On 28/02/2020 08:07, Tim+ wrote:
Steve Walker wrote:

The alternators are far bigger than anything needed for an electric fan
- on my previous car, it could drive a 1kW electric heater to speed up
heating of the car, as the highly efficient diesel was too slow to warm
up in the winter!

This bit about diesels being so efficient that they are slow to heat up a
car has got to be nonsense.

Think about it. ICEs turn fuel into heat and heat into motion. An
efficient engine turns more of that fuel into motion by generating more
heat from the same volume of fuel.

Therefore a 100 bhp petrol engine or a 100 bhp diesel are both producing a
100bhps worth of heat, its just that the diesel is burning less fuel to
produce that heat.

No. The higher efficiency means that there is less waste heat for a
given amount of useful energy produced. Supposedly real world figures
are around 80% for petrol and 70% for diesel.

Less waste heat means slower to warm up.

As a consequence, power for power, efficiency *isnt* the reason that some
diesels are slow to warm up. Much more likely its just down to the weight
of cast iron in the engine.

Indeed the extra mass does slow warming, but that is even more of a
problem because of the smaller quantity of waste heat being produced.

SteveW