05/28/2003

Rereading SAE "Vaporized alcohol fuel boosts engine efficiency" brings out the
first requirement of an R-Fuel - high latent heat of vaporization.

"Energy recovery through vaporization requires a solid or liquid fuel; only
liquid fuels will be considered here.  The relationship necessary to
understand the potential heat recovery through fuel vaporization can be
derived from Fig 1 where methanal serves as a numerical example. Fig 1 can
apply to other liquid fuels provided they can be vaporized without
decomposition.

Since water remains uncondensed in practical combustion processes ( which
means that the heat of vaporization of water formed during combustion cannot
be utilized ), the lower heat value of a fuel represents its usable energy.
The lower heat value of fuel vapor, i.e., its usable energy, is greater than
that of the liquid, exactly by the heat of vaporization"

Thus, if we vaporize the fuel from previously burned fuel, we will increase
the heat energy of the current fuel by exactly the heat of vaporization and we
will have the use of the upper heat of combustion.

For methanal, the usable heat can be increased by 5.86 percent.

"Relative to diesel fuel, one liter of methanol requires 4.4 time more heat
for vaporization and ethanol 3.5 times more heat.  Since the large fuel flow
and high vaporization heat are multiplied, methanol needs 9.8 times more heat
than diesel fuel to evaporate the fuel for a given output if the same engine
efficiency is assumed.  For the same conditions, ethanol requires 5.8 times
more heat"

Consider the alcohol as a means of absorbing and regenerating heat for the
engine.  The higher the heat of vaporization, the more heat from the exhaust
or cooling system can be regenerated into the intake charge.

Mercedes noted that water up to 10% by volume had no detrimental effect on the
engine, but the power was reduced appropriately by the lowered heating value
of the fuel.

They also noted that the engines were able to run with considerably leaner
mixtures than petroleum engines.

Which brings us to a second desirable characteristic of an R-Fluid - extended
lower limits of explosiveness in a homogeneous charge.  Gasoline typically has
a lower limit of explosiveness of about 25% Excess Air.  Both methanal and
ethanol have lower limits of explosiveness of around 100% excess air.

Thus, for the base requirements of an R-Fluid are:
A.  High Latent Heat of Vaporization
B.  Boiling Temperature below the water temperature of the engine - about 96C
C.  Extended lower limit of explosiveness of the fuel - preferably at least 
    100% excess air or more.

If the ignition accelerants have a higher boiling temperature, we may have to
use cooling water preheat into a "boiler" using exhaust heat.

In all cases, the heat of vaporization of these fluids is recovered and
regenerated into the fresh charge.

The pursuit of R-Fluid is beginning to be defined and a delivery system for it
is under way.

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12/29/2003

Nothing to do with Cetane Improvers - no interest here - move along.

Again from Bios 1612

"In German aero engines, considerable difficulty was experienced by
failure of the spark ignition system at high altitudes. Trouble with the
ignition also arose because of excessive plug fouling with high octane,
lead containing fuels. An attempt was made to overcome these
difficulties by the use of a low tension ignition system operating at
about four hundred volts. Later, however, investigations centred on the
use of the "Ring" process. This process had the additional advantage
that it made feasible the use of high boiling point safety fuels. The
work on the "Ring" process had been summarised by O'Farrel in BIOS
Report No.1609, which also contains an extensive bibliography on the
subject.

In the "Ring" process, ignition was produced by spraying a liquid into
the combustion chamber, at the appropriate moment in the compression
stroke. This liquid spontaneously ignited at the cylinder temperature,
thus igniting the main fuel charge. Diglycol diethyl ether and butandiol
diethyl ether were found particularly suitable as ignition fuels. The
former, which had a cetane number of 188, was manufactured in quantity
and was also used as a diesel starting fuel. The mechanism of the self
ignition of this fuel was thought to be a rapid disintegration of the
molecule under the action of heat. This reaction, being exothermic,
produced a rapid temperature rise causing the products of the
decomposition to ignite.

Operation of the "Ring" process could be made at a compression ratio of
7 : 1, but in practice a ratio of 8:1 was normally used. For weak
mixture operation the optimum ignition fuel (R-fuel) quantity increased
slightly, whilst with overrich mixtures the performance deteriorated
because of longer ignition delays. In practice, the timing of the
R-fluid injection was not too critical, and was usually kept constant.

Cylinder head temperatures were considerably lower with R-fluid
injection than with spark ignition, although no appreciable difference
in exhaust temperature was observed. If the operating temperature was
too low, ignition difficulties arose. In this respect a great
improvement was obtained when the R-fluid was injected on to the hot
exhaust valve. This increased fuel consumption, which, however, was
still an improvement on that obtained using spark ignition.

Compared with the spark ignition process, the maximum power output, when
using R-fuel, was approximately the same at rich mixtures, but was
considerably improved at weak mixtures. Although at high compression
rations knock was considerably reduced because of the multipoint
ignition of the mixture by R-fluid, at the compression ratios normally
used there was little improvement over the usual method of engine
operation. "