A revolutionary new steam engine, described by its inventors as "an underwater jet engine", may soon be powering speed vessels more efficiently, cleanly and safely than a conventional outboard motor.
The Pursuit Marine Drive produces thrust by using the energy from high-pressure steam to draw in water through an intake at the front and expel it at high speed through the rear. The steam emerges at high speed from a rearward-facing ring-shaped nozzle into a cone-shaped chamber, where it mixes with the water (see the device sketch). Shock waves created as the steam condenses are focused by the chamber to blast water out of the nozzle. Look how the engine could operate, (CFX simulations) and read more about the design, (steam ejector pump option?). This device weak point is that steam is produced in a heat-exchanger placed in exhaust gases. It requires special water preparation. It is better to put the exhaust directly into the chamber filled with (sea) water to produce steam.
The drive was invented by Australian engineer Alan Burns and developed in Britain by engineers at Pursuit Dynamics in Royston, Hertfordshire. Recently, New Scientist witnessed a version just 20 centimeters long develop around 30 horsepower (22 kilowatts) in a test tank, enough to power a speedboat. But the company says it can be scaled up to about 300 horsepower. There is another group which claims new developments in this field. Traditional view on Al/h2o combustion. A crucial element of the design is that water flowing into the engine draws in air through a vent ahead of the steam jet. The air bubbles change the way the steam mixes with the water, and this significantly increases the engine's efficiency.
Hydroreactive materials (e.g. AL in a form of sherd from machining) could be used to produce steam and hydrogen for different applications. My ideas are summerized as follows. For hydrogen production the process of the circulation attritor grinding when Al powder/water slurry is used. There is the advantage in such means of hydrogen (another elegant way to do this is developed at Purdue, but it generates small amounts of steam and hydrogen) production that there is no oxygen (which coexists with H2) formation that can be expected if hydrogen will be produced by the "pure" thermal (e.g., radiolysis) decomposition of the water. Look at the results of chemical equilibrium calculations for the system AL(S)/H2O(L). It works! See also our publication, where the whole concept was analized. Aluminum seems to be inert because its oxides coat is inert. but the bare aluminum surface reacts instantly with air or water, etc. The water reaction can be confirmed by putting an aluminum surface under water and there scratching it with a file. The new surface takes oxygen and leaves hydrogen, which appears as minute bubbles. This is why in citu produced sherd (filings) should be used.
Such a concept could be applicable to the littoral combat ships like corvette, propulsion system (e.g., by replacing gas turbines). Currently, there are a number stealth vessels in series production in different countries, and placing exhaust gases beneath the hull is not violating the stealth efficiency, since the water emerging from engine sprays is no more than 3 or 4 °C warmer than the water it draws in. Another benefit could be a reduction of the ship drag by using a part of the exhaust for a "gas lubrication" of the hull surface.
The usage of AL/water combustion can also substantially reduce the vulnerabilty of the naval ships due to the elimination of the fuel (diesel oil/kerosene) tanks. The presence of hydrogen bubbles (replacing air) improves the performance of the device which could be especially suitable for new types of underwater crafts. Hydrogen could be also used to feed fuel cells similar to "un sofisticato sistema di propulsione indipendente dall'aria, che affianca il motore elettrico e viene fatto funzionare da celle alimentate da una miscela di idrogeno e ossigeno" used in Italian sottomarino invisible. The details can be found in the Panorama publication. Salt-water combustor, this is also a new (?) way to split water molecules in electromagnetic field forming hydrogen, but this is another story.