Does premium unleaded burn hotter than regular

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People with turbos and high boost often use richer mixtures to cool things.
Wasteful, but it allows higher pressure and more power.

A lean mixture therefore runs hotter in comparison, in hard use or forced induction. But that lean mixture is still richer than 14.7 to 1.

A true lean mixture can not run hotter than the chemically perfect ratio.
 
What's hot and what's not depends on where it's measured. Lean mixtures flame out so you get get less heat and pressure where you want it and lots of waste heat late in the piston travel and after the exhaust opens as unburned regions periodically stumble upon ignition sources. Engine power and efficiency is reduced, pistons and valves can burn, the exhaust radiates a lot of heat, and the catalytic is unable to perform some of it's functions. If the part that won't ignite is at the spark then most of the charge will be wasted resulting in a misfire and maybe a backfire.

Since radiated heat from the exhaust is the first place engine heat can be measured with simple techniques, we say that an engine with a hot exhaust and burnt valves is running hot even though back there where we wanted the heat was colder than it should have been.

Lean burn engines use engineering tricks to make the entire charge burns at the right time.

Diesels run fine lean because the entire combustion chamber serves as an igniter so there's no possibility flame out. Any quantity of fuel zero to stoich will burn with the unused oxygen serving as a space filling inert gas.
 
Quote:
A leaner A/f ratio than stoic will burn hotter.


Running leaner than stoic will exhaust the insulating layer of unburned fuel.
 
Anybody remember the old Hondas with carburetors and the extra intake valve? This valve was the size of a dime. It was a separate circuit that ingested normal to rich mixtures to light off the very lean normal mixture.
Goofy, but somehow it worked OK.
 
Mitsubishi had that as well...pretty crude stratified charge concept.

Are doing similar with diesel/propane down here ATM.

Once started, the lean Gas mix burns.
 
Yes, the MCA-Jet. From Wiki:
Quote:
The MCA stands for Mitsubishi Clean Air which meant that the EX passes both Japan and US emission standards whilst the new cylinder head design of the engine gave way for a third or Jet valve that introduces an extra swirl of air to the combustion chamber swirling the fuel-air mixture for a cleaner, efficient and thorough burn.

In 1979 I read their SAE paper on the development. The valve was originally intended to inject a richer mixture but when they experimented with all A/F ratios they found air alone worked just fine.
 
Wrong - octane prevents detonation due to compression. 8 to 1 low compressiion motor and 87 octane doesnt ping because not enough compression to ignite without spark. 10 to 1 ratio and 87 octane ignites before spark due to pressure in cylinder. Thats why higher compression motors need higher octane - it prevents predetonation.
 
Let us also not forget another factor that promotes pre-ignition - combustion chamber deposits. These effectively raise the compression ratio by lowering the available gas volume in the compression chamber. They can also heat up and act as glow plugs

This is why an older engine may benefit from higher octane fuel. In the end a de-coke is the ultimate fix, but higher octane can ease the symptoms.

I remember an anecdotal tale told to me by a colleague. He claims to have been at a natural gas fuelled powergen station that were running big recip engines. They had a build-up of ash in the cylinders (as confirmed by endoscopic inspection). The chief engineer started the engine up and advanced the ignition - the engine apparently rattled and pinged for a few seconds, after which they took another look and all the ash was gone!

I'm not sure I would have done it - I have seen exhaust valves torched when hard ash became embedded in the valve seat and prevented it from sealing.
 
If you have a Volvo V70 XC, the turbo does in fact feel noticeably better from 87 to 89, and again from 89 to 91. 93 and 94 were almost impossible to feel gain over 91 octane. This car was a "low-pressure turbo." And yes, you could run it on 87. It would act fine. It would simply "feel faster" on the octanes I described.

I know this from having two.. one in Massachusetts (hello, everyone,) and getting gas from the Sunoco at Braintree Circle, and another in NJ - A silver 1999 that I got for free, had in NJ, and that BITOG does not know about.

Put in for points of reference to the discussion about octane.
 
Originally Posted By: Bluestream
Premium fuel burns slower than Reg; everyone knows that. That's why it can give more power in an engine that has been designed for premium, as it ignites it will expand and apply even force as the piston moves down. Reg may be burned up before the piston is all the way in it's downstroke and a "ping" or "knock" is the result. Any difference in the temp of the burn would be insignificant

I have owned 2 cars that called for Premium, and I always ran regular or mid-grade. On my Olds, and my Jag, the knock sensor will retard the timing if any pinging starts...



Not really.

Octane is a value given based on resistance to pre-ignition. Which means prevention of the fuel charge igniting due to compression,cylinder hot spots,any ignition that ISN'T from the spark.
So your incorrect.
Octane and burn temp aren't connected.
 
Originally Posted By: GMBoy
I'm so sick of trying to educate friends and co-workers who run 93 in cars designed for 87. They still think that they are treating their cars to better gas!


This is what the oil companies love. And this also means that the marketers have done their job. The marketing has gotten ahold of them!
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Not entirely on subject, but I did a mpg test using 87 and 89 octane in my Challenger. The 89 got 1 1/2 to 2 mpg better every time I used it, so that's what I run in the car now. I tried 93 once, but it didn't do any better than 89.
 
As mentioned, Octane measure is resistance to detonation. The more it has (93 vs 87, or 94 octane if Sunoco Ultra 94 or whatever) then the more resistant it is to detonation.

I think we need to talk about how that "stops knocking and pinging." I think there is some confusion there.

It also may yield more power in a higher comoression engine, IIRC. We should talk about that, too.

I think what the OP may be getting at is that some do believe that premium gas is better at "burning off carbon deposits" and that perhaps this was done by a higher temperature?

Some also DO believe that they get better fuel economy on oremium gas. Why? Because of a ... "slower burn?" ..
 
Originally Posted By: another Todd
In pump gas, the higher the octane the slower it burns, thereby reducing the explosion that causes the ping. This may not be true though when getting into exotic racing fuel.


this is not correct. Deflagration is the same from 87 to 93 octane.
 
Originally Posted By: another Todd
In pump gas, the higher the octane the slower it burns, thereby reducing the explosion that causes the ping. This may not be true though when getting into exotic racing fuel.



Nope. Burns at the same speed whether it's 87 octane or 93 octane.

It's been simplified and explained how many times in this thread. Heck even GHT has it right. Yet we still see this nonsense posted after a correct post.
I suggest you read the posts in this thread. And absorb it,because your wrong
 
Originally Posted By: Clevy
Originally Posted By: another Todd
In pump gas, the higher the octane the slower it burns, thereby reducing the explosion that causes the ping. This may not be true though when getting into exotic racing fuel.



Nope. Burns at the same speed whether it's 87 octane or 93 octane.

It's been simplified and explained how many times in this thread. Heck even GHT has it right. Yet we still see this nonsense posted after a correct post.
I suggest you read the posts in this thread. And absorb it,because your wrong


thumbsup2.gif


And if GHT can get something..
 
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