DURING an investigation conducted at the Bureau of Standards under the sponsorship of the National Advisory Committee for Aeronautics, visual and photographic observations were made of the spread of flame to all parts of the combustion chamber of a single-cylinder L-head engine. Heads equipped with a large number of small windows symmetrically distributed over the combustion chamber were observed through a stroboscope, flame diagrams being obtained for a wide range of engine-operating conditions and for a variety of fuels, combustion-chamber shapes, and arrangements of single and twin ignition.
In this paper, the major factors influencing flame movement in the engine are discussed and their effects upon the diagrams are indicated.
As a means of studying more intensively conditions in and behind the flame front, measurements were made of the variations in intensity and spectral distribution of the infra-red radiation emitted through selected windows during normal and knocking explosions. The character of this radiation indicates that it is emitted almost exclusively by the final reaction products, water vapor and carbon dioxide, and the variations in its intensity show that reactions producing these substances continue in a normal explosion of 20 deg. or more of crank angle after inflammation of an element of charge. In those portions of the charge where fuel knock occurs, the reactions appear to be much more rapid.