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).
Investigation into engine knock characteristics, analysing flame movement and pressure variations using oscillograms.
| Identifier | ExFiles\Box 63\2\ scan0076 | |
| Date | 27th April 1935 | |
| 582 Engine Knock Characteristic IN the course of an investigation of flame movement within a gasoline engine, conducted in the Mechanical Engineering Laboratory of Stanford University, certain peculiarities of knocking explosions were found by the writers, which they believe to be of general interest. The method of investigation was essentially that employed by Schnauffer plied across each gap. By means of suitable vacuum-tube amplifiers the current fluctuations within the gap circuits are magnified and may be recorded by an oscillograph of the ordinary Duddel type. Heretofore the gaps in the path of the flame have been used solely to determine the velocity pattern of the flame’s movement across the combustion chamber. However, the writers believe that the method can be made to yield certain additional information about the combustion reaction. Fig. 1 shows the general arrangement of apparatus. Two gaps were located within the combustion chamber of a 3 by 3¼-in. single-cylinder, air-cooled engine; one adjacent to the spark plug (Gap 1), a second at a point over the piston about an inch and a half from the far end of the chamber (Gap 2). By means of small extensions, the location of the gaps was changed from time to time during the course of experimentation, in order to explore a greater area in the vicinity of each plug. Pressure variations within the chamber were recorded by a McCollum-Peters carbon-pile telemeter. Since the oscillograph used did not have sufficient current sensitivity to be operated by the telemeter bridge circuit alone, it was found necessary to construct a vacuum-tube amplifier for the indicator. Fig. 2 is a copy of a typical oscillogram. Time is read from left to right. Fig. 1—Diagram of experimental apparatus (see Automotive Industries of May 14, 1932, and July 16, 1932, and S. A.{Mr Adams} E.{Mr Elliott - Chief Engineer} Journal, Vol. 34, No. 1), and more recently by Rabezzana and Kalmar (see Automotive Industries of March 9, 1935), who utilized the increased ionization of a burning gas to record the arrival of the flame front at successive points within the combustion chamber. This method has been independently developed and used successfully by one of the present writers in a previous preliminary study of flame propagation. (Thesis for the Degree of Engineer, William A.{Mr Adams} Mason, Stanford University, June, 1932.) Briefly, the method may be summarized as follows: Small, spark-plug-like gaps are located within the combustion chamber, and a small potential is applied across each gap. April 27, 1935 Fig. 2—Typical oscillograms from knocking engine Automotive Industries [Text from Fig. 1] Carbon Pile Pressure Indicator To Amplifier for Gap 2 Gap 2 Gap 1 Engine Head Amplifier for Gap 1 +135v 2A3 tube 2.5v. a.c. -22.5v Amplifier for Gap 2 identical to above Indicator Amplifier Oscillograph [Text from Fig. 2] “Secondary Peak” -(b) Trace from Amplifier - Gap No. 1 Trace from Amplifier - Gap No. 2 High Frequency Pressure Vibrations Following Knock Pressure Record Timing Wave - 60 Cycle Lbs. per sq. in. 300 200 100 Spark at 35° Before T.C. T.C. 11 1/2° 35° 70° Degrees of Crankshaft Rotation | ||