FLYING STEAM ENGINES - Fuel

Fuels and Burners.

So far l have used meths (Wood Alcohol) and propane for model aircraft. l have yet to use petrol or mixtures of kerosene and petrol.
The meths burner in Comet Too is a simple half round tank with wick tubes extending into the furnace volume. The furnace is fed with air from a forward facing air scoop under the burner casing. The scoop as two functions, it feeds air to the flame of course but it also controls to some extent the rate of evaporation as the cool air hits the flat bottom of the fuel tank before it enters the furnace volume. This is not my design it is David Parkers' and for simplicity and light weight it is very good. Such simple burners are not so nice if the aircraft noses over on take off spilling boiling alchohol around.
It sounds disastrous but it is not! In these circumstances the plane is close by and an alcohol fire is very easily killed by a little water. l always have a two litre plastic pop (soda) bottle full of water near to hand with its lid perforated with a dozen or two 1.5m.t14. (1/16'') diameter holes. This has worked every time (three times in 100 or so take offs) with only minor blackening of the airframe and no damage to the engine, boiler, or radio gear. This was with doped covering,. lf had left the covering undoped it would have burned far less rapidly. The worst fire only took a evening or so to fix. The air frame now bears a few scars with honour and they are all good talking points. 1 have never had a fire in flight.
The burner for the Groves engine is propane and 1 may well opt to change this fuel for either butane or petrol in future projects. I initially chose propane because it has a significantly higher calorific value weight for weight than butane. It also has a much higher vapour pressure which demands a much stronger tank which is correspondingly heavier. Net gain Negative! My ten gram fuel tank weighs in at 52 grams empty. I have read various recommendations regarding test pressures for LPG tanks, l test butane tanks at 120 psi and propane at 500 psi.
These pressures are a little higher than those required by the UK Model Power Boat Association. l have an uncomfortably bloated looking propane tank to remind me of what could happen if 1 got really careless!
Skylark's burner is a yellow flame oil burner known normally as a pot burner, it has been very reliable but it is a smoky flame which requires a significant space between the end of the flame and the cooler tube of the Monotube to ensure that heavy soot deposits do not become a problem.