Diesel Musings

By Staff

1102 Box Canyon Road Fallbrook, California 92028

This little visit is to dwell upon some of the wondrous
developments of internal combustion engines during that innovative
period near the turn of the century when many people wondered if
there would really be any other prime moving power to relieve the
loads placed upon the old steam engines during that period.

You may recall that much experimenting had been conducted with
early ‘gas’ engines, some of which burned natural or
artificial gas, as well as vaporized liquid fuel oils. But these
forerunners usually relied upon breaker points or spark plug points
within the cylinder to ignite the gas sified fuel charge at the
beginning of each power stroke. Both ‘carburetion’ or
vaporization of the liquid fuels as well as the sparking ignition
apparatus were the big stumbling blocks in these early attempts to
do away with steam boiler response time, low efficiency, and water
impurity troubles which gave rise to higher maintenance problems.
Steam was still most reliable, of course, and is just about that
even today.

But we must doff our hats to the English, French and German
engineers in those early works. The Italians were not far behind.
So it was at that time that Rudolph Diesel of Germany gave birth to
the idea that a gaseous charge within the working cylinder could be
ignited by the adiabatic heat of compression. Or nearly to that
point as we shall see. He must have studied the phenomenon of
production of heat as a byproduct when a gaseous substance was
suddenly compressed within a closed cylinder. We youngsters
discovered that when pumping up our old bicycle tires by hand; but
we did not carry the idea beyond. Rudy’s ‘invention’
was so promising that it has been attributed to the cause of his
‘mysterious’ disappearance while travelling to England from
Germany to discuss his works before a society of engineers. His
idea lived on to a perpetual commemoration of his genius.

Oil was not so common in Rudy’s day, so he had contrived to
utilize coal dust in his first engine. The principle was simple: he
merely compressed a charge of air in his engine until sufficient
heat was generated to ignite a measure of coal dust that was blown
into the cylinder at the beginning of the power stroke. Now that
was a real ‘solid injection’ engine, also of the ‘air
injection’ type.

It is not my intention to discuss the mathematical and physical
equations relating to the amount of heat raised during such
compression cycles, nor the measure of terminal pressures arrived
at, since these have been previously discussed in various articles.
Suffice it to say that, if the volume of an enclosed gas is
suddenly halved, its terminal pressure will not simply be doubled,
but increased by an exponential value depending upon the nature of
the gas itself. For we are doing work on the gas by compressing it,
and that work must also show up as an accelerating factor. If the
work is sudden enough to prevent loss to the enclosing container,
the compression is said to be adiabatic. If the work is slow enough
to allow absorption of increased heat to the container, we are in
the realm of isothermal compression, which would result in a lower
final pressure and of course no rise in temperature to ignite any
fuel charge.

We find that, for sufficient ignition temperature in such
engines, an actual compression ration comes to about 22 to 1. This
yields a final pressure of approximately 500 psi gauge. Thus,
following up on Rudy’s original conceptions, air injection
engines required a sufficient injection pressure to assure blowing
of the liquid or solid fuel into the cylinder against the terminal
compression pressure by an excess of some 100 psi. In present day
power plants we find in utilizing this type of engine that the
injection ‘bottles’ carry about 600 psi, while the starting
bottles may carry up to 100 psi for reserve; since these engines
are usually started by air pressure also. Thus each cylinder
usually has at least four valves: the air intake, the exhaust, the
fuel check, and the starting valves. A pressure relieve and
auxiliary valve/plug is also usually incorporated. The latter may
have provision for insertion of a burning cigarette or other
‘punk’ to assist in ignition in event of real cold inlet
air temperature when starting.

In this type of engine, the fuel charge is distributed to the
fuel inlet valve during the exhaust stroke of that cylinder. This
allows sufficient time to help avoid drizzle, etc. The 600 psi
injection air pressure is of course on the engine all the time. The
air injection valve must begin opening then at the beginning of the
power stroke. The exhaust valve operates conventionally, while the
starting valve is cam operated only during that initial period of
turning the engine over. The injection pressure must not be
maintained too high above 600 psi, else the added cooling effect of
its expansion down to 500 psi may cause starting problems.

But now we come to ‘hot build’ types of
‘semi-Diesel’ engines. To avoid such high compression
pressures, designers cut the compression to approximately 225 psi.
This necessitated additional heat for fuel ignition, which was
secured initially by torch heating an uncooled portion of cylinder
head projection or appendage. After starting, this uncooled bulb
retained enough heat to continue ignition. These engines were also
called ‘hot’ head engines; and no doubt many engineers
became likewise over starting problems.

Another development to simplify construction and operation was
the introduction of so-called ‘solid-injection’ principles.
This term is a misnomer, but it stuck, like nominal plumbers’
pipe threads and diameters, as well as many electrical and other
mechanical mistakes. We find this in smaller Diesel type engines,
and now particularly in automotive power plants all the way from
cars to locomotives. In this sort of engine, which cannot burn its
fuel so efficiently and cleanly as the air-injection type, we find
that, while the terminal compression pressure still is about at 500
psi, the liquid fuel is mechanically injected at the beginning of
the power stroke. The fuel injection pressure at this moment may be
up in the several thousands of psi for its time of duration is very
short in the comparatively high speed engine. Note, I have called
out a misnomer. Elements are normally declared to exist in three
physical states: gaseous, liquid, and solid. Now, other than
Rudy’s coal dust engines, by no means can fuel oil be described
as ‘solid.’ But we are stuck with it.

Next comes another deviation of the solid injection engine for
tractor purposes. This consists of substituting a spark plug with
all its accoutrements in lieu of the hot bulb. We have quite a
combination of the regular gasoline engine with the Diesel engine.
And some farmers have found favor with them, while others have even
sworn off drinking.

Oh yes; I might have mentioned that, aside form an auxiliary air
compressor plant in the case of the air injection power plant, the
pressures are maintained during operation by a three-stage
compressor built in as part of the engine itself.

I have worked with, and studied Diesel engines for some sixty
years, along with my regular and principle electrical engineering
work. At age 81, I find both as interesting and intriguing as ever.
At one time during the Great Depression, I even had a hand in
teaching Diesel engineering in a prominent vocational school. And
of course I am very proud of my steam railroading experience while
yet a very young chap; for at one time I could shovel thirty-five
tons of coal during an eight-hour period. The dear old railroad
shops were at a division point of the C & NW, where engines
running to the east burned coal; while those destined westward
burned oil. How many times I crawled into hot fireboxes when, if
one would spit on the grates, it would boilingly flash up into your

My first Diesel experience followed closely thereafter, when I
became operating engineer during construction of one of the newer
highway bridges across the Missouri river. The engine driving the
all-necessary air compressor was probably the finest I have ever
seen,a Worthington three-cylinder ‘solid injection’ job.
This remarkable animal was a two-stroke design; but unlike the
crankcase compression variety, had a lower cylinder head and seal
together with crossheads, similar to a steam engine. The exhaust
ports were simply openings in the lower portions of the vertical
cylinders; while the intake valves (one into the enclosed lower
cylinder head space, a second from this compression space to the
lower port of the cylinder) much like conventional two-strokers. In
this construction, the force is continually downward on the piston
rod and connecting rod. An engine of this type was known to
continue operation without trouble with a broken piston rod. Not
until shutdown and inspection was the break discovered. Also, this
design operated without the detonation knock so common in
automotive engines. For the terminal combustion pressure was not
allowed to rise considerably above that necessary for fuel
ignition. One of those engines had established a world record for
continuous faultless operation in those dear old daysover a year as
I recall!

My greatest embarrassment during this particular experience was
while performing a cleanup maintenance during a shutdown spell, I
installed three of the ‘feather’ intake valves backwards
(they were mounted in reversible grid plates). Try, try, again.
Then the super came in, and we both proceeded to light cigarettes
and stuff the burning butts into the auxiliary starting plugs, but
still no run. It was only after much puzzlement upon the parts of
both the super and myself, that we finally removed the valve grid
retainer covers and discovered my foolish error!

In closing, it may be worth mentioning that, while in big
stationary Diesel power plants the combustion pressure is
controlled to very little more than ignition pressure, the practice
in small automotive work is to run the combustion pressure up
similar to that of the gasoline explosive types. This gives rise to
the ‘ungodly’ clanking noise which is enough to drive most
people away from the Diesel powered cars, in spite of their higher
efficiency. So now, good bye, good fellows, until I may be moved to
write again. (I am anxiously awaiting arrival of the new computer
with its most remarkable convenience of ‘word

Gas Engine Magazine
Gas Engine Magazine
Preserving the History of Internal Combustion Engines