NOVELTY - Combustor apparatus comprises power generator; compressed air inlet line to the power generator; single compressor (15) for supplying all compressed air requirements of power generator through compressed air inlet line to the power generator; fuel inlet; power generator outlet; exhaust gas outlet line; line for bleeding a portion of compressed air to decrease an amount of compressed air to the power generator for deceleration of driven machine; valve in the bleed line for regulating amount of compressed air bleed; motor (28); and turbine (28).    USE - For supplying power to a driven machine (12), e.g. automobiles.    ADVANTAGE - The apparatus provides a compressor-expander system which can provide variable air (oxygen) flows for high power as well as idle operation to a fuel cell (or other combustor), without employing guide vanes or other expensive, high maintenance complications. The system allows rapid transition between high power and idle conditions to provide good robust performance in applications such as automobiles.    DETAILED DESCRIPTION - The combustor apparatus comprises power generator; compressed air inlet line to the power generator; single compressor for supplying all compressed air requirements of power generator through compressed air inlet line to the power generator; fuel inlet for supplying fuel to power generator; power generator outlet for supplying power to the driven machine; exhaust gas outlet line for exhausting gas from the power generator; line for bleeding a portion of compressed air to decrease an amount of compressed air to the power generator for deceleration of the driven machine; valve in the bleed line for regulating amount of compressed air bleed; motor for supplying power for operating the single compressor; and turbine for receiving exhaust gas from the exhaust gas outlet line for providing additional power for operating the single compressor. The bleed line routes the compressed air bleed to the turbine. The apparatus further comprises a common shaft on which the motor, compressor, and turbine are mounted; and hydrodynamic foil bearing for bearing the common shaft. A heat exchanger is included for heating the compressed air bleed.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view of the compressor-expander system for fuel cell.    Fuel cell arrangement (10)    Machine (12)    Combustor (14)    Compressor (15)    Motor (22)    Exhaust (26)    Expander turbine (28)