Propulsion Unit Thrust Split for Engine Efficiency

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Solution Overview

Problem

Aircraft engines face inefficiencies in specific consumption due to the mismatch between takeoff and cruise phases, where takeoff requires maximal thermodynamic efficiency but cruise requires lower thrust, leading to increased fuel consumption and operational constraints.

Innovation Solution

A propulsion unit configuration with a main engine and an auxiliary engine, where the thrust split between the two engines is optimized for different operating conditions, with the auxiliary engine contributing between 5% to 70% of the total thrust during takeoff and top of climb, allowing the main engine to operate at maximal thrust irrespective of conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the engine is rated for maximal thrust during takeoff with optimal thermodynamic efficiency, then the takeoff performance is improved, but the specific consumption increases during cruise phase

Engineering Contradiction:

Improvetakeoff thrustVSAvoidspecific consumption during cruise

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The propulsion unit is divided into two separate engines: a main engine optimized for cruise efficiency and an auxiliary engine optimized for takeoff thrust. This segmentation allows each engine to be independently rated for its specific operating condition, resolving the contradiction between takeoff performance and cruise fuel efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically switches between different engine configurations: during takeoff the auxiliary engine provides additional thrust while during cruise only the main engine operates. This dynamic operation allows the propulsion unit to adapt to different flight phases, maintaining optimal efficiency in each regime.

Inventive Principle:

Principle #15Dynamics

2Power

If the temperature at output of combustion chamber is reduced for lower thrust during cruise, then the engine power is reduced, but the thermodynamic efficiency decreases

Engineering Contradiction:

Improveengine power during cruiseVSAvoidthermodynamic efficiency

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

By separating the propulsion function into two engines with different optimization goals, the main engine can operate at reduced power during cruise without suffering the same efficiency penalties as a single engine rated for takeoff. The auxiliary engine handles the high-thrust takeoff requirement, allowing the main engine to operate in its optimal efficiency range during cruise.

Inventive Principle:

Principle #1Segmentation

3Use of energy by moving object

If the input and output temperature of combustion chamber are increased to reduce specific consumption, then the thermodynamic efficiency is improved, but the size of high-pressure parts must be reduced

Engineering Contradiction:

Improvespecific consumptionVSAvoidsize of high-pressure parts

Core Design Contradiction:

Use of energy by moving objectVSVolume of moving object

Solution Approach 1:

The two-engine configuration allows the main engine to be designed with smaller high-pressure parts optimized for cruise efficiency, while the auxiliary engine provides the additional thrust capability needed for takeoff. This eliminates the need for the main engine to be oversized to handle both regimes, thereby reducing the volume of high-pressure parts in the cruise-optimized engine.

Inventive Principle:

Principle #1Segmentation

4Device complexity

If a single engine is used for both takeoff and cruise, then the device complexity is reduced, but the specific consumption during cruise increases

Engineering Contradiction:

Improvepropulsion system configurationVSAvoidspecific consumption during cruise

Core Design Contradiction:

Device complexityVSUse of energy by moving object

Solution Approach 1:

Despite the increased complexity of having two engines, the segmentation into a main cruise-optimized engine and an auxiliary takeoff-optimized engine delivers significant fuel savings during the extended cruise phase. The patent demonstrates that the operational benefits outweigh the additional system complexity.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11807376B2Method for rating a propulsion unit comprising a main engine and an auxiliary engine

Publication Date: 2023.11.07 SAFRAN AIRCRAFT ENGINES SAS

AI summary

The invention relates to the rating (S) of a propulsion unit (2) comprising a main engine (3) providing main thrust assisted by an auxiliary engine (4) providing auxiliary thrust, according to the following steps: (i) determining (S1) a distribution between the main thrust and the auxiliary thrust so as to obtain the takeoff thrust of the propulsion unit, the auxiliary thrust making a 5% to 65% contribution to the takeoff thrust, (ii) depending on the distribution determined for the takeoff condition, determining (S2) distribution between the main thrust and the auxiliary thrust so its to obtain the top of climb thrust of the propulsion unit, the auxiliary thrust making at most 70% contribution to the top of climb thrust, and (iii) rating (S3) the propulsion unit (2) in such a way that the main thrust of the main engine (3) determined fir the takeoff condition corresponds to the maximum thrust likely to be achieved by the main engine (3).