On 21/08/15 23:22, Tim+ wrote:
The Natural Philosopher wrote:
On 21/08/15 10:35, therustyone wrote:


The only time I've noticed a slightly smoother engine (though no
significant improvement in mpg) was when I accidently filled up
with premium diesel instead of standard diesel - and a lot of that
may have been wishful thinking to compensate for paying through the
nose for the "gold plated" fuel :-) I wouldn't have minded quite
so much but I'd driven past loads of garages on my journey, holding
out for the cheapest garage that I happened to pass, and then when
I found a cheap garage I went and used the premium holster instead
of the standard one. Shame they aren't different colours (eg black
versus black with yellow stripes, or something like that).

might depend on the car's sophistication. A quality engine will
monitor pinking and adjust the timing and fuel ratio to optimise
burning with the better quality (petrol anyway) it finds. An older
car will just be set to run on the worst fuel around.

However a car adjusted to run on low grade fuel either by fixed design or
automatically will still run better on better fuel.


Only if it has knock sensors or other ways of detecting and actually
capitalising on the better fuel's properties. Not all cars show
improvements with premium fuels.

You still don't get it do you?

There is a world of difference between 'runs acceptably without damage'
and 'best power output/smoothest running/best economy'


To take an extreme example. IF you add - say - nitromethane to your
tank, you will without any retunes at all get a massive power increase.

Simply because its an oxidiser. it adds oxygen to the mix. So where a
conventional engine might run out of breath the nitro engine will keep
going to higher revs.

The shape of the bang - not just its timing - makes a real difference to
power output and fuel economy.

All IC engines ignite before top dead centre, so a sharp bang then
actually slows the piston down. You will optimise to get MOST of the
ignition pressure after top dead centre where it does the most good, but
automagically adjusting the ignition timing can only compensate so far.

A short sharp bang is not as efficacious as a longer slower one.

However the fuel mix and timing is only part of the story - the engine
designer has compressions ratios, turbo boosting and combustion chamber
shape to play with to affect the ignition explosion character.

And with direct injection these days, the injection can be more than
once per combustion.


The final point being the engine is designed and mapped for one
particular grade of fuel. And tested to ensure that others don't cause
problems, but it is not optimised for them. All cars will run best on a
particular grade and better or worse on others. And the RON number means
nithg8ingm as any F1 aficionado will tell you. F1 fuel at one time was
restricted to some RON number, but that didn't stop them putting in all
manner of additives to constrict a highly toxic witches brew that gave a
huge amount more power than 'pump fuel' of the same RON number would
have dopne.


And that is why you get such widely varying reports as 'my car runs best
on X' or 'my car ran worse on X' or 'my car runs the same on all grades'

Having a misspent youth tuning up small sports cars, I am particularly
sensitive. One time I had a distinct vibration in my latest vehicle, a
sort of engine thrumming at 70mph+. After refilling it at a different
station, that disappeared.

Mind you the fuel pump was failing and did fail nearly completely some
few hundred miles later, which may have been a contributory factor.



Basically if you actually care at all, try every single brand of fuel
you can, and test them against YOUR car and YOUR driving style, and
realise that its *more* likely that you will get a predictable fuel
grade from a branded station than a supermarket.

Otherwise accept that if you fill up where its cheap, you *may* get
reduced performance and shorter engine life on some or other components.
Or you may not. It depends.

If you are driving a mass produced shopping trolley with 'tesco rash'
dents everywhere that you will scrap at 100k miles anyway, well fine.


Tim



--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.