Temperatures in Internal Combustion Engines

If your intention is to reduce kinetic energy loss by reducing possible friction, than what about kinetic energy loss by reduced pressure (escape of expanding gas) ?

The whole idea of internal combustion is the high difference of temperatures, between the inner combustion chamber, and the outer, cooler ambiance. If that difference is allowed to somehow be reduced, your output of usable power is also reduced.

Granted, in Electromagnetic Motors, reduction of any possible friction is top priority.

But in Combustion Engines, I would think Adiabatics first, and only then think Friction, given that efficiency is my goal

Thank you for your reply. I understand the concern relating to loss of pressure through blowby. I should mention that the reciprocation rate of this engine, as was reported on the engine I'm modelling mine after, was in the area of 40,000 recip. / minute. I was not overly concerned with pressure loss as the stroke of mere inches and the very short time duration involved would present minimal losses, I believe. The intent of the engine is overall efficiency through thrust augmentation, which I have not touched on, construction a light weight, simple, powerful engine with a power to wt. ratio of approximately 4. What would be a reasonable delta t of such a engine in order to size up piston to cylinder clearances. I had also posted a question on the behaviour of blow by air flow around a floating piston ring. Have any comments of that question. Input has been appreciated!

There's a good bit of information available on temperature profiles in ICE pistons. Search this out before you put a lot of effort into this project of yours. Variations in power output as an analog of energy release in the combustion chamber will produce wide variation in piston and cylinder temperature profiles. It is likely that a design such as you suggest will have a very limited range of power with acceptable efficiency. Successful implementation will place a premium on the use of materials with near zero CTE such as carbon/graphite composites and silicon nitride. Precision fabrication of these materials are established technologies. General Motors has a history of successful application of silicon nitride in diesel engine valve lifters. Carbon graphite composites have a long (like50+years) history of use as sleeve bearings in high temperature non lubricated applications.

Ed Weldon, Los Gatos, CA, USA

The materail you use to build pressure against. The cylinder head limitation will determine what you use as delta t

I found these values:340C centre of the piston top,first ring groove:270C,lowest groove:175C,bellow last groove medium value:125C.Hope be useful.-

Hello Mike, welcome to CR4.

At 666 2/3 cycles per second you will also have some heating from the pressure waves transmitted trough the piston. ( like a slow speed ultra sonic welder )

Your compressed (mostly) air will be the gas floating the piston/ bearing. The faster the gas passes and the greater the difference in temp the more heat transfer. Your heat will be going from the compressed gas to the piston until equilibrium.

If you cool the outside of your cylinder to reduce heat you lose efficiency. No metal will survive for long at these temps without shielding and cooling. Yes ceramics can but your energy transfer will fail from the heat.

You are on the right track. I'm working on something similar Solve the heat efficiency vs. survivability and build a efficient ICE.

Brad

Mike,

What do you expect to gain by doing what you are doing?

Friction is not a large part of the loses. The thermodynamics is...

What new cycle are you wanting to use?

There are hundreds of people who have tried what you seem to be trying and none have made anything with what you are doing. What is different in your case?

An Otto cycle gets 25% and a Diesel around 35%, but there are cycles and multicycles that can get 60%++. How does what you are doing get you there???

Just curious...

Seaplaneguy

Sorry,i don't understand what you mean exactly because i read several times about a free piston air compressor was developed to work in a turbine engine when it seems a great idea in the 60's.I think it was GM with some goverment help.Is that true?.-

Hi!, Yes ultimately the engine could be used as a high temp. / pressure generator for the purposes of driving a turbine of sorts. They have utilized the free piston concept in both air and hydraulic type pumps.

If you have more information about i'd be glad to look that:where to look at?.-

Mike,

I am working on such a system myself, if I understand what you are talking about. I would like to engage you on ideas, but you seem to be avoiding a discussion...and don't answer questions.

To answer your initial temperature question one would need to model it in time. A spreadsheet program (microsoft excel) would do. You need to decide on a cycle and know the heat transfer in time to determine temperatures. If you look at a mapping of an engine you will notice that the lowest BSFC is at a given rpm, and this is due, in part, to the time factor.

For example, if you compress air slowly you will loose the heat of compression out of the piston wall (approximate isothermal compression), but if time is short you will have the temperature rise and approach adiabatic compression where heat transfer is zero. (I am sure you understand this, so sorry for starting at such a basic level...)

To predict the temperatures you will see in a piston, I recommend you model what your system will be doing, or take data from a prototype, which would require you first build it and then iterate, which may or may not be possible or cost effective. Remember that most emmisions requirement drive engine designs, not performance, and the bridge from startup to running temperature is critical.

Do you have a Link to the GM free piston research? What are you trying to accomplish?

So if you want help, engage...

Seaplaneguy

I think what I'm doing is unique and an improvement on whats out there today, first of all the power to wt ratio far exceeds anything today at approx. 4:1. The weight of the engine is a mere 20 lbs. develping about 80 hp. When one considers a vehicles overall efficiency you need to look beyond the efficiency of the power plant. Reduction of the power plant wt. for instance reduces the fuel load required. An eventual application, because I'm a pilot, is for a small aircraft. The fuel of choice would be diesel or an equivelant as heat of compression ignition is incorporated. The engine is very simple and thus has built in reliability. There will be augmentation of the gasses generated, I am not going to discuss at this time. There were a couple of French guys in the 70's that had utilized a free piston engine to drive a linear alternator with much success. The article was in Popular Science or a magazine like that. They reported overall efficiency in the 50 + range. I'm not saying that this power plant is useful for all applications but that it certainly has a few niches that it could fill nicely and therefore a worthwhile endeavor!

the

Your Power to wt ratio of 4:1 is 8 times better than a Lycoming (Otto) cycle engine. I believe such is possible also, and my application is also for small aircraft, or at least it originated with a seaplane design in mind.

Why has nobody taken what the French guys did and used it?

Again, do you have some references? Patent numbers?

I can see 50+ efficiency, as most oceanic diesel freighters get 55%+ on a Diesel cycle. With a free piston you could control expansion by electronics, but that would require an electric motor. Do you use, or plan on using, an electric motor?

Besides electromagnetic motors, which have the highest known efficiency overall, gas turbines have the highest rating in combustion type engines.

There are many variants to this general idea, and as much uses from jet engines (merely as distant relatives) to truck, tank anf helicopter powerhouses, and the main efficiency factor there, is that the farther the gas stream is from the rotating fan axis, the weaker the stream required to produce the same effect.

In other words: the farther from the axis, the stream of gas pushing the blades, the more torque the axis is able to produce.

This, of course influences the size of the engine, derived from the effective diameter of the gas intake fan.

Early helicopters had to resort to gas turbines, simply because even the lightest and most powerful internal combustion engines did not have enough weight to power ratio, to allow for the helicopter to carry any useful load, as it barely lifted itself...

Yuval,

A turbine efficiency is due to the sealing and boundary layer scale effects, and compression ratio, not the distance from the axis, which is conserved.

Electromatic gas motors are NOT the highest. A GE Brayton - Rankine cycle turbine system is the world record at 60%.

There are problems with electromagnetics that out "weigh" other solutions.

A. Rankine Cycle turbine is in fact a gas turbine by definition, although a closed-loop one. - It's only natural, that it has a high efficiency score !

B. "...not the distance from the axis, which is conserved..."

- If you insist...

Ideas are a dime a dozen can--you produce any tangible evidence of any of your theories or claims?

You will only succeed in finding out what so many others have found out: Nothing is easy as it seems.

The only free piston engines I have ever seen are Stirling Cycle and it is EXTERNAL combustion!

A free piston engine you describe will certainly be difficult to start and most certainly burn itself up in a very short order with any materials I know of. The future may bring new materials, but something will have to seal the cylinder to get enough pressure to heat diesel fuel hot enough to ingite. Oh, by the way, with a free piston, how do you plan to deliver the fuel to this engine?

I'll repeat my first reply in case you did not read it:

Just how will you extract any power if it has combustion on both sides of the piston?

What will push the piston on the compression stroke?

Better find a good supplier of Virtual Piston Rods, Virtual Crankshafts, Magnets, Mirrors, and Smoke!

You will also need a Quantum Computer for the controller!

I think you are trying to joke around with this community!

Hey Bill, Your input has not been very helpful, and I don't know why I'm wasting my time responding. I guess maybe I can help you in your unbelief not that its really important that you grasp what I'm doing. I hope you have read all the entries relating to my question. Some of the guys have been helpful and do understand where I'm coming from. Why do you insist on your slandering? If the only free piston engine you have seen is one involving the Stirling Cycle, you need to keep looking. To help you to that end see if you can look up on the internet Mechanix Illustrated Feb. 1969 starting on page 66. It hurts me deeply that you think that I'm abusing the priviledge of being on this site. My intentions are real with goals in mind. I will not respond to any more of your responses unless they can help me toward my goal. Sincerely.....

First of Thanks to U V for the link. I get that concept very well and have seen articles based around the general design the link shows since the 1950's. Free Piston's are one thing, Floating pistons are another.

Unbelief has nothing to do with this. Deal with facts not beliefs. My intent is to make you think, not slander you. Some of my previous comment was actually intended to be humorous, not slanderous.

What I have a problem with concerning your question/idea, Mr.VanNieuwenhuizen, is the lack of your ability to properly connect to the real world aspects of manufacturing an engine in which the piston doesn't contact anything.

Small piston engines without rings have been manufactured for decades--Keyword here is SMALL!

Scaling them up reaches a point where not having rings does not work with current materials technology---NOT that it won't change, just not yet. Not to mention the fact that the piston will not "float" for long because carbon will build up and make this engine not start at all, be very difficult to start, or require cleaning so often it isn't affordable.

I get the idea you have some "Book Smarts", but little actual experience with "Real World" manufacturing. Manufacturing requires a lot of compromises in tolerances, affordable materials, and processes if it is to be profitable.

A typical diesel engine requires about a 16 to 1 compression ratio requiring a fuel injector pump to overcome cylinder pressure (which is around 225 psi). If the piston doesn't contact anything how do you do the injection? The timing? What do you do when the air isn't dense enough to allow enough compression heat to burn the fuel?

I quote you:

I think what I'm doing is unique and an improvement on whats out there today, first of all the power to wt ratio far exceeds anything today at approx. 4:1. The weight of the engine is a mere 20 lbs. developing about 80 hp.

Actually nothing I have seen in your post is really unique, but perhaps an new combination. Another issue is you make this statement about power to wt. ratio and horse power as fact, yet you haven't made a prototype run yet. Sounds more like you are trying to convince a venture capitalist rather than get engineering advice.

Try this:

Stand out of sight of someone and have them draw a very simple object. The best way is to stand behind a blackboard (or whiteboard) so they can only hear you. Then, don't say: draw a house, tell them to start at a point on the paper and draw a line, then draw 2 vertical lines, connect the 2 lines, then draw 2 lines from there to a common point. You'll see that you leave out important details (as I did intentionally) and what you think you describe is far from what others understand.

Here is what I can help with:

A design like this will require years of research not just a few questions on the internet, there is a great deal of knowledge which is not online yet. Start at the beginning an you won't repeat mistakes already made by others.

Good Luck!

Hey Bill, I think we can talk again but please just spare me the humor. I am serious about the project and , yes maybe I took your comments in the wrong light. First of all, did you get a chance to view the article I made reference to? When I made statements about the engine they were in reference to that existing engine. I felt it was safe to say that the improvements I feel I am making to that engine would not seriously alter those published details. The fuel was to be altered but the btu value was not all that different. For further understanding as to what I'm working with, try looking up " Loudmouth - Free piston engine." That would at least give a picture of the thing. Now I never did say, but if I did I stand corrected, that I intended to have the piston float. It was the rings to float as the piston and the ring was to be of different materials and if these two materials were directly fastered I felt that the ceramic ring material would crack. If you feel that larger displacement engines would not work without rings making contact, why not? Concerning fuel charge introduction, it is not under pressure as the diesel engine because the fuel does not have to over come the high compression pressures. The fuel charge is added prior to the start of compression following the scavaging of the exhaust gasses. I realize that what I intend may be unorthodox but feel that ceramic cylinder liners and rings are very tolerant of combustion enviroments. If you feel other wise educate me. You see the whole idea of floating rings is the need to compensate for the thermal expansion. If I had rings that made contact with the cylinder then I would be obligated to lubricate this area with lubricants ending up in the exhaust and that makes it no better than a two stroke engine. It would go far if you were able to get the origional plans off of e-bay. The timing of the introduction of the fuel charge is fixed as in the origional, just basically prior to compression. If the air is not dense enough due to altitude or intake air being excessively hot, have the air pumped in as with a super or turbo charger. at this point I don't want to go there. With most of the engine already engineered just the changes require engineering. May I ask what your background is and do your words have any weight to them. You and maybe one other have shed a negative light on things and the other person , I felt, had no idea of what I was talking about. I am not an engineer but what I'm starting with did work.

Not entirely of topic, maybe a near miss but definitely interesting.

In the search for a better engine this link is a good side line for this thread.

http://www.autospeed.com/cms/A_0948/article.html

It is an Internal Combustion Engine ICE based on the scotch yoke. It is a Flat bed engine with con rods so our Bill H. will be happy.

I would like to thank everybody that has contributed so far the links have been great.

BAB

Thank you for be courteous enough to put up with my onerousness and help clear up what I misunderstand. I, however, do not quite get the rings having no contact with the cylinder. What purpose would they serve if not to block blow by?

I apologize for the joking around with the forum comment. You apparently have researched the topic better than I realized.

Conventional rings are placed in a groove in the pistons and not really fastened so I am having difficulty with that, too. Are you wanting to use a ring which is continuous rather than having a gap?

As for my background, I will email something separate directly to you instead of doing it here.

Thanks and Good Luck!

Esbuck,

Would you please explain WHY you chose to do all you did with cams and such?

Was is just to save weight?

1 hp/lb is possible in a two stroke. See www.recpower.com F-30 engine with fuel injection. http://www.recpower.com/f302c11.htm This is the lowest weight/power engine on the market, as far as I know. I own one, and they seem to perform well. I think they could be made lighter still, with a little "Navy" money to fine tune the beast.

Perhaps the limit of 1 hp/lb is there because the cycle drives the weight. Did you look at other cycles, or just a Otto / diesel cycle?

Seaplaneguy

<<Would you please explain WHY you chose to do all you did with cams and such?>>

This was about twenty years ago, and the available diesels were heavy. (Were they not, why did the navy need R&D?) The cam design was to save weight. It is also compact, perfectly ballanced, simple (potentially inexpensive) to build, with a slow speed output for the propeller, and novel enough to get funding to develop it. The patent title is "Modular Power Unit"; the idea being that if you want 100 hp, just bolt another on, end to end. It seemed there would be a market, for light aircraft/ultralights, portable pumps, etc., even if the navy didn't buy it. The prototype had one too many novelties, an injectorless fuel system, which injected air from the cylinder into a chamber full of fuel vapor. It worked, sometimes, but it needed more development. (Simplify and keep it cheap is not always a good policy)Another goof was a telescoping housing (turned on a lathe) with too many fiddly screws. I should have cast a simple two-piece housing, bolted together. The cams were expensive to make and needlessly heavy, and the company which machined them messed up, but we didn't have time or money to fix them. We were on a tight schedule and budget and had to make compromises. I have a better, "foolproof" design.

Cooling, at full rated power, was iffy. The heat would have to go through a cylinder wall, across an oil film, and through the aluminum housing to (preferably) fins or a water jacket. However, experienced engineers agreed that cooling would not likely be a problem. Oil cooling was a possibility.

Of course, I'm prejudiced, but I thought it was a good idea. If anyone wants to pick it up, the patent must have expired by now.