>
>I would not recommend building Multifuel Engines as you suggest. Remember "the
>Right tool for the Right job", as well as the proper application of parts. You
>may be advising fellow listers improperly with this cavalier attitude towards
>Diesel Engine repair and maintenance. Improper timing will Blast holes in
>Pistons, as well as a lean running condition.
>
Worth taking a moment to review the diesel principle and its realisation in
hardware. Only the military seemed to have a courtship with a multi-fuel
injection pump but in essence all injection systems have to meet the same
criteria. It is commonplace to find injection pumps with lead seals, over here
no injection shop will entertain re-calibrating this very high precision device
if these are missing.
You can't have "lean" running with a diesel as the actual operation has the
fuel/air ratio vary enormously between idle and full power, the diesel always
takes on a _full_ cylinder of air (less dynamic efficiency) every induction
stroke as there is no throttle butterfly and fuel is injected depending on power
demand - accelerator pedal position, at idle its a tiny quantity, at full power
the pump is calibrated to inject enough to burn the total volume of cylinder air
in that particular type and model of engine. Any more fuel than this will
produce black smoke which is actually microscopic drops of unburnt fuel oil in a
carbon shell.
With a turbocharged engine some form of maximum fuel modulation has to be
arranged since the maximum fuel setting is necessarily less with the turbine
spooled down to that under boost conditions, for example when starting from
rest. This is normally done with a pump mounted diaphragm device sensing
manifold pressure and effectively limiting the full power injection quantity to
the normally aspirated level until boost pressure is available.
It is quite common for supercharged diesels to have quite "wild" valve timings
with substantial overlap as gas escaping via late closing exhaust valves is only
air and not useable fuel as would be the case in a gas/petrol engine, in fact
there is some benefit in totally purging or scavenging the cylinder of all burnt
gas.
Not all things that seem to be superchargers are in fact so, as a rule of thumb
if the cylinder pressure is reasonably above atmospheric at the onset of the
compression stroke then it is supercharged, if it is not but there is some
induction air pump device then it is scavenged and the device is called a blower
or scavenge pump rather than a supercharger. The two-cycle/two-stroke Detroit
Diesels are an example of the latter.
Other things besides combustible liquids could be used as diesel fuel, flour or
coal dust would do and burn exceedingly well if surrounded by enough air, indeed
Dr Rudolf Diesel's first production project taken up by M.A.N. in 1893 was to
use the plentiful, waste, coal dust. Solid, airless injection as we know it
today is relatively recent, only in 1920 was the first production solid
injection system made, up to then it was achieved using HP air.
Richard
(Southampton UK)
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