E2Flight Presentation: Concept Electric Flight Energy ...

E2Flight Presentation: Concept Electric Flight Energy Efficient Hybrid Propulsion Concept for Twin Turboprop Aircraft

Georgi Atanasov DLR Institute of System Architectures in Aeronautics Hamburg

DLR.de • Chart 1 > Symposium E2Flight Presentation > Georgi Atanasov > 28.03.19

Introduction

DLR.de • Chart 2

The main goal of the presentation is to provide an overview on the possibilities to improve the performance of regional twin engine turboprop aircraft by using hybrid propulsion.

The initial discussion covers the basic hybrid concepts: • Parallel Hybrid Architecture • Series Hybrid Architecture

The general benefits and drawbacks of each are discussed and an estimate of the potential aircraft-level effect on fuel efficiency is given.

Further follows a discussion on a merged hybrid concept: • Combined Hybrid Architecture

which incorporates the philosophy of the two basic hybrid concepts to push the limit of the achievable fuel efficiency potential even further.

> Symposium E2Flight Presentation > Georgi Atanasov > 28.03.19

Propulsion Architectures for a Twin Turboprop

DLR.de • Chart 3

Parallel hybrid propulsion:

• Propeller driven by gas turbine and e-motor + battery.

eMotor/Generator

Gas Turbine

Propeller

Battery

PC&D E-Power Control and Distribution

Gearbox

Mechanical Shaft

Electric Power Line

Conventional twin turboprop: • Propeller driven by gas turbine. • No power cross-feed.

Series hybrid propulsion:

• Propeller driven by e-motor • Gas turbine generates

E-power • Battery for power boost

Legend:

Improved propulsion off-design performance

Operation & Integration Flexibility

Weight & complexity increase

Weight & complexity increase

PC&D

PC&D


Off-Design Efficiency Improvement with Hybrid Propulsion

DLR.de • Chart 4

Off-design electric power benefits: • -10% block fuel potential for <500nm missions (due to taxi & descent). • Less noise and emissions near airports. • Relaxed engine takeoff rating.

Regional Aircraft Mission Profile: 500nm


Pow

er O

utpu

t

Time

Fuel

(Ene

rgy)

Flo

w

Time

takeoff

climb

cruise

descent

approach & landing

taxi taxi

Electric Takeoff Boost

Electric Idle Segments

Hybrid A/C

Turboprop

Energy Saving Potential ~10%

Series Chain Operation Flexibility

DLR.de • Chart 5

Decoupled RPM optimization for improved performance & more flexible energy management

Decoupled Power & Thrust

Mitigated One Engine Inoperative Case.

Half power but no prop loss Half thrust & prop windmilling but full power available

Optimal RPM Optimal RPM

Operational flexibility due to mechanical decoupling

PC&D

PC&D PC&D


Integration & Configuration Flexibility

DLR.de • Chart 6

One main gas turbine for cruise: • Improved thermal efficiency

due to scaling effects

Solution supporting gas turbine • In case the main fails • for takeoff/climb boost

PC&D PC&D PC&D

Design specifics: • Main Gas Turbine

designed for efficiency • Supporting Gas Turbine

designed for min. weight / cycle cost

Challenge: • A bigger battery needed

due to diversion in case the gas turbine fails.

• Not a viable tradeoff


One Main Gas Turbine vs Two Gas Turbines

DLR.de • Chart 7

Configuration Tradeoff

Benefit: ~10% eff. improvement

Penalty: Added mass of the supporting gas turbine

PC&D PC&D

A trend for gas turbines in the regional aircraft class and below observed in previous studies:

Gas

Tur

bine

l Eff

icie

ncy

Gas Turbine Power

~10% relative efficiency steps for each 2x power

P2 = 2 x P1

P1

P3 = 2 x P2

P4 = 2 x P3


Performance Comparison Estimate

DLR.de • Chart 8

Reference: Twin Turboprop

Power Units (GT + Gearbox) ~5% from MTOM

Reference A/C

+12% Block Fuel Mass of Hybrid

Series

+7% Block Fuel Electric Losses

PC&D

Hybrid-Series

PC&D

Hybrid-Series 1 Main Gas Turbine

-10% Block Fuel Efficiency of 1 big gas turbine

+3% Block Fuel Mass of

Supporting Gas Turbine

-10% Block Fuel Hybrid Off-Design

Optimization

PC&D

Hybrid-Parallel


Parallel

-7% BF

-4% Block Fuel Operation Flexibility • Component Sizing • RPM Optimization

Hybrid-Parallel and Hybrid-Series generally struggle to achieve double-digit block fuel improvement.

-2% BF


The shown estimates are based on knowledge from

internal projects.

+5% BF

Hybrid Combined Architecture Concept

DLR.de • Chart 9

Generator

E-Motor

One gas turbine in cruise driving two

propellers

50% power transferred in

parallel

50% power transferred in

series

Direct AC-Line:

• No power convertors

• Propeller RPM synchronized

E-Motor & Generator sized for 50% PCRUISE

~25% of PTAKEOFF

Supporting gas turbine: • takeoff/climb power • In case the main fails

Clutch. Coupled for: • Takeoff / Climb • Main gas turbine failure

PC&D Battery for idle power segments.

Clutch Only decoupled for: • Idle • Main turbine failure


Hybrid-Split Architecture Operation

DLR.de • Chart 10

Design Point (Cruise) Takeoff / Climb Idle – Taxi / Descent

PC&D

• Main gas turbine drives both propellers.

• Supporting gas turbine turned off & decoupled by clutch.

• Battery turned off.

• Main gas provides power to both propellers.

• Supporting gas turbine provides power to one propeller (in parallel).


• Both gas turbines turned off & decoupled.

• Battery powers both propellers.

PC&D PC&D PC&D

Worst Case Failure

• Gearbox is jammed – both propeller and main gas turbine cannot be used.

• Supporting gas turbine powers operating propeller mechanically (as in conventional turboprop).



Hybrid-Split Architecture Performance

DLR.de • Chart 11

Reference: Twin Turboprop

-10% Block Fuel Hybrid Off-Design

Optimisation


Combined -10% Block Fuel

Efficiency of 1 big gas turbine

+2% Block Fuel Electric losses

due to 50% series power in cruise.

-12% BF PC&D

Hybrid Combined

+1% Block Fuel Drag from bigger

nacelles

Integrated Hybrid Combined

Reference A/C

Over 10% block fuel saving possible with hybrid combined architecture.

Power Units ~ 5% MTOM


The shown estimates are based on knowledge from

internal projects.

Conclusions

DLR.de • Chart 12

It was shown that by making use of the advantages of both parallel and series hybrid concepts, the combined hybrid architecture is potentially able to achieve a double-digit block fuel benefit.

Main technological bricks of the hybrid combined concept:

• Off-design operation optimization.

• One main gas turbine instead of two in cruise.

Constraints of the hybrid combined concept:

• Regional and commuter class aircraft.

• Twin engine operation.

• Increased benefits on shorter missions. -20%

-15%

-10%

-5%

0%

5%

10%

Bloc

k Fu

el v

s Tw

in T

urbo

prop

Pot

entia

l

Hybrid Parallel

Hybrid Series

Hybrid Series 1 Main Gas

Turbine

Hybrid Combined


DLR.de • Chart 13

Thank you for your attention!


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