Great article
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Joined: May 2005
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From: North Bay, Ontario
Great article
Thought I'd share, it's a loooong read but well worth it. A little old, but lots of valuable information about knock, octane ratings, fuel composition and even AI.
http://blizzard.rwic.und.edu/~nordli.../gasoline.html
Apologies if this has been posted before, I've never seen it around.
http://blizzard.rwic.und.edu/~nordli.../gasoline.html
Apologies if this has been posted before, I've never seen it around.
Joined: Mar 2001
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From: https://www2.mazda.com/en/100th/
Thread Starter
Joined: May 2005
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From: North Bay, Ontario
I believe it was a 80+% Toluene mixed with Heptane or something else lower-octaned. I never realized why until this article, nor did I understand the differences between RON and MON.
Joined: Mar 2001
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From: https://www2.mazda.com/en/100th/
i think i understand RON and MON, but imma go read it, just in case!
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From: Czech republic
Increase in fuel temperature and air temperature promoted evaporation of fuel which lowered BSFC with negligible loss of power.
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From: North Bay, Ontario
I guess that's a possibility if your power output isn't approaching the limit of the octane rating of your fuel.
Anyways, I thought they mixed the Toluene with the Heptane in order to lower not only the Octane rating to the maximum allowed limit, but also the sensitivity of the fuel (difference between RON and MON)?
Anyways, I thought they mixed the Toluene with the Heptane in order to lower not only the Octane rating to the maximum allowed limit, but also the sensitivity of the fuel (difference between RON and MON)?
talking head
Joined: Apr 2008
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From: Perth, WA, OZ
The tendency to knock increases as spark advance is increased, eg 2 degrees BTDC requires 91 octane, whereas 14 degrees BTDC requires 96 octane. If you advance the spark, the flame front starts earlier, and the end gases start forming earlier in the cycle, providing more time for the autoigniting species to form before the piston reaches the optimum position for power delivery, as determined by the normal flame front propagation. It becomes a race between the flame front and decomposition of the increasingly-squashed end gases. High octane fuels produce end gases that take longer to autoignite, so the good flame front reaches and consumes them properly.
this is why i argue at high boost and high inlet temps near the fuels limit
that the leading to trailing split is reduced to safe the tune a little
i run in the 8 - 10 degree region for anything past 1 bar ,,housing type ( plug location ) dependent
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From: North Bay, Ontario
Also, things that we have generally practiced but few understand is:
On the last one re: burning oil, wouldn't OMP be considered as having the same effect?
-Increasing the engine temperature, particularly the air/fuel charge temperature, increases the tendency to knock. The Sensitivity of a fuel can indicate how it is affected by charge temperature variations. Increasing load increases both the engine temperature, and the end-gas pressure, thus the likelihood of knock increases as load increases
-Faster engine speed means there is less time for the pre-flame reactions in the end gases to occur, thus reducing the tendency to knock. On engines with management systems, the ignition timing may be advanced with engine speed and load, to obtain optimum efficiency at incipient knock. In such cases, both high and low engines speeds may be critical. Likely why we see many people losing apex seals at 5-6K RPM while tuning
-A new engine may only require a fuel of 6-9 octane numbers lower than the same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to the formation of a mixture of organic and inorganic deposits resulting from both the fuel and the lubricant. They reach an equilibrium amount because of flaking, however dramatic changes in driving styles can also result in dramatic changes of the equilibrium position. When the engine starts to burn more oil, the octane requirement can increase again. ORIs up to 12 are not uncommon, depending on driving style [17,19]. The deposits produce the ORI by several mechanisms:-
-Faster engine speed means there is less time for the pre-flame reactions in the end gases to occur, thus reducing the tendency to knock. On engines with management systems, the ignition timing may be advanced with engine speed and load, to obtain optimum efficiency at incipient knock. In such cases, both high and low engines speeds may be critical. Likely why we see many people losing apex seals at 5-6K RPM while tuning
-A new engine may only require a fuel of 6-9 octane numbers lower than the same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to the formation of a mixture of organic and inorganic deposits resulting from both the fuel and the lubricant. They reach an equilibrium amount because of flaking, however dramatic changes in driving styles can also result in dramatic changes of the equilibrium position. When the engine starts to burn more oil, the octane requirement can increase again. ORIs up to 12 are not uncommon, depending on driving style [17,19]. The deposits produce the ORI by several mechanisms:-
BDC Motorsports
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From: Grand Prairie, TX
i like the way they have described this process,
this is why i argue at high boost and high inlet temps near the fuels limit
that the leading to trailing split is reduced to safe the tune a little
i run in the 8 - 10 degree region for anything past 1 bar ,,housing type ( plug location ) dependent
this is why i argue at high boost and high inlet temps near the fuels limit
that the leading to trailing split is reduced to safe the tune a little
i run in the 8 - 10 degree region for anything past 1 bar ,,housing type ( plug location ) dependent
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