[teragram]

The maximum power obtainable from modern electric motors is limited by their temperature rise. You can water-cool a motor to optimise its continuous-power to weight ratio, and allow short-term overdrive of around 20% of max continuous for takeoff. This is common with aircraft engines which have cruise (optimum fuel consumption), METO ("maximum except takeoff") used for continuous climb, and MAX2MIN settings for getting off a short runway. Might just be useful for road transport, particularly for heavy goods vehicles.The "range extender" logic baffles me. If your car needs say 50 horsepower to maintain 60 mph, then you need a 50 HP electric motor AND a 50 HP petrol engine for when the battery runs out. Either that, or you have to run say a 10 HP engine continuously to trickle charge the battery, and in either case carry enough liqjuid fuel to run the car for x miles at 60 mph where x is the range extension. 

I mentioned the BMW i3 because I know it is what used to be called a "series hybrid", and because I know someone who owns one. The series hybrid is where the petrol engine is not mechanically connected to the vehicle transmission, and can only produce electrical energy to charge the main battery and/or power the electric motor (as you describe). The 10hp engine in your description is apparently rated at 33HP (25KW), while the main electric drive motor is rated  at 168HP (125KW) or 184HP (137KW) depending I think on model. The point is that the electric motor does all the work of directly driving the vehicle, for accelerating, cruising, hill climbing, and town traffic, and contributing to braking by regeneration. It does all this admirably with only one gear (even for reversing)  and no clutch , friction or hydraulic. But this is what electric motors do. I like to say that my Nissan Leaf can go from 0 to 90mph in 1st gear, it can also go from 0 to 90mph in top gear.
The average energy consumption of an electric car is 330Watts per mile. In theory, a comparatively small petrol engine/generator can maintain the state of charge (SoC) of the battery fairly effectively, without having to cope with high torque and power requirements.
How successful this is in real life I'm not sure, but the i3 and it's peers are called "range extended" because the preferred mode of use is to charge the battery from mains, and only call the petrol engine into play if the vehicle cannot reach a charging point before the battery is exhausted. Many people (including my i3 owner friend) find that the journeys are such that the petrol engine is never called into action.
According to Wiki, the fuel consumption of the i3 operating on petrol only is about 50mpg. Not brilliant by todays standards, but I have yet to determine whether the car can be driven with a fully charged battery, and with the petrol engine doing what you suggest, keeping the battery SoC healthy. Again, Wiki says that BMW claims a fuel consumption figure of 400mpg!! Whether this figure is obtained by using the petrol engine as a "trickle charger" I can't say, although it smacks of smoke and mirrors.
A couple of general points:-
I prefer to use KW instead of HP (incidentally, why PS these days?), and
We seem to have drifted from the original topic somewhat, "Can Diesel be made clean?"
With regard to that, I think "No", even with all particles and NOX etc removed, petrol and diesel engines convert atmospheric oxygen into CO2.

[alancalverd]

330 W/mile is not a measure of energy consumption. 2.5 megajoule/mile (around 60 mpg) is a good target for a diesel engine in a small-to-medium car. The electrical consumption of an equivalent car will be less because the inefficient bit, the generation of electricity, has been done somewhere else.

CO2 is not a pollutant: it is essential for life.

[Bored chemist]

CO2 is not a pollutant: it is essential for life.

So is water, but that doesn't stop people drowning.

The average energy consumption of an electric car is 330Watts per mile.

No it isn't

[teragram]

330 W/mile is not a measure of energy consumption. 2.5 megajoule/mile (around 60 mpg) is a good target for a diesel engine in a small-to-medium car. The electrical consumption of an equivalent car will be less because the inefficient bit, the generation of electricity, has been done somewhere else.

CO2 is not a pollutant: it is essential for life.

GUILTY AS CHARGED! Thanks for everybody for pointing out my mistake. The average consumption of an electric car is 330WATT HOURS per mile.
The discussion as I am aware was not about the efficiency of electric cars versus ICE powered cars, but I think that the inefficient part is not the generation of electricity,  generators have a very high efficiency. Using heat engines to power the generators is the inefficient part. The nearer we approach total electricity generation without burning stuff, the less will be the importance of thermal efficiency.

[alancalverd]

That's about 1.2 MJ/mile, roughly half the end-user energy consumption of an equivalent diesel, when running on electricity alone. Exactly as expected.

The problem arises when you introduce a range extender or build a standard "half-and-half" hybrid: you are carrying twice the engine weight and using the same 50%-efficient prime mover. Friends with a classic Prius are pleased if they get more than 35 mpg now that the battery is approaching middle age. The useful power output is around  60 kW, compared with 110 kW  from a standard 1.9 liter/ 50 mpg diesel. It is indeed a delight to drive in town, very quick and quiet off the mark up to 30 mph, but on the open road you can definitely feel  the consequences of weight minimisation and the need to overtake with caution. Clearly designed with the Californian speed limit and emissions laws in mind.

I'm more impressed with my neighbour's electric-only BMW, provided you aren't in a hurry to go anywhere at short notice. Overnight charging gets her to the office smoothly and quietly, and the acceleration and roadholding are more like a Tesla than a milk float, but if she has to visit a client more than 100 miles away, there's an ancient petrol-driven Renault for serious motoring!

[teragram]

I think the Prius didn't quite fulfil it's promise on fuel economy. I agree it came into existence to supply the market in America. The early versions were powered by an Atkinson cycle engine, which is slightly more efficient than a traditional 4stroke. I don't know whether that engine type is still in use.
I have a confession. My electric car is the early Leaf which only has a 24KWh battery. I had to keep my old Peugeot 1.6 Diesel to keep my wife quiet when planning the 420 mile trips to see her grandchildren in Scotland. If only I could afford an EV with 300mile range, and manage the journey with only one stop for charging each way. I'm now far too old for that to happen.

[RandyWilliams]

I'm waiting for it

Me too

[syhprum]

Pferdestärke (PS) is German for Horse power, slightly different  1% as it is based on SI units

[alancalverd]

And on that subject, it is only just beyond living memory that the streets of London were ankle-deep in horse sh1t and the  traffic jams lasted for days. But as it was organic and inefficient, I guess those were the Good Old Days that the green lobby wants to replicate. 

[Bored chemist]

I guess those were the Good Old Days that the green lobby wants to replicate. 

Guess again.

Pferdestärke (PS) is German for Horse power, slightly different  1% as it is based on SI units

Thus far, that's the most interesting thing I have read in this thread.

[teragram]

Pferdestärke (PS) is German for Horse power, slightly different  1% as it is based on SI units

I see, thank you for that.

[alancalverd]

from: alancalverd on Today at 08:13:39 I guess those were the Good Old Days that the green lobby wants to replicate.

Guess again.

Not a guess. I was briefly involved in a pro-horse anti-car group until I pointed out that the horse, standing still in a field, produced as much CO2 in a year as a small car driving 10,000 miles.

[BeJimmiecot]

The wankel is very smooth and can rev very high, but fuel economy has always sucked a bit.  But theres good power to weight ratio to be had.  The Mazda 13b rotary was a popular choice for experimental aircraft that had need of high hp/w.

IIRC, a 4-stroke diesel is about as efficient as an internal combustion engine can be made, efficiency being defined as mechanical power output per mass of fuel burned.