Injection Equipment and Performance
Page 29
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VESTERDAY, Mr. H. G. Dunn, M.I.A.E , engineer of the fuel-injection division of Simms Motor Units, Ltd., East Finchley, London,' N.2, read before the Institution of Road Transport Engineers, an interesting paper dealing with fuel-injection equipment and its influence on the performance of oilengined road vehicles. Mr. Dunn points out that the duty of the fuel injection system is to deliver to the combustion chamber at the correct time, rate, ;.:nd degree of dispersal, the exact amount of fuel required to burn the available air. On an average engine running at 1,800 r.p.m., this process of injection takes about 1/450 sec., and it must be repeated many millions of times a year throughout the life of the engine, observed the speaker.
Dealing with some design features, the author revealed that the clearance between a pump plunger and its barrel is about 0.00004 in. Contrary to common belief, he said, wear is not caused by metallic contact, but is mainly brought about by minute particles of dirt which may bridge the small clearance space and scratch the highly finished surfaces. This point emphasizes the importance of efficient filtration of the fuel oil.
Importance of Timing Mr. Dunn said that. incorrect timing of injection, in relation to the cam contour, as well as timing in relation, to the engine crankshaft, can have a marked effect on engine power and fuel con sumption. . •
Referring to governors, the author,said that of the various types—centrifugal, pneumatic and hydraulic—each has its advantages for certain applications. The most vital, and Probably the most neglected, item in the system is the injector. It has the most arduous duty, he said, of forming the correct spray patternin the combustion chamber under conditions of extreme heat, high pressure, and contamination by carbon. . .
It is easy to assume that the most important function of a nozzle valVe is to open at a predetermined pressure to adroit the fuel spray, and to forget that a still more important function is for it to close, at a given pressure, Mr. Dunn emphasized.