Quote Originally Posted by henk4 View Post
Thank you, one question though, does it necessarily have to be turbocharged? I remember the Volkswagen SDI engines came up with very good fuel economy figures, but they were simply not powerful enough for modern requirements and increased car weights. 80 BHP from an 2000 cc diesel engine, non turboed, should however be easily possible. Any figures on the specific fuel consumption of both diesel and petrol engines under such stationary conditions? What revs would they be running at?

I guess that adding a turbo will also help to reduce the noise a little.

Why the Volt engine should run on premium is a mystery to me.
Unfortunately there aren't official figures for these conditions.
Having a turbocharged diesel generator would be quite necessary for a few reasons.
First of all, we now have only turbocharged diesels engines, and all injection systems, components, exhaust lines and particulate's filters are designed according to what a turocharged diesel can or cannot do.
Removing the turbo would require quite some design work, and higher costs.
Talking about gainings, well the turbo surely improves efficiency, and the gain would still be higher than the loss due to the heavier and larger drivetrain. On the other hand for this level of output (around 100 kW), they should use a small displacement diesel engine, like say the 1.3 liters from Fiat. This engines are not particularly frugal compared to their performance, are still relatively heavy and quite noisy too (implying also vibrations).

That would be the same with a petrol engine, but the level of power made it possible to get away with an already existent and cheap naturally aspirated engine. Using a turbocharged version would have been even better, but they couldn't ask an higher price for a better result.
Now they are selling this car for 40.000 $, regardless of its specific data. A better product would have probably been priced at the same figure, or people would have just ignored it. Now they can rely on a future update, basically for free while they use this naturally aspirated engine as a first step.
There wasn't a chance to do the same with a diesel ICE.

Talking about its operating revs, on top of my head preproduction prototypes have their engines tuned to work between 1.400 and 4.000 rpm. Production models should work between 1.400 and 3.000 rpm at worst.
The reason why they are not running at constant speed is because the system is developed to respond to its own requests, and not to what the driver is asking (as in the Fisker Karma). The main target is maximizing the load, so to improve efficiency. That required to recalibrate the engine so to lower the speed at which the efficiency was best, of course reaching a lower overall power.
On a diesel engine, given the smaller range of revs, it would be more difficult to have the engine running at lower speeds while having a "good" efficiency, also because the aforementioned turbo needs high pressures and temperatures to work properly and give decent results. Without the turbo it would be even harder to have a good efficiency at low speeds because of the difficulty on vaporizing the fuel.