Cold start up and run and shut down of a rather large 3 cylinder Blackstone spring injection open crank diesel engine.
In the mid to late 1920s most other manufacturers of large oil engines were using pneumatic or 'air blast' fuel injection. Fuel oil was injected into each cylinder with compressed air, at around 800 to 1,000 psi, from an air bottle or receiver. The air blast provided atomisation of the fuel and turbulence to ensure an even distribution of the air and fuel mixture. Maintaining a high pressure air supply required a compressor which typically absorbed about 5% of an engine's power output.
In 1924 Blackstone & Co Ltd of Stamford introduced their patented 'spring injection' device, a form of what is termed mechanical, solid, or airless injection, which was incorporated in their horizontal oil engines. A metered quantity of fuel was delivered by a governed pump at about 10/15 psi to a chamber on the cylinder head, where it was totally confined and only subjected to pressure immediately prior to injection. Injection occurred at about 1,000 psi and produced a prolonged and almost perfect combustion. Benefits claimed for 'spring injection' included lower fuel consumption at all loads, a clean exhaust, and efficient functioning even at very low engine speeds. A more detailed explanation of its operation is given below.
Spring injection was developed by two brothers, Frank and Evershed (known as Tod) Carter who worked for Blackstone & Co at Stamford. Frank and Tod were responsible also for a number of other innovations in oil engine design and became respectively Works Manager and Chief Engineer at Blackstone.
What follows is a summary of some of the advantages of the system and an explanation of its operation.
The advantages of "Spring Injection" were summarised in a Blackstone catalogue as being:
It dispenses with the high pressure oil system and its attendant troubles. Instead - a measured quantity of fuel is delivered by a governed pump, at a pressure not exceeding 10/15 lbs. per square inch, to a chamber on the cylinder head where it is imprisoned and only subjected to pressure just prior to injection.
Injection takes place at a pressure of approximately 1000 lbs. per square inch instead of the abnormally high pressure usually employed. This produces a prolonged and almost perfect combustion with the following highly important results:-
A low initial pressure coupled with a high mean effective pressure, reducing shock and strain upon the working parts to the absolute minimum.
A consistently low fuel consumption at all loads.
A clean and almost odourless exhaust enabling the engine to be employed in many places hitherto barred to oil engines (as for example - dairies, food product factories, laundries, cotton mills, etc.).
The operation of the "Spring Injection" device is in no way affected by the engine speed - it functions perfectly whether the engine be just turning over or running at several hundred revolutions per minute. It is this characteristic that enables us to vary the speed of the Blackstone engine under load.
The oil suddenly escapes past the injection valve at full pressure, enters the combustion chamber in a steady jet and is then as suddenly cut off. The effect of this action is to obviate the dribble at start and finish that seems to be unavoidable with cam injection.
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