Rotary Diesel?? - PeachParts Mercedes-Benz Forum

BoomInTheTrunk · #1 05-01-2008, 01:07 AM

has this ever been done? I think a few poeple tried when rotaries first gained interest. Can it be done with todays technology ?

Diesels by design cant burn the fuel fast enough to rev very high in a piston motor, at least - but a rotor spins once for each 3 spins of the e-shaft. So, that might help in some ways, being 1/3rd the speed of the output shaft. do you think that this could aid in a high compression diesel rotary engine?

Knightrider966 · #2 05-01-2008, 01:14 AM

Quote:

Originally Posted by BoomInTheTrunk

has this ever been done? I think a few poeple tried when rotaries first gained interest. Can it be done with todays technology ?

Diesels by design cant burn the fuel fast enough to rev very high in a piston motor, at least - but a rotor spins once for each 3 spins of the e-shaft. So, that might help in some ways, being 1/3rd the speed of the output shaft. do you think that this could aid in a high compression diesel rotary engine?

I don't see how a rotary engine could be a diesel though. Diesel engines need the compression of squeezing a small amount of fuel and air so it gets hot enough to explode!

With a rotary, it's the spark plug firing that turns the gasses into heat to shove that rotor around for another spin while they're being spent! I can't see how a rotary could build up much compression to run like a diesel.

BoomInTheTrunk · #3 05-01-2008, 01:21 AM

alright what if, just a what if, what if you had one of the rotors act as a supercharger and then you have a fairly large starter on the car. So picture this one larger rotor for the supercharger and a smaller for the combustion camber. you make compression with the supercharger instead of just having it. Then until the engine warms up inject the fuel onto the glowplug at TDC. this would give you the extra heat to combust the fuel. So the concept is to use a supercharger built into the engine and make compression, the only challenge there is to start the engine so a electric motor would have to spin it up to speed first to make compression.

The only reason i say this is because the rotary engine is more efficient this means more power and greater gas mileage.

Knightrider966 · #4 05-01-2008, 01:26 AM

Quote:

Originally Posted by BoomInTheTrunk

alright what if, just a what if, what if you had one of the rotors act as a supercharger and then you have a fairly large starter on the car. So picture this one larger rotor for the supercharger and a smaller for the combustion camber. you make compression with the supercharger instead of just having it. Then until the engine warms up inject the fuel onto the glowplug at TDC. this would give you the extra heat to combust the fuel. So the concept is to use a supercharger built into the engine and make compression, the only challenge there is to start the engine so a electric motor would have to spin it up to speed first to make compression.

The only reason i say this is because the rotary engine is more efficient this means more power and greater gas mileage.

That's true about being more efficient, but to make a diesel out of this would take more energy than the motor was capable of supplying and still maintaining a performance and reliability standard at a cost effective price.

A compression piston engine was designed as a diesel, but a rotary was desgined for highly volatile fuels like gasoline.

rcounts · #5 05-01-2008, 01:54 AM

Rotaries use graphite as apex seals, and I don't think you could make them seal tight enough to build the neccessary level of compression for autoignition....

BoomInTheTrunk · #6 05-01-2008, 02:14 AM

ok so what if they used something else besides graphite on the apex seals.

Knightrider966 · #7 05-01-2008, 02:32 AM

Quote:

Originally Posted by BoomInTheTrunk

ok so what if they used something else besides graphite on the apex seals.

I still can't see it being done for cost and reliability reasons!

diametricalbenz · #8 05-01-2008, 03:22 AM

Quote:

Originally Posted by BoomInTheTrunk

ok so what if they used something else besides graphite on the apex seals.

Mazda has worked with that problem for 25 years and they're still not perfect even in gasoline form. It's caused emissions problems and oil consumption.

It's sealing technology that is simply not available.

...it's like this simple equation which will resolve all our world's power needs

H + H = He + heat (forgive the stoichiometry if it's wrong

)

turbobenz · #9 05-01-2008, 04:19 AM

Quote:

Originally Posted by diametricalbenz

Mazda has worked with that problem for 25 years and they're still not perfect even in gasoline form. It's caused emissions problems and oil consumption.

It's sealing technology that is simply not available.

...it's like this simple equation which will resolve all our world's power needs

H + H = He + heat (forgive the stoichiometry if it's wrong

)

I still dont get what fusion has to do with rotary engine reliablilty

#10 05-01-2008, 07:13 AM

The apex seals can't even seal well or reliably last more than 150k miles with low compression and gasoline, I doubt it would see 50,000miles as a Diesel.

A 1.3L rotary consumes as much gas in normal use as a 3.0L V6...

Bama1 · #11 05-01-2008, 08:03 AM

Wankel rotary engines typically consume more fuel than a piston engine because the thermodynamic efficiency of the engine is reduced by the long combustion-chamber shape and low compression ratio. That low compression thing is problematic for using diesel...but a positive thing for the reliability of an engine.
Your question is a good one and I'll bet MAZDA or the airplane engine industry has some topnotch engineers working on just that kind of an issue.
Search grasshopper, search...

79300sdtd · #12 05-01-2008, 08:35 AM

Quote:

Originally Posted by ForcedInduction

The apex seals can't even seal well or reliably last more than 150k miles with low compression and gasoline, I doubt it would see 50,000miles as a Diesel.

A 1.3L rotary consumes as much gas in normal use as a 3.0L V6...

close... i have had and seen RX-7's go 250k just fine... they are delicate engines but reliable... you have to run em so that carbon does not build up on the apex seals, and then you use compression.

they are rated at a 1.3L using conventional rating (all the spark plugs firing once) but you have 3 faces to each of the 2 rotors so you have to multiply the 1.3 by 3 so the displacement is really 3.9L...

i have gotten 26mpg in mine.

it would be neat to see a diesel rotary but it would be hard... their water jacket and all that is close to the combustion chamber... in high compression i cold see on e of the seals between the rotor housing and the counterweight housing blowing (read as rebuild sooner)

do i think it could be done...yes... will it ... no ... i have seen these engines apart...fascinating work and design just not able to withstand the pressures of diesel IMHO

babymog · #13 05-01-2008, 09:54 AM

The WANKEL engine, named for the German company that invented it, now a part of Audi via the Auto Union, ... which is why Mazda pays royalties to Audi for every RX- sold, ... I digress.

The Wankel is efficient, but like a turbine, it has at this point only been able to be efficient at a fairly narrow RPM band. Good for fixed-rpm pumping applications like John Deere manufactures for the Navy, bad for automotive applications where a broad RPM range is necessary.

The problem I see with making it a diesel, on top of the pressures necessary over a large surface area and seals, is the heat loss to the large surface area and keeping it hot enough for efficient diesel operation. The surface/volume ratio on a small one would be a big problem IMO.

KarTek · #14 05-01-2008, 12:28 PM

Speaking of turbine, THERE'S your rotary Diesel engine!

79300sdtd · #15 05-01-2008, 02:08 PM

Quote:

Originally Posted by babymog

The WANKEL engine, named for the German company that invented it, now a part of Audi via the Auto Union, ... which is why Mazda pays royalties to Audi for every RX- sold, ... I digress.

The Wankel is efficient, but like a turbine, it has at this point only been able to be efficient at a fairly narrow RPM band. Good for fixed-rpm pumping applications like John Deere manufactures for the Navy, bad for automotive applications where a broad RPM range is necessary.

The problem I see with making it a diesel, on top of the pressures necessary over a large surface area and seals, is the heat loss to the large surface area and keeping it hot enough for efficient diesel operation. The surface/volume ratio on a small one would be a big problem IMO.

the WANKEL is named after the MAN who created it... dunno who owns the rights now but ford owns mazda.

as far as not being efficent through a variety of RPM that is bunk... the RX pulled very well from 2800 to 7000... torque monsters they are not but power wise they are good through a broad range.