pe reivers

Questions about RON. MON. PON.
RON is research octane number, purely defined in a lab test engine with variable compression and detonation sensors. (RON is mostly used in Europe)
MON is motor octane number introduced by SAE. Roughly the same as MON, but the engine is run under "street conditions". MON ratings are from 4 to 10 points lower than RON, depending on fuel quality.
PON is pump octane number (USA). It is the mean value of RON and MON : (MON + RON)/2 ... This is the octane that gas pumps in the USA advertize. It is roughly three to five points lower than RON.
In Europe, regular gas is 95 RON (90 - 91 PON), premium is 98 RON (93 - 94 PON) Some gas stations sell 100 RON , all lead free.
European engine manufacturers prescribe 95 RON regular. In the USA that is 90+ PON (premium gas) 87 PON regular is inferior, and does not fulfill the demands of European engines.

Questions arose concerning my comment on mix degradation in time, especially the 1:50 oil ratio going down to 1:100 EQUIVALENT.
I got the information from a large two stroke service center. A very knowledgeable source.
The 1:100 is of course not the real oil ratio, which even goes up a little in time. However, the oil additives that improve the oil properties degrade in time due to the mixing with gasoline, so the EQUIVALENT lubrication and engine preservation values degrade to 1:100 as compared to the fresh 1:50 mix, all depending on the base stocks used in oil concocting. If high grade base stocks are used, the effect of aging is much less pronounced.

TimBle

Actually, the octane increases over time, not decrease...

just saying


Synthetic will not degrade over a storage period of a year. The main problem we're worried about is a reduction in the volatility of the fuel as the butane leaves the mix. Butane leaves the mix and takes octane with it so we think the octane drops. But the reverse it true. We're left with higher octane components in the mix so the octane increases.
We're purely concerned with volatility and water absorption.

TimBle

This matter is being over analysed.

If you're using mineral oil, under certain conditions the oil can "crack' i.e. he molecules break apart. This is due to the presence of trace amounts of contaminants like catalyst carry over from refinery processes and metal pick up through the gasoline supply chain. These metals under certain cnditiosn will act as catalysts for light cracking reactions. Its not a major concern because they're in trace amounts and they act over a long period of time at STP (Standard temperature and pressure).

If you're using a synthetic oil, the percentage of mineral oil in tha mix is very low anyway so the effect is negligable over the same period.

With long term gasoline storage you're mostly concerned with volatility and water absorption. Period. With E10, things like gum formation can be a challenge, as well as water absorption but Volatility is less of a problem than with E0 because there is much less butane in the BOB / RBOB.

Simply keep the can well closed, at least half full so there as little free space as for butane t evaporate into.
BOB/RBOB has less Reid vapour pressure due to less butane. This affects volatility and therefore cold start can be problematic.
Rough runing engines on old gasoline is usually indicative of water absorption. Either top up the can with fresh gasoline orget a fresh can and use the older stuff in your garden equipment.

I have run my engines on gasoline I've stored for more than 6months. Slightly harder to start but once running they run as long as there is no free water in the fuel.

pe reivers

That would be the day!

TimBle

its does, I"ve tested it

pe reivers

Even then it cannot be considered a general rule. Too many gasolines show a reduction in time.

TimBle

well it depends. How long is the time, what are the storage conditions (temperature, Reid apour pressure of the fuel, free volume in the container).
The rule is general for the period in question i.e 6months.

AN octane drop would require high octane components to evaporate off but the higher octane components are generally the longer chain fuel molucules in the C7 and C8 range with a dash o C9 perhaps, depnding on how the white ol blenders cut the naphtha stream.

SO if you take a gasoline blend consisting of (note: not actual number for any particular plant or process, but the Butane compnent is about right)

C4 Butane @ RON 96 @ 2%v/v
C5/C6 Isomerate @RON 88 @ 20%v/v
C6/C7 Reformate @RON 103 @ 38%v/v
C8 Alkylate @ RON 96 @ 40%v/v

You're going to loose the high octane Butane but theres <2% of it in the pool so it's octane value is minimal. But you also loose some C5whichis lowRON so initially you do see a slight drop by a fraction (around 0.2RON) before the octane starts to rise again as the C5 portion reduces.

NOTE: for a plant that blends accordin to MON the ratio's would be different but the implications the same.

Attached is the fuel storage recommendation from BP that will bareout what I'm saying above.

Truckracer

My Feedback: (19)

Wow, I'm just happy if old fuel passes the "sniff" test after a few months. My airplane fuels get used up quickly so no problem there but lawn equipment fuels can go for long periods. For example at our Minnesota cottage, two weeks ago I used some mixed fuel that was at least (2) seasons old and it ran just fine. It was a bit cranky about starting but once running it ran perfectly.

av8tor1977

My Feedback: (6)

That's one of the drawbacks of using old fuel. The lighter components evaporate making the fuel less volatile, and therefore causing the engine to be harder to start.

AV8TOR