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Puller Fuel and Additives

Before we start, this is what the ETPC has to say on what fuel can and cannot be used in competition Pulling (ETPC Pulling Rules, Section 2-20): -

'Legal fuels are alcohol, diesel fuel, petrol, aviation and turbine fuel, methyl-alcohol. Oxygen carriers and combustion accelerators are illegal...'

'Diesel fuel is defined by the ETPC as a pure hydrocarbon... Diesel fuels used in ETPC sanctioned events shall have a dielectric value of no greater than 4.9, nor a value of no less than 2.0.'

'The use of additives containing oxygen, such as nito methane (sic), propylene oxide, dioaxane (sic), MTBE, alcohol or nitrous oxide are strictly prohibited. These additives, and others of the oxygen-bearing family, will significantly change the dielectric constant value of any diesal (sic) fuel...'

As you all probably realise, Tractor Pullers run on a variety of fuels, in many cases dictated by the class in which they run but we thought it might be useful and informative to list not only the base (what the Puller actually runs on) but also some of the 'performance' additives they may be using. This list is in alphabetical order and is not in order of usage: -

Avgas

Avgas (aviation gasoline), also known as aviation spirit in the UK, is an aviation fuel used in spark-ignited internal-combustion engines to propel aircraft. Unlike conventional road petrol (mogas), which has been formulated since the 1970s to allow the use of platinum-content catalytic converters for pollution reduction, the most commonly used grade of avgas still contains tetraethyllead (TEL), a toxic substance used to prevent engine knocking (detonation), with ongoing experiments aimed at eventually reducing or eliminating the use of TEL in aviation gasoline.

In the UK the two standard grades available are Avgas 100 and Avgas 100LL (Low Lead), both of which are 100 octane rated.

Probably the only Puller engines which would run on this fuel would be the Allison V-12, Continental AV1790, Curtiss Wright R-3350 (see 'Roude-Léiw Junior' below) and RR Griffon V-12 which are using carburettors.

Avgas 'Roude-Léiw' (LU) Radial

Dioxane

Dioaxane produces no search results in Google however, assuming this was misspelled dioxane comes up with this. 1,4-Dioxane is a heterocyclic organic compound, classified as an ether. It is a colourless liquid with a faint sweet odour similar to that of diethyl ether. The compound is often called simply dioxane because the other dioxane isomers (1,2- and 1,3-) are rarely encountered.

Like some other ethers, dioxane combines with atmospheric oxygen after prolonged exposure to air to form potentially explosive peroxides. Distillation of dioxanes concentrates these peroxides, increasing the danger. Prohibited as an additive under ETPC Rules.

Diesel

In diesel engines, unlike their petrol counterparts, ignition takes place without any spark, as a result of compression of the inlet air mixture and then injection of fuel. The heat generated by the compression of the air in the combustion camber results in the the ignition of the injected fuel.

In the UK, diesel fuel for on-road use is commonly abbreviated DERV, standing for diesel-engined road vehicle, which is subject to a tax premium over equivalent fuel for non-road use, which is known as Red Diesel.

Diesel engines have become popular because of their higher thermodynamic efficiency which results in better fuel efficiency. This is particularly true where diesel engines are run at part-load; as their air supply is not throttled as in a petrol engine, their efficiency still remains very high.

Note: Puller diesel engines are by nature 'over fuelled', in other words they have to be run with more diesel being injected than it may need to ensure it will always works at maximum power. The 'black smoke' you see is actually partially combusted fuel being ejected as soot. These partially combusted hydrocarbons have been broken down and no longer present any threat to the environment. Unsightly maybe but harmful to the environment, not...

There are three distinct forms of Diesel fuel available in the UK: -

Diesel - 'Bredahl Brothers' (DK) Made 2016

Ethanol

Ethanol, also known as alcohol or ethyl alcohol is a volatile, flammable, colourless liquid with a slight characteristic odour. It is a psychoactive substance and is the principal type of alcohol found in alcoholic drinks. Ethanol is naturally produced by the fermentation of sugars by yeasts or via petrochemical processes. As a by-product of the metabolic process of yeast ethanol will be present in any yeast habitat. Ethanol can commonly be found in overripe fruit. Although some animal species such as the pentailed treeshrew exhibit ethanol-seeking behaviours, most show no interest or avoid food sources containing ethanol.

The largest single use of ethanol is as an engine fuel and fuel additive. Brazil in particular relies heavily upon the use of ethanol as an engine fuel, due in part to its role as the globe's leading producer of ethanol. Petrol (gasoline) sold in Brazil contains at least 25% anhydrous (it contains no water) ethanol. Hydrous ethanol (about 95% ethanol and 5% water) can be used as fuel in more than 90% of new petrol fuelled cars sold in the country. Brazilian ethanol is produced from sugar cane and noted for high carbon sequestration (the process involved in carbon capture and the long-term storage of atmospheric carbon dioxide). The US and many other countries primarily use E10 (10% ethanol, sometimes known as gasohol) and E85 (85% ethanol) ethanol/petrol mixtures. UK petrol may contain 15% ethanol (marked E15).

Use as an automotive fuel dates back to 1908, with the Ford Model T able to run on petrol (gasoline) or ethanol. Ethanol has an octane rating of 108.6 (RON), 0.1 lower than methanol. Ethanol's high miscibility (the property of substances to mix in all proportions) with water makes it unsuitable for shipping through modern pipelines like liquid hydrocarbons. Mechanics have seen increased cases of damage to small engines (in particular, the carburettor) and attribute the damage to the increased water retention by ethanol in fuel.

Ethanol is problematic in that, being drinkable, Customs and Excise want to know what you are doing with it and require you to be licensed to hold stocks and pay duty on purchases!

Prohibited as an additive under ETPC Rules.

Hydrazine (Included for information only)

Hydrazine is a total no-no as a Tractor Pulling fuel additive but has been included for information only. Please click here to see a fascinating article by Tony DeFeo which has been reproduced by kind permission of the author... Historically hydrazine was also mixed with nitromethane producing an unholy highly unstable potential explosive. The explosive salt produced by this mix was the cause of the exploding carburettors Tony mentions in his article.

Curiously hydrazine is not listed as a prohibited additive by the ETPC, presumably because they assume no one would be mad enough to even consider using it and the fact that its partner in crime nitro is already prohibited!

Result of a hydrazine explosion in a dragster

Jet Fuel (see kerosene)

Only used in gas-turbine powered Pullers, see below.

Kerosene

Kerosene is a thin, clear liquid comprising hydrocarbons from the fractional distillation of petroleum between 150 °C and 275 °C. Kerosene is quite often referred to as paraffin in the UK however paraffin includes additives to reduce the smell. Kerosene is widely used to power jet engines (jet fuel) and some rocket engines and is also commonly used in domestic heating systems*. Heat of combustion of kerosene is similar to that of diesel fuel.

Most jet fuels in use since the end of World War II are kerosene-based. Both British and American standards for jet fuels were first established at the end of World War II. British standards derived from standards for kerosene use for lamps (lamp oil)—known as paraffin in the UK—whereas American standards derived from aviation gasoline practices.

Jet fuel, aviation turbine fuel (ATF), or avtur, is designed for use in aircraft powered by gas-turbine engines. The most commonly used fuels for commercial aviation are Jet A and Jet A-1, which are produced to a standardized international specification. The only other jet fuel commonly used in civilian turbine-engine powered aviation is Jet B, which is used for its enhanced cold-weather performance.

Jet fuel is a mixture of a large number of different hydrocarbons. The range of their sizes (molecular weights or carbon numbers) is defined by the requirements for the product, such as the freezing or smoke point. Kerosene-type jet fuel (including Jet A and Jet A-1) has a carbon number distribution between about 8 and 16 (carbon atoms per molecule); wide-cut or naphtha-type jet fuel (including Jet B), between about 5 and 15.

Kerosene - 'Argos Oil Wishering Giant' (NL)

* If kerosene is being used for heating in the UK, two grades of kerosene are defined. BS 2869 Class C1 is the lightest grade used for lamps, camping stoves, wick heaters, and mixed with petrol (gasoline) in some vintage combustion engines as a substitute for TVO (tractor vaporising oil). BS 2869 Class C2 is a heavier distillate, which is used as domestic heating oil.

Methanol (as a base fuel)

Methanol, also known as methyl alcohol is an alternative fuel for internal combustion engines, either in combination with petrol (gasoline) or directly (neat). Although (like ethanol) it burns at a lower temperature than petrol, which makes starting, particularly at low temperatures much harder, it has a much higher thermal efficiency. As a result it offers a much higher power output because of a higher octane rating.

How much higher? Well here I hit a bit of a snag. According to the Wikipedia article on Methanol Fuel the octane rating is 114 however in Octane Rating article this figure is less at 108.7! By comparison standard pump petrol (gasoline) has a rating of 95 to 98 in Europe and the UK.

Because of the problems starting an engine on methanol, most Pullers start the engine with petrol (gasoline) then switch over to methanol when the engine has warmed up enough to run. Fuelling is also counter-intuitive, in that you would normally run an engine rich initially, then reduce the fuel to increase power. This causes the engine to run hotter, as you lose the cooling effect of the excess fuel, until you reach maximum power and the engine melts down.

Excess methanol fuel may vaporise in the cylinder, providing cooling by the latent heat of vaporisation, or remain in liquid form on the piston crown or pass to the exhaust manifold.

Fuel remaining in the cylinder will tend to blow-by the piston rings and contaminate the oil. The oil will change from its normal dark colour to a yellow-green sludge, with liquid fuel sitting on its surface, and must be changed regularly to avoid engine damage. Many have tried to separate the fuel and oil by boiling off the fuel, but this usually results in a fire in the workshop!

The fuel that passes to the exhaust is usually burnt off at the end of the run, causing the spectacular flames that pulling fans enjoy. Fuel can also be seen coming out of an exhaust pipe in a cloud if there is a spark plug failure or misfire.

Following a seven-car crash on the second lap of the 1964 Indianapolis 500 which resulted in the deaths of Eddie Sachs and Dave MacDonald when their petrol (gasoline) fuelled cars exploded. The petrol (gasoline) triggered fire created a dangerous cloud of thick black smoke that completely obscured the view of the track for oncoming cars. The USAC (United States Automobile Club) decided to encourage, and later mandate, the use of methanol in racing.

Indy 500 - 1964

Now you know methanol gives you more power, so apart from the starting problem, what are the down sides?

  • Lakeland Protective PVCMethanol occurs naturally in the human body and in some fruits, but is poisonous in high concentration. Ingestion of 10 ml can cause blindness and 60-100 ml can be fatal if the condition is untreated. In other words, don't drink the damn stuff!
  • Methanol does not have to be swallowed to be dangerous since the liquid can be absorbed through the skin, and the vapours through the lungs.
  • Initial symptoms of methanol poisoning include central nervous system depression, headache, dizziness, nausea, lack of coordination, and confusion. Sufficiently large doses cause unconsciousness and death. Once the initial symptoms have passed, a second set of symptoms arises, from 10 to as many as 30 hours after the initial exposure, that may include blurring or complete loss of vision, acidosis, and putaminal haemorrhages, an uncommon but serious complication.
  • Methanol poisoning can be treated with fomepizole (a medication used to treat methanol and ethylene glycol poisoning), or if this is not available, ethanol, in other words booze.
  • Methanol is highly corrosive to aluminium components, so anodised fittings are required.
  • Although methanol is far less combustible than petrol (gasoline) the vapour is heavier than air and burns giving off very little visible light, making it potentially very hard to see the fire or even estimate its size in bright daylight. If the concentration of methanol vapour is above 6.7% in air it can be lit by a spark and will explode above 62° C/54° F.
Methanol - 'Zeinstra Green Gangster Deere' (NL)

Methanol (as an additive to water injection)

Methanol is often added to Puller water injection system, typically a 50/50 mix. Why would you add water to your engine? Spraying a fine mist of water into the inlet manifold cools the air. The cooler the air the denser it is and the denser the air, the more oxygen it delivers! A secondary benefit is to help cool the cylinders, particularly the piston crowns and valves.

So, why would you mix methanol with the water? Methanol draws much more heat out of the system as it changes from its liquid to gaseous state, making the injection system even more effective, especially when it comes to cooling the piston crowns. For a 50/50 mix the effects on combustion are fairly negligible but if you were to opt for 100% methanol injection there would be a noticeable increase in engine performance but at the cost of increased corrosion. Methanol is highly corrosive to aluminium components, so anodised fittings are required.

Please remember the fact that methanol is highly toxic so bear that in mind!

Methyl tert-butyl ether - MTBE

Methyl tert-butyl ether (also known as MTBE and tert-butyl methyl ether) is an organic compound which is a volatile, flammable, and colourless liquid that is sparingly soluble in water. It has a minty odour vaguely reminiscent of diethyl ether, leading to unpleasant taste and odour in water.

MTBE is a petrol additive, used as an oxygenate they (raise the oxygen content of petrol) to raise the octane number. Its use is controversial because of its contamination of groundwater and legislation favouring ethanol. However, worldwide production of MTBE has been constant owing to growth in Asian markets. Prohibited as an additive under ETPC Rules.

Nitromethane

Nitromethane is an organic compound with the chemical formula CH3 NO2 and is the simplest organic nitro compound. Nitromethane is used as a fuel in various motorsports and hobbies, e.g. Top Fuel drag racing and miniature internal combustion engines in radio control, control line and free flight model aircraft. In this context, nitromethane is commonly referred to as 'nitro', and is the principle ingredient for fuel used in the 'Top Fuel' category of drag racing.

The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen. The amount of air required to burn 1 kg (2.2 lb) of petrol is 14.7 kg (32 lb), but only 1.7 kg (3.7 lb) of air is required for 1 kg of nitromethane. Since an engine's cylinder can only contain a limited amount of air on each stroke, 8.7 times more nitromethane than gasoline can be burned in one stroke.

Nitromethane, however, has a lower specific energy: petrol provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen. Nitromethane can also be used as a monopropellant, i.e., a fuel that burns without added oxygen.

Nitromethane is usually used with rich air–fuel mixtures because it provides power even in the absence of atmospheric oxygen. When rich air–fuel mixtures are used, hydrogen and carbon monoxide are two of the combustion products. These gases often ignite, sometimes spectacularly, as the normally very rich mixtures of the still burning fuel exits the exhaust ports. Very rich mixtures are necessary to reduce the temperature of combustion chamber hot parts in order to control preignition and subsequent detonation. Operational details depend on the particular mixture and engine characteristics. A small amount of hydrazine blended in nitromethane can increase the power output even further. With nitromethane, hydrazine forms an explosive salt that is again a monopropellant. This unstable mixture poses a severe safety hazard and is forbidden in the United States.

Nitromethane was not known to be a high explosive until a railroad tanker waggon loaded with it exploded on 1st June, 1958. After much testing, it was realized that nitromethane was a more energetic high explosive than TNT, although TNT has a higher velocity of detonation (VoD) and brisance (shattering capability). Apart from the explosive properties, exhaust gas from an internal combustion engine whose fuel includes nitromethane will contain nitric acid vapour, which is corrosive, and when inhaled causes a muscular reaction making it impossible to breathe. People exposed to it should wear a gas mask! Prohibited as an additive under ETPC Rules.

NOS (Nitrous oxide)

NOS, or to give it its proper name, Nitrous oxide, commonly known as laughing gas or nitrous is used as a performance enhancer which allows the engine to burn more fuel by providing more oxygen than air alone, resulting in a more powerful combustion. Before you get too excited, the use of NOS is expressly banned by the ETPC (the ruling body for competitive Tractor Pulling throughout Europe). If you are running a demonstration Puller you may be allowed to run with NOS injection on the track but please don't take that as a given. Check with the organisers first!

Nitrous oxide is stored as a compressed liquid; the evaporation and expansion of liquid nitrous oxide in the intake manifold causes a large drop in intake charge temperature, resulting in a denser charge (even more effective than water injection), further allowing more air/fuel mixture to enter the cylinder. Sometimes nitrous oxide is injected into (or prior to) the intake manifold, whereas other systems directly inject, right before the cylinder (direct port injection) to increase power.

Nitrous oxide is a strong oxidant, roughly equivalent to hydrogen peroxide, and much stronger than oxygen gas. NOS allows the engine to burn more fuel by providing more oxygen than air alone, resulting in a more powerful combustion. One of the major problems of using nitrous oxide in an engine is that it can produce enough power to damage or destroy the engine. Very large power increases are possible, and if the mechanical structure of the engine is not properly reinforced, the engine may be severely damaged, or totally destroyed!

Epic NOS Fail!

Although we all associate the use of NOS with petrol engines it does work equally well in a diesel lump! At least one demonstration Puller has been running NOS on a 7½-litre Ford/New Holland power-plant for over 5-years with no apparent ill effects however I suspect even he is very cautious regarding the amount of NOS injected. When the NOS kicks in the engine note becomes almost unbearably harsh and I shudder to think what is going on inside. If you want to go down this route, on your head be it. I certainly would not recommend this route towards enhanced performance. Prohibited as an additive under ETPC Rules.

NOS - Tom Prout (UK)

Petrol (gasoline)

Petrol or gasoline as it is called in the US is a transparent, petroleum-derived liquid that is used primarily as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. On average, a 42-gallon barrel of crude oil (159-litres) yields about 19 US gallons (72-litres) of petrol when processed in an oil refinery, though this varies based on the crude oil source's assay.

The first automotive combustion engines, so-called Otto engines, were developed in the last quarter of the 19th century in Germany. The fuel was a relatively volatile hydrocarbon obtained from coal gas. With a boiling point near 85 °C (octanes boil about 40 °C higher), it was well suited for early carburettors (evaporators). The development of a "spray nozzle" carburettor enabled the use of less volatile fuels.

Further improvements in engine efficiency were attempted at higher compression ratios, but early attempts were blocked by knocking (premature explosion of fuel). In the 1920s, antiknock compounds were introduced by Thomas Midgley Jr. and Boyd, specifically tetraethyllead (TEL). The fuel and performance efficiency of engines improved hand in hand with developments in the refining process until the 1970's. Serious concerns were raised about the harmful environmental impact of the lead additive (TEL) which eventually resulted in what we now know as lead-free petrol.

The octane rating of typical commercially available petrol varies by country. In Finland, Sweden, and Norway, 95 RON is the standard for regular unleaded petrol and 98 RON is also available as a more expensive option. In the UK, ordinary regular unleaded petrol is 95 RON (commonly available), premium unleaded gasoline is always 97 RON, and super unleaded is usually 97–98 RON. In 2006 the supermarket chain Tesco began to sell super unleaded petrol rated at 99 RON. In the US, octane ratings in unleaded fuels can vary between 91–92 RON for regular, through 94–95 RON for mid-grade (equivalent to European regular), up to 95–99 RON for premium (European premium).

Quality petrol should be stable for six months if stored properly (in an airtight container) but petrol will break down slowly over time due to the separation of the components. Petrol stored for a year will still burn in an engine without too much trouble but the effects of long term storage will become more noticeable with each passing month.

Eventually a time comes when the petrol should be diluted with ever-increasing amounts of freshly made fuel so that the older petrol can be used up. If left undiluted, poor combustion will occur and this may include engine damage from misfiring and/or the lack of proper performance of the fuel within a fuel injection system. Engine damage may also occur as a result of the ECU trying to compensate for the poor ignition.

Petrol - 'Le Titan' (FR)

Propane

Like NOS, propane is injected into the inlet manifold. The only example of this performance enhancement was fitted to a Perkins 6354 diesel with the propane injection fitted to the inlet side of the turbo. Did it enhance the Pullers performance? Yes it did however I suspect that in a less robust power plant the extra boost could have been fatal!

Propane is a gas at room temperature, but is compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for barbecue grills (hence the term 'cooking on gas'). It is the third most popular vehicle fuel in the world, behind petrol and diesel fuel. In must parts of the world, propane used in vehicles is known as autogas. In 2007, approximately 13 million vehicles worldwide use autogas.

Propane injection - 'Trailblazer' - Alex Wilson (UK)

Propylene oxide

Propylene oxide (also known as Methyloxirane) is a colourless volatile liquid organic compound with and smell resembling ether. Between 60 and 70% of all propylene oxide is converted to polyether polyols by the process called alkoxylation. These polyols are building blocks in the production of polyurethane plastics.

Propylene oxide was once used as a racing fuel, but that usage is now prohibited under the US NHRA rules for safety reasons. It is a probable human carcinogen, and listed as an IARC Group 2B carcinogen. Prohibited as an additive under ETPC Rules.

Octane Ratings

An octane rating, or octane number, is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance petrol (gasoline) engines that require higher compression ratios.

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane. The engine is run at 600 rpm for the test.

Fuel RON
Diesel 15-25
Butane 94
Regular Unleaded Petrol 95
BP Ultimate 98 / Shell V-Power 98 98
Shell V-Power Nitro+ 99 / Tesco Momentum 99 99
Avgas 100 and Avgas 100LL 100
Shell V-Power in Italy and Germany 100
Ethanol 108.6
Methanol 108.7
Propane 112
Methane 120
Hydrogen > 130

Primary Sources

I am indebted to UKTP's resident Consulting Engineer, Phil Cavanna for his invaluable contributions to this article.

If you would like to add anything to this article or you've spotted a mistake, please e-mail admin@uktp.co.uk.