A Preliminary Study of Flame Propagation in a Spark-ignition Engine
A 1937 NACA technical report by the National Advisory Committee for Aeronautics, a government aeronautics research body, studying how flame spreads through the cylinder of a spark-ignition engine, written for engine engineers and researchers. Its pictures are plain engineering graphics: streak-photograph strips of combustion timed against crankshaft degrees, a labelled cutaway schematic of a fuel injection and camera setup, and a line graph of fuel consumption against air-fuel ratio. A designer might take the sparse black-on-cream linework, dense tick-marked grids and hand-lettered labels as a model for technical diagram styling.
