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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).
Ignition experiments for a 25HP engine, focusing on distributor and spark plug performance.

Identifier  ExFiles\Box 178\3\  img191
Date  30th May 1932
  
HS{Lord Ernest Hives - Chair}/WST. FROM R.{Sir Henry Royce}
C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} BY.{R.W. Bailey - Chief Engineer}
C. to PN.{Mr Northey} E.{Mr Elliott - Chief Engineer} RM.{William Robotham - Chief Engineer}
WST ORIGINAL. R2/M30.5.32. *6095.

25HP. IGNITION.

While at Le CanadelHenry Royce's French residence we made several experiments on the 25HP. ignition, one or two by Dodd, but chiefly by GWH.{George W. Hancock - Head Chateauroux}

(1) We cut off the tail of the distributor to prove whether at slow speed it might not be firing the cyl. behind the proper one, but however it made no difference.

(2) Many experiments were made to prove whether the grouping of the wires in the single ignition tube was, or was not, causing mutual induction between the wires. There was no advantage in well separating the wires.

(3) We had available two types of plug - a single point Lodge with porcelain insulation, and a 3 pointer KLG. with mica insulation and a very substantial central electrode.

The single point Lodge was the one that failed in every instance. The 3 point KLG. although opened to .030 still gave satisfaction.

As far as we could gather from the experiments the whole trouble is due to the oxidisation of the plug contacts, but there is just a slight doubt as to whether it may not be due to the insulation failing inside the plug.

The KLG. plugs here mentioned appear to be extremely good and I should like you to send me 2 or 3, so that I may test them on my electric light engine, which naturally overheats and oxidises the plugs unless I use doped fuel. The car engine here is now running with small size plugs (14 mm.) so I cannot test this particular plug of 18 mm. on the car.

A feature about this ignition trouble is that it only occurs at very low speed when the throttle is opened wide for acceleration. It has lately come to my mind that the reason it fails at the very low speed only may be that the automatic timing of the ignition at these low speeds causes the spark to occur practically at T.D.C. when the compression is at its maximum, whereas at a higher speed the spark occurs before T.D.C. is reached, where the compression pressure may be much lower. This could easily be demonstrated when one knows what to look for.

R.{Sir Henry Royce}
  
  


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