Was reading an article about a new car that has an atkinson cycle engine. NASA invented this thing called the Advanced Stirling Radioisotope Generator to be a more efficient way to power deep space probes. As I was reading about this engine cycle, it occured to me: if your end goal is electric power, why not dispense with the entire crankcase and let the pistons drive a linear alternator directly a la the ASRG. Since at least 10 other people have previously conceived of every idea you ever will, it turns out this is a thing: the free-piston engine.