Too good to let go by - Miller Cycle

[Robert Harris]

Most Miller Cycle engines ASSUME adequate power is available and
there fore trade POWER for FUEL Efficiency.  The specific mechanism
is that raising the compression ratio raise's the efficiency of an engine
quite startlingly.  Research suggests that POWER and EFFICIENCY
increase  with compression ratio up to about 17 to one.  The problem
is detonation.  A Miller Cycle conversion made by Crane or Crower 
after the 79 Crude Control Crisis ran a small block Chevy at a 15 to
one compression on unleaded low octane pump gas.  They had to 
stroke the crap out of it to both get the compression and regain the
power.   By limiting intake charge, you can safely compress the 
reduced charge back to the original low compression chamber pressure
of say 9:1  and have an EXPANSION ratio of 15 or 16 to one and all
the bennies of really good forced exhaust extraction.

Running a higher octane fuel reduces the advantages of extreme compression
and by the time you are running methane - there is no advantage.

Increasing the charge density by mechanical means simply means the 
Miller Cycle becomes detonation limited at ridiculously LOW manifold 
pressures.  Just drop the compression and put a power cam in.

One thing tho - every one of you has watched Miller Cycle engines in 
triple digit competion - pret near every weekend.  NASCAR. Yup.  The
restrictor plate effectively turns the engine into a Miller Cycle at RPM
and thats why they are limited to 14 to one.  Some smart ass's figured
out that with restricted intake, you could go to 18 to one or more and
get back most of the lost power without detonation.  Cam's aren't the
only way to limit the charge to less than 100% VE

"When some one gets something for nothing -
             some one else gets nothing for something "

If the first ingredient ain't Habanero, then the rest don't matter.
Robert Harris <bob at bobthecomputerguy.com>


----------
> From: steve ravet <steve at sun4c409.imes.com>
> To: Terry Martin <terry_martin at mindlink.bc.ca>;
diy_efi at coulomb.eng.ohio-state.edu
> Subject: Re: Too good to let go by
> Date: Monday, August 11, 1997 8:13 AM
> 
> 
> > I know a heavy duty mechanic in charge of the mechanical shop at a
> > mill that thinks installing a magnetron out of a conventional oven
> > into the manifold will "energize" the gas charge and produce smaller
> > droplets resulting in greatly improved efficiency.
> 
> Let him work on the oven for a few days, then when he's frustrated
> tell him that's it's easier to find magnetrons in microwave ovens than
> conventional ovens.
> 
> ha ha, just a joke... :-)
> 
> > Has nobody ever heard of volumetric efficiency? If you "vibrate"
> > something hard enough, it gets hot, hence micro-wave ovens work.
> > Unfortunately, hot + manifold charge = expansion of the mixture, and
> > less of a charge per volume of intake stroke. It's the same as
> > taking your foot off the gas.
> 
> Well sure, but what about a turbo or supercharger to force the 
> original amount of air back in?  sounds like you might have a more 
> efficient engine.  The Miller cycle engine makes the power 
> decompression stroke longer than the compression stroke by 
> intentionally leaving the intake open during part of the compression 
> stroke.  That burns less fuel and produces less power, but the engine 
> is more efficient overall.  Add a little forced induction to bring 
> power levels back up and you are making original power on less gas.  
> Mazda put an engine like that into the 929, don't know if they still 
> are or not.
> 
> just fuel for the fire...
> 
> --steve