History of the Diesel Engine

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History of the Diesel Engine

Origin of the Diesel.–Dr. Rudolf Diesel, a German engineer,
designed an engine to operate on the Carnot cycle, which calls for
the heat to be added at the highest temperature and thrown away
(exhausted) at the lowest temperature. In this engine the air
charge on the compression stroke was to be compressed to a
pressure such that the resulting temperature was above the
ignition temperature of the fuel. The fuel was to be introduced
into the cylinder at a rate such as to cause the work performed
on the moving piston to absorb enough of the heat of combustion
to keep the temperature constant. This would cause the
cylinder temperature to remain constant during the period of
fuel introduction extending over some 10 per cent of the piston
stroke. After “cut-off” the gases were to expand adiabatically
(without absorbing or losing any heat save that consumed in
doing work). The compression of the air charge was to be at
constant temperature (isothermally) for part of the stroke,
followed by adiabatic compression (no heat lost). The engine
was originally designed without water-jacket cooling since there
was to be as little heat loss as possible.
The original patent, dated 1892, outlined an engine wherein
the fuel used was to be pulverized coal or coal dust. This coal
was to be stored in a hopper immediately above the engine
cylinder head. Between the hopper and the cylinder was inter-
posed a rotary valve having a cavity or pocket. The valve
received a charge of coal dust and in rotating in its seat came in
communication with cylinder. The coal dust then dropped into
the combustion space as the piston reached the end of the
compression stroke. The fuel charge was to be varied to suit
load conditions through the governor control of the valve
movement.
Another interesting feature was the proposed introduction of
a water charge at the beginning of the compression stroke for
the purpose of securing isothermal compression during part of
the stroke.
A second claim embodied in the same patent covered the use of
liquid fuels with the employment of a spraying valve but without
the air-injection feature. The engine was to be started by some
explosive agent in the cylinder for the initial stroke. The expan-
sion was to be carried to such a point that the exhaust gases were
to be cold enough to be used as the cooling medium in the cylinder
jacket.
An engine was constructed along these lines but never turned
over beyond the initial stroke, during which it was completely
wrecked. At this late date no information seems available as
to the cause of this wreck, but it is to be presumed that the start-
ing charge of explosives was the destructive agent.
This disappointment caused the builders of this engine to
abandon Dr. Diesel’s original ideas, and a water-cooled engine
was built in which the admission of heat was at constant pressure
instead of at constant temperature as originally contemplated
by Dr. Diesel. The first of these later engines actually ran but
never was able to carry any load, due to the fact that isothermal
combustion gave too little power to overcome friction. Ulti-
mately, alterations were made which transformed the experiment
into a practical machine.
The development of the Diesel proceeded slowly for some time.
Various modifications were introduced in the engine which was
built at the shops of the Maschinenfabrik of Augsburg; this con-
cern in conjunction with Krupp bore the expense of the experi-
ments carried on by Dr. Diesel and Ing. Vogel. It was not until
1897 that a commercial engine was produced, which was a single-
cylinder 25-hp. engine of vertical design and using a crosshead.
This was followed by the exhibition at Munich, 1898, of three
Diesels by the M. A. N., Augsburg, by Krupp, and by the
Deutz Company.
Starting with the modest powered engine of 25 hp. it was but
a question of a relatively few years before engines of 1,000 hp.
were in commercial use. The engine was patented in practically
every country, and for a few years all European manufacturers
operated under a license; this, however, was discontinued
around 1904, and but few manufacturers paid royalties. The
popularity of the Diesel engine in Europe has been due to a
large extent, to the type of manufacturer building these engines
and to the high cost of fuel. In Germany a number of the strong-
est steam-engine builders, having the facilities to do the extensive
experimenting necessary, soon took up this engine. In Switzer-
land and the Scandinavian countries the engine found early favor.
The British Diesel Engine Company, even when the engine
temporarily fell into disrepute in Germany, continued its
labors, and much credit for the successful outcome of the diesel,
usually attributed to German firms, actually is due to the
activities of the British manufacturers.
The Ackroyd Cycle.–The engineer will conclude, after finishing
this volume, that the engine now marketed as the Diesel does
not follow Dr. Diesel’s theories. Since Charles Ackroyd Stuart,
long before Diesel’s treatise, had patented an engine in which the
air charge only was compressed in the cylinder, the fuel being
introduced by a pump,  and ignited by the heat contained
in the air charge although assisted by a hot vapor ,it would
seem that the cycle could  properly be termed the Ackroyd
cycle. True, Stuart employed a low-compression pressure and
depended upon the hot walls of the cylinder to raise the tem-
perature to the ignition point of the fuel, but he was the first to
advocate the compression of pure air and the ignition of the fuel
by the cylinder temperature without the aid of an electric spark.
Having made his engine prior to Dr. Diesel’s work, there are
many who claim that the latter used the Ackroyd engine as the
basis of the rational heat motor.
The Diesel Principle.–As has been outlined, the chief point
which distinguishes the Diesel from other forms of the internal-
combustion engine is the compression of a charge of air until the
resulting high temperature is sufficient to ignite the fuel without the
aid of any external object. The fuel is forced into the cylinder
by a blast of high-pressure air coming from an air compressor.
At the present time there are a number of oil engines manu-
factured both here and in Europe which, while using a fairly
high compression sufficient to secure ignition of the fuel, do not
operate on the Diesel cycle but on what is a combination of
combustion at constant volume (the Otto cycle) and at constant
pressure (the Diesel cycle). These engines do not make use of
an air blast as the means of oil injection, but depend, instead, on
a direct pump action. For this reason, they are familiarly
known as “solid-injection” oil engines and have also been
called “dual-cycle” engines on account of the constant volume
and constant pressure combustion, as well as “mechanical-
injection” and “pump-injection” Diesels.
The features which set the true Diesel apart from other oil
engines are (a) compression sufficient to produce autoignition
of the fuel; (b) injection of the fuel by an air blast; (c) combustion
with practically no change in pressure from the maximum com-
pression pressure.

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