'Sea-going launch for the Political Agent, Bahrain. Corr. re: Kelvin Engine.' [‎1cr] (7/398)

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Introduction
^ In designing these engines we have considered it desirable to avoid certain X *
features common to some engines already on the market. One of these is the q/V
injector nozzle with a number of very small holes ; another is the use of accumulated airy
, ,or electricity f or starting ^ a third the lack of sufficient access to internal parts!
In petrol engines the air and fuel are mixed before entering the cylinder. In Diesel
engines the air is within the cylinder before the fuel is injected and to mix them
thoroughly in the short time available is the major part of the Diesel problem. In
large engines this is usually accomplished by blowing the fuel into the cylinder by
means of air. The high pressure necessary involves a pump so elaborate that most
makers are endeavouring to adopt airless or solid injection,
Solid injection engines are of two types—those in which the air within the com
bustion chamber is stagnant at the time of injection and those in which the air is in a
state of turbulence. ^
Perfect combustion entails bringing the fuel in contact with sufficient air. To
accomplish this in a stagnant combustion chamber requires a nozzle with several holes
pointing in different directions, and to penetrate the highly compressed air the fuel
pressure must be very high and the holes so small as to be scarcely visible or capable
of being cleared, v
The combustion chamber which we employ produces so high a degree of turbulence
that it is possible to use a single nozzle of practical size and a fuel pressure which
imposes no undue load upon the pumps.
Owing to the high compression employed, the starting of Diesel engines has proved
quite a problem. Some small engines are started by vigorous cranking; larger engines
rely entirely on accumulated air or electricity. As it is difficult in practice to avoid
leakage of air or electricity we do not consider either system sufficiently reliable
for an engine on which life sometimes depends. After much research and experiment,
we have evolved a system of starting by hand and petrol . It is simple and, being part of
the engine, avoids the numerous accessories necessary to air or electric systems.
Any engine which depends for starting heat solely on compression is liable to
become a non-starter when slightly out of condition. The pre-heating effect of
petrol completely avoids this ris k.
As a rule, good accessibility to internal parts is not sufficiently considered at the
time of purchase. In most Diesel engines of the size under consideration the adjustment
of the bearings involves lifting the upper part of the engine, and, while this is no great
disadvantage to an engine on land, it is intolerable in a marine engine as these are practi
cally built into the vessel. Should bearing trouble develop in such an engine, the work
of rectifying it is quite beyond the power of the man in charge and the vessel is disabled.
Our aim has been to produce an engine which may be completely serviced in position.
In the matter of cylinder wear, Diesel engines up till now have been inferior to
petrol engines . This is caused by the high gas pressure forcing the rings against the
cylinder. As it seems impossible to avoid the cause, we have considered it necessary
to fit hardened cylinder liners and hardened piston rings.
It is common practice to expose the outside of the cylinder liner to the cooling water.
This entails a soft joint and, should the engine become overheated , this j oint shrinks and
ad mits water to the crankcase. To renew the joint entails dismantling most of the
engine. In our design the liner is not exposed to the cooling water.