Quote:
Originally Posted by twitchyzero
few thoughts
I am continually blown away that a relatively small manufacturer can continue to push the envelope...Skyactiv-X squeezing out another 25% on top of the ultra-high compression the 2012 Skyactiv-G
this rotary-range extender in the article has already been tested since 2013
and sorry but even a late-model RX-8 mpg is 18 accordingly to Fuelly and EPA hence not bouncing off the rev-limiter...which is basically half of Skyactiv-G's efficiency as the sole powerplant
Also, do you still need to warm up a Rotary for longevity sake?
the hassle and durability of a rotary probably means I would not want one in a daily |
Mazda has always been known to pursue quirky engine technologies.
And yes, RX-8 gas mileage is pretty bad, but again, as it has to drive the wheels, the load will constantly change as you accelerate the car. The highway mileage also suffers because of the short gears and thus more pumping losses. My RX-8 will rev at 3k RPM at 92 km/h in 6th(last) gear. It's to the point that some RX-7 owners claim that they get better gas mileage on highways. Also, remember that these are sports cars - performance will be a bigger concern than fuel economy.
As for warm-up, that has always been a myth in ANY modern car. The "idle until warm" should have died with carburetors. The only time I would do that is if my windshield is covered in ice and I can't safely drive until everything is warmed up. Otherwise, I idle for 15 seconds after a cold start and off I go. Any engine shouldn't be driven hard when cold, piston or rotary.
And one last thing to clear up since we are here: flooding. I have never flooded my 8. I stalled my car while cold twice, and both times it fired right back up. If an RX-8 floods, something is wrong. Either your ignition systems are dying, your battery is taking a dump or your engine has low compression.
Quote:
Originally Posted by welfare
actually when i said dwell i was referring to piston dwell time. Which promotes a fuller burn and higher thermal efficiency.
There's no dwell in a rotary since the rotor is constantly spinning. During combustion, the charge mixture at the trailing side of the rotor is pretty much thrown out the tailpipe.
Hence the trailing plug. But it doesn't help much.
One of the reasons for the multiple cats and high hc.
Maybe they'll implement hcci. That would probably remedy it. Or maybe laser ignition.
|
One key difference between the RX-7 and RX-8 engines is the fact that the RX-8 uses side exhaust port vs. RX-7's peripheral exhaust port.
The RX-8 side exhaust port gets rid of the port overlapping and makes it so that there is a greater chance that some unburnt gas will be burned in the next cycle.
I think Mazda will be sticking to the side exhaust ports.
HCCI could be a solution, but wouldn't that require a higher compression ratio? A Wankel rotary engine is only capable of 11:1 or so by design. That's why Rolls Royce's concept diesel Wankel had two rotors - a big rotor as a compressor and a small rotor as the actual engine.
As for laser... Just the cost alone will mean it won't be in an econo car. And is it even in use in any road vehicles, anyway?
Quote:
Originally Posted by underscore
I would think that since the load/rpm can be fixed they can design the motor for maximum efficiency/longevity under those conditions. So instead of needing seals and oiling designed for a wide range of operating conditions and abuse levels they can dial it back to seals that will work well for what the generator will be running at and only need to provide enough oil to support that.
|
True, and in an RX-8 that's driven genetally, it wouldn't burn much oil. Again, the constant load and RPM means they can optimize everything for that particular condition.