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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).
Design of a P.2 semi-expanding carburetter, including historical context and solutions for snap acceleration.

Identifier  ExFiles\Box 13\3\  03-page395
Date  12th March 1932
  
E.{Mr Elliott - Chief Engineer} HS.{Lord Ernest Hives - Chair}) FROM R.{Sir Henry Royce}
BY.{R.W. Bailey - Chief Engineer} ) (At Le CanadelHenry Royce's French residence.)
C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} HS{Lord Ernest Hives - Chair}/LOV.{Mr Lovesey}
C. to RG.{Mr Rowledge} PN.{Mr Northey} EP.{G. Eric Platford - Chief Quality Engineer}

17080
R2/My.3.32.
Sent from WW. 12.3.32.

REC'D 11 NOV 1932

CARBURETTERS GENERALLY.
P.2. SEMI-EXPANDING CARBURETTER.

I thank HS.{Lord Ernest Hives - Chair} for his memo. of 3. 3. 32.

(1) We all agree to a single carburetter for cars as preferable for ordinary use.
(2) That it need not be completely expanding, or even down to our past standard.
(3) My original attempt was much more like the SU. but I did not at that time think it practical enough, and in 1904 - 6. used a single jet with our special double piston air valve. From 1906. onwards we used our double jet, which is still standard, but should give way to something else that is better.
(4) Claudel and others have introduced the emulsion jet, and throttle edge; both of which we think are too good to leave out of an up-to-date design.
(5) On my suggestion Derby have found how far they can go with fixed jet with these No. (4) improvements, and they say 50% of full HP., after which the carburetter should be expanding. This is our idea and we think it is about the best, because it leaves the delicate adjustments permanently fixed, and there will therefore be no change in these with wear.

In the design we have made we are troubled with a few features not being quite right. I expected this, but we shall get them alright in a few weeks.
HS{Lord Ernest Hives - Chair}/LOV.{Mr Lovesey} shews us that we must take throttle edge petrol from the diffuser side of the restriction. E.{Mr Elliott - Chief Engineer} will be making this right.

SNAP ACCELERATION.

I thought we might need a displacer pump to give extra petrol at throttle opening, and rob the supply at closing - i.e. backwater displacer plunger on engine side of restriction, but I prefer our old scheme of delay of extra air valve movement, if this will do it.

Mr. Elliott's delay actions I understand to refer to lap, as we use in our present standard. Mine refers to the sluggish movement of the valve and piston, which I think would be better, though we can have a little of each, but lap loses motion, which is a loss of efficiency in the space at our disposal.

(1)
  
  


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