[Diy_efi] Timing Advance Curve?
A6intruder
A6intruder at adelphia.net
Thu Dec 19 19:40:09 GMT 2002
Mike,
I appreciate your more detailed analysis of the subject. These discussions
are often a learning experience for me. I certainly looked at my own
understanding of combustion more critically after reading your input.
That's the beauty of these forums, there's always someone with more detail
or experience that will share it, and if we don't know the answer, someone
else likely will.
Take care,
Daniel R. Nicoson
Equipment Exchange Company
Phone: (814) 774-0888
Fax: (814) 774-0880
-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org]On Behalf
Of Mike
Sent: Thursday, December 19, 2002 12:53 PM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] Timing Advance Curve?
<hrrrm> Well <cough> wasnt intending to er um thrash, just driving the
point with a bit of rationale to make it as crystal as possible given
the affects of white whine, crackers, cheese and glaced ginger and
the after-effects of a day at 40deg C <groan> and 39Deg C tomorrow !...
Seriously, in reference to your first para response, there is an
implicit assumption you might be making re energy levels,
That is; Bear in mind the energy level available to detonate fuel
some way ahead of the flame front is far less than the energy the
flame front imparts to enable it to propogate and maintain the
advancing more or less orderly ignition, therefore (and I
dont know the ratio) the effect of octane on flame front propogation
(overall) is likely to be small - if I infer correctly that there
is a huge differential in the energy levels just described.
In reference to your 2nd para response, there are huge disturbingly
present psychological factors readily noticable (ie amoungst the
young not practised at self observation) that what they expect is
what they get with a high level of positive feedback and satisfaction :)
I've observed this from personal experience, many years ago I fixed
the knob on the gear lever (when I was 19) on my ford escort and
it actually felt like it ran smoother, and my autonomic nervous
system doubtlessly assisted the process by less eratic throttle
movements (unknown to me at the time) - so a noncausal trigger
did result in a change in engine behaviour - just like magic <:o)
There are other probabilistic variables and as a consequence of
experience amoung the uninformed this becomes a myth and can also
be propogated by the evils of the internet...
I hear you and understand the potential dilema but, there aint no
real reason for that perception though it can be explained
circumstantially if it can be quantified - who knows - there may
actually have been fuel from differnt suppliers with different
energy levels.
Oh ! And the other issue is 'silent detonation', Its entirely
possible the original operation on unleaded could have been
marginal and switching to premium got around the silent
detonation issue which robs power but isnt readily noticeable
hence switching to premium did actually give a seat of the pants
effective improvement. To be sure one could go back and observe
the details at the lower grade of fuel but, frankly what the
hell - just get more white whine, cheese, glaced ginger and
licorice and go to sleep with interesting dreams ~`:o)
cest la vi,
<sigh> Off to sleep its 1:30am here,
Mike
http://www.iinet.net.au/~erazmus
At 11:30 AM 12/19/02 -0500, you wrote:
>OK Mike, Thrashing received. Next time I'll only post if I have my list
of
>SAE papers as references. But since I've entered into an interesting area
>of discussion I'll continue my thought process because I obviously didn't
>convey my complete thought. And yes you're right I haven't read every post
>ever made on this list, AND, this list isn't my only source of learning.
>
>My beginning statement:
>>Octane has everything to do with the speed of burn. Higher octane
actually
>>controls ping by slowing down the burn.
>I actually have read about the octane, studied combustion thermodynamics
>going through college, and no I'm sure I don't have your level of
expertise.
>However, my understanding of the typical combustion event is that as the
>flame front starts, pressures and temperatures start to rise. As temps and
>pressure rise this allows the flame front to move faster and the goal is to
>complete the burn in an orderly manner before the temp/pressure conditions
>allow the fuel to go high order, detonate. The net effect of a higher
>octane fuel is to delay that critical temp/pressure point long enough to
>avoid detonation. My understanding has been (this is why I like to
continue
>the learning process even in my old age) that high octane fuels achieve
this
>by slowing the combustion process. This sounds counter productive but
since
>the speed of the flame front increases drastically as temp-pressure builds,
>actually forming a shock wave as it approaches the detonation level, slower
>combustion actually delays the build up of the shock wave ever so slightly
>effectively allowing the flame front to finish it's travel throughout the
>mixture before hitting the critical temp-pressure point. I think, and you
>might actually agree with this, that the octane rating system is fairly
>imperfect system of inferring a pre-ignition and detonation resistance.
>
>Second part of my original statement: This is why a very low HP/cubic
>>inch engine doesn't necessarily gain power with higher octane.
>
>My point here is that many commoners I know take a normal street car, we'll
>use a 1994 Mustang GT with purely stock 215 HP motor, and put premium in
the
>car and say it gives them better performance. The stock tune on that car
>needed 89 octane to keep from pinging under any thrashing based on my
65,000
>of use in purely stock trim. Since this engine control system does not
have
>knock sensors, it maintains whatever spark table it has and does not on
its
>own make use of the advantage premium offers. As you authoritatively state
>the only power difference between the two fuels in this case would be based
>their formulation and actual BTU released in combustion, probably not
>measurable by the "seat of the pants". Without changing timing one could
>not expect any significant change of power by just changing fuel. That was
>the point of that statement.
>
>Thank you,
>
>Daniel R. Nicoson
>Equipment Exchange Company
>Phone: (814) 774-0888
>Fax: (814) 774-0880
>
>-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org]On Behalf
>Of Mike
>Sent: Thursday, December 19, 2002 9:10 AM
>To: diy_efi at diy-efi.org
>Subject: RE: [Diy_efi] Timing Advance Curve?
>
>At 08:35 AM 12/19/02 -0500, you wrote:
>>Octane has everything to do with the speed of burn. Higher octane
actually
>>controls ping by slowing down the burn. This is why a very low HP/cubic
>>inch engine doesn't necessarily gain power with higher octane.
>
>Daniel,
>
>You are wrong on all points, I take it you either havent been on this
>list for long or havent read anything about octane, what it is or how
>its measured...
>
>Referring to your three sentences above, denoted as a to c:-
>
>a. Octane has negligible effect on speed of burn,
> ability to resist spontaneous ignition due to rising temperature
> or pressure has negligible relationship to the speed of burn,
> these are separate issues. It is possible to contrive a
> mixture of fuels to achieve higher octane whilst also reducing
> the burn rate but it is also possible to do the exact opposite.
>
> Think about the fuels used in F1, highest octane and faster
> burn then our engines, how else could they operate with reasonable
> power outputs at 15,000 rpm.
>
>b. Higher octane doesnt 'control' ping, it *only* means its less
> likely to ping ie more resitant to ping but has negligible
> relationship to speed of burn.
>
>c. Any HP/ci engine may not have any imporvement in power out if
> higher octane is used *because* higher octane fuels may not
> necessarily have more energy than lower octane fuels. However,
> if an engine is retuned for higher octane - such as advancing
> the timing or raising the boost then its possible to both
> improve economy and raise power output as required. So bear in
> mind there are four separate issues which 'might' overlap,
> and these are:
>
> - Octane rating
> - Speed of burn
> - Energy content
> - Volatility
>
>Its possible with the large variety of fuel components available
>(ie. Flammible petrochemicals) that a particular combination can
>be reached for a particular aim - but it in no way means there
>is an automatic causal relationship between octane and speed of burn,
>none, zero - zilch !
>
>I'm sure others on this list can articulate this better than can, I
>dont know where you got your information from but its rather one
>dimensional and makes woefully invalid generalisations which can
>lead people astray - the issue is not at all as simple as you
>suggest.
>
>Eg. Here in Australia (amoung others) we have these fuels:-
>
>1. Unleaded, 92 octane (sometimes reaches 94)
>2. Premium, 96 octane, same energy as 1, same effective speed
> of burn - or actually a little faster as a porsch tuner has
> suggested to me.
>3. BP Ultimate, 98 octane *and* a little higher energy than
> 1 or 2 plus a detergent/friction modifier of sorts but BP
> arent saying precisely. Recommended for high performance
> engines where higher speed of burn is more likely to occur.
>
>There are others but I think you get the picture, have a search
>for research octane number (RON) and motor octane number (MON).
>
>rgds
>
>mike
>
>
>
>>Daniel R. Nicoson
>>Equipment Exchange Company
>>Phone: (814) 774-0888
>>Fax: (814) 774-0880
>>
>>-----Original Message-----
>>From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org]On
Behalf
>>Of Mike
>>Sent: Thursday, December 19, 2002 5:26 AM
>>To: diy_efi at diy-efi.org
>>Subject: RE: [Diy_efi] Timing Advance Curve?
>>
>>At 11:23 AM 18/12/2002 -0800, you wrote:
>>>--- "Geddes, Brian J" <brian.j.geddes at intel.com>
>>>wrote:
>>>Well, if you are talking in that sense, simply up the
>>>octane to cover the extra compression. However, you
>>>can run into a point of diminishing returns as far as
>>>power output at higher rpms with the slower burn...
>>
>>Huh ?
>>
>>WHat has octane to do with the speed of the fuel burn ?
>>
>>Isnt octane a measure of the fuels ability to resist knocking ?
>>
>>Mike
>>
>>
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