96 & 98 octane

We're already halfway through harsh week? Time flies!

Theo

 

Hammo is having a flashback to a few weeks ago.

Theo

 

I kept track of fuel usage on an XX a few years ago, did approx 3000km
using only ULP and approx 3000km using only PULP and at the end of that
the difference in fuel consumption between the two fuels was noticeable
in the third decimal point. For that reason I only buy 91 octane for my
bike. However... every few tankfuls I give it a run with PULP to give
the fuel system a dose of whatever cleaning agents they have added to
them... After a few thousand km of running only 91 octane a tank or two
of PULP does make a noticeable difference.

Nev..
'04 CBR1100XX

 

Of harsh week? It has only just begun!

Hammo

 

The premise is to provide a fuel that has a reduced volatile inhalant level.
It is the hoped that this will prevent its abuse.

As to its equivalence with ULP, that is a can of worms I'm not going to
breach.

Hammo

 

No, Hammo. Marketing, not chemistry.

 

I wish I could find / work out the parameters around which it makes a
difference - the obvious/intuitive ones(1) don't seem to correlate real
well. For example the TRX ran noticeably better mileage on 98 PULP (as
much as an extra 40 or 50Km per tank) particularly under light load
(highway). Whereas it didn't matter a damn to the Bandit - probably
would have run the same on Kero. 2 stroke doesn't seem to care, Raptor
didn't before it was tuned but it was running damn rich so I doubt it
would be possible to tell. It's been dyno tuned with a tank of PULP and
I've run the PULP since - fuel economy since the tune has improved
dramatically (an extra 60 or 70K per tank in mixed highway, scratching
and a bit of town work, it would seem).

JL
(the intuitive ones to me would be compression ratio, HP per cc and
water vs air/oil cooled)

 

As another data point, the Spada reliably gets an extra 20km to reserve
on premium (~180km on ulp, ~200km on pulp), the but in Monster it makes
little or no difference (except that the super-premium fuels like
optimax make it run worse that regular fuel when the needle jets in the
carbs are worn and it starts running rich).

Like you, I don't understand whats going on here, as I understand things
using fuel with an octane rating higher than you need shouldn't make any
difference... I used to suspect the Spada had a knock sensor and was
retarding the ignition timing a little on lower grade fuel, but there's
no sign or a knock sensor either on the bike or in the wiring diagrams...

big

 

How much grimacing would I induce by suggesting that it might be a
consequence of the slower-burning higher-octane fuel managing to
maintain a higher cylinder pressure over more of the power stroke,
resulting in more work being done by the combusting mixture on the piston?

 

Lots of grimacing.... but only from me ... coz you may as well be speaking
Greek.... one day, however, I will understand....

betty

 

Get Hammo to explain it to you... he is, after all, the chemist...

 

I did not know that. Is that a fact or just a though??

Wouldn't a higher octane fuel burn faster and at a higher intensity, hence
extra HP ect?
Just a thought.

--
Regards

Andy

2001, ZX9R

 

Lots.

What makes you think that the situation you suggest is likely?

Assuming there is not significant blow-by, what would you expect to
happen to reduce the pressure generated by the faster burning fuel as
the power stroke progresses? As long as the faster-burning fuel doesn't
cause pre-ignition, there should be no problem.

Moike

I am not a chemist.

 

......anyway, we have videos to watch, don't we Mike!

Hammo

is that cos it's denser?

 

Primary objective achieved, then.

Absolutely fucking nothing...

A greater proportion of the fuel being used up by the time the piston
comes around to a given position on the power stroke. The lower-octane
fuel burns more intensely to begin with, when there's lots of it, then
tapers off as it's used up, while the slower-burning, higher-octane
fuel, manages to maintain a higher reaction rate at later stages of the
power stroke.

The total work done by the combusting mixture is, give or take a
simplification, an integral over the full cycle of cylinder
pressure(which is time-depentend) multiplied by the piston surface area.
If the pressure manages to drop off less with time, there'd end up
being more work done on the piston over the full cycle even if the peak
pressure achieved is lower than with a lower-octane, faster-burning fuel...

....still making everything up, of course.

 

I was going to say it would be because there are more carbon-carbon
bonds to break (how *does* an alkane molecule burn; does it snap in
half, or do the carbons start breaking off at one end first?), but, once
again... you're the chemist. You tell us. I'm making this up as I go along.

 

Hammo Dense? Never....


G-S

 

Nah, couldn't be.

Theo

 

Who?

Theo