SIMPLE MICHAICS
Page 46
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The compression ignition engine, 4
THE TWO main differences between the petrol and the compression ignition (diesel) engine are the way in which the fuel is introduced into the cylinder and the way in which the fuel is ignited. In the petrol engine an electric spark ignites the fuel, whereas in the diesel the high temperature of the air, brought about by the high compression, is responsible for the ignition. The fuel, in the case of the Cl engine, is injected into the cylinder by a highly sophisticated system and it is this fuel injection equipment which I shall be discussing in this and subsequent articles.
The -in-linepump, an example of which is illustrated in Fig 1, has been used on diesel engines since the very early days. Fig 2 show a pump of this type fitted to a Gardner engine installed in a vintage Scammell chain-driven tractor as used by showmen. The pump is generally fitted on the side of the engine and because there is only one power stroke for every two revolutions of a four-stroke engine, the pump is driven at half engine speed directly from the timing gears.
The pump consists of a series of separate pumps, usually called elements, one for each cylinder on the engine, eg a six-cylinder engine will be fitted with an injector pump with six separate elements.
A section through a "Minimecpump appears in Fig 3, which is reproduced by kind permission of Messrs CAV Ltd. It will be seen that the element consists of a plunger and plunger barrel, a delivery valve, a control fork which is connected to a control rod, return
spring, tappet roller and camshaft.
Rotation of the camshaft produces a vertical movement of the plunger, while further rotation of the camshaft lobe per
rpumping plunger tt r!nvvards by the actior (Anger return spring is repeated on eacl r of the camshaft. Di enrard stroke of thi uel is pumped througl iry valve at the top o I and thence througl or pipes to the injecto into the cylinder
obviously, means rnus led to vary the amoun jected into the cylinde variations in engin! nd speed can be pro d the method employei re this will be describei !xt article in this series.
e right of the illustratioi it will be seen there is . d pump which. supplie Ti the tank to the injec 'op. This particular typ ip is also fitted with . or, auto advance cou nd a boost control. Th. evice restricts maximun livery on turbochargel
s at low engine speed iv throttle openings whei ost provided by the turc ger is reduced, thu ing the possibility of • exhaust.
re about fuel injectioi ent in the next article.
• by Precept°