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Fuelling - more advanced issues
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Octanes are nice little fellas swimming in the fuel - the more the merrier. Just look at the pump: 95 octane is 'regular', 97 Octane is 'super'. Back in the early unleaded times we even had 98 octane fuel. Further back in the leaded era, 4-star 'super' was around 100 octane. Yeeehaaa... Stick some more octanes and way you go... But what is octane? Is it a solid? Maybe it's an additive that grows in bottles (just pour in the tank and hold on for dear life!)
Well, close - the octane rating is an indication of a fuel's resistance to detonation. There are two arbitrary ways of measuring this: the Research Octane Number (RON) method, and the Motor Octane Number (MON) method. Both involve single-cylinder engines running under carefully controlled conditions.
The RON method runs the test engine at 600rpm with intake temp of 83F. The MON method runs it at 900rpm and 300F. Neither is very relevant to real life, but the MON one is less far away from reality.
What we really mean when referring to "Octanes" is the Anti-Knock Index (AKI). This is defined as the average of RON and MON. In the States it's also known as Pump Octane Number (PON)
AKI = (RON + MON)/2
But that's not the whole story: Petrol is a mix of nasty chemicals, some of which are there to deter detonation. Tetraethyl Lead is a very effective additive, resulting in MON increases mainly. Due to health & safety concerns though, adding this in the fuel is now illegal, because the proliferation of two-headed armless retards was blamed on lead and not inbreeding and/or recreational drugs. Nasty stuff lead poisoning - so alternatives to lead were needed. In vain. Knock-resistant substances don't exactly grow on trees, nor distillation of flowers helps much. Save-the-whales movements don't go together with high performance vehicles. The majority of legal octane-boosting fuel additives mainly affect RON, and even that by a tiny amount. But when it comes to calculating AKI, it doesn't matter if it's RON or MON that went up - beware, for the loads inside super/turbocharged engines it's MON that is important!
Another 'gotcha' is when bottles of octane-boosters claim 'up to' 2 extra octane points. The thrill-seeker assumes that means raising 97 up to 99. Not bad for a tiny bottle. The reality is that the promise is for 'up to' two decimal points, i.e. 97 up to 97.2 (if you're lucky!). Less impressive now, isn't it?
The truth is that even if the bottle had pure antisocial-poisonous-evil-illegal-tetraethyl lead in there, it still wouldn't bring the 50liters of a tankful up by two whole octane points. You would need several litres of the stuff. What you actually get in a bottle is fizzled-out unverifiable promises for a wall of power. That's just a drop in the ocean when mixed in the tank.
Millers recently published a 'test' for their Octane booster product (local copy here). It claims to raise the RON value of Optimax by 11 (eleven!) points - from 98.3 up to 99.4. They fail to specify any conditions under which Optimax was sourced, or even the quantity of their product needed to give these results. It will probably be a 30-50% mix which in a full tank would cost several hundred pounds: a lot more expensive than proper race fuel.
Perhaps best out of a bad bunch is this one.
Most expensive of the lot, but at least you get some improvement in knock-resistance
A nice tech page on Octane and Horsepower (local copy here)
An older (but still perfectly valid) article from Fast Car: Does higher octane equal more horsepower?.
If the link doesn't work, below are slightly lower-rez images:
If you feel that your life is empty because you don't know what DeltaRON means, or want to know what mothballs have to do with octanes, then here is the Gasoline FAQ, courtesy of the internet
Some people think in the lines of hey, I've heard that Optimax has 98.6 Octanes, if I add a few bottles of OB surely I can exceed 100, right?
Wrong
First of all Optimax is NOT rated at anything like that - in the eyes of the law it is standard unleaded petrol, so it only has to meet the requirements for 95RON. That's below even supermarkets' Super Unleaded. Maybe while it's still in the refinery it starts life as 98+, but on the way to the forecourts it fizzles out rapidly, and waiting in the underground tanks (that might not seal 100% the inert gas they're supposed to contain) doesn't stop the loss of the lighter ingredients (responsible for the octane uplift). And that's before it gets into your own tank. Shell doesn't trust the fuel to exceed 95RON in the random checks of Customs&Excise - I don't see why anyone else should trust it to. In the Optimax forum their 'expert' admitted to Optimax having a guaranteed MON value of 86, which is just over the legal minimum (85MON). According to Shell, a typical MON value would be around 87, but that would be pot luck. Therefore at worst, Optimax (AKI=90.5) will be slightly better than bog-standard supermarket unleaded (AKI = 90)
Here is an embarrassing shrinkage of the Optimax hype (local copy here)
Secondly adding certain OBs in Optimax might end up in 'rusty' sort of deposits all over the engine. Here is an extract from a post by Dr Iain Wiltshire (aka Mycroft). He usually knows what he's talking about. In a nutshell, combining Optimax with OBs is a no-no. Below are LET plugs after 100 miles on Optimax and Miller's Octane booster:
The whole associated threads (very long but quite interesting) are in the GTR forum, but the internet being what it is, they could disappear at any moment...
Here is another interesting extract from ScoobyNet. A guy unofficially tested Optimax in a petrochemical lab. In a nutshell, Optimax fresh out of that forecourt pump was 97.2RON and within 5 days it was 95.3RON. Definitely not a scientific test - no control fuel, storage conditions etc - but I wouldn't ever expect an official, unbiased fuel comparison: too many billions at stake!
Here is an internet rip-off comparison of commercial Octane Boosters, all of them well-known. See what you make of it.
For the sake of completion, here is yet another extract from a knowledgeable forum regarding homebrew effectiveness and safety
Here is an excellent document written by hands-on racers: Everything you ever wanted to know regarding racing fuels. It was compiled based on info on Ray Hall's first-class website.
Chris Wilson's take on fuels
At the moment, the best fuel in the UK is Tesco 99RON (local copy here).
It is meant to be 99RON and 87MON (local copy here)
It is available in these Tescos. Who would tell that supermarket fuel would be cheaper and better than 'super' unleaded eh?
What we have here is an extract for a high-octane mix, doing the rounds of the internet (OK, maybe you have to know where to look!) It originated in the States, so gallons are NOT imperial. Also when they say '92 Octane' that is the rough equivalent of 98-99 SUL in the UK. I'll elaborate:
Typical Regular Unleaded in the UK is rated at 85MON and 95RON, so the equivalent AKI would be (85+95)/2 = 90 (american octanes)
Typical Super Uneaded in the UK is rated at 86MON and 97RON, AKI = 91.5. [Octane numbers are not the whole story of course, US fuel has different density as well, but now we're nit-picking...]
Now that you know how to interpret the US octane figures, enjoy... ------------------------------------------------------------------
Editor's note: I would NOT suggest that a person use the following fuel mixtures without considering the detrimental effects on your engine, vital engine components (O2 sensor, etc), and other potential damage. That said, the information is interesting.
Original published in:GS-Xtra
1213 Gornto Road
Valdosta, GA 31602
(912) 244-0577Editor: Richard Lasetter, president Gran Sport Club of America (GSCA)
Formula #1 - Toluene
R+M/2.........114
Cost...........$2.50/gal
Mixtures with 92 Octane Premium
10%...........94.2 Octane
20%...........96.4 Octane
30%...........98.6 Octane
Notes: Common ingredient in Octane Boosters in a can. 12-16 ounces will only raise octane 2-3 *points*, i.e. from 92 to 92.3. Often costs $3-5 for 12-16 ounces, when it can be purchased for less than $3/gal at chemical supply houses or paint stores.Formula #2 - Xylene
R+M/2.........117
Cost...........$2.75/gal
Mixtures with 92 Octane Premium
10%...........94.5 Octane
20%...........97.0 Octane
30%...........99.5 Octane
Notes: Similar to Toluene. 12-16 ounces will only raise octane 2-3 *points*, i.e. from 92 to 92.3. Usually mixed with Toluene and advertised as *race formula*.Formula #3 - Methyl-tertiary-butyl-ether (MTBE)
R+M/2.........118
Cost...........$3.50/gal
Mixtures with 92 Octane Premium
10%...........94.6 Octane
20%...........97.2 Octane
30%...........99.8 Octane
Notes: Oxygenate. Very common in octane booster products. Has lower BTU content than toluene or xylene, but oxygenate effect makes the gasoline burn better and produce more energy.Formula #4 - Methanol or Ethanol
R+M/2.........101
Cost...........$0.60 - $1.75/gal
Mixtures with 92 Octane Premium
10%...........94.3 Octane (Methanol)
10%...........94.7 Octane (Ethanol)
20%...........Not Recommended
Notes: Methanol is wood alcohol. Ethanol is grain alcohol and found in Gasohol in 10% ratios. Both alcohols are mildly corrosive and will eat gas tank linings, rubber and aluminum if used in excessive ratios. Main ingredient in "Gas Dryers", combine with water.Formula #5 - Isopropyl Alcohol and Tertiary Butyl Alcohol
R+M/2.........101
Cost...........$0.60-$1.50/gal
Mixtures with 92 Octane Premium
10%...........94.5 Octane
20%...........Not Recommended
30%...........Not RecommendedNotes: Similar to Methanol/Ethanol. Isopropyl Alcohol is simply rubbing alcohol.
Sample Mixture
To make your own octane booster, it is easiest to make up a large batch, and then bottle it up in "dosage-size" uses.
Below is the basic formula of one of the popular octane booster products. To make eight 16 ounce bottles (128 oz = 1 gal):100 oz of toluene for octane boost
25 oz of mineral spirits (cleaning agent)
3 oz of transmission fluid (lubricating agent)
This product is advertised as "octane booster with cleaning agent *and* lubricating agent!". Diesel fuel or kerosene can be substituted for mineral spirits and light turbine oil can be substituted for transmission fluid. Color can be added with petroleum dyes.---------------------------------------------------------------------------------
MAX-BOOST note:
It is my opinion that there are errors and inaccuracies in the homebrew above. It doesn't account for facts like that some of the octane-boosting substances work just by their presence. So a dose that would lead to an increase of 5 AKI points on Indian petrol would be nowhere as effective in a tank of European blend.
I am also aware of other 'gotchas' but will not elaborate here, since this is not meant to be a ready-to-use rocket fuel recipe.
Acetone in fuel?
According to this a tiny amount of acetone mixed in the tank may reduce the surface tension of the fuel, ensuring full atomisation and consequently reducing fuel consumption - reducing carbon deposits perhaps.
I'm not sure how relevant surface tension is when it comes to something as volatile as petrol, but it may be something considering in an experimental setup. Acetone has a high RON value, over 110 but it is unclear how it will react with the other ingredients of the fuel, especially suspended lubricants.
Local copy here
Flame Temperatures
This program will find the theoretical flame temperatures either starting with the ambient temperature or starting with the temperature after the compression stroke but before the spark event. Although these are calculated values, and may not be the real temperatures in the combustion chamber, the differences between the values for various compression ratios, will remain constant, which can then be used as a guide for engine design.Please note that I did not write it, I got it long ago from a website which I can't trace anymore.
It is DOS-based, so the command-line interface might feel alien to the Windoze Generation. If it keeps crashing after you've entered all the data, try the following:
1) Click "Start" on the Start Bar.
2) Click "Run".
3) Type "CMD"
4) Finally, hunt down the program using DOS commands and
execute it.This method should prevent the window from closing once the
program has displayed its results.
TetraBoost: lead additive for the UK. Your oxygen sensor might get grumpy though
Commercial source for methanol/ethanol etc. Shame it's in the States
More about racing fuels and octane boosting here
More nasty stuff (but nice!) If the link doesn't work, try my copy here
Local copy of a widely known internet article on toluene
...on to "Gotchas & Tips"
You CAN be too Rich
By Klaus Allmendinger, VP of Engineering, Innovate Motorsports
Many people with turbochargers believe that they need to run at very rich mixtures. The theory is that the excess fuel cools the intake charge and therefore reduces the probability of knock. It does work in reducing knock, but not because of charge cooling. The following little article shows why.First let’s look at the science. Specific heat is the amount of energy required to raise 1 kg of material by one degree K (Kelvin, same as Celsius but with 0 point at absolute zero). Different materials have different specific heats. The energy is measured in kJ or kilojoules:
Air ~ 1 kJ/( kg * deg K)
Gasoline 2.02 kJ/( kg * deg K)
Water 4.18 kJ/( kg * deg K)
Ethanol 2.43 kJ/( kg * deg K)
Methanol 2.51 kJ/( kg * deg K)Fuel and other liquids also have what's called latent heat. This is the heat energy required to vaporize 1 kg of the liquid. The fuel in an internal combustion engine has to be vaporized and mixed thoroughly with the incoming air to produce power. Liquid gasoline does not burn. The energy to vaporize the fuel comes partially from the incoming air, cooling it. The latent heat energy required is actually much larger than the specific heat. That the energy comes from the incoming air can be easily seen on older carbureted cars, where frost can actually form on the intake manifold from the cooling of the charge.
The latent heat values of different liquids are shown here:
Gasoline 350 kJ/kg
Water 2256 kJ/kg
Ethanol 904 kJ/kg
Methanol 1109 kJ/kgMost engines produce maximum power (with optimized ignition timing) at an air-fuel-ratio between 12 and 13. Let's assume the optimum is in the middle at 12.5. This means that for every kg of air, 0.08 kg of fuel is mixed in and vaporized. The vaporization of the fuel extracts 28 kJ of energy from the air charge. If the mixture has an air-fuel-ratio of 11 instead, the vaporization extracts 31.8 kJ instead. A difference of 3.8 kJ. Because air has a specific heat of about 1 kJ/kg*deg K, the air charge is only 3.8 C (or K) degrees cooler for the rich mixture compared to the optimum power mixture. This small difference has very little effect on knock or power output.
If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can't burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.
So where does the knock suppression of richer mixtures come from?
If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.
So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power.
Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard.
Optimum mix with “later” ignition can produce more power because more energy is released from the combustion of gasoline. Here’s why: When hydrocarbons like gasoline combust, the burn process actually happens in multiple stages. First the gasoline molecules are broken up into hydrogen and carbon. The hydrogen combines with oxygen from the air to form H2O (water) and the carbon molecules form CO. This process happens very fast at the front edge of the flame front. The second stage converts CO to CO2. This process is relatively slow and requires water molecules (from the first stage) for completion. If there is no more oxygen available (most of it consumed in the first stage), the second stage can't happen. But about 2/3 of the energy released from the burning of the carbon is released in the second stage. Therefore a richer mixture releases less energy, lowering peak pressures and temperatures, and produces less power. A secondary side effect is of course also a lowering of knock probability. It's like closing the throttle a little. A typical engine does not knock when running on part throttle because less energy and therefore lower pressures and temperatures are in the cylinder.
This is why running overly-rich mixtures can not only increase fuel consumption, but also cost power.
Supercharged/Turbocharged Performance Guide
This data is intended as a guide only. It is the result of thousands of dyno runs and street testing. Special thanks to Jim Bell of Kenne Bell for the following information.
1. 1psi of boost is equal to an increase of 1/2 point of compression CR (effective compression ratio)
2. 1 point of compression ratio is equal to 2psi of boost pressure (cylinder pressure)
3. 1 point of compression ratio is equal to a 2% increase in Horsepower (100 H.P. @ 10:1 CR is 102 H.P. @ 11:1 CR everything else being equal)
4. 1psi of boost requires 1 additional octane increase of the fuel (minimum)
5. 1psi of boost equal 6.5% increase in Horsepower max (1psi divided by 14.7:1 equal 6.8%) (100 H.P. N/A is 106.8 H.P. max at 1psi of boost)
6. 1 compression ratio increase requires an increase of 3-5 points in octane rating.
7. 1 air/fuel ratio equal 2 octane
8. 1 degree advance in ignition timing requires an increase of fuel octane rating of 3/4 to 1 octane.
9. 10 degree rise in engine coolant (from base of 160-180 degree range) temp. requires 1 octane rating increase.
10. 20 degree rise in ambient temp. requires 1 octane increase.
11. 1 can NOS Octane boost equal 1.5 - 3.6 octane increase
12. For every 1,000 feet of altitude require an increase of .5 octane
13. For every 1,000 feet of altitude requires .5 psi (2"Hg)
14. 1% change in air density equals 1% power change.
15. 10 degree increase in air charge temp. equal 1% power change. (50 degree increase in air charge temp is 5% power loss)
16. 20 degree air charge temp reduction through intercooling equal .5 (1/2) psi additional boost with the same octane fuel.
17. 10% H.P. increase equal 7% AF ration (based on 70% VE) (volumetric efficiency) 70% VE is standard for the "average" engine.
18. 10psi increase in fuel pressure results in 8% increase in AF ratio (we are talking EFI here)
Least known fuel temp fact: did you know that gasoline begins to boil at 95 degrees F? ALWAYS keep fuel as cool as possible!
If at all possible, avoid fuels that use alcohol as an addictive to increase fuel octane. We understand that Mobil does not use alcohol in most states. Alcohol, being more volatile than gasoline, tends to evaporate and lower fuel octane. Large in tank or in line pumps "re-circulate" excess fuel at idle, part throttle and cruise. This results in hotter fuel and increased fuel evaporation (octane reduction) from not only the "re-circulation" but the continuous pressurizing and de-pressurizing of the fuel. Why do you think that Ford has gone to returnless (no return) fuel systems? One reason was to reduce fuel octane losses.
Stay Tuned, More to come!
Reprinted from: Affordable Performance - Tech Tips - Mustang and Ford Performance.
