RE: Lotus Unveils 'Range Extender'

[The Wookie]

kambites said:

The Wookie said:

Stuff

So the power figure they're giving is for the generator not the motor? How utterly irrelevant.

It's irrelevant in terms of a normal vehicle, but to someone who's aware of power demands at cruising speeds it sort of points out what Lotus were aiming for with this engine.

Arguably it's a bit misleading to put it in a general press release, but then no doubt plenty of people would ask what the power output was if it weren't in there.

[ctallchris]

kambites said:

The Wookie said:

Stuff

So the power figure they're giving is for the generator not the motor? How utterly irrelevant.

Indeed - pretty much the only thing you can get from this is that lotus have scaled an engine to allow a car to cruise at about 80mph.

The motor could be 50,000 bhp as long as the batteries are capable of providing the power. Nevertheless an important component of potential future drive systems.

[kambites]

The Wookie said:

kambites said:

The Wookie said:

Stuff

So the power figure they're giving is for the generator not the motor? How utterly irrelevant.

It's irrelevant in terms of a normal vehicle, but to someone who's aware of power demands at cruising speeds it sort of points out what Lotus were aiming for with this engine.

Arguably it's a bit misleading to put it in a general press release, but then no doubt plenty of people would ask what the power output was if it weren't in there.

Well yes, but they should have given the power output of the electric motor first, and the output of the engine as an aside.

[The Wookie]

kambites said:

Well yes, but they should have given the power output of the electric motor first, and the output of the engine as an aside.

Perhaps, but don't forget, Lotus have designed the engine, not the car. This engine is designed to go in anything anyone wants to put it in.

The generator on the back of the engine is purely a generator, it wont drive the car.

[oilit]

so does this mean that the engine is now a disposable/non serviceable item as we know a 'traditional engine' with a removable head etc to be?

[kambites]

The Wookie said:

Perhaps, but don't forget, Lotus have designed the engine, not the car. This engine is designed to go in anything anyone wants to put it in.

This is true. I was assuming that Lotus had designed the motors that would form part of the system as well, I obviously didn't read the article thoroughly enough first time through. In that case I take it back, 35kw sounds plenty.

[otolith]

How well do wheel motors do on unsprung weight?

[The Wookie]

oilit said:

so does this mean that the engine is now a disposable/non serviceable item as we know a 'traditional engine' with a removable head etc to be?

Although you do raise an interesting point, generally speaking, the only servicing most engine's see with the head off is to replace the head gasket, as there isn't one there's less maintenance requirement. If there were a problem with the valves (the only item I can think of that can't be serviced from above), then you could still work on the engine, but you'd have to drop the bottom end out

As a slight aside, it does raise the prospect of having a small removable generator unit that slots into your EV when you want to do a long run

[The Wookie]

otolith said:

How well do wheel motors do on unsprung weight?

Not as bad as you might think, once you've eliminated braking, driveshafts etc. There are more significant issues that need to be resolved with them though

[kambites]

An engine designed to run under constant load and rev only to 3500rpm should last a damned long time anyway.

[kambites]

The Wookie said:

otolith said:

How well do wheel motors do on unsprung weight?

Not as bad as you might think, once you've eliminated braking, driveshafts etc. There are more significant issues that need to be resolved with them though

Surely you still need brakes unless you actually supply a reverse PD to stop the car (which isn't much use for a hand brake)? Using the back-EMF to charge the battery will have diminishing returns as the car slows down - your car will tend towards zero speed but will never actually stop.

Edited by kambites on Wednesday 9th September 11:03

[xyphod]

Question?
Given an internal compustion engine running at optimal efficiency all the time, what is the effieciency compared to say a power station?

My thinking is lets not charge the car via the mains at night, but have a smaller set of batteries (reducing weight) and up the power a little of the range extender Constantly charging the battery rather than driving the wheels.

I'd imagine that the car would be a lot lighter considering no gear boxes, etc are required.
How much more efficient would the car be, given a much smaller engine (50kg compared to 120+kg for a normal engine) no gearbox, but a few more batteries and electric motor.

Could we have a car running with comparible performance to todays cars using half the fuel (say 100mpg) and 60g/CO2 per mile? Running on a sustainable fuel (rapeseed oil???)

[The Wookie]

kambites said:

Surely you still need brakes unless you actually supply a reverse PD to stop the car (which isn't much use for a hand brake)? Using the back-EMF to charge the battery will have diminishing returns as the car slows down - your car will tend towards zero speed but will never actually stop.

Edited by kambites on Wednesday 9th September 11:03

Pretty much nail on the head.

Also, the torque applied on the wheels by a decent set of disc brakes is fairly massive, even when compared to a powerful engine, hence why I say braking ability is limited. Round about the same as a not particularly brilliant drum brake.

Current wheel motors would definitely have to have a supplementary conventional braking system to be feasible

[The Wookie]

xyphod said:

Question?
Given an internal compustion engine running at optimal efficiency all the time, what is the effieciency compared to say a power station?

My thinking is lets not charge the car via the mains at night, but have a smaller set of batteries (reducing weight) and up the power a little of the range extender Constantly charging the battery rather than driving the wheels.

I'd imagine that the car would be a lot lighter considering no gear boxes, etc are required.
How much more efficient would the car be, given a much smaller engine (50kg compared to 120+kg for a normal engine) no gearbox, but a few more batteries and electric motor.

Could we have a car running with comparible performance to todays cars using half the fuel (say 100mpg) and 60g/CO2 per mile? Running on a sustainable fuel (rapeseed oil???)

That's pretty much what a series hybrid is compared to a range extender. As has been said before, the benefits would still be great at low speed, and diminished but significant at high speed.

I hesitate to give a figure, as I haven't run a decent simulation yet, but I'd imagine in a mondeo sized car a flat 60mpg from both high and low speed driving happy to be corrected though if anyone has some good figures.

As for power plant efficiency, I've heard various figures punted about. Wikipedia says something around 35% for older plants up to 50% for brand new ones

Edited by The Wookie on Wednesday 9th September 11:26

[simonrockman]

They mentioned this engine at the Louts open day last summer. I think it will support variable compression ratios.

[MrTrilby]

The Wookie said:

xyphod said:

That's pretty much what a series hybrid is compared to a range extender. As has been said before, the benefits would still be great at low speed, and diminished but significant at high speed.

I hesitate to give a figure, as I haven't run a decent simulation yet, but I'd imagine in a mondeo sized car a flat 60mpg from both high and low speed driving happy to be corrected though if anyone has some good figures.

I hope it will be much more than that - 60MPG isn't that much better than real world Prius economy (ours sees 50MPG in both high and low speed driving). Another curiosity I have is how the climate control systems are going to work in range extended hybrids, and what impact they have on economy. Burning battery power to run a heater is surely going to have a big impact, as is an electrical A/C system.

[Terry Barr]

Talksteer said:

xyphod said:

Diesel engines on trains drive the wheels directly.
Current High speed trains with electric motors and local generation use gas turbines.

Pretty much wrong on every count:

Most diesel trains are diesel electric where the diesel engine drives a generator which powers a traction motor mounted at the wheels. The reason is because the train is much to heavy to use a conventional gearbox. Smaller trains such as "rail buses" may use various fluid drive systems but virtually no trains directly connect a diesel motor to the wheels.

Gas turbine trains have never gone past the prototype stage, gas turbines are expensive to build and operate compared to diesels and to get the fuel economy of one better than a diesel requires significant complexity.

xyphod said:

I would however had thought that a really small Gas turbine would provide the same efficiency/weight/power as this little Lotus design.

To provide the same efficiency a gas turbine would have to run at a pretty high pressure ratio and/or run in a cycle that involved recovery of exhaust heat. Most likely to be expensive, very expensive, as an example an R-R 250 helicopter engine that generates ~500 bhp costs in the region of $25,000 (used) and that is a fairly simple un-stressed low performance helicopter engine.

On the weight front gas turbines are massively better than piston engines, the LH800 engine for the new Lynx helicopter weighs 150kg but puts out 1500bhp so around about ten times the power to weight of a car engine. Even a conservatively design 50bhp gas turbine is likely to fit in a shoebox.

I think that the new price of the R-r 250(Allison) engine is around the $350,000 mark, the £25,000 used one would be due a complete overhaul. In the helicopters wher they are most use the fuel burn is a bit over 20 gph putting out somewher inthe 250-300 bhp region. I don't know the figures for the 250 but I would expect the fuel burn to be pretty horrendus when it is run off design. If I remember the PT6 used in the Jetprop DLX will burn somewher in the 25-30 gph at crusie but at ground idle somewhere around 12-15 gph.
Rove did in fact use a heat exchanger system in their turbin powered Le Mans cars. They did get reasonable fuel efficiency with extremly high cost and a lot of weight.

[Terry Barr]

Ozzie Osmond said:

otolith said:

Ozzie Osmond said:

IMO all governments need to do if they're serious about car emissions is to ban everything except cars with an engine of 1,000cc or less and let the market do the rest. The current approach screws Mr Average into the ground while people with money go on buying huge thirsty monsters. Put 'em in a 1,000cc X6 and it'll level up the playing field nicely!

Historically, restrictions on engine capacity (through taxation) result in sub-optimal engineering solutions like Italian market only heavily turbocharged two litre V8s. Governments should (if they must interfere) set goalposts and allow engineers to work out how best to meet them.

Good point, but the basic principle still stands. Simply expressed by capping g/km as opposed to engine capacity.

I quite like the idea of road tax being based on vehicle weight except that wouldn't be very helpful for families with 5 kids. But then again...

The family with the 5 kids should be paying a lot more tax in any case.

[The Wookie]

MrTrilby said:

The Wookie said:

xyphod said:

That's pretty much what a series hybrid is compared to a range extender. As has been said before, the benefits would still be great at low speed, and diminished but significant at high speed.

I hesitate to give a figure, as I haven't run a decent simulation yet, but I'd imagine in a mondeo sized car a flat 60mpg from both high and low speed driving happy to be corrected though if anyone has some good figures.

I hope it will be much more than that - 60MPG isn't that much better than real world Prius economy (ours sees 50MPG in both high and low speed driving). Another curiosity I have is how the climate control systems are going to work in range extended hybrids, and what impact they have on economy. Burning battery power to run a heater is surely going to have a big impact, as is an electrical A/C system.

More than likely it will be better than that, a quick look shows that the Jag is expected to undercut 120gCO2/km, which equates to about 65mpg in a car that's bigger and heavier than a Mondeo. Don't forget that this is brand spanking new tech, so personally I think a 20% odd improvement on existing tech in a car that's heavier, less aerodynamic and designed to be primarily an EV rather than a conventional hybrid straight out of the box is pretty damn impressive.

Amazed that your Prius actually hits 50mpg in both motorway and town driving, you must drive it very gently. Worth pointing out that I would expect this Jag to get close to it's peak fuel economy regardless of driving style.

Many vehicles already have A/C powered directly by electric compressors, in fact I believe the Prius does, along with all of the Lexus hybrids. Cabin heating could be more of an issue, but I suspect that a decent control strategy will sort that out.

Edited by The Wookie on Wednesday 9th September 13:09

[The Wookie]

Terry Barr said:

Talksteer said:

xyphod said:

Diesel engines on trains drive the wheels directly.
Current High speed trains with electric motors and local generation use gas turbines.

Pretty much wrong on every count:

Most diesel trains are diesel electric where the diesel engine drives a generator which powers a traction motor mounted at the wheels. The reason is because the train is much to heavy to use a conventional gearbox. Smaller trains such as "rail buses" may use various fluid drive systems but virtually no trains directly connect a diesel motor to the wheels.

Gas turbine trains have never gone past the prototype stage, gas turbines are expensive to build and operate compared to diesels and to get the fuel economy of one better than a diesel requires significant complexity.

xyphod said:

I would however had thought that a really small Gas turbine would provide the same efficiency/weight/power as this little Lotus design.

To provide the same efficiency a gas turbine would have to run at a pretty high pressure ratio and/or run in a cycle that involved recovery of exhaust heat. Most likely to be expensive, very expensive, as an example an R-R 250 helicopter engine that generates ~500 bhp costs in the region of $25,000 (used) and that is a fairly simple un-stressed low performance helicopter engine.

On the weight front gas turbines are massively better than piston engines, the LH800 engine for the new Lynx helicopter weighs 150kg but puts out 1500bhp so around about ten times the power to weight of a car engine. Even a conservatively design 50bhp gas turbine is likely to fit in a shoebox.

I think that the new price of the R-r 250(Allison) engine is around the $350,000 mark, the £25,000 used one would be due a complete overhaul. In the helicopters wher they are most use the fuel burn is a bit over 20 gph putting out somewher inthe 250-300 bhp region. I don't know the figures for the 250 but I would expect the fuel burn to be pretty horrendus when it is run off design. If I remember the PT6 used in the Jetprop DLX will burn somewher in the 25-30 gph at crusie but at ground idle somewhere around 12-15 gph.
Rove did in fact use a heat exchanger system in their turbin powered Le Mans cars. They did get reasonable fuel efficiency with extremly high cost and a lot of weight.

Think more along the lines of an APU rather than a driver engine