A little bored here, so I thought Id get my head around the whole Steam powered arms, weapons etc thing, which for me was very important to work out before writing anything. Frankly, I was stuck in the realm of the "highly unlikely" for a while, until I discovered the Flash Boiler which Felix du Temple used on his Monoplan in 1874. It's weight, an astounding 39 to 40 pounds. Totally feasible for personal use. So, being bored, I decided to put a little something together, this was just an exercise. I'm sure the actual engine looked nothing like this. I just wanted to see what it might look like. So I searched for various pics of flash boilers on the Internet, to construct the following.
Excuse my geekiness
Strap that on your back and your ready to go
FLASH BOILERS FOR PERSONAL USE (The du Temple Monoplane "1874" was a large aeroplane made of aluminium, built in Brest, France, by naval officer Félix du Temple)
very compact, light, high-speed circulation steam boiler (steam engine) weighing from 39 to 44 lbs. The engine used a series of very small tubes less than 1/8 inch in internal diameter, packed together, through which water circulated very rapidly, and was "flashed" into steam by the surrounding flame "to obtain the highest possible contact surface for the smallest possible volume" This type oil-fired steam engine, which boils the water instantly by feeding steam to a very advanced four-cylinder enclosed engine, has come to be known as a flash boiler. Flash boilers are lighter and less bulky than other types, and take less time to raise steam from a cold start. On the other hand they are more prone to overheat, because there is no large reservoir to cool the tubes if the water flow is interrupted or inadequate.
The Water-Tube Engine is a boiler in which water circulates in tubes heated by the fire. Fuel is burned inside the engine, creating hot gas which heats water in the steam-generating tubes. The heated water then rises into the steam drum. The steam will then reenter the engine through a superheater to become superheated. Superheated steam is defined as a dry steam that is heated above the boiling point at a given pressure. Cool water at the bottom of the steam drum returns to the feedwater drum via 'downcomer tubes', where it pre-heats the feedwater supply. Eternal exhaust gases are also used to pre-heat the air blown into the engine and warm the feedwater supply.
Perhaps the only problem would be the oil fuel, though this could be solved by adding another smaller tank (which might bring the weight up a few pounds). This might be solved by having the waterfeed tank compartmentalized to hold both water of fuel.