NOVELTY - The engine (110) has engine sets (111) equally and circumferentially spaced from each other about a rotation axis (126). Each set has a fixed volume primary chamber (112) in which hydrogen peroxide is catalytically decomposed into pressurized gas by a catalyst, a fixed volume secondary combustion chamber (114) in which diesel fuel is introduced into and is pressurized and heated by the gas to the point of spontaneous ignition, and an exhaust passage (116) to release the combusted mixture to produce thrust.    USE - Orbital engine, particularly of fixed volume, multi-propellant type for use in fuel cell or another engine.    ADVANTAGE - The engine can operate without need for any mechanical or electrical devices for compression and or ignition, simplifying structure. The catalyst can decompose the hydrogen propellant into at least an oxidizer to increase efficiency of combustion of the mixture, or into at least a compound other than an oxidizer to promote ignition and or combustion in the secondary combustion chamber. The rotation of the engine is used to draw the propellant such as diesel fuel into the engine, eliminating need for pumps, and enhances pressure in the combustion chambers as well as reduces relative ambient gas pressure at the exhaust passages. The useful exhaust gases, including hydrogen and carbon monoxide, can also be used to fuel the engine sets, other engines, or fuel cells.    DETAILED DESCRIPTION - The engine (110) has engine sets (111) equally and circumferentially spaced from each other about a rotation axis (126). Each engine set has a fixed volume primary chamber (112) in which hydrogen peroxide is catalytically decomposed into pressurized gas including steam and oxygen at high pressure, a fixed volume secondary combustion chamber (114) in which diesel fuel is introduced into and is pressurized and heated by the gas to the point of spontaneous ignition, and an exhaust passage (116) to release the combusted mixture to produce thrust. The exhaust passage is tangential to a circle concentric with the rotation axis such that the thrust causes the engine sets to rotate about the same axis. The fixed volume primary chamber receives a metal type catalyst of e.g. platinum, for decomposing hydrogen peroxide.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of an orbital engine.    Orbital engine (110)    Engine sets (111)    Fixed volume primary chamber (112)    Fixed volume secondary combustion chamber (114)    Exhaust passage (116)    Rotation axis (126)