Differential Gearbox Apportioning Torque in Gas Turbine APU
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Solution Overview
Problem
In conventional auxiliary power units (APUs) with gas turbine engines, the load compressor is mechanically linked to the electric generator, resulting in a single speed operation, leading to wasted compressor work as unused compressed air is dumped into the exhaust stream due to inability to reduce air flow to zero.
Innovation Solution
A conduit is established for directing compressed air from the load compressor to an injection location upstream of the turbine in the gas turbine engine's gas path, allowing for the conversion of excess compressed air into useful work and reducing waste by enabling its injection at various locations within the engine, such as the turbine or compressor sections, and potentially through a recuperator for heat exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the load compressor is mechanically linked to the electric generator for single speed operation, then the generator can be driven reliably, but the compressed air flow cannot be reduced to zero and unused air is wasted in the exhaust stream
Solution Approach 1:
The patent introduces a differential gearbox that segments the mechanical linkage between the gas turbine engine and the load compressor, allowing them to rotate at different speeds. This enables the load compressor to be decoupled from the single-speed constraint, permitting it to reduce its rotational speed and compressed air output to match actual system needs, thereby eliminating the waste of compressed air in the exhaust stream while maintaining reliable generator operation.
2Device complexity
If the load compressor rotates at a single speed, then the mechanical linkage is simple, but the air flow cannot be adjusted to match demand and compressor work is wasted
Solution Approach 1:
The patent applies the dynamics principle by introducing a differential gearbox that enables variable speed operation of the load compressor. Instead of a fixed single-speed mechanical linkage, the system now allows the load compressor to dynamically adjust its rotational speed independently of the gas turbine engine speed, matching compressed air production to actual demand and improving overall system efficiency.
3Productivity
If the load compressor is decoupled from the gas turbine engine to enable variable speed operation, then compressed air flow can be optimized, but the device complexity increases with additional components
Solution Approach 1:
The differential gearbox serves as an intermediary mechanism between the gas turbine engine and the load compressor. It mediates the power transmission between these two components, enabling variable speed operation of the load compressor while maintaining a manageable mechanical architecture. The intermediary allows the system to achieve compressed air flow optimization without requiring complete redesign of the power transmission system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for the efficient utilization of excess compressed air, improving the overall performance of the APU by converting it into useful work, reducing energy waste, and optimizing the operating range of the engine components.
Implementation Method 1
a recuperator is downstream of the gas turbine engine, and the conduit passes through the recuperator between the load compressor and the injection location
Data Source
AI summary
A gas turbine engine system includes a boost compressor configured to compress air; a combustor in which the compressed air is mixed with fuel and ignited to generate a stream of combustion gases; and a turbine configured to extract energy from the combustion gases, the turbine being drivingly coupled to the boost compressor and to an output shaft via a differential gearbox configured to apportion an input torque from the turbine between a first output torque applied to the output shaft and a second output torque applied to the boost compressor.