Compression stroke question

[caesar1]

Does anyone know what the consistancy of the charge is at TDC (maximum compression in cylinder)?

I'm asking because I am wondering if you could "pipe" the charge from one part of an engine to another so all the compression would take place in one area and all the combustion in another

 

[GregLocock]

It is a hot gas at around 180 psi at several hundred degrees mixed with some liquid droplets of fuel that are evaporating.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dicer]

I would say its a bit higher than 180 psi. Thats about what compression normally is with out ignition.

 

[CCycle]

Historically there have been many engines that compress their combustion air outside of the combustion and expansion area. Perhaps the best known is the Brayton engine, after George Brayton, Boston who patented the cycle in 1875. The Brayton engine used a separate cylinder to compress the fuel and air charge which was then transferred to the combustion cylinder for the burn and expansion. The Brayton engine enjoyed considerable service in steel and well industries. They would run on almost any fuel including various refinery gases and well head gas. They did not require any octane rating. They usually used hot finger ignition which was better understood by operators. I remember them as a child in the 50's in northern Michigan where they were used on drilling platforms. The Brayton engine is two cycle and does not breath well on its own. Operators soon learned that you could increase power considerable by putting a long straight pipe on them. They could be heard miles away.

In the early 1900s many patents were granted to inventors who realized that the work required for compression would be less if the compression were done outside of the hot working chamber. I do not know of any of them other than the Brayton that were successful.

The wankel rotary compresses its combustion gas then transfers it to another area for combustion. The Louis Kramer engine is a composite that uses some outside compression and finishes compression in the working cylinder. And then there are gas turbines and jet engines that use different areas for compression, combustion and expansion.

 

[patprimmer]

I think a steam engine generates it pressure outside the cylinder.

Regards

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[Warpspeed]

I believe the original poster had something more in mind like a Miller cycle engine.

So yes Ceasar, at least part of the compression stroke can be accomplished at a central supercharger, and the high pressure air piped to each cylinder with appropriate inlet valve timing. Mazda have done a lot of work on this.

 

[murpia]

One of the cars at this years IMechE formula student competition (600cc 4-stroke capacity limit but forced induction is allowed) used a 1000cc V-twin with one cylinder acting as a 2-stroke compressor feeding the other cylinder through an intercooler. They didn't have much data on it that I saw, but it made me curious whether this had been tried before with any success?

Regards, Ian

 

[turbomotor]

While the Stirling engine is not internal combustion (the original question implies internal combustion), the Alpha and Gamma versions of the Stirling do transport the compressed working fluid from one cylinder to another.

 

[GregLocock]

murpia - the Bourke engine uses that, in effect. I am sure there are other examples.

Cheers

Greg Locock

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[Fabrico]

You might take a look at the old 2-stroke Puch motorcycles. Transfer ports in one cylider, exhaust in the other. Try a search on "puch twingle". I owned a few of the beasts.

http://physiology.usouthal.edu/restore/allstate.htm

 

[izzmus]

That Puch design is interesting (to say the least). Looks like an inventive way to prevent intake charge from blowing right out the exhaust.