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Diesel Rotary Engine?

 
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Jingyee
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Joined: 11 Jul 2005
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Location: Portland, OR

PostPosted: Sun Aug 07, 2005 12:54 am    Post subject: Diesel Rotary Engine? Reply with quote

Did Mazda ever make one?
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 135
Location: Portland, OR

PostPosted: Sun Aug 07, 2005 2:51 pm    Post subject: Reply with quote

No. Rotaries are not good candidates for diesel power. It could be done, at least in theory, but I can't imagine why anyone would do such a thing. Diesels use super-high compression to essentially cause a detonation event as fuel is pumped in at hundreds of PSI. Building a rotary to take such abuse would be challenging, plus the engine would end up being quite heavy, I believe. Hydrogen, on the other hand, is rather ideal. Propane is also a good alternative fuel.
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DMRH



Joined: 28 Oct 2005
Posts: 5
Location: Sydney, Australia

PostPosted: Fri Oct 28, 2005 4:09 pm    Post subject: Re: Diesel Rotary Engine? Reply with quote

kazisdaman wrote:
Did Mazda ever make one?


No, but Rolls Royce did.

They built experimental versions for a British military contract back in the 60's or early 70's

REgards
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Arawn



Joined: 06 Nov 2005
Posts: 11
Location: Bridgeport, Conn

PostPosted: Sun Nov 06, 2005 11:25 am    Post subject: Ancient Thoughts Reply with quote

From what I recall of the PopSci article, a Diesel Rotary would involve a large Rotary Supercharger, forcing air into a smaller engine. Diesels use a ~20:1 Compression Ratio, for greater efficiency, but always tend to be heavy.

OTOH, you'd only need a single HP Fuel Injector, for each cylinder, as you could inject as the combustion space swings by.

Once this country develops Coal to Diesel, Diesel will be cheaper, and such an engine would save weight over the older reciprocating style. Just put the Catalysts on the the Housing Surface.

Arawn
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TCooperDesigns



Joined: 20 Feb 2006
Posts: 4
Location: UK

PostPosted: Mon Feb 20, 2006 8:46 am    Post subject: Re: Diesel Rotary Engine? Reply with quote

DMRH wrote:
kazisdaman wrote:
Did Mazda ever make one?


No, but Rolls Royce did.

They built experimental versions for a British military contract back in the 60's or early 70's

REgards


see
http://www.millville.org/Workshops_f/kess_mech/tools/1tools/engines.html

http://www.der-wankelmotor.de/Motoren/Rolls-Royce/rolls-royce.html
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Graviman



Joined: 24 Feb 2006
Posts: 6

PostPosted: Sat Feb 25, 2006 5:28 pm    Post subject: Good thread... Reply with quote

2 cents worth...

From memory 12:1 is about the highest practical compression ratio achievable in a rotary. Much higher than that and the eccentric movement nibbles into the piston structure, and any oil seals, since smaller piston is having moving further. You could turbo it without an intercooler, since this would get the charge hotter before injection. Trouble is engine would not fire until turbo was spooled up - not a problem with turbo rpm sensors. This is likely why Rolls decided to use staged compression. However, charge air cooling is a very good way to improve efficiency while reducing NOx emissions.

Other difficulties would be arranging the correct swirl for a good air/diesel mix. Best would be several vortices around the circumference of the chamber. These would speed up near "TDC", with diesel having to be injected into each vortex centre. Diesel would inject as piston moved around, so combustion would be well underway before the injection finished. This might well adversely affect efficiency, since there is an optimum cutoff point (~2000'K for NOx). Multi point injection would thus likely be required. In general it would be more difficult to arrange complete combustion compared to simple piston geometry.

The main problem is that diesels struggle to run at high RPM due to the time for combustion initiation. The high RPM capability of a rotary would be wasted, since you would not better 4000 RPM. The lower RPM gives more time to lose heat, so you would need to design a rotor with the width the same as each chamber length. This would give the smallest surface area for volume, but doesn't help with side wall ports gas flow. Circumference ports would work well though, since valve overlap does not adversely affect emissions in a diesel - it just lets more unburnt air through. Even this geometry still results in an effective "stroke/bore" ratio that is undersquare, while the slowest ship engines regularly run 2:1 oversquare ratios.

There are technologies on the horizon that help with the RPM limitations of diesels, but not the mixing or geometry problems. Surfact coatings allow the adiabatic engine to be approached, but these techniques apply just as well to piston engines. I suspect it is hard to justify development costs, but that said there are many rotary features that may be transferable to a high performance diesel piston engine. Probably diesel will likely remain piston as first choice, although examples of rotary diesel will always pop-up...

Mart
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