From days gone bye there is a Griffin 6-stroke at the Anson engine museum, but not runnable I don't think as they run most of the engines that are fit to (or they are allowed to). The Griffin was designed to get around Otto's patent.
This invention looks 'cool', but I suspect the steam stroke will be a bit limp, and the extra revolution waiting for the next power stroke will waste what you gained. You might do better to use the waste heat from the exhaust to drive a steam engine and run the alternator. I think some researchers at BMW once threw everything they could at an engine in this way to squeeze max efficiency, and got a few percent, but all the expense, complexity and reliability suggested that it remained an engineering exercise.
Steve