Today I tried mixing gas and diesel to pour over some garden waste that was damp. Even after several dilutions with more diesel, every test I did led to a classic petrol 'whumph' with a huge gout of flames that quickly died out. The only thing the diesel send to do was make it harder to light... Once it did same result.
What is a safe ratio to be flammable but not inflammable, and are the two liquids hard to mix...I wondered if this might be the issue?
The "whumph" is the volatile constituents igniting after they evaporated. Those will mainly come from the gasoline.
Lighting the liquid fuel as compared with the vapour is difficult. The liquid only burns when the burning vapour starts to heat it up and vaporize more of it. That's why you get a big, relatively cool, sooty flame which don't do much to get the rest of the fire going.
A typical aircraft fire safety demonstration usually involves attempting to light a 2-gallon bucket full of jet fuel (which is basically kerosene, and vaporizes less than diesel) by dropping a lighted cigarette into it. The fuel puts the cigarette out just as effectively as dropping it into a bucket of water. Of course lighting it with a blow torch that is powerful enough to heat the liquid has a different outcome!
The way to light a wet fire (and also a dry fire) is from the bottom up, not the top down. Even if you only have "wet" wood, the inside of a reasonable diameter log will be dry. Split off the bark, chop up the core into thin sticks, and you will be able to light them with a match and a bit of dry cotton cloth - or even paper, but cloth is better because it burns slower.
Then build your wet fire on top of the dry one, so the wet material first dries out and then burns.
If you need to light fires regularly, get a "Swedish firesteel." This is a steel bar or rod, made from a special alloy that includes magnesium. If you scrape it with another metal tool like the back of a knife blade, it will produce a shower of sparks, even if it is dripping wet because it is raining. Google will file video demos, and suppliers.
Diesel is useless for lighting fires - kerosene is better. Diesel is, however, considered by many a very good cheap external wood preserver for sheds, doors and window frames, especially if mixed with creosote or other oil based product. An alternative bonfire catalyst is used candlewax - get it from your local restaurant or church.
Do not use gasoline. If gasoline wasn't used in vehicles so much it would likely be classified as "Dangerous Goods" and you would need a permit to use it.
Use straight diesel, and wet a paper towel with it. light the paper towel.
Note that using either gas or diesel is an environmental no-no. A lot of it soaks into the ground.
If you are doing this regularly soak sawdust with diesel. Drain the excess, and spread the sawdust where you want your fire.
Giving the material you want to burn a month or two to dry before burning will make it a lot easier.
The correct ratio is 3:1 diesel to gasoline, for a "hot mix" in a drip torch. If you need a longer burn time and less "whoomph", them mix 4:1 diesel to gasoline, or even 5:1, but that gets difficult to ignite easily. Not using a device like a drip torch, like mixing fuel in a container and pouring cup-fulls of fuel likely won't help and could be risky. You'll need a tool like a drip torch to pour metered fuel on your burn material until the moisture is driven out of it and begins to burn. Something like green wet grass likely won't burn at all.
