On 03/04/18 11:31, wrote:
On Tue, 3 Apr 2018 08:59:25 +0100
TMS320 wrote:
On 31/03/18 16:37, James Wilkinson Sword wrote:

That does make me laugh this hybrid bull****, you save **** all fuel
with those.Â* It's been shown that a diesel VW Polo uses less fuel than a
hybrid Toyota Prius.Â* Pointless waste of Lithium.Â* ALL electric cars,
fine, but hybrids are pointless.

A diesel Polo will emit far more toxic material. Besides, miles per

But somewhat less CO2.

gallon is the wrong measure when comparing petrol and diesel because
they have different energy densities. Miles per kilogram is the proper
comparison.

Thats true, but these days its CO2 emissions matter and diesels emit less
CO2 than petrols for a given amount of power generated. Quite why is something
a chemist would have to answer.

The conventional reason is that compression ratio gives a better
conversion efficiency from fuel energy to mechanical energy.

You'd think given that diesel fuel has a
higher percentage carbon content than petrol it would be the other way around.

Diesel does have a higher percentage of carbon (relative to hydrogen)
and has a higher specific gravity. So even if the two engines had the
same conversion efficiency, the diesel would consume a lower volume but
a greater weight.

It would be good to know the correct values but take your pick from:

https://en.wikipedia.org/wiki/Energy_density
diesel 48.0MJ/kg 35.8MJ/l
petrol 46.4MJ/kg 34.2MJ/l

https://neutrium.net/properties/spec...sity-of-fuels/
diesel 44.8MJ/kg 37.2MJ/l sg 0.830kg/l
petrol 47.3MJ/kg 33.9MJ/l sg 0.776kg/l

https://arewetoast.com/energy-conten...ted-fuels.html
diesel 44.8MJ/kg 38.7MJ/l
petrol 43.5MJ/kg 34.6MJ/l

From first principles, wiki says graphite produces 32.7MJ/kg, hydrogen
120MJ/kg, hence petrol at 96:18 (relative weights of C & H) is 46.5MJ/kg.

Diesel centres around C15 which is 180:32, giving 45.9MJ/kg.

Shrug. No wonder politicians don't know how to tax them. But it should
be clear that part of the reason petrol engines need a bigger tank is an
innocent difference in the fuel.