Miller cycles are up to about 10% more efficient than Otto cycles. The Miller cycle is different from an Otto cycle because of the compression stroke. The only real difference between the two is that the intake valve is left open for part of the compression stroke in a Miller cycle (Miller cycles require a supercharger). When the intake valve is left open and intake gases are compressed into the supercharger and then re-compressed back into the cylinder, the engine gains efficiency because the supercharger compresses the charge using less energy than the piston would have.

Well, my idea is to use this concept on the Wankel engine. The Wankel would be direct-injected and would have camshaft-operated slide valves to uncover a port in the compression section. Just like in a piston Miller cycle, there would have to be a supercharger. The more efficient the supercharger is at compressing the air, the better, so the supercharger would be centrifugal with gearing as to provide maximum gains off idle to about 4000 RPM. The supercharger would be connected to both the intake and compression ports. Now with Miller cycles, the efficiency of the supercharger's compression wears off at high RPM since at that point the engine is more efficient at compressing the air than the supercharger. So in my idea I propose a supercharger and turbocharger combination like in the Volkswagen Golf 1.4L. However in a Wankel engine, this method would almost certainly work better, with a supercharger creating a lot of low-end torque and a turbocharger boosting the rotary's high rpm powerband. Oh yeah and around the same RPM that the supercharger stops creating any real boost gains, the Miller effect really stops coming into play so the camshaft that opens the compression-cycle ports would be de-activated.
-- acurafan07, Jul 15 2007

Wikipedia's page on Miller Cycles http://en.wikipedia.org/wiki/Miller_cycle
Only mentions piston engines [acurafan07, Jul 15 2007]

It's not hard to tell it's your idea, only takes a few lines :-) (+)
-- normzone, Jul 15 2007


This might work, but I'm not sure I understand everything in the idea. First of all, rotary engines don't have camshafts. Many do have variable-geometry ports that act like variable valve timing in a piston engine.

What do you mean by "compression ports"? Are you adding another port to the engine or just expanding the intake port?

Also, I don't think a centrifugal supercharger would work for this application; I think you would need a roots type or something similar.
-- discontinuuity, Jul 15 2007


I mean that there would be a new port in the compression area with a sliding valve operated by a camshaft to cover/uncover the port. I do know that rotary engines don't use cams, but this idea would require one and I know it wouldn't be hard to implement. Yeah a centrifugal supercharger might not work, but then again if it's geared so that it makes all its boost at only low rpms, maybe it would.
-- acurafan07, Jul 15 2007


Would the cam be operated by an electric motor (with a worm gear?), which would hold the valve open in the lower RPMs?
-- BJS, Jul 22 2007


No it would be an actual camshaft. The cam would be above the entire rotary assembly with valves that would be shaped like the port and (instead of moving up and down into and out of the port) would move along side it, covering and uncovering as the lobe would go from larger to smaller.
-- acurafan07, Jul 22 2007


I like this Idea. What if an intake port was cut directly opposite the existing port? Would it be possible to direct inject through the trailing spark plug hole? The combustion chamber would be exposed to the blower right up to the end of the compression cycle. With direct injection the trailing plug is really unnecessary isn't it?. Could an injector survive the combustion chamber?
-- uncleskunky, Mar 08 2009


You don't need a valve to accomplish this on a Wankel. You just need a port located in the right spot to bleed the pressure.
-- kevinthenerd, Sep 27 2012


Wankels are prone to detonation. A true Miller cycle (employing an intercooler) would reduce pre-ignition.
-- kevinthenerd, Sep 27 2012


I think the Mazda RX8 had this.
-- travbm, Nov 02 2015



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