Mixing Your Own Fuel.

PLEASE READ NOTE 1) Safety Hazards FIRST. You have been warned.

Many Modellers are reluctant to mix up their own fuel for a variety of reasons some of which are listed below:-

With some premium fuels costing £17 per US gallon. (note that a US gallon is smaller than a UK gallon) Model Aircraft Fuel makes ordinary lead free petrol look cheap. In fact none of the above statements 1 - 6 are true if the process is approached in a proper manner and you use premium grade materials. There is little point in using cheap materials if you are going to the trouble of mixing your own fuel. After all, you are trying to produce a fuel at least as good, if not better, than a commercial fuel.

Do not forget that the major model fuel suppliers have the benefits of bulk buying and even when making your own fuel, unless you have access to cheap raw materials, you may find that you are not saving all that much money despite your DIY efforts. See the Fuel Calculator. The prices in the costing column are actual ones from local suppliers in November 2005.

1) Safety Hazards

We are making very powerful fuels and most of the ingredients are HIGHLY FLAMMABLE. For this reason all these materials should be stored in a cool dry place, well away from the house. Only buy enough of the really dangerous materials such as Ether, Nitro & Methanol to last about a month and store in good solid airtight containers, off the floor in a cool DRY location, well away from children and pets. Always mix in a well ventilated area, out in the open on a dry day, wear a mask, gloves and goggles and keep well away from sources of ignition. Avoid fumes and ingestion. Methanol in quite small doses can cause blindness and death if ingested and Amyl Nitrate can also be LETHAL. Avoid metal tools and containers that may cause sparks etc. Methanol readily absorbs water so airtight storage is very important. Please read the Safety Documents (COSHH) in Appendix II. Make sure all containers are scrupulously clean before use. Clean all tools and containers thoroughly after use as oil attracts dirt and dust like a magnet. It is a good idea to store all measuring instruments & containers etc. in a sealed plastic bag.

2) Mixing Your Own

There are two ways to measure liquids when mixing, by weight or by volume. All fuel is mixed by volume. For example an 80% Methanol 20% Castor Oil fuel will have 8 gallons of Methanol and 2 gallons of Castor Oil in a 10 gallon mix etc.

Mixing is fairly straightforward and should be carried out in a well ventilated area well away from the house etc. (see note 1) Measure out each of the ingredients carefully, double check and slowly add to the base material, usually Methanol for Glow Fuel.. Stir all the time with a plastic spoon and when the mix is completed decant into a suitable strong container. (I use ex Cool Power Model Fuel Bottles as these are very robust and have anti-tamper caps) Stir well for about 15mins. Mark up the container with its Function, Date and Mix. i.e.: 2 Stroke Glow Plug-Running In, October 2005, 3% Castor, 14% Synthetic, 83% Methanol etc. Order of mixing is not important, but mix well.

So if we wish to mix up a 5 litre batch of 83/14/3 (Methanol/Synthetic Oil/Castor) how do we calculate the required amounts. If you download the Fuel Spreadsheet this will do it for you. If you are clever you can even use this calculator to re-calculate the additions if you wish to change from say an 80/20 to an 75/25 etc. Once you have put ingredients in you cannot get them out, you can only alter the ratio's. Not always possible !

Problem:- We have purchased a full gallon of Methanol and wish to convert the whole lot into Fuel. An easy problem if you are good at maths. If not the little Excel Spreadsheet will work it all out in a flash. Download fuel.xls and enter your gallons in the top line. (it converts to millilitres' for ease of measurement) Then enter the required percentages of all the other ingredients. Put a zero if any are not required. (the total ingredients must add up to 100%) In a flash it will calculate the volumes for the other ingredients with the Methanol set at the original 1 gallon.(or whatever) This is really the Fuel Spreadsheet working in reverse, and will produce a final volume of approx. 1.25 Galls. If you know the prices it will also work out the cost of the mix or a gallon and even convert to US gallons. As a check it will calculate the final SG as well. This can be useful if you loose the label on a mix.

3) Engine Damage

Many top competition modellers mix their own fuel, a friend who is a BMFA National Champion always mixes his own fuel. It should be noted that the lower the oil content the more powerful the fuel. If a mix has 20% oil it only has 80% actual fuel for any given volume. The oil is only there as a lubricant, giving no power at all. However you reduce the oil ratio at your (engines) peril. Most, if not all, of the main Fuel Suppliers are quite happy to sell the base ingredients, and some even include mixing details and formulae. Always follow the engine manufacturers recommendations as your guarantee may be affected, particularly as regards 'running in'

Before the advent of Synthetic Oil, Castor was the main lubricant for both Diesel & Glow Plug Motors. Castor Oil is a natural product made by pressing the Castor Bean and as such tends to vary slightly in quality. Only use so called 'First Pressing' as this is by far the best lubricant but it is expensive compared to 2nd & 3rd pressings. The main problem with Castor Oil is its tenacity. It is such a superb lubricant it is very difficult to remove from both engines and models. It also tends to gum up as it gets old. Good quality Castor is de-gummed. Synthetic Oils on the other hand are consistent in quality, easy to remove and the better ones equal Castor Oil. (however many 'Synthetic' commercial fuels still contain 2-3% Castor Oil as a backstop under extreme running conditions) Castor Oil is very good at high temperatures and prevents scuffing, it is often added to 'running in' mixes for this reason. There are a number of Synthetic Oils on the market, prices vary considerably and it is good policy to buy at least one of the brand leaders. ML70, Klotz or EDL are some well known names and have stood the test of time. Klotz seems to have a very good reputation. Diesel fuel (Compression Ignition Engines) generally use Castor Oil only.

4) Material Supply

Methanol and Ether cannot be sent via normal post due to the fire hazard, but small quantities can be delivered by carrier, at a premium price. The best way to buy these ingredients is to find a local supplier or buy in bulk at the various Trade and Model shows. Nitro Methane, IPN and the various Oils can be sourced in the same way. When buying Methanol make sure it has a very low water content. Cool Power claim a purity of 99.97% in their Methanol.

5) Quality

Most reputable fuel suppliers are quite happy to publish the formulae of the fuels they sell, so if you follow these and use top quality materials you should have no problems. However see note re costs.

6) Formulation.

Glow Fuel

There are literally dozens of formulations. Visit any of the three supplier sites in Appendix 1 where you will find all the information you will ever need. Some suppliers add Anti-Foam, Extreme Pressure and After Run Oil, these additives are generally beyond the scope of home brews, unless you are a chemist. They are not essential for normal sport flying. Due to a confined operating space and lack of a cooling airflow Helicopter fuels generally contains more oil. See the suppliers formulations for guidance. Four Strokes are particularly prone to internal rusting and it is a good idea to add an anti rusting agent. Particularly towards the end of season. I use Lubysil SC100.

The following fuel mix is recommended by ENYA Model Engines.

(1) Methanol 80% Castor 20%. (2) Methanol 75% Nitro-Methane 5% Castor Oil 20% You can substitute the Castor Oil for Synthetic or use 18% Synthetic and 2% Castor.

4 Strokes can reduce the Oil content to 15% i.e.: 85% Methanol 15% Oil. No Nitro. See makers recommendation's.

Diesel Fuel. (Compression Ignition)

All the above comments apply to Model Diesel Fuel. The main ingredients are Castor Oil, Ethyl Ether, Kerosene, and Iso Propyl Nitrate (IPN). Amyl Nitrate is used in some North American fuels. This is a HIGHLY DANGEROUS CHEMICAL and should NOT be used by home blenders. It is a Heart Stimulant and can cause DEATH. You have been warned. These should be obtained from a reputable supplier of Model Fuels to guarantee the purity and fitness for purpose. Again suitable formulations can be obtained from any of the suppliers in Appendix 1. When buying these materials always state the end use requirements. IPN, an Ignition Improver, is is in short supply but is a must for Diesel fuel.

The following mix is recommended by ENYA Model Engine. See also the Diesel link below.

Kerosene 36% Ethyl Ether 36% Castor Oil 25% IPN 3% Synthetic Oil is NOT recommended for Diesel use.

7) Specific Gravity

Measurement of Specific Gravity or SG is a very useful method of determining the Oil content in a batch of fuel. However this method has its limitations and without proper care can lead to errors. It can only be used with a two part mixture, when used with 3 or more parts the other ingredients can play off against each other. For example if the Methanol is contaminated by Water the results are useless. Klotz Oil KL 100 has an SG more or less the same as water.(1.00 - 1.04) and Castor is only a tad lower.

It is a good plan to measure the SG of each ingredient WHEN PURCHASED and note this on the can. If possible note the temperature as well, SG is usually measured at 25degs C. If there is any change, for example, if the SG of the Methanol has changed from 0.790 to 0.800 it has probably absorbed water. If you download fuel.xls there is a little sub routine that works out the SG of the final mix. Check the expected SG's from the COSHH sheets. You will need a 'trial jar' and a Hydrometer. These are similar to the ones used for Winemaking but calibrated 0.700 to 1.000. If you are mixing say an 80/20 fuel the final SG is 0.824.

One very crude method of determining the oil content is to mix about a cupful of fuel in a jam jar. Add warm water and mix well by shaking, the water/fuel will turn milky as the methanol and the water mix. The warm water will displace any oil in the fuel (Water and Oil do not mix) which will then settle to the bottom of the jar. If you can measure the volume of fuel before you start and then measure the amount of oil displaced a fair idea of the oil content can be obtained. If no oil is displaced you can be pretty sure all you have is methanol. I am not sure of the chemistry involved but it seems to work OK in practice.

Appendix I

For those of you in the Northwest (UK) here is a good supplier of base materials in Golborne (North of Warrington) Prestwich Model Boats

Here is a link to the Red Max Fuel Site c/w some Material Safety Data Sheets.

And a link to the Model Technics web site. The main UK supplier of Model Fuels.

Another one to the Morgan Company who trade under the name Cool Power Fuels A very respected supplier based in the USA.

This is a link to the Aircraft Proving Ground Site Full of useful information re Model Fuels.

An excellent site for Diesel Fuel Blenders.

Klotz Oil Web Site http://www.klotzlube.com Also a good source of COSHH Data.

Appendix II

Specific COSHH (Control of Substances Hazardous to Health) Data sheets can be found at:-

Ethyl Ether

Methanol

Kerosene (refined Diesel oil)

Nitro Methane

Castor Oil

Isopropyl Nitrate

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Text © Colin Usher 2007 Illustrations © Colin Usher 2007

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