A lot of the fuel efficiency of modern aircraft comes from having giant turbofans instead of turbojets. By attaching a giant fan the front of your compressor an

A lot of the fuel efficiency of modern aircraft comes from having giant turbofans instead of turbojets. By attaching a giant fan the front of your compressor and redirecting most of the air around the engine you can get great efficiency at subsonic speeds. However, the nature of the fan has fundamental limitations when approaching the speed of sound and turbo/ram jets are basically just pouring gas in a tube of precompressed air.