what I think anyway.

JL

I pretty much agree with everything you've said. It wasn't clear who you are disagreeing with. Assuming it was me, I didn't mean to imply that I thought gas engines will become more efficient than diesels. I assume that the same types of advances will be applied to both diesels and gas engines. If I was to bet, I would say that diesels will remain more efficient for the foreseeable future. I'm a big fan of diesels, I have two.

Also, gas engines only approach their theoretical efficiency under full throttle conditions. Under low load they are controlled by throttling the inlet air, which is not included in the Otto Cycle model. In other words, diesels operate closer to their maximum efficiency than gas engines in the real world.

One clarification to what you said. Modern diesels do not actually operate on a classic "Diesel Cycle," they are actual operating closer to a "Air-Standard Duel Cycle" (had to look that up) which is more efficient and similar to a gas engine at full throttle. The difference has to do with the fuel injection timing. I think this helps support your point.

Craig, my reply was directed at Jim H, but you replied first, therefore the confusion. You are right, the real Diesel cycle has both constant volume and constant pressure burning, which further increases its efficiency and makes it very similar to the gas cycle.

JL

Sorry, I didn't notice Jim H's reference to the Otto Cycle. I agree with you about diesels. I'm so confused .

The technical issues are clear, but our driving habits and preferences will not change until they cost us a lot of $$$. Which may be pretty soon!

JL

This helps,and it's mostly where I was in the other thread,but doing a terrible job trying to explain.I appreciate being given a chance to explain better,and for you'r correcting the military's figures,which were the biggest cause of the misunderstanding.Craig,I don't remember the 1/3 loss of heat out of the exhaust.I don't know if I missed it before,or forgot it.It's really to bad someone hasn't come up with a design for the rotory engine that can overcome the blowby losses.Because of it's much better mechanical efficiency,It would be an immense improvement over the piston engine.Yes the vapor carburator was extreemly lean burn.And like I said,the design I built from plans worked great,but damaged the engine.The 90% I was talking about in jet design is the combustion efficiency told to me by a former military C5-A cargo jet mechanic friend of mine.I don't remember what the overall efficiency was.But I do know the mechanical efficiency is really poor.Great thermal and combustion though in jet designs.

I agree fuel cells are definitly a great improvement.But it's a shame they currantly still use fossile fuels because these are the simplest for of hydrogen to utilise at present.I know there are claims out there of people seperating H2 from water in small onboard reactors to power their piston engines.But EVERYTHING I have read also,says it currantly takes more energy to seperate the water,then you recieve in energy potential from the hydrogen.And one of the big problems with the process as of this time are the mineral deposits that accumulate on the electrodes,reducing their effectivness.But I wouldn't be suprised if H2 & O seperation can be made efficient simply by finding the right metals for the electrodes.And the right design.Something like the improvements made in lead acid battery design.

One last question on the Pinto we experimented with.Could the MPG improvements have come from that poor engine being pushed to it's thermal limits?I'm starting to believe the tar residue might have been coked oil instead of having anything to do with the fuel.

And my wife and I have talked several times in the past year about the feasability of using alcohol for fuel cell use.Glad to know were not the only ones.And to set up an alcohol infrastructure,we only need look to Brazil.They've had an alcohol economy for several decades now.