From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Test report on John Graybler Aero Sparking Plugs submitted by Sir Malcolm Stewart.
| Identifier | ExFiles\Box 27\3\ Scan179 | |
| Date | 27th September 1939 | |
| 8 To - Sg.{Arthur F. Sidgreaves - MD} Copies to - Hs.{Lord Ernest Hives - Chair} Rm.{William Robotham - Chief Engineer} JOHN GRAYBLER AERO SPARKING PLUGS SUBMITTED FOR TEST BY SIR MALCOLM STEWART. We have now tested these plugs under the following conditions :- They were first placed in our Single Cylinder engine and run under fairly light load conditions for 2 hrs. at 2400 RPM. with a BMEP. of 173 without any trouble at all. Upon increasing the load as soon as a BMEP. of 180 was reached at the same speed violent preignition occurred resulting in a forced stoppage of the engine. The plugs were removed from the engine and a set of standard Lodge plugs fitted type RS.{Sir Henry Royce's Secretary}3's and the engine ran very steadily under full load conditions approximating 195 BMEP. As it was considered that the heat factor of these plugs was not suitable for the engine in question the plugs were then placed in a Merlin Single Cylinder Unit and pre-ignition occurred almost immediately at very low BMEP's. The plugs were therefore removed from the engine and examined for gas leakage and this was found to be excessive being in the region of 25 ccs/min. In view of this extra leakage we are of the opinion that the cause of the plugs preigniting on the engine was due to excessive gas leakage which gradually increased, thus lowering the heat factor of the plug. The design of the plug has several very interesting features and providing the gas leakage trouble can be solved we shall be pleased to carry out further tests. ---------- Plugs handed to Sg.{Arthur F. Sidgreaves - MD} at Duffield Bank House. Lr{Mr Ellor}/Wst. | ||