CALLING knock “the cancer of engine combustion,” Mr. Boyd explains that his paper- a review of research on engine combustion which has been pursued steadily for many years - is concerned chiefly with this phenomenon. Of the many aids to observation which have been developed for the research, or adapted to it, he describes first an optical engine indicator by means of which it was observed early that knock is not caused by preignition, as was then thought, but that it arises from a pressure disturbance which occurs several degrees after the ignition spark.
Other aids to observation utilized in the course of the research are named as the bouncing-pin indicator for matching fuels or for comparing one degree of knock with another; auxiliary sampling valves for tracing reaction progress by chemical means and for detecting incipient oxidation within the dark region ahead of the flame; windows of various sizes and shapes through which events inside the combustion space were observed by eye, photographed in sections and in full view, and examined with the aid of spectroscopes. Through such windows also radiation from the flames was registered by a thermopile, and flame temperatures were measured by a spectrographic technique. To summarize the information about engine flames accumulated by all these various means is the purpose of this paper.