Aircraft Auxiliary Power Unit Generator Cooling via Exhaust Integration

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Traditional gas turbine engine auxiliary power units require significant power losses and drag penalties due to cooling systems and high-temperature exhausts, necessitating costly high-temperature materials in exhaust ducts.

Innovation Solution

A compound engine assembly with a rotary internal combustion engine and integrated cooling system that includes a dedicated coolant for the engine and generator, minimizing heat loss and using a fan-driven cooling air flow to reduce power losses and material costs by lowering exhaust temperatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If traditional cooling systems with fans and ejectors are used for the generator, then the generator is effectively cooled, but significant power losses and drag penalties occur

Engineering Contradiction:

Improvegenerator cooling effectivenessVSAvoidpower losses

Core Design Contradiction:

TemperatureVSLoss of energy

Solution Approach 1:

The patent combines the generator cooling function with the exhaust system by routing exhaust gases through the generator cooling ducts. This merges two functions (exhaust discharge and generator cooling) into a single integrated system, eliminating the need for separate fan-driven cooling systems and reducing power losses.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The exhaust gases from the combustion engine are utilized to provide cooling for the generator. The system uses its own waste thermal energy and exhaust flow to cool critical components, rather than requiring external power-consuming cooling systems.

Inventive Principle:

Principle #25Self-service

2Temperature

If traditional cooling systems with fans and ejectors are used for the generator, then the generator is effectively cooled, but drag penalties in flight occur

Engineering Contradiction:

Improvegenerator cooling effectivenessVSAvoiddrag penalties

Core Design Contradiction:

TemperatureVSObject-generated harmful factors

Solution Approach 1:

The patent merges the exhaust discharge function with the generator cooling function by routing exhaust gases through the generator cooling ducts. This integration eliminates separate ejector devices that would create drag penalties, as the exhaust flow itself provides the cooling action.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent converts the harmful hot exhaust gases, which would otherwise require expensive high-temperature materials and create drag, into a useful cooling resource for the generator. The exhaust flow and thermal energy are repurposed to cool the generator, transforming a harmful factor into a beneficial one.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Temperature

If high temperature materials are used in the exhaust duct walls to handle high temperature exhaust, then the exhaust system can withstand the temperature, but significant cost increases

Engineering Contradiction:

Improveexhaust temperature toleranceVSAvoidmaterial cost

Core Design Contradiction:

TemperatureVSEase of manufacture

Solution Approach 1:

The patent converts the hot exhaust gases into a cooling resource by routing them through the generator cooling ducts. This heat extraction lowers the exhaust temperature before it reaches the exhaust duct walls, allowing the use of less expensive materials that cannot withstand high temperatures.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the thermal parameter of the exhaust gases by extracting heat through the generator cooling system. This temperature reduction transforms the exhaust from a high-temperature flow requiring expensive materials into a moderate-temperature flow that can be handled by conventional materials.

Inventive Principle:

Principle #35Parameter changes

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 reduces power losses and drag penalties, allows for the use of less expensive materials in the exhaust ducts, and improves efficiency by minimizing heat generation and gear losses, while maintaining effective cooling for both the engine and generator.

Implementation Method 1

circulating a coolant through the engine and generator

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

using a fan-driven cooling air flow

Methodology Applied

Scientific EffectForced convection: Forced Convection

Data Source

PatentEP3492721B1Auxiliary power unit with combined cooling of generator

Publication Date: 2020.12.23 PRATT & WHITNEY CANADA CORP

Figure 1
Figure 2
Figure 3

AI summary

An auxiliary power unit (10) for an aircraft, including an internal combustion engine (12) having a liquid coolant system, a generator (64) drivingly engaged to the internal combustion engine (12) and having a liquid coolant system distinct from the liquid coolant system of the internal combustion engine (12), a first heat exchanger (66) in fluid communication with the liquid coolant system of the internal combustion engine (12), a second heat exchanger (68) in fluid communication with the liquid coolant system of the generator (64), an exhaust duct (70) in fluid communication with air passages (66b, 68b) of the heat exchangers (66, 68), and a fan (78) received in the exhaust duct (70) and rotatable by the internal combustion engine (12) for driving a cooling air flow through the air passages (66b, 68b). The liquid coolant system of the engine (12) may be distinct from fuel and lubricating systems of the auxiliary power unit (10).