The significance of flame development in the process of energy conversion in Otto engines has not been well explained. The study investigates through photographic means the relationship between pressure values and flame development.Tests were run on a Daimler-Benz four-stroke Otto engine. Engine modification for incorporation of photographic equipment is described; testing procedure and engine operation are presented. Flame propagation was photographed between 60° before and 150° after top dead center. Evaluation methods and test limitations are discussed.Results show that the visible aspects of flame propagation are highly dependent on engine operation. This dependency is strong enough that energy conversion may be charted in the combustion chamber either by photographic means or by conventional pressure measurements. However, relatively high costs, difficulty of the testing procedure, and testing limitations make this process generally impractical.