A multi-stage turboexpander and a method for generating mechanical power therewith are disclosed. The multi-stage turboexpander includes a casing and a shaft, arranged for rotation in the casing. The shaft is supported by a first bearing at a first shaft end portion and a second bearing at a second shaft end portion. A first radial impeller and a second radial impeller are arranged between the first bearing and the second bearing on the shaft for co-rotation therewith around a rotation axis.

A method of operating a gas turbine engine in a multi-engine aircraft, the gas turbine engine having an engine shaft mounted for rotation in a bearing and a gearbox connected to the engine shaft for torque transmission therebetween, includes axially preloading the bearing using an axially biasing element disposed between the gas turbine engine and the gearbox. The axially biasing element reacts against the gearbox to exert an axial preload force on the bearing and the engine shaft of the gas turbine engine.

A method of maintaining rotor tip clearance and compressor operational line during a transient operation of a gas turbine engine is disclosed. In various embodiments, the method includes applying high spool auxiliary power to a high speed spool for a first time period, applying low spool auxiliary power to a low speed spool for a second time period, sensing one or more operational parameters of the gas turbine engine during the transient operation, and ceasing application of power to the high speed spool, based on the one or more operational parameters.

A method of maintaining rotor tip clearance and compressor operational line during a transient operation of a gas turbine engine is disclosed. In various embodiments, the method includes applying high spool auxiliary power to a high speed spool for a first time period, applying low spool auxiliary power to a low speed spool for a second time period, sensing one or more operational parameters of the gas turbine engine during the transient operation, and ceasing application of power to the high speed spool, based on the one or more operational parameters.

Provided herein is a power generation system and method for transforming thermal energy, such as waste heat, into mechanical energy and/or electrical energy. The system employs features designed to accelerate start times, reduce size, lower cost, and be more environmentally friendly. The system may include multiple compressors on separate pinion shafts with multiple expanders, a temperature valve upstream of compressors with a mass management system downstream, an intercooler between compressors, and a cascade exchanger. In one embodiment, the system is configured to drive a synchronous generator, with the separate pinion shafts rotating at two separate, but constant, speeds.

Provided herein is a power generation system and method for transforming thermal energy, such as waste heat, into mechanical energy and/or electrical energy. The system employs features designed to accelerate start times, reduce size, lower cost, and be more environmentally friendly. The system may include multiple compressors on separate pinion shafts with multiple expanders, a temperature valve upstream of compressors with a mass management system downstream, an intercooler between compressors, and a cascade exchanger. In one embodiment, the system is configured to drive a synchronous generator, with the separate pinion shafts rotating at two separate, but constant, speeds.

An energy storage system includes a heat generation apparatus configured to generate heat from electric power and a heat storage device configured to store the heat generated by the heat generation apparatus, the heat generation apparatus including an electric motor connected to an electric power system and rotated by surplus electric power received from the electric power system, and a heat generator having a rotary unit rotated by the electric motor and a heat generating unit configured to generate heat through electromagnetic induction, and configured to convert rotational force of the electric motor to heat.

A gas turbine engine for an aircraft includes an engine core including a first, lower pressure, turbine, a first compressor, and a first core shaft connecting the first turbine to the first compressor; and a second, higher pressure, turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor, and a fan located upstream of the engine core and including a plurality of fan blades extending from a hub. A low pressure turbine temperature change is defined as:

[00001]$\frac{\mathrm{the}.Math..Math.\mathrm{first}.Math..Math.\mathrm{turbine}.Math..Math.\mathrm{exit}.Math..Math.\mathrm{temperature}}{\mathrm{the}.Math..Math.\mathrm{first}.Math..Math.\mathrm{turbine}.Math..Math.\mathrm{entrance}.Math..Math.\mathrm{temperature}}.$

A fan tip temperature rise is defined as:

[00002]$\frac{\mathrm{the}.Math..Math.\mathrm{fan}.Math..Math.\mathrm{tip}.Math..Math.\mathrm{rotor}.Math..Math.\mathrm{exit}.Math..Math.\mathrm{temperature}}{\mathrm{the}.Math..Math.\mathrm{fan}.Math..Math.\mathrm{rotor}.Math..Math.\mathrm{entry}.Math..Math.\mathrm{temperature}}.$

A multi-engine aircraft includes first and second gas turbine engines for providing motive power to the aircraft, each of the first and second engines comprising an air system, an air pressure line extending between and fluidly connecting the air systems of the first and second engines, and a pressure wave damper communicating with the air pressure line extending between the first and second engines.

A gas generator has at least one compressor rotor, at least one gas generator turbine rotor and a combustion section. A fan drive turbine is positioned downstream of a path of the products of combustion having passed over the at least one gas generator turbine rotor. The fan drive turbine drives a shaft and the shaft engages gears to drive at least three fan rotors.