here are some links for implementations that have optimized to close to 45% efficiency. plus a very simple lightweight design. https://en.wikipedia.org/wiki/Fr

here are some links for implementations that have optimized to close to 45% efficiency. plus a very simple lightweight design. https://en.wikipedia.org/wiki/Free-piston_engine https://en.wikipedia.org/wiki/Free-piston_engine https://www.aquariusengines.com/ https://www.aquariusengines.com/ https://engineerine.com/omega-1-piston-less-near-zero-emissions/ https://engineerine.com/omega-1-piston-less-near-zero-emissi... (optimize for power but can be tuned for efficiency) its nowhere near what a turbine can get (60% about max with heat recovery) but high enough to design around need for large batteries. edit: formatting