TOT: heating the cab of an electric vehicle

[Bill Wright]

It looks like it's a real problem.

various electric car manufacturers' websites seem to skirt around the question of range reduction caused by heater use.

Bill

[Tim]

It did cross my mind that a lot of folk may well have died this winter if they had been stuck in snow in an electric car.

Tim

[Albert Ross]

One reason for Gardner diesels' efficiency was their low temperature burn. This often produced no excess heat for the cab heater in winter, especially in the old plastic cabbed trucks with huge holes for the pedals to go through the floor.

I've noticed that even modern petrol cars take a lot longer after start-up before the heater becomes effective

Everything's a trade-off

[Steve Thackery]

I wonder why that makes them efficient. I'm not very good at the science of thermodynamics, so a simpleton's guide would be welcome!

I thought the efficiency was somehow dependent on the temperature difference between the highest and lowest points of the cycle. Or summat like that. It's how they crank up the efficiency of power stations, I vaguely seem to remember.

An ic engine converts heat to mechanical energy via the expansion of a hot gas. I'd have thought - in my innocence - that a very high combustion temperature combined with minimal heat loss to the surroundings would be the way to go. Of course, maybe one excludes the other. Maybe a low temperature burn is efficient because it reduces the rate of heat loss to the cooling system.

Anyway, all elucidation is welcomed.

STeveT

[Albert Ross]

I remember reading it at the time. It's all to do with achieving a maximum conversion of fuel to energy. Later engines used an intercooler after the turbo since cool air is denser than hot air and the more air you can fit in the more fuel you can burn.

Other factors were the attention to reducing internal friction, seen in later models of car and truck engine by reducing the number of moving parts as well as better bearings. The less heat you generate the more energy is available as power.

[Tim Downie]

I'm sorry, but I'm having real difficulty believing that last sentence. Surely heat IS energy/power in an internal combustion engine?

Tim

('scuse the cross posting but I think more heads are needed to answer this one.)

[John Williamson]

Work (from the crankshaft) + waste heat (From the exhaust and cooling system) = chemical energy in.

That's the thermodynamic principle involved.

If you find a way to reduce the waste heat, that leaves more energy to do the work. Very simplified.....

The cooler the exhaust is and the less heat wasted through the cooling system, the more efficiently the engine converts chemical energy into mechanical energy and vice versa.

The intercooler on a turbocharged engine is to do with increasing the power available from a small engine, as you can get more fuel/ air mixture through it, by increasing the volumetric efficiency, and reducing undesirable combustion products, partly by permitting the mixture to be weaker. The incoming air is compressed by extracting energy from the waste heat in the exhaust gasses.

[Tim Downie]

I'd agree with everything you've said about turbochargers but the point I was arguing with was the one at the top of this page, namely "One reason for Gardner diesels' efficiency was their low temperature burn.". Note BURN, not EXHAUST.

That's the bit I'm struggling with.

Tim

[The Natural Philosopher]

Conversely the hotter the fuel burn, the more efficient they can be. which makes this statement

"One reason for Gardner diesels' efficiency was their low temperature burn."

mystifying..

[The Natural Philosopher]

Its BS.

From a thermodynamic POV. Len burn is best for diesels..gives high explosion temps and high BMEP specially with a turbo to cram more air in.

But a turbo is more a way of using a smaller diesel to give more power than making a large one efficient. Essentially you can IIRC extend part throttle efficiency - which is good on a diesel - further up the rev band.

>

[jgharston]

Or even kWh and kW.

[The Natural Philosopher]

OOH. You BITCH!

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember John Williamson saying something like:

And it's long been possible to extract much more from the fuel by running the engine hotter - leading to melted pistons in short order. Ceramic pistons and liners are the way forward, sussed out long ago, but material science is sadly lagging there.

[GB]

Indeed, the Carnot Cycle becomes more efficient as you increase the temperature differential between the heat source and the heat output, and I'd expect the same to apply to a diesel.

[Tim Streater]

It's true of any heat engine that does work. But as it's now nearly 45 years since I studied thermodynamics at Uni I can't remember why.

[John Williamson]

It's not even linear with the temperature difference, but closer to a square law.

What may have made Gardners more efficient was their use (IIRC) of aluminium pistons, as against the cast iron of most other engines of the time, which reduced reciprocating mass and possibly reduced friction, but needed lower combustion chamber temperatures.

I do remember with some awe using the decompressors and the fuel injection cutoff levers to have a Gardner 180 ticking over on any one of the six cylinders.

[Albert Ross]

OK, *wasted* heat, like excess noise (vibrational energy) and excess energy in the exhaust (captured by a turbo) are all forms of energy that the fuel is converted into but are not used as output.

The more you reduce wasted energy the more efficient the engine.

[The Natural Philosopher]

:-)

[Albert Ross]

Well mostly not the Yanks. UK people like Ricardo Research did a lot of work on burn characteristics for both petrols and diesels, paying attention to stuff like injection droplet size and injecting into swirling air etc.

The Yanks just stuffed more fuel in.

[The Natural Philosopher]

since they could afford it, why not? You totally miss the point, first that your original comment is totally facile and secondly that your response that the Americans didn't know this, is even more so.

There was no reason to make engines more efficient in the USA. so they never bothered.

They knew how to all right.