Alternative fuel enrichment

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Re: Alternative fuel enrichment

Post by FC-Pilot »

Even the same SBC could make use of different fuels based on the intake manifold alone. I bet it could have three different preferred fuels if say you had a heated intake vs. and air gap style intake vs. a port injected intake. (And no, I do not know which would be best for each combination. I am only smart enough to know that there is an optimum fuel for each one). A thread explaining how to “choose” the optimum fuel would be beneficial to individuals like me. (Then again I am stuck in the stone age building old methanol stack injected engines). I enjoy my caveman roots.

Paul
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Re: Alternative fuel enrichment

Post by HQM383 »

FC-Pilot wrote: Sun Jan 29, 2023 11:58 pm Even the same SBC could make use of different fuels based on the intake manifold alone. I bet it could have three different preferred fuels if say you had a heated intake vs. and air gap style intake vs. a port injected intake. (And no, I do not know which would be best for each combination. I am only smart enough to know that there is an optimum fuel for each one). A thread explaining how to “choose” the optimum fuel would be beneficial to individuals like me. (Then again I am stuck in the stone age building old methanol stack injected engines). I enjoy my caveman roots.

Paul
Agree. Great example with the manifolds. I know I harp on about this but an engine is not an air pump, it is a machine that converts the energy in the fuel being used into power. Yes, more air pumped in has the potential for more fuel to burn but all the work put into head and manifold porting, cam timing, ignition timing, short block prep etc etc will not realize its full potential with non optimal fuel. Some are stuck with what’s at the pump, and in some respect the engine should be built around that pump fuel but those racing may have freedom of choice to be exploited. It would be great if we could tap into David’s knowledge and others in the know to be more wise on the choice of our fuel amongst the myriad of fuels out there.

Knowledge is power.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Alternative fuel enrichment

Post by digger »

RDY4WAR wrote: Sun Jan 29, 2023 2:42 pm
rgalajda wrote: Sun Jan 29, 2023 1:27 pm
Higher octane rating gasoline then the motor needs usually results in a slight drop of horsepower.
False. The octane has no impact on power aside from allowing more power if the engine was octane limited previously.

Take a 10.5:1 compression 383ci SBC making 450-500 hp NA on premium pump gas. Swap the pump gas for VP C25 (>117 AKI), and it'll gain response and power. Swap in Sunoco Supreme (112 AKI) and it'll likely lose response and power. All the octane references is the auto-ignition point of the end gases. Once the mixture is lit, the octane is mostly irrelevant. The distillation, RVP, and oxygen % are far greater factors than octane when it comes to response and power.

The myth that too high of octane kills power likely came from people putting in a fuel that has a high distillation curve and low RVP, like Sunoco Supreme or VP C16, that doesn't vaporize as readily, leave more liquid fuel droplets in the chamber that hurts combustion efficiency. Then mistakenly think the octane is hurting the power when the real issue is a mismatch of fuel to application.
It’s mostly from pump fuel, if the engine is not knock limited usually makes slightly more power on lower octane pump fuel
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Re: Alternative fuel enrichment

Post by FishFry »

I found this quite interesting - AFR vs timing

https://youtu.be/aDSZhy551bo
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Re: Alternative fuel enrichment

Post by David Redszus »

The question regarding fuel enrichment when selecting alternate fuels is not
easily answered from simple inspection of presented data. Before we examine
the proceedure, let's look some fuel basics.

In order to burn, the engine needs both air and fuel. The fuel must be in a vapor
form, not a liquid.

The chemical composition of a fuel will determine how much air will be required
to fully combust the fuel. When the amount of air and fuel are chemically balanced,
it is called stoichiometry, or stoich for short.

The units of measure for all combustion is mass, or in our case, pounds. Stoich then
refers to the number of pounds of air necessary to combust one pound of fuel.
Excess air is called lean, and excess fuel is called rich.

The stoich number often given for gasoline is 14.7. But it is a fictious number and is
rarely found in actual practice. Examine the stoich values in the posted charts.
Therefore, 14.7 should never be used (even for pump gas), and the correct stoich
number for a given fuel should be located.

It is tempting to simply rank the above fuels by stoich number; but that would be wrong.
Reason being, while stoich is determined by fuel (and air mass), we actually meter
fuel (and often air) by volume. It becomes necessary to consider the fuel density,
or specific gravity of the fuel to correct to volume.

If we multiply the stoich value by the specific gravity, we created a fuel enrichment
index number, which can be used to compare fuel blend enrichment.

As an example, we can compare any two fuels with very similar stoich numbers but
with different specific gravity.

260GTX: stoich - 14.6, SpG - 0.763, Index = 11.14
C-16: stoich - 14.7 - SpG - 0.735, Index = 10.80

The higher index number indicates the 260GT will run richer than the C-16, with the
same jetting. How much richer can be determined by dividing the index numbers:
260GTX - 11.14 / C-16 - 10.80 = 1.03148, or 3.1%.
The 260GTX will run 3.1% richer than th C-16 or about one jet size depending on
the fuel delivery system, carb or injection.

Wait a minute, how can that be? 260GTX has 3.7% oxygen in it; how can it run richer?
Because fuel oxygen is not considered when added at the refinery and is included
in the stoich number. The stoich number summarizes the effect of all components.

What about C/H, the carbon/hydrogen ratio? The C/H ratio determines the stoich
value for each type of fuel component, i.e., paraffins, olefins, aromatics, by carbon
number. If the overall C/H ratio is known, it will predict the stoich number.

While we can predict how much fuel is required for any blend, we do not know
how the fuel will evporate, its evaporative cooling, its ignitability, combustion properties,
power production, completeness of burn, flame temperature, carbon deposits, etc.

Blend......SpG......Stoich......O2 %......EnrichIndex
260GTX........0.763....14.6........3.7.........11.14
HCR+...........0.739....14.8........0.0.........10.94
C-16............0.735....14.7........0.0.........10.80
260GT..........0.764....14.1........3.3.........10.77
Supreme.......0.715....15.0........0.0.........10.73
SV-05...........0.745....13.9........4.7.........10.36
MS109reg......0.720....13.4........9.3..........9.65
Q-16............0.716....13.4........9.4..........9.59
CHP+...........0.742.....11.7......18.3..........8.68
C-85............0.794......9.2......32.0..........7.30
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Re: Alternative fuel enrichment

Post by FC-Pilot »

Thanks for the lesson. I know, that I don’t know crap. And knowing my ignorance is my greatest strength. Feel free to continue to expound when time permits.

Paul
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Re: Alternative fuel enrichment

Post by Erland Cox »

Another interesting thing that people believe that engines run hotter when you lean them out.
They make the most heat in the combustion chamber at the AFR where they give max hp and run cooler above and below that.

Erland
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Re: Alternative fuel enrichment

Post by Tom68 »

Erland Cox wrote: Wed Feb 01, 2023 6:50 pm Another interesting thing that people believe that engines run hotter when you lean them out.
They make the most heat in the combustion chamber at the AFR where they give max hp and run cooler above and below that.

Erland
They do run hotter when lean. Combustion temp is lower but longer. The energy goes into the cylinder walls and exhaust system instead of pushing the piston down.
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Re: Alternative fuel enrichment

Post by swampbuggy »

With all due respect Erland, the two cycle engines we raced in the Karting world would run faster and faster as one turned the high speed needle further inward / leaner until it seized at appx. 415-425 deg. so indeed the fuel was a part of the cooling . The NASCAR Boys would melt holes in pistons with restrictor plate gambling ideas , not enough fuel = excessive Heat . Mark H.
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Re: Alternative fuel enrichment

Post by HQM383 »

Is there not a difference between heat created and efficient heat transfer to lower the heat post combustion?

So I can see both sides. With conservation of energy the greatest torque is made due to greatest combustion energy that would become heat as we know. Faster more efficient burn has more exposure to cylinder walls for heat transfer. The leaner slower burn is attempting to transferring its heat to components less conducive to removing the heat. Aluminum pistons will suffer first.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Alternative fuel enrichment

Post by Tom68 »

HQM383 wrote: Wed Feb 01, 2023 8:19 pm Is there not a difference between heat created and efficient heat transfer to lower the heat post combustion?

So I can see both sides. With conservation of energy the greatest torque is made due to greatest combustion energy that would become heat as we know. Faster more efficient burn has more exposure to cylinder walls for heat transfer. The leaner slower burn is attempting to transferring its heat to components less conducive to removing the heat. Aluminum pistons will suffer first.
There's not two sides, a fast efficient burn timed right pushes on the piston and flames out quickly, heat turned to energy.

Too rich or too lean is a slow burn, if you set it off early it resists the rise of the piston and cooks it, if you set it off late it heats the cylinder walls (coolant) and exhaust tract, it provides little useful work because the piston is already descending faster than the burn is expanding. If you set it off just right.....there is no just right when you're too rich or too lean, it comes at a cost.

People do have different ideas on what's rich and what's lean, we say a rich mixture gives max power when jetting on a dyno, I'd call that max power AF, more fuel than that is rich, less fuel than that is lean, even though less fuel than that can be above stoichiometric.
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Re: Alternative fuel enrichment

Post by HQM383 »

Tom68 wrote: Thu Feb 02, 2023 12:01 am
HQM383 wrote: Wed Feb 01, 2023 8:19 pm Is there not a difference between heat created and efficient heat transfer to lower the heat post combustion?

So I can see both sides. With conservation of energy the greatest torque is made due to greatest combustion energy that would become heat as we know. Faster more efficient burn has more exposure to cylinder walls for heat transfer. The leaner slower burn is attempting to transferring its heat to components less conducive to removing the heat. Aluminum pistons will suffer first.
There's not two sides, a fast efficient burn timed right pushes on the piston and flames out quickly, heat turned to energy.

Too rich or too lean is a slow burn, if you set it off early it resists the rise of the piston and cooks it, if you set it off late it heats the cylinder walls (coolant) and exhaust tract, it provides little useful work because the piston is already descending faster than the burn is expanding. If you set it off just right.....there is no just right when you're too rich or too lean, it comes at a cost.
Both sides as in what Erland was saying and what you were saying in previous post. I think Erland meant instantaneous or local heat and you are talking engine temp?
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Alternative fuel enrichment

Post by Erland Cox »

Some engines like power adders or two strokes are partly fuel cooled.
They cannot take leaning out to best power AFR without overheating.
Maybe they could with less ignition lead?
21% of the air is oxygen and that burns with the fuel.
The nitrogen expands when heated together with the parts taking part in combustion.
Highest charge heat gives most expansion and most pressure.
So it is when going towards maximum pressure you can burn stuff, richer or leaner runs cooler.
There can be some surfaces like 2 stroke pistons that need the extra fuel cooling though.

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Re: Alternative fuel enrichment

Post by HQM383 »

David Redszus wrote: Tue Jan 31, 2023 5:35 pm While we can predict how much fuel is required for any blend, we do not know
how the fuel will evporate, its evaporative cooling, its ignitability, combustion properties,
power production, completeness of burn, flame temperature, carbon deposits, etc.

Blend......SpG......Stoich......O2 %......EnrichIndex
260GTX........0.763....14.6........3.7.........11.14
HCR+...........0.739....14.8........0.0.........10.94
C-16............0.735....14.7........0.0.........10.80
260GT..........0.764....14.1........3.3.........10.77
Supreme.......0.715....15.0........0.0.........10.73
SV-05...........0.745....13.9........4.7.........10.36
MS109reg......0.720....13.4........9.3..........9.65
Q-16............0.716....13.4........9.4..........9.59
CHP+...........0.742.....11.7......18.3..........8.68
C-85............0.794......9.2......32.0..........7.30
So David, when choosing an optimum fuel for a given engine and it’s intended purpose the octane rating must be a primary consideration. If there are multiple fuels to choose from that will have a suitable octane rating but have different specific gravity is a higher or lower specific gravity preferable or, is it inconsequential?

I dare say by your last paragraph above there is more to it and an interrelationship with other aspects like the rvp and h/c ratio?
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Alternative fuel enrichment

Post by Rick! »

Fuel, as a percentage of heat rejected by the cooling system, goes down at WOT compared to part throttles.
This is with WOT fueling at just richer than max HP.
I've done a bunch of testing when designing cooling systems for 2-stroke snow adrenaline machines.
Part throttle one can observe upwards of 30% of the fuel energy being rejected by the cooling system.
WOT, the percentage of fuel energy rejected by the cooling system lowers to around 6%. It was interesting to note that both a turbo 4S and NA 2S were in the ballpark of each other for heat rejection as a percentage of fuel energy at this output level (187hp/l to 193hp/l).
The net-net is that fuel does perform some engine cooling at WOT in a properly tuned engine, edge cases notwithstanding.
If you really want to dive further down the rabbit hole, the camshaft is actually the engine heat control valve. You have two choices; blow the combustion heat out the exhaust to help limit cooling system work or keep the heat in the cooling system by opening the exhaust later and carry around a bigger cooling system, the choice is yours,
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