What was the key advantage of the Otto-Langen engine over the earlier Lenoir engine regarding fuel use?

It achieved fuel consumption rates less than half that of the Lenoir engine.

The Otto-Langen engine, developed in 1864, represented a significant step forward in thermodynamic efficiency compared to the commercial engine it followed, the Lenoir engine. While both were atmospheric gas engines relying on expansion after ignition, the Otto-Langen design proved far more economical. It was documented that this improved machine achieved fuel consumption rates that were less than half of what was required by the Lenoir engine and its commercial derivative, the Hugon engine. This efficiency gain was substantial, although the fundamental operational principle still relied on atmospheric pressure rather than true pre-compression.