1. Can compression ratio be converted into an actual psi number?

2. whats the lowest compression an engine will run on?

3 can roots style blowers put out the same high pressure numbers as the ATI centrifugal blowers (45psi)

4 on a very large turbo what is the max boost it can put out


any info would be very much appreciated

 

1. You can calculate psi from dynamic compression. So yes.

2. Again, dynamic always varies in a running engine. The lowest "it can run on"? Don't really know how to answer that.

3. Roots or Lysholm screw compressors can put out as much. Just differing adiabatic efficiencies.

4. A lot.

Very general questions (a book could be written on each) and you'd get a lot better responses if you narrowed them down a bit with specifics.

-Mindgame

 

I have to disagree on the first one, but very politely of coarse.

How can you calculate physicaly cylinder pressrue from a DCR?
Engine temp, RPM (VE at that rpm), air temp, exuast setup, residual exhuast left in the cylinder, forced induction vs NA- just about everything effects cylinder pressure- and thats just BEFORE combustion




and to the original poster, why do you want to run as low compresion as possible, you really want most compression. compression is a great thing.

 

i just wanted to know what the lowest possible compression an engine would stay idle at and not die i know compression is good but ive got a couple ideas where compression would be very very low

sorry about not being to specific btu i dont know much about turbos other than how they work i just wanted to know baisically what i asked i just want to know where the boost maxes out

and how exactley do you calculate the PSI in a cold engine baisically as though you were running a compression test on it .. but how do you figure out what its supposed to be at such as my engine having a 10:1 comp ratio should be at X PSI but i was just interested in a formula that would help me to calculate it
but thanxs for your replies i was getting woried no one knew what i was talking about

 

What exactly do you want to do here?

A low compression that doesn't die at idle may not be what you are looking for.

Bret

 

i just need to know the lowest compression that will create an explosion powerful enough to move the rotating assembly baiscally this isnt for your conventional motor just a crazy idea

 

Ok guess you didn't get it....

WHERE DO YOU WANT TO GO WITH THIS??????

It's hard to say do this or do that unless there is a clue to what is going on here.

 

sorry for being somewhat missleading this is a new style of engine that i came up with while talkin to one of my friends like i said its not a conventional style engine with pistons and such (kinda why i have not dropped many clues to whats goin on) but there will be very little load for the explosion to move. I dont want you to tell me do this or that cause its something that no one will really know about i just want some advice for figuring if there will be enough bang to get this thing goin befor i go invest uber amounts of cash trying to build one

 

Well good luck with it, but no real good way to help you with that then.

Bret

 

I hate to sound cynical (if that is how you spell it) but I assure you EVERYTHING has been done before. Everything, most likely tried before WWII. And durring WWII, R&D budgets for the internal combustion engine did not exist, basically try anything, and they did.

pnumatic valves, rotary, variable vane turbos, non-recipricating valvetrain, CVT, OHC- ANYTHING you think is new and exciting has been done since forever ago.

 

are you just wanting to know whats the lowest CR you can go and the motor still actually run?

 

i still cant understand for the life of me why he wants this.

Maybe he needs to better understand the importance of compression ratio in performance. The number 1.4 comes to mind very quickly

 

Reciprocating engines have been run on less than 4:1 static CR. My engine simulator allows as low as 3:1 static. I ran a single cylinder engine that way. It had a 2.6 Dynamic CR and achieved a peak cylinder pressure of about 240 psi. Same engine with 9:1 static had about 720 psi peak. The 3:1 was extremely inefficient, but the program indicated it would run. The testing was at wide open throttle, full load and required very little spark advance.

At idle it predicted about 3 in. hg. vacuum, and a theoretical cranking compression of 37 psi.

Now if what you are contemplating is not a piston engine this information won't be much help to you. If you were more specific, you might get more specific answers. You might get more negative responses also, but that's a chance you take.

If you are "reinventing the wheel" as far as internal combustion (IC) engines go, you might do some research into what has been done, as well as IC engine theory. Look for textbooks by Taylor and Taylor. A basic understanding of IC theory and the thermodynamics associated with it would be very useful to you. Your initial questions indicate a somewhat limited knowledge. No offense intended.

While EVERYTHING may not have already been tried, MOST everything has been, and has been reported. It would be a shame, IMO, to spend your time and money persuing something that won't work either mechanically or thermally. A wise engineer once said "You can't rape Mother nature." IOW, you can't do something that conflicts with the physical "laws", even if you are ignorant of them or don't believe them. We didn't make the "laws", we just discovered them.

End of philosophy 101 lecture. Good luck to you.