I came across the attached article on a proposed steam generator in a
1952 Model Engineer Magazine. I hope it is of interest to other experimenters.
The principle of using the water to
extract heat directly from the combustion products is the same as that used
on the Brayton Engine with water injection.
In the Brayton engine, one cylinder provided compressed air while a second was used for combustion on a 2 stroke principle. It was essentially a supercharged 2 stroke. In the case of the Brayton, water injection may have been employed primarily for internal cooling purposes.
One appeal is that water expands some 1700 times on conversion to steam at atmospheric pressure. A
second attraction is that the very high temperatures which give rise to
NOx byproducts are avoided. Engine cooling should not be required and the maximum amount of heat is obtained from the combustion process.
The thermodynamic issue to consider relates to the principle that
highest efficiency is achieved when expansion of the gases involved occurs
across the widest possible temperature difference. This is based on
Carnot's thermodynamic model of a perfect gas. Using Carnot's
principles, the "Air Standard Cycle" is employed for comparing different
internal combustion engine configurations.
The presence of steam limits the upper temperature. However, steam is
anything but a perfect gas and the combustion process is similarly complex.
Real engines are not remotely "Carnot" in operation.