Audi Wankel

[Cody Forbes]

It's also worth noting that stroker engine max RPM and the reasoning  
behind F1 short stroke has very near NOTHING to do with friction. It's  
all about piston speeds. For a piston to travel more distance (longer  
stroke) in the same given time it must travel faster. Faster travel  
means more decel and accel forces at the top and bottom of the travel.  
Spin a long stroke engine too fast and the upward momentum overcomes  
the strength of the connecting rod and the piston simply doesn't stop  
when it reaches top dead center... (very) soon after that some very  
bad things happen. F1 runs high RPM because that is the only way for  
them to make big power. Displacement and induction are regulated.  
Since HP = torque x RPM / 5252 you can increase HP by increasing RPM  
when increasing torque isn't an option. With all that RPM you also use  
smaller gear ratios, which puts more torque to the pavement.

Just like Grant said, the Wankel rotary design is just not fuel  
efficient. The biggest recent advancement in rotary design has been  
graphite apex seals (piston ring equivalent) and that was 20+ years  
ago. Pick up a copy of "The Wankel Rotary Engine: A History" (http://www.amazon.com/gp/aw/d/0786429054/ref=mp_s_a_1?qid=1277242195&sr=8-1 
) which happens to have been written by a co-worker of mine. It's a  
great read. The design has problems with the fuel mixture not being  
able to burn fully before the rotor reaches the exhaust port. This  
means wasted energy, lots of noise (remember the GTP Mazdas with the  
5ft long muffler?), and lots of heat put the tailpipe. The best  
feature of the Wankel is no reciprocation which means it can spin very  
fast (remember that piston speed thing? Yeah, that's no issue here),  
but the faster you spin it the less time the fuel has to burn and the  
more energy is wasted. There are very good reasons that Mercedes and  
GM invested large sums of money into Felix Wankel, but never used the  
engine.

-Cody (mobile)

On Jun 22, 2010, at 5:07 PM, Grant Lenahan <glenahan at vfemail.net> wrote:

> wankels are widely used in generators?
>
> incidentally, the RX-8 is STILL know for awful fuel economy.
>
> Pushrods have never been known for inefficiency - for low RPMs, yes.  
> But
> then, high rpms mean high frictional losses :-)
>
> Wankels, OTOH have problems with "valve" timing whcih is very hard,  
> (or
> is that well near impossible? sure seems difficult) to vary, and with
> short rotor dispalcement, as you noted.
>
> I'm still skeptical.
>
> interested in the experience from generators. are these portable,
> industrial, what? I'm only familiar with reciprocating and, of course,
> industrial turbines.
>
> Grant
>
> On 6/22/2010 4:32 PM, NIck Miller wrote:
>> Wankel's are inefficient just like pushrod motors are outdated and
>> "old techology."  Right, Mr. C6-z06 Vette?
>>
>> Rotary's were pretty bad in the 70's during mazda's wankel Hey-day,
>> but the Rx-8 is not terribly bad for what it is, and you do find
>> rotary's in a lot of applications (like generators) outside of the
>> automotive industry.  They are a small segment of every market they
>> are in, but they have continued to develop just like every other sort
>> of internal combustion engine has through the years.  Supposedly the
>> newest rotary, going from 1.3l to 2.0l, will have even better
>> charecteristics because one of the issues was drag/size of the motor,
>> and supposedly this will help a lot with efficiency in the newest
>> rendition.   This concept can be compared to "stroking" a motor,  
>> where
>> you get too much drag on the piston up and down the sidwall, lowering
>> its rpm limit.  Same idea behind F1 motors having big pistons + small
>> stroke = lots or rpms...
>>
>> Either way its a cool concept.
>>
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