slightly off topic, my little diesel shopping trolly commuter..
4.7ltrs/100km on the open road, 5.1 around town, 1.6 ltr with 280Nm torque. equiv performance of a V6 medium sized car. especially on the hwy. 1800 rpm at 120kph, right at peak torque.
be a long time before petrol engines get those torque figures with that fuel burn.
as for aircraft, the Pipistrel Virus, 147kts cruise buring 15ltr per hour. sure its only 100 Hp, but maybe just some more modern technology in our current aircraft engine design might be the key? electronic ignition? How many cars have aluminium intake manifolds now? how about fuel rail direct injection as opposed to the old fashioned spider system currently in use?
Rotax has proven that magneto less electronic ignition can be reliable in an aircraft application, not to mention water cooling, dry sump setups, why not 4 valves per cylinder?
there are a lot of tried and proven efficiency upgrades that can be done to the base current design engine that i think would improve economy significantly before we need compression ignition powerplants.