Combustion engines

The invention provides an alternative fuel for internal combustion engines in which the exhaust heat is used to thermally dissociate water to its constituent gases hydrogen and oxygen. The hydrogen and oxygen so produced is introduced into the combustion chamber of the engine to at least partially replace the conventional fuel. In a preferred embodiment of the invention, water is dissociated into hydrogen and oxygen in a dissociation chamber in the form of a transition tube containing a spirally wound ribbon arranged to urge water in the transition tube outwardly into contact with walls of the transition tube, said walls being heated by exhaust gases of an internal combustion engine.