Variable compression engine

[Lazy JW]

Smitty,
I do remember the Coates valves, that's exactly what I had in mind. Seems to me that they would be ideal for an opposed piston engine, thus allowing a four-stroke design rather than two-stroke.

I have long been fascinated by the opposed-piston engine ever since reading about those Junkers engines when I was a kid. By eliminating the cylinder head they captured some of the energy that is normally lost as heat through the head. Trouble is, they were all two-stroke diesels. Since it is impractical to convert all crude oil to diesel, someone is gonna be stuck with burning gasoline. I would sure like to see someone develop a more fuel efficient gasoline engine.

We have been so spoiled with cheap fuel that everyone thinks of high power-to-weight as being "efficient". This mindset isn't likely to change until gasoline hits at least $10 per gallon.

I don't think my variable compression design is practical except as a small stationary engine; I don't have the resources or talent to try to develop it anyway.

I do believe that an opposed piston four-stroke engine with an appropriate valve system could be built that would have an acceptable power to weight ratio with reasonable performance and superior fuel economy. This isn't really a radical idea; rather it is combing several existing concepts into a new package.
Joe

 

[Anonymous]

One objection to an opposed-piston engine might be that it has to be strong (massive, heavy) at both ends, whether it uses two crankshafts or one crankshaft plus linkage. Small aircraft engines are mostly flat-fours/sixes/eights instead of Vees partly because they save weight in not having separate main bearing caps. But your notional engine gets rid of one or two cylinder heads, so maybe that's a wash. What about exterior dimensions; would it be a packaging problem? Your engine has a lot of things to lubricate and would likely require dry-sump pressure oiling, an added expense.

If the goal is utilizing more of the wasted heat, surely a simpler place to start is with ceramic coatings and ceramic parts, wider use of turbocharging, etc.. If the goal is higher compression, factory-engineered water/alcohol systems have always seemed an obvious answer. With modern computer controls, aerospace air/fluid injectors, knock sensors actuating emergency limp-home ignition retarders, all set up to last 100,000-plus miles by the manufacturers rather than amateurs, we could have more efficient versions of the engines we have spent nearly a century developing. Gasoline venders would have to install extra pumps and tankage; garbage could be rendered into methanol.

Yes, it would be inconvenient. No, it wouldn't pay off for some time. No, it is NOT THE ANSWER. Ceramics and little turbochargers are NOT THE ANSWER, either. But they should be part of the answer . . . and should have been initiated in 1973.

 

[Lazy JW]

One objection to an opposed-piston engine might be that it has to be strong (massive, heavy) at both ends, whether it uses two crankshafts or one crankshaft plus linkage. Small aircraft engines are mostly flat-fours/sixes/eights instead of Vees partly because they save weight in not having separate main bearing caps. But your notional engine gets rid of one or two cylinder heads, so maybe that's a wash. What about exterior dimensions; would it be a packaging problem? Your engine has a lot of things to lubricate and would likely require dry-sump pressure oiling, an added expense....

Yup, there are a great many drawbacks to my concept engine. I do believe that a delta arrangement with three cylinders, three crankshafts, and six pistons has the most potential for power, economy, and compactness. With proper port timing and turbocharging for good scavenging it could be run as a two-stroke and still be clean. Might need direct fuel injection though. I dunno. Just like to dream a bit.
Joe

 

[Anonymous]

joe, you got my wheels turning... i have the 3-D drafting tools and stuborness to try and design it..... plus i live in " it can't be done" area... case in point" you'll never hit anything with a 12 ga shotgun slug" explain why there was two dear hanging in the garage. 8)

 

[Lazy JW]

Somewhere in my archives (fancy name for junkpiles) I have an old Popular Science magazine that has an article about some large radials built for stationary use as power generators. They had a mechanism that eliminated the master connecting rod and all of the rods were equal with equal orbits around the crank. IIRC they were "Nordhoff's"? Not sure about the name though. They were installed in a power plant in Texas and fueled with natural gas. I believe the design was balanced.
Joe

Wrong name. Should be "Nordberg". I will post the article in a new thread.
Joe

 

[Lazy JW]

joe, you got my wheels turning... i have the 3-D drafting tools and stuborness to try and design it..... plus i live in " it can't be done" area... case in point" you'll never hit anything with a 12 ga shotgun slug" explain why there was two dear hanging in the garage. 8)

Please feel free to draw up, modify, or build this contraption. I only posted it as a starting point, hope someone can take the ball and run with it.

On a small dispacement, low output engine I figured that sealed ball bearings would suffice for prototype work.
Joe

 

[Anonymous]

Personally, I have always thought that a swash-plate design would work best. Less moving parts, and compression could be varied by spring-pressure overcoming centrifugal force/inertia. I'm no engineer, but the first time I ripped apart a swash-plate A/C compressor I thought it had potential.
The hard parts, I think, would be the valve-train and trans connection, but at least the valve-train is a low impact section. With only 4 moving parts under torque load (3 double-headed pistons and the crankshaft) you would think that it would be a fairly efficient design.
Just my thoughts, but again, I'm not an engineer...

 

[Anonymous]

In my fading memory, one or more previous attempts at swash-plate engines got stuck because materials-science was not up to the job. Maybe it is now . . . .

 

[wallaka]

http://en.wikipedia.org/wiki/Swashplate_engine

Interesting stuff.

EDIT: Also interesting.

http://www.sae.org/ohmag/techinnovations_10-00/04.htm

 

[Anonymous]

an interesting note. i asked an engineer here about variable comp. engines, he found it interesting. somehow we go onto the discusion of large diplacement engines on ships. he mention that some ships run on straight filtered crude. have to heat it up to 180 degrees, but i though if one was building a variable compression engine, you could make a deisel style to burn waste motor oil. vary the compression for what ever you were burning... i just may have way to much time on my hands..... :roll:

 

[Anonymous]

an interesting note. i asked an engineer here about variable comp. engines, he found it interesting. somehow we go onto the discusion of large diplacement engines on ships. he mention that some ships run on straight filtered crude. have to heat it up to 180 degrees, but i though if one was building a variable compression engine, you could make a deisel style to burn waste motor oil. vary the compression for what ever you were burning... i just may have way to much time on my hands..... :roll:

Alternative fuels would be one of the biggest advantages of a variable compression engine.

Take the Chevy trucks that can run on E85 for example. They are designed to change the fuel/air ratio based off of what type of fuel is being used in order to get stoichiometric mixture. However, everyone knows that running E85 in an engine designed for pump gas gets lousy fuel mileage. This is because the compression ratio is so low.

E85 has some rediculously high octane rating like 105 or something like that. So if you bump the compression ratio way up to take advantage of that extra octane, you can get much of your fuel mileage back by improving thermal efficiency.

Now if you could create that same alternative fuel vehicle that could change the fuel/air ratio based on fuel type, but also include the function of changing compression ratio, you could run nearly any fuel, and still get good fuel economy. It would be a HUGE leap forward.

 

[Lazy JW]

... you could make a deisel style to burn waste motor oil. vary the compression for what ever you were burning...

A diesel type uses maximum cylinder filling all the time, the higher the compression the better (within practical limits).

The old Lister type stationary diesel engines used a device that allowed higher compression for starting and then switched to lower compression for running in order to put less stress on the bearings, etc. Those engines are perfectly suited to running various oils as fuels. Someday I want to own one.
Joe

 

[Anonymous]

i would like to have one myself. i have done alittle bit of reading on the lister engine. would be nice to have on a gen set or something.

 

[lyonsy]

perkins expermented in the late80's early 90's with ceramics in desiel and ran at operating temps of around 140degC
the troble they where having drama with pistons failing when using alloy and steels where to heavy and pounded the hell out of big end small end bearings as well as cranks snaping from the extra loads.
at the time exotic materials like titinium where to expensive even for deisels to use as pistons or even piston tops in 2 peice designs.
this could most likly be used now.

if your chasing compression effecency with compression id also go for increased operating temp coupled together whould make a very nice little engine.

btw i also whouldent consider anything other then direct injection of fuel nat/lpg gas for easy conversion to hydrogen injection later on

 

[dieselmaster]

caterpillars intake valve actuators, IVA's, was an attempt to make emissions in 2004. Did so by holding them intake valves down a little longer to make sure the 52 pds of boost made it in the cylinder. These engines actually make worse fuel mileage from the previous c-15 and 3406E. Variable compression does spike my intrest alot, that drawing is well lets say a real good start. Another idea would be to cut some cylinders out, 6 inline running on 1 and 6, 2 and 5, and 3 and 4. Run all 6 cylinders to highway speed and cut some out just enough to keep going at rated speed. most likely would only work with a direct port fuel injected setup, probably would sound like a 620 john deere but saving money is better then sounding good. Would require a heavy flywheel to keep the rotating mass rolling along.

 

[rf8-gt1]

hmm, wonder if the compression mechanism be throttle link controlled instead of crank control. So instead of two pistons, just have the normal otto combustion engine.. but with the head lifting up and down based on tps. :idea: