Auxiliary Power Unit Variable Speed Ratio for Aircraft Efficiency
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Solution Overview
Problem
Traditional gas turbine engine auxiliary power units have low thermal efficiency during flight, leading to increased fuel burn and inefficiency in secondary power generation, which requires the main engine to generate secondary power, resulting in significant fuel consumption.
Innovation Solution
A rotary intermittent internal combustion engine-based auxiliary power unit with a turbine section and compressor system that provides configurable speed ratios, allowing for efficient bleed air and electric power generation, comparable to main engine thermal efficiency, thereby reducing fuel burn and optimizing secondary power generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional gas turbine engine auxiliary power units are used, then secondary power can be generated on ground, but thermal efficiency is much lower than main engine at high power, increasing fuel burn during flight
Solution Approach 1:
The patent changes the fundamental operating parameters of the auxiliary power unit by using a rotary intermittent combustion engine instead of continuous combustion, achieving thermal efficiency comparable to main engines at high power conditions during flight operation
Solution Approach 2:
The patent introduces variable speed ratio mechanisms between the engine shaft and compressor shaft, allowing the system to dynamically adjust operating conditions to maintain high thermal efficiency across different flight regimes and power demands
2Loss of energy
If main engine generates secondary power during flight, then auxiliary power unit is not needed, but significant fuel consumption occurs due to reduced thermal efficiency at part load
Solution Approach 1:
The patent segments the power generation function from the main engine by introducing a dedicated auxiliary power unit with its own combustion system, allowing independent optimization of secondary power generation without compromising main engine performance
Solution Approach 2:
The auxiliary power unit is designed to provide multiple functions including bleed air generation, electrical power generation, and potential thrust augmentation, making it a versatile system that can operate efficiently across various flight conditions
3Loss of energy
If auxiliary power unit size and weight are increased to improve efficiency, then thermal efficiency can be improved, but size and weight of the auxiliary power unit increase
Solution Approach 1:
The patent employs intermittent combustion cycles in the rotary engine, where combustion occurs periodically rather than continuously, reducing the size of combustion chambers and associated thermal management systems while maintaining high average thermal efficiency
Solution Approach 2:
The patent replaces traditional heavy gas turbine mechanical systems with a rotary intermittent combustion engine that has fewer moving parts and lower mass, achieving comparable or superior thermal efficiency without the weight penalty of conventional auxiliary power units
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
The solution enables full-time in-flight operation with reduced fuel consumption by matching the thermal efficiency of main engines, allowing the main engine to focus on propulsion, and provides efficient pneumatic and electric power without increasing the size or weight of the auxiliary power unit.
Implementation Method 1
a rotary intermittent internal combustion engine drivingly engaged to an engine shaft
Implementation Method 2
a turbine section having an inlet in fluid communication with an outlet of the rotary intermittent internal combustion engine, the turbine section including at least one turbine compounded with the engine shaft
Implementation Method 3
a compressor having an inlet in fluid communication with an environment of the aircraft and an outlet in fluid communication with a bleed duct for providing bleed air to the aircraft
Data Source
AI summary
An auxiliary power unit for an aircraft includes a rotary intermittent internal combustion engine drivingly engaged to an engine shaft, a turbine section having an inlet in fluid communication with an outlet of the engine(s), the turbine section including at least one turbine compounded with the engine shaft, and a compressor having an inlet in fluid communication with an environment of the aircraft and an outlet in fluid communication with a bleed duct for providing bleed air to the aircraft, the compressor having a compressor rotor connected to a compressor shaft, the compressor shaft drivingly engaged to the engine shaft. The driving engagement between the compressor shaft and the engine shaft is configurable to provide at least two alternate speed ratios between the compressor shaft and the engine shaft.