08/13/2003

Lean Burn

Why lean burn engine?  Lets use Rogowski for some approximate reasons.

Peak Combustion temperature is virtually identical with 85% theoretical fuel
as with 140% theoretical fuel or in the close vicinity of 4750 rankine at 7:1
compression.

At 8:1 compression ratio, at 80% theoretical fuel, we are at 1000 psi max
pressure, rising to 1150 at 120% theoretical fuel and dropping to 1100 at 140%
theoretical fuel.

At 7:1 compression ratio, at 3000 degrees Rankine EGT - raising to a peak of
3700 at vicinity of stoic dropping back to 3000 degrees at 140% theoretical
fuel.

And most importantly, with a mep of 200 psia, at both 90$ and 140% theoretical
fuel.

The rise in thermal efficiency is sufficiently fast to overcame major
reductions in fuel used at the same compression ratio.

Within the limits of combustibility of normal gasoline, above 80% theoretical
fuel, or 25% excess air or under 18.5 or so to 1 air fuel, we can get about a
50% increase in the effective power of a unit of mass of fuel.

Supercharging is almost a pure requirement, because of the limits in getting
sufficient excess air to make the same temperatures as knock limited excess
fuel.  But with a Mack Truck turbocharger which is almost as big as a rice
rats turbo, excess air should be doable.

Following Macginnes, one degree reduction of intake temperature is followed by
one degree output temperature, allows us to eliminate the intercooler and
reducing the EGT to the same point by going to 80% theoretical fuel.

The use of a turbocharger for excess air and the RAISING of the charge air
temperature by elimination of the intercooler may make 80% theoretical fuel
practical on normal gasoline.  Vaporization of the fuel becomes increasingly
critical as the theoretical fuel decreases and the ability to do so may limit
the mixture to a higher theoretical fuel.

Currently, there is significant current research on the use of hydrogen to
"spike" mixtures and run with extremes of excess air.  Hydrogen both lowers
the limit of flammability ( H2 with Air is about 1000% excess air ) and speeds
combustion ( about 9x hydrocarbon speed ).  Most of these involve thermally
reforming hydrogen from a hydrocarbon base using EGR and the water produced in
combustion.

Alcohols will remain combustible with between 80% to 100% excess air, and
thus, a little joy juice will go a long way towards both better and cooler
combustion and more power.

Ignition accelerant such as R-Fluid (diethylglycol) or ethers allow even more
excess air.  Keep in mind that while such accelerant may severely knock near
stoic mixtures, at the edges may be needed to even have combustion.

A major transportation limiting factor is that sudden changes in mixtures as
in acceleration for example, will quite literally blow the fire out.  Enter
the conquering hero of fuel leads air.  Since the power is determined by the
throttle position and thus the fuel, under acceleration, the mixture will
greatly richen back up towards stoic.  Thus energy release and temperature
will tend to increase.  Air will then be added to reduce temperatures back
downward.

Knock control will simply be the addition of increasing excess air.