Superchargers are known for increasing efficiency on gasoline engines...but I assumed that was when at partial throttle, shoving more air in to each cylinder, getting it in to the more efficient part of the fuel map...something diesels don't have to be nearly so concerned with.
The 90's+ Buick 3.8 S/C cars get better gas mileage than the naturally aspirated versions, for example.
With a diesel no suffering from as much pumping losses, I'd have thought a turbo - that only really kicks in when you need a lot of power - would be the most efficient way of doing it.
Maybe it comes down to gearing...with even more low-end torque, you could run that sucker at like 1300rpm and still make enough power to keep it moving.
Probably UK gallons.
From Wikipedia:
Quote:
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An extremely fuel-efficient two-cylinder diesel was prototyped in the mid-1980s with a G40 supercharger to overcome its small capacity, although this did not make production. A high-fuel-efficiency model which did make production was Formel E (E for Economy), introduced in 1983. This used a high-compression 1272 cc engine, longer gear ratios and an early-stop-start ignition system (called SSA) that would cut the engine when idle for more than two seconds to save fuel whilst temporarily stopped in traffic, and restart the engine when the gear lever was moved to the left in neutral. The system could be enabled or disabled by means of a toggle switch below the light switch. Similar systems were later used on the Volkswagen Golf Mk3. Similar systems were developed by other car manufacturers.
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That about covers it...an undersized engine with a supercharger to make up for it, potentially having the tall gearing and everything else they put in the non S/C versions later on. In a car that weighed about the same as a late 90s Geo Metro. And, being a prototype, there is not "real world" MPG...just potentially ideal driving.
I like the combination and results though. Stuff it in my insight, please!