Double walled fuel lines have been a very common fitment on marine engines for years to eliminate the threat from rupture - although the Australian Navy lost a destroyer or possible something a little larger by replacing the HP fuel line with flexibles..........
To get really high power (over 50hp per litre) from a diesel engine the use of common rail technology is necessary. Look at the evolution of the VW 1.9lt engines - from 75 bhp to now over 180 - quite a development and made possible by precise injection and careful matching to boost.