Compression ratio question
Compression ratio question
(OP)
Does anyone know what the highest compression ratio that has been tested is? And who or where? Recip or free piston?
And test results in terms of power, efficiency etc.
And test results in terms of power, efficiency etc.





RE: Compression ratio question
In my opinion, regular compression ratio is ~ 15 to 20 [/].
I have no idea what the achievable highest compression ratio is.
The higher the compression ratio, the more difficult it gets to make it work ...
In general, there is always some kind of an optimum combination of compression ratio, equipment design, maintenance and associated cost ...
Here are a few general compression plots:
Thnaks,
Gordan
http://www.engineering-4e.com
RE: Compression ratio question
The earlier indirect-injection VW diesels were above 22:1.
High specific power output was not one of the features of those engines.
RE: Compression ratio question
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RE: Compression ratio question
IN the 70s or 80s during another energy crisis Bruce Crower (Cams) played with peculiar intake timing and a high mechanical compression ratio to create unequal compression and expansion ( more complete expansion) ratios.
For performance piston port 2 strokes of the 70s the exhaust port closes around mid-stroke. Thus the oily low octane mixture inhaled by a Montesa 125 with over 13-1 brochure compression is really not much more tightly squeezed than a Yamaha with 7.X-1
RE: Compression ratio question
RE: Compression ratio question
RE: Compression ratio question
I'm a french so excuse me if i speak a bad english.
When you upgrade your compression ratio, you have more power.
The principale effect caused by the increase of Cr are improve your cycle yield (thermodynamic effect) and augment your pollution (combustion effect).
The main problem of a Cr too high, is the apparition of detonation (like knock in the cylinder). But, in race engine the detonation is counter detonation by a different Air Fuel ratio (AFR), they augment fuel on AFR and less ignition advance.
It's difficult to give you the highest Cr has been tested because of this effects but in an ignition engine, like SMOKEY44211 say, it's near of 17:1 with gasoline. There's an other gasoline engine without ignition (it work like a diesel, it's the HCCI process) and the Cr is more about 20:1 to 22:1
Bests regards, pecki
RE: Compression ratio question
RE: Compression ratio question
It also does not surprise me that even little engines like the Prius or several of the other VVT engines are operating of pump gas with CR's of 13+:1 !
Rod
RE: Compression ratio question
All the listed ratio's so far are pretty standard stuff, no one knows of any special tests in this area?
RE: Compression ratio question
Also, when detonating there was black smoke coming from the exhaust - my simplistic explanation was that the "bang" of the detonation actually put the fire out resulting in unburnt or only partly burnt fuel. This is in the same sense that explosives have been used in the past to put out oil well fires etc.
The highest CR I have seen on an unrestricted engine is about 30:1 used on a model plane "diesel" engine.
RE: Compression ratio question
RE: Compression ratio question
I vaguely remember a NASA paper about a free piston engine with compression ratios of about 100. I think that this was analysis only, but I am not certain.
It was completely impractical.
As compression ratio goes up, peak cylinder pressure goes up for the same power level. All real engines have peak cylinder pressure limits. Example: I recall GM bragging 5-7 years ago that their new in line six gasoline engine could take "high" peak cylinder pressures. They thought that 1000 psia was high. Diesels are typically limited to about 3000 psia.
Also, as peak cylinder pressures go up, temperatures go up, so NOX goes up.
j2bprometheus
RE: Compression ratio question
Regards
Pat
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RE: Compression ratio question
I ran into information some time ago, that had mentioned 300:1 and this is why I asked the question, I'm thinking it was free piston arrangement.
RE: Compression ratio question
What's really more important than simple geometric CR's are cycle pressure ratios and temperatures. These really determine how much work the engine system has extracted from the thermal cycle. Large turbine engines are now getting close to PR's of 45 or more.
With regards to efficiency and emissions in a highly boosted DI diesel, a geometric CR around 12:1 would be ideal, but it would be very difficult to start. Most medium sized diesels use something around 17:1 with lots of boost and charge cooling, which results in good efficiency and low emissions. Very large bore loop-scavenged 2-strokes (like ship or stationary engines) with auxiliary supercharger drives and mega turbocharging can get away with geometric CR's around 12 or 13:1. The best compromise for efficiency in recip engines appears to be to limit the compression and expansion work done in the cylinder, while also doing as much as possible with external turbo machinery. Thus, you will not likely find too many examples of recip engines with extreme CR's.
Regards,
Terry
RE: Compression ratio question
RE: Compression ratio question
RE: Compression ratio question
Regards
Pat
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RE: Compression ratio question
The question that came to mind immediately upon reading your question is: single stage or multi-stage? As tbuelna suggests, an engine system with multiple stages of compression may have a very high "compression" ratio.
Were you thinking single stage of compression?
Regards,
Vincent
RE: Compression ratio question
They had many aborted runs and starting the thing was a major operation. Not sure that push starting at really high speed is a common occurrence. There was no reference to starting fluids or the engine's CR as it was, in my opinion, just a "puff piece" to push diesel power.
I find the diesel powered road race "prototypes" far more interesting. At least the technology in the Le Mans racers is closer to what could reasonably be expected to filter down to common road usage in our future (hopefully).
Rod
RE: Compression ratio question
Wow outlaw695, my metro could use that.
Must have a good starter on it, and 45 psi more wow. Cool stuff any more info?