12/29/2003

BIOS and Nitroparaffins

>From bios 1612 on the use of nitro-parrifins.  Again - something none of
us would consider.........

A comprehensive investigation was made by Penzig on the use of
nitroparaffins as fuels. In his report he tabulated the properties, and
presented other data in respect of nitromethane, nitro-ethane,
nitropropane, nitrobutane, and nitrobenzene. Approximately 25% more
energy was obtained from a given amount of air when using nitropropane
than when using n-heptane. When burning heptane in air to which nitrous
oxide had been added in such proportion as to give 3 mols N2O/mol C7H16,
however, almost the same energy was obtained, as with nitropropane and
normal air. Thus when ordinary air was brought up to the same oxygen
content by the addition of free oxygen, the energy liberation, although
better than with normal air, was not so great as with the nitrous oxide
containing air. 

In a reference to the work on glow ignition, it was stressed that
nitroparaffins are readily ignited at hot surfaces, even though they are
difficult to spark ignite. Glow ignition temperatures were obtained by
passing the fuel vapours over an electrically heated coil. It was
suggested that the nitroparraffins might be used as fuels for high
altitude flying, and thus eliminate the necessity for the conventional
spark ignition system. 

The glow ignition properties of the nitro parraffins were also shown by
their cetane ratings. With direct injection the technical product S 3 (
a mixture of 1 and 2 nitropropane) had a cetane number of only fifteen.
In a prechamber engine where the fuel contacted the chamber walls to a
greater extent, it had a cetane number of forty five. 

The admixture of nitropropane ( in the form of S 3), with a number of
gasolines gave surprising results. The fuel S 3 had an octane number of
72, but when mixed with certain gasolines it gave rise to mixtures with
octane numbers lower than those of either component. The minima occurred
with mixture containing approximately 30% of S 3. With other gasolines
no such phenomenon was observed. Nitro-ethane and nitrobutane behaved
similarly to nitropropane. The octane number of nitrobenzene could not
be determined because of glow ignition, but experiments were made in
which it was mixed with gasoline VT 702. Up to 50% nitrobenzene addition
the octane number of the fuel was only slightly changed, but further
increase in the nitrobenzene content, however, resulted in a
considerable improvement in the octane rating.

Experiments were made using a number of diesel fuels. Corresponding to
their effect on the octane numbers of gasoline, the nitroparaffins gave
mixtures with cetane numbers greater than those of either component. The
maxima, however,  were not so pronounced as the minima in the octane
number curves, although the improvement was greater the higher the
cetane number of the original fuel.

On recycle diesel operation, use of nitropropane as a fuel was estimated
to be able to give a saving on the total weight of fuel and storage
equipment of 16%. Its use in submarine operation would, however, be
limited because of the bubbles that would arise from the evolved
nitrogen.