Turbos and CNG

[robert dingli]

Jonathan writes,
> 
> Actually, even methane (or good CNG) isn't a good option...  once you
> get over about 10.5:1 effective compression, methane burns hotter than
> gasoline...  and it already burns significantly slower than gasoline.
> The result is ridiculous EGT's.  I've heard that 14:1-14.4:1 is the
> limit for a naturally aspirated methane fueled engine because you start
> melting the plasma off the top compression ring... not sure how that
> would translate for a boosted engine.  You can make more power with 114
> octane high-lead race gas, anyway.

This is an interesting subject although I didn't mention methane as a
serious alternative to petrol to allow Giles to run 10.5:1 + turbo.

I haven't heard of melting plasma of compression rings but our research 
CNG engines have been running at 16:1 for a couple of years now.  The engine
I personally worked with was installed in a stationary application driving
a heat pump.  It ran for over 2500 hours before being dismantled and checked
by engineers at Ford's engine labs.  It had barely worn and they didn't even
bother to change the bearings.  The same engine design has run for months 
in taxi cabs with better performance than the original petrol engine.
I suppose it comes down to good optimized engine design.