Note on Effect of Cylinder Head Design on Detonation

Abstract

I the course of the development and subsequent use of the M.I.T. knockmeter 1 at the Massachusetts Institute of Technology, information on the effect of combustion chamber design on detonation has been , discovered which seems worthy of attention. The physical nature of detonation has been analyzed by C. S. Draper. This work showed that the characteristic noise of detonation originates in pressure waves in the cylinder gases which result from sudden burning and very rapid rise of pressure in a portion of the fuel-air mixture. The frequency of these waves has been computed for the cylindrical form of combustion chamber, and has been found to agree with measured values. The M.I.T. detonation indicator, or knockmeter, is shown diagramatically in Figs, la and lb. The cylinder element consists of a relatively thick diaphragm mounted in an assembly which screws into a threaded hole in the cylinder head. The diaphragm carries an aluminum cup-shaped armature located between the poles of ah electro-magnet. A small winding is mounted on the inside pole in line with the armature. Pressure waves in the cylinder cause motion of the diaphragm which, in turn, moves the armature axially and varies the magnetic field surrounding the coil, which thus generates an electro-motive force.