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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).
Analysis of a direct injection combustion chamber and multi-hole nozzle from the National Gas & Oil Engine Co.

Identifier  ExFiles\Box 134\1\  scan0144
Date  18th March 1939
  
1129?

Rm.{William Robotham - Chief Engineer}.. from Da{Bernard Day - Chassis Design}/AM.

Da{Bernard Day - Chassis Design}/AM.1/N.18.3.39.

Information obtained from Mr.Blea, late of the National Gas & Oil Engine Co. now at Rolls-Royce.

The National Co. use an open (Direct Injection) combustion chamber because it gives the best fuel consumption.

The admitted drawbacks to this type are that it cannot be run at high M.E.P's with a clear exhaust; it is a rough, noisy engine; and it gives rise to high cylinder pressures. Mr. Blea's personal opinion is that such an engine would be contrary to the Rolls-Royce tradition of smoothness and silence.

The combustion chamber form is as sketched below.

[Handwritten initials 'Jm{Mr Morley}' or 'Am' over a sketch of a piston crown combustion chamber]

A multi-hole nozzle is used and the angle of spray is such that the jets are directed towards the change of curvature of the piston hollow. Initially the holes were about .010" diameter. Progressively the size has been increased, to diminish trouble with nozzles choking up due to carbon formation, up to the present size of .020". The B.M.E.P. attained in their 8" x 12" four cylinder engine is 85 lb/in², and the fuel consumption is .365 lb/B.H.P.Hr.

The multi-hole nozzle is the least desirable type, but is necessary in the interests of fuel economy in a direct injection engine. Pintle type nozzles are most satisfactory, where they can be used, inasmuch as they never fail completely. Efficiency falls off after a time due to erosion of the projecting nib of the valve plunger. Another practical disadvantage is that this nib is liable to be damaged by having a

Cont'd....
  
  


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