Some potential rotary news for you rotorheads
Depending on how you choose to measure it, Mazda's Wankel rotary could be as big as 2.6 liters already, but to most people, the engine has always been 1.3 liters. While the engine has never been known as a fuel-sipper, it has always been known for its excellent power-to-weight ratio. With the last update of the venerable design, Mazda offered up a partial solution to the engine's past emissions and oil-consumption woes by controlling the oil injection via a computer. We had an RX8 in our family which barely used any oil at all. Being suckers for technology, my family is always ready to try something new, and the power output of the rotary was plenty for our purposes. The rub was always keeping the engine under 4000 rpm or so. You see, there are extra valves which open at preset rpm levels, regardless of how much power the engine really needs to make. So, when kept under the point where the first extra set of valves open up, the engine consumes much less fuel.
Here is an article which claims that the next rotary from Mazda, the Renesis 2, will be enlarge somewhat. This could open up the possibility of extra power for one, but could also allow engineers to allow for better mileage under low-throttle conditions, which would be a big step in the right direction. If any Mazda engineers are reading this, flex-fuel capability would be nice too! We may find out more details at the Tokyo Motor Show in a few months.
[Source: Rotarynews via Autoblog]
Reader Comments (Page 1 of 1)
Cody Miller 1:57AM (2/05/2008)
Keeping it under 4000 RPM? Where's the fun in that?
Rotaries are born to rev high, they love it. Sure it uses more fuel but it isn't supposed to be a Camry or Civic by design.
Cheers,
Cody
http://www.mazdarxnews.com
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rgseidl 7:03PM (9/19/2007)
The 13b (Renesis) engine features axial rather than radial intake and exhaust ports, on either side of each rotor. It may well be that there is a flap in one of the intake ports on each rotor that the ECU opens up at 400RPM. This will increase fuel consumption only if you rev the engine hard at low power, i.e. you - or the AT - have waited too long to shift up a gear. Given how little low-end torque a naturally aspirated rotary can muster, that is understandable behavior.
If the engine were equipped small diameter turbo with a wastegate, low-end torque could be increased at the expense of a lower rev limit at the top.
Note that there are no poppet valves in a rotary, only ports.
As for flex-fuel capability, the kinematics of the rotor yields a suboptimal elongated combustion chamber. This is why each rotor is equipped with not one but two spark plugs. If you want to use E85 rather than gasoline in a rotary, you may have to compensate for the higher octane rating by using iridium-tipped points. Natural gas is even harder to ignite.
Mazda has been doing some research on burning neat hydrogen in a rotary, because of the high flame front propagation rate chracteristic of that fuel. However, BMW's hydrogen7 features a V12 engine and liquid hydrogen tank. It has already proven that H2ICE delivers excellent toxic emissions values but an absolutely terrible well-to-wheels balance. Rotaries are always less less fuel-efficient than conventional reciprocating engines, so they should be even worse in green terms.
The following short video clip illustrates how the Renesis engine works.
http://www.youtube.com/watch?v=_0uOk_FbW34&mode=related&search=
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kert 7:35PM (9/19/2007)
how the heck did you keep your RPMs under 4K in RX ? Mine never dips below 5-6ish when driving to work, apart from hangover mornings.
Well, yes, i use backroads with little congestion.
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Robert 8:17PM (9/19/2007)
@rgseidl
My only guess is he means the Variable Fresh Air Duct (VFAD), which is vacuum controlled and not not really valve. It just opens another hole in the cold air intake (in the top of the bumper). Some thought it was for resonance tuning but were found to be wrong later.
I also don't recall anyone on RX-8 Club finding that it made a big difference in economy ay 3,400 RPM and 3,600 RPM (which is where I remember reading the valve opened), outside of the fact that higher RPM = lower fuel consumption in general. Could be wrong about that, though. I haven't done my own testing.
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MikeW 10:31PM (9/19/2007)
This pdf seems a bit old
http://media.ford.com/pdf/rotary3_e.pdf
6 port, 3750rpm the secondary open, and at 6250 the tertiary opens.
Also the reason the mileage stinks, no exhaust gas recirculation, and a bit too short gearing with the stick 20mph / 1K in top gear.
and the 6 speed automatic gearing is too tall, 30mph/1K in top gear.
Hopefully Mazda will stroke the wankel [extrude] to 90mm, and implement an 8 port intake system 0-2500 low speed on one side of the rotor, 2500-5000 the other low speed port [other side], 5000-7500 the high speed (pick a side), then 7500-10,000 the other high speed port.
A very linear response.
and direct injection would be nice, everyone is doing it now a days.
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