Patent ID: 8631637

Claim:
A system comprising: an auxiliary power unit comprising: a turbine; a compressor; a shaft supporting the turbine and the compressor; a combustor section including: an inlet for receiving compressed air from the compressor; and an outlet for discharging gas to the turbine; an engine case circumscribing the turbine and the compressor, the engine case comprising a compressor section and a turbine section; an exhaust case including: an inlet connected to an outlet of the turbine section at a first joint; and an outlet for discharging exhaust from the auxiliary power unit; and a combustor case including: a first end connected to an outlet of the compressor section at a second joint; and a second end connected to the exhaust case at a third joint; wherein the engine case, the compressor section of the engine case, the combustor case, the turbine section of the engine case and the exhaust case form a serpentine flow path; and a fire enclosure including: a first end joined to the auxiliary power unit by a fourth joint, the fourth joint comprising an expansion joint; and a second end joined to the auxiliary power unit by a fifth joint, the fifth joint comprising an expansion joint.