Brayton's engine was displayed at the Centennial Exposition in Philadelphia in 1876, and the Simon variant was displayed at the 1878 Paris Exhibition, and for a few years was well regarded, but within a short time the Otto engine became more popular. However, it was considered the first safe and practical oil engine and also served as inspiration to George B. Selden. As a production engine the design evolved over time, and according to Henry de Graffigny in "Gas and Petroleum Engines", it was available in both vertical and horizontal forms.