wankel engine or normal engine
Discussion
wot are the advantages of a wankel engine, i heard they suffered from poor low end torque, i cant seem to find much info on them, the problem is, i can only find teh rx7 to get get any decent info on, and they have a turbo, and are already tuned, can rotary engines be designed for good mpg too,
www.howstuffworks.com/rotary-engine4.htm
And if you're interested, join up at www.nopistons.com or www.rx7club.com and learn more than you ever thought you'd need to know.
And if you're interested, join up at www.nopistons.com or www.rx7club.com and learn more than you ever thought you'd need to know.
wot are the advantages of a wankel engine, i heard they suffered from poor low end torque, i cant seem to find much info on them, the problem is, i can only find teh rx7 to get get any decent info on, and they have a turbo, and are already tuned, can rotary engines be designed for good mpg too,
Advantages:
Mechanical simplicity, excellent power/weight ratio. No reciprocating parts means smooth operation across entire RPM range, nearly flat torque curve and a much higher "red-line" than most piston engines. Stock RX-7 engines typically place limits at 7000-8000rpm but with minor modifications, this can be pushed up by 50% or more.
Originally, there were problems getting the engines to seal correctly which resulted in poor reliability. Mazda solved this with their 12a model which was introduced in the RX-7. From then on, a typical engine's lifespan could easily exceed 200,000 miles.
Disadvantages:
Low thermodynamic efficiency. This means poor mileage and much dirtier operation running on petroleum-based fuel. Mazda claims to have mitigated this problem by relocating the intake and/or exhaust ports (I forget which). The result is the "Renesis" engine which will (hopefully) be making its debut in the RX-8 so we can all get a chance to see how successful they have been. The red-line is reportedly at 10,000 rpm.
Mazda's design is a departure from Felix Wankel's original design. Technically, it isn't even a true rotary engine, it is an epitrochoid design which, I believe, came from one of Wankel's engineering staff.
The original Wankel engine was more efficient but impractical to run in consumer vehicles. For one thing, the spark plugs were inside the engine so replacing them meant a full rebuild.
However, I suspect the design may make a comeback because one of the ideal fuels for a Wankel engine is hydrogen. Burning this would eliminate the carbon fouling which is the cause for the vast majority of spark plug replacement. Ergo, the inacessability of the spark plugs is no longer a problem. IIRC, the rotational limit of the original design was around 25,000rpm. Nice...
>> Edited by JonGwynne on Friday 20th December 13:14
roospuppet said: thankyou JonGwynne that was really helpful, u say the original design was more efficient, do u no why it was more efficent, because that would be really helpful to know
I've been on the lookout for info on the original design for some years but haven't yet had any luck. I've always assumed it was more thermodynamically efficient (i.e. more effective conversion of thermal energy into kinetic energy, perhaps due to a lighter rotor and/or more efficient chamber structure).
I gather TE is a rather severe weak spot for the epitrochoid design. Still, given the power it does manage to put out, I think it does quite well. Probably because it suffers none of the piston engine's inevitable losses due to reciprocation and mechanical complexity.
the problem as i c it, with the rotary engine, when the combustion takes place, there is a large surface area, to get rid of heat ( conduct) so lots of energy is lost in heat, if u can coat , or make the rotor out of a material with a low thermal conductivity, and the rotor's case( not sur eowt it is called) out of a similar material but with low friction, then more of teh energy can be turned into kinetic energy, and therefore more torque, and there more power
i no the new rx 7 has a compression ratio of 9:1 but how could this be increased, assuming, that no detonation or pinking would occour, wot physically could be done to increase the ratio , could a ratio of 15:1 be achieved, could this be done by creating a cavity at the top of the cylinder just after th einlet port, and just before the closing point when it sparks, so that a bigger compression be acheived,
So I'm now listed as a gasbag eh? Thanks a lot Ted. Look, I've told you before, I can't help it if I have a flatulence problem... 
Regarding compression ratio on a rotary engine, I think this would be down to the relative volume between rotor and chamber wall on induction phase and the volume on compression phase and would therefore be governed by the shape of the chamber. i.e. The closer the chamber wall to the rotor in compression phase, the greater the compression.
Think the first production car to ever use a rotary engine was the NSU R080, and Norton also made rotary engine bikes at one time which did rather well in racing. Also think the Mercedes C111 prototype used a rotary engine. Maybe you can glean more info from research into those.
Regarding materials with low thermal conductivity, sounds like you want ceramics, which do seem to be increasingly considered for use in engines.
Regarding compression ratio on a rotary engine, I think this would be down to the relative volume between rotor and chamber wall on induction phase and the volume on compression phase and would therefore be governed by the shape of the chamber. i.e. The closer the chamber wall to the rotor in compression phase, the greater the compression.
Think the first production car to ever use a rotary engine was the NSU R080, and Norton also made rotary engine bikes at one time which did rather well in racing. Also think the Mercedes C111 prototype used a rotary engine. Maybe you can glean more info from research into those.
Regarding materials with low thermal conductivity, sounds like you want ceramics, which do seem to be increasingly considered for use in engines.
ceramics are good, but they dont really posses the streghts of metal, a good marsenite metal, with a coated properties of low thermal conductivity would be best, for instannce the strongest ceramic zirconia, has nearly same strength as un forged steel, so for performance the coating would be best, but zirconia isnt as good at thermal conductivity as silicon carbide or double bonded silicon, also double bonded silicon has a very low friction co efficent,
IIRC there was a company at the Classic Car Show at the NEC recently displaying their six (I think) rotor Mazda engine (seemed liked they are fairly modular in their construction?). Claimed some ridiculous power figures from what still looked like a pretty compact package. Got me wondering why you don't see them used in more conversions?
I would have thought it impossible to alter the compression ratio, without altering the shapes involved. Kinda the equivalent to altering the compression of a piston engine by trying to fit square pistons.
Also l'm pretty sure that rotary engines are basically knackered after 100,000 miles, unless they've been rebuilt. (yum expensive)
Also l'm pretty sure that rotary engines are basically knackered after 100,000 miles, unless they've been rebuilt. (yum expensive)
the wonderful thing about a rebiuld of a rotor is how cheap it is to do.
most worn roror engines just need the rotor tips(equivelent job to piston rings)replaced ,crank wear is rare.
usual twin rotor rebuild is less than £200 parts
then garage adds on bs factor pricing"well its one of these rotary engines,very complex,have you any idea of whats required to work on these?" most people dont know and stump up the cash.
rotory engine is simplicity in a box.
great engine,great power,lowsy fuel economy
most worn roror engines just need the rotor tips(equivelent job to piston rings)replaced ,crank wear is rare.
usual twin rotor rebuild is less than £200 parts
then garage adds on bs factor pricing"well its one of these rotary engines,very complex,have you any idea of whats required to work on these?" most people dont know and stump up the cash.
rotory engine is simplicity in a box.
great engine,great power,lowsy fuel economy
roospuppet said: ceramics are good, but they dont really posses the streghts of metal, a good marsenite metal, with a coated properties of low thermal conductivity would be best, for instannce the strongest ceramic zirconia, has nearly same strength as un forged steel, so for performance the coating would be best, but zirconia isnt as good at thermal conductivity as silicon carbide or double bonded silicon, also double bonded silicon has a very low friction co efficent,
Several years ago, when I bought my first RX7, I took it to an independent who used to work for Madza. He claimed that they built a prototype rotary engine entirely out of a ceramic material (well, rotor and housing anyway, I doubt a ceramic crankshaft would be a good idea). They claimed that this material not only lent performance advantages and allowed the engine to be air-cooled but could also burn a variety of fuels that would normally be unsuitable for metal-based engines due to the higher operating temperatures (e.g. alcohol).
Mazda has also developed a hydrogen burning rotary. The rotary design is ideal for burning hydrogen since there is no risk of pre-detonation.
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