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Aviation History
1950
1950 - 0694.PDF
6 APRIL 1950 Contributing to sleeve-vulve fuel O-5O O-48 O-46 O O-44O i y u. O O42 O-4O 8. 040 5OO 6OO IIOO I2OO THE REDUCTION IN SPECIFIC FUEL CONSUMPTION DOE TO THE •BRISTOL" AUTOMATIC IGNITION ADVANCE MECHANISM (CONSTANT R.PM.,VARYING BOOST.) Variable ignition tinting engines power the majority of British airliners in current production, Ignition timing has an important influence on the combustion efficiency, and hence the fuel consumption of an engine. On "Bristol" sleeve-valve engines the optimum ignition timing for each engine operating condition is automatically effected by the use of a variable ignition timing mechanism, which is linked with the fuel injector to give advancement of ignition with reduction in selected boost pressure. The value of this arrangement is illustrated by the accompanying curves, from which the advantage of variable ignition timing is readily apparent. Movements of the injector control lay- shaft produce longitudinal movements of the sliding spindle in the timing control mechanism (see diagram). The spindle is splined to the crankshaft driven spur gear. The spindle also carries helical splines engaging with the magneto driving bevel, so that longitudinal movements of the spindle cause angular displacements of the magneto driving bevel relative to the spur gear. In this manner, the ignition timing is varied to suit the particular engine operating condition selected. THE B BIST O L AERO P L A N E COMPANY LIMITED F. K f, L A N 89C
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