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).
Complete specification for improvements to combustion chambers in internal combustion engines.
| Identifier | ExFiles\Box 147\4\ scan0149 | |
| Date | 20th January 1940 | |
| 2 COMPLETE SPECIFICATION Improvements in or relating to the Combustion Chambers of Internal Combustion Engines I, WILLIAM ARTHUR ROBOTHAM, of Park Leys, Duffield, near Derby, England, a British Subject, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:— This invention is for improvements in cylinders of internal combustion engines and applies to that type of cylinder in which there is a combustion chamber arranged in the head of which one portion is arranged wholly or principally above and open to the cylinder bore and has in its base an exhaust valve, the two portions communicate by a throat portion and the top of the cylinder where not open to the inlet portion is covered by a wall normal or approximately normal to the axis of the cylinder. A cylinder with a combustion chamber so formed is hereinafter called “a cylinder of the said type.” This invention has for its object to increase the compression ratio in the combustion chambers of cylinders of the said type while avoiding serious detonation. According to this invention an internal combustion engine with a cylinder of the said type has a protuberance on the piston crown which at top dead centre passes up into the combustion chamber but not more than two thirds of the way up into the same and masks the mixture lying in the space between other parts of the piston crown and the said projecting portions of the cylinder head from the mixture in the combustion chamber. In using the expression “masks” I mean that there will be no straight passage between any two particles of mixture one of which is in the combustion chamber and one of which is in the said space unless the said particles are close to the extreme adjacent edges of the said combustion chamber and space respectively. I believe that the effect of such construction is to prevent any detonation wave which occurs at top dead centre in the combustion chamber reaching the gases in the said space since such wave would have to turn through two angles one over the rim of the said protuberance and one under the said projecting portions of the cylinder head. I do not wish to commit myself to the theory that it is the localisation of the detonation wave as aforesaid which secures the benefit of this invention but I have found that by so forming the combustion chamber advantages are secured and that using a fuel which would be suitable with a flat top piston and, for instance at 6:1 compression ratio, the compression ratio can be raised to a figure in the neighbourhood of 8:1 without increase of intensity of detonation. Preferably the walls of the combustion chamber where these spring from the said projecting portions of the head and the walls of the said projection adjacent to such last mentioned walls are both normal or substantially normal to the said projecting portions of the head and these two sets of walls lie close together so as to leave a comparatively small space between them. Preferably the top of the said protuberance is in a plane inclined from a position normal to the axis of the cylinder toward the centre of the combustion chamber. The protuberance is preferably shaped so that on the side of the combustion chamber lying to one side of the cylinder, the walls of the protuberance are a continuation of the walls of the piston or lie slightly within the same and are parallel with the axis of the cylinder. An example of this invention is illustrated in the accompanying drawings. Figure 1 is a section through a cylinder according to this invention with the piston shown in elevation. Figure 2 is a plan view of the cylinder there illustrated. A is a cylinder in which reciprocates the piston B the piston rings of which are at B¹. At the top the cylinder head has a portion with walls normal to the axis these walls being shown at C. A combustion chamber E is formed in the head lying partly to one side of the cylinder and this part houses the exhaust valve E¹. The inlet valve is shown at E² and the ignition plug at E³. The combustion chamber is arranged in the manner described with reference to Figures 1, 2 and 4 of the Specification of Letters Patent 505,895. A protuberance F is formed on the crown of the piston B shaped in plan as shown in Figure 2, which also shows the shape in plan of the combustion chamber E.{Mr Elliott - Chief Engineer} The top of the protuberance is cut away so as to incline it slightly toward the centre of the combustion chamber. It will be seen that the protuberance F leaves only a small clearance between itself and the vertical walls of the combustion chamber where these overlap the cylinder bore and spring from the projecting portions C of the cylinder head, that is to say to the left of the points marked “Y” in Figure 2, and elsewhere, that is to say to the right of the points marked “Y,” only a small clearance is left between the walls of the protuberance F and the walls of the cylinder bore. It will be seen that there is no straight pathway between any two particles of gas one of which is in the combustion chamber and one in the space between the projecting portion C of the head and the top of the piston B unless these two particles are close to the adjacent edges of each of these two masses of gas and lie immediately above and immediately below the space between the walls of the said protuberance and the walls of the combustion chamber. The effect of this as I believe is that any detonation wave which is generated at top dead centre in the combustion chamber is confined to the combustion chamber and will not affect the gases between the projecting portions of the cylinder head and the top of the piston. Owing to the fact that the walls of the combustion chamber and of the protuberance are parallel with each other and with the axis of the cylinder, the masking effect is maintained during the initial movement of the piston away from top dead centre until the protuberance has moved out of the combustion chamber. Owing to the fact that at top dead centre the highest point of the protuberance (at the left hand side) on the piston is not more than two thirds of the way up into the combustion chamber a substantial space is left between the top of the protuberance and the top of the combustion chamber for combustible mixture which I have found to be an advantage. Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:— 1. An internal combustion engine with a cylinder of the said type with a protuberance on the piston crown which at top dead centre passes up into the combustion chamber but not more than two thirds of the way up into the same and masks the mixture lying in the space between other parts of the piston crown and the said projecting portions of the cylinder head from the mixture in the combustion chamber. 2. An internal combustion engine as claimed in Claim No. 1 in which the walls of the combustion chamber where these spring from the said projecting portions of the head and the walls of the said protuberance adjacent to such last mentioned walls are both normal or substantially normal to the said projecting portions of the head. 3. An internal combustion engine as claimed in Claim 2 in which the two sets of walls lie close together so as to leave a comparatively small space between them. 4. An internal combustion engine as claimed in Claim Nos. 2 or 3 in which the top of the said protuberance is inclined from a position normal to the axis of the cylinder toward the centre of the combustion chamber. 5. An internal combustion engine as claimed in Claim 4 having a combustion chamber as described in Letters Patent 505,895. 6. An internal combustion engine with a cylinder of the said type and a combustion chamber and a co-operating protuberance on the piston crown substantially as described with reference to Figures 1 and 2 of the accompanying drawings. Dated the 20th day of January, 1940. CLAREMONT HAYNES & CO., Vernon House, Sicilian Avenue, Bloomsbury Square, W.C.1, Applicant’s Solicitors. Leamington Spa: Printed for His Majesty's Stationery Office, by the Courier Press.—1940. | ||