Today I read about a company based here in San Diego (and Detroit) which is developing 1-3 cylinder engines to work in hybrid vehicles and military or commercial applications (like Auxiliary Power Units, compressors, generators, etc). Earlier in the 20th ...
...diesel engines. 2-stroke compression ignition and you guessed it, supercharged AND turbocharged. powerful four cylinder. Lovely sound too: https://m. There were also some aircraft engines like this.
The added economy comes from efficiency of combustion. Remember a typical internal combustion engine is only about 25% energy efficient. Achates can achieve 40% due to much higher compression (like a diesel), less energy lost to valve train, etc. better m...