Research supports next generation hybrid aircraft technology to halve NOx emissions

The University of Nottingham is working with UK-based aerospace technology firm Derwent Aviation to assess the performance of their new Dual Drive Booster (DDB).

The DDB is an epicyclic gearbox, that aims to halve nitrogen oxide (NOx) emissions from aircraft and deliver significant cost benefits to airlines.

A 40 percent scale 3D-printed model of the DDB can currently be seen at the University of Nottingham’s stand at the Farnborough Air Show (Innovation Zone in Hall Three) from 16 - 22 July.

Nottingham’s involvements in the Innovate UK-funded project has been to generate a computer model of the gearbox to simulate oil and air flows, so that heat generation is reduced to a minimum.

This performance analysis, which also included an assessment of the stress levels in the gears, aimed to confirm the viability of the DDB, which Derwent claims could be available to operators by 2025. Patents have already been granted for the DDB in the United States, China and the UK and are pending in the rest of Europe.

The flow simulation required expert capability which, in the UK, is only found in the University of Nottingham at the Gas Turbine & Transmissions Research Centre (G2TRC). The G2TRC provides world-leading expertise in the application of multiphase Computational Fluid Dynamics (CFD) to gas turbine transmission systems.

Gas Turbine & Transmissions Research Centre

The G2TRC team comprises academics from engineering, maths and physics, full-time research fellows, rig design engineers, project managers, ex-Rolls-Royce engineers, and numerous PhD students. The team has verified the loads and stresses of the mechanical design of the DDB and are currently optimising the oil scavenging system.

Dr Stephen Ambrose, project lead at the G2TRC, said: “We hold leading capabilities in modelling all aspects of complex transmissions systems, with many of our research outcomes currently implemented within industry.”

“Within the group we have the capability to run large computational models thanks to our access to the University High Performance Computing (HPC) facility, which allows us to quickly perform large-scale calculations and analysis,” Dr Ambrose adds.

Derwent’s Dual Drive Booster is also being developed in conjunction with performance analysis experts within industry as well as universities in the UK and Germany.

DDB brings aviation industry benefits

Charles Cuddington, Derwent’s Chief Executive and former managing director of Rolls-Royce’s civil engines business, says the DDB concept can
deliver major benefits to a variety of applications, in particular more-electric and hybrid aircraft.

“We are excited by the potential of the DDB and we believe we have the industry’s attention. Now we’re looking to the leading manufacturers, with their resources, to join us in taking the project to the next level,” he added.

Using like-to-like comparisons of narrow body aircraft operations currently served by the Airbus A320 and Boeing 737, Derwent’s projections anticipate
the DDB hybrid application will cut poisonous NOx by up to 50 percent and result in fuel burn benefits of three to four percent for flights of up to 1,000 miles, a sector which covers 85 percent of aircraft movements.

They are also in the process of quantifying reductions in maintenance costs resulting from lower turbine operating temperatures made possible by the new-style booster.

The DDB transforms the performance of the booster compressor on conventional two-shaft high bypass ratio engines by driving the booster from both the low pressure (LP) and high pressure (HP) shafts. This involves an epicyclic gearbox in which the LP and HP shafts provide the input while the output drives the booster compressor.

Utilising advances in gearbox design, studies have found that the DDB enables significant amounts of additional power to be extracted from, or returned to the engine. This can be achieved without compromising engine operability, which is not possible with conventional two-shaft gas turbines.

Future electric / hybrid DDB version

Given the likely option for the new booster’s use with more electric configurations, Derwent’s development team is also investigating the potential for an embedded generator/motor driven directly by the internal gearbox, which would rule out the current requirement for an accessory gearbox mounted externally on today’s engines.

Derwent is now beginning discussions with the University Nottingham to explore the possible involvement of its Electrical and Electronic Engineering Department in future studies of the more electric/hybrid version of the DDB.

In addition to Nottingham, Derwent is also collaborating with Aachen University in Germany which has used a modified version of its Gasturb software for performance modelling of the DDB engine including comparisons with current two-shaft and geared fan engines.

UK-based RAW Aviation Consulting Ltd., design and performance analysis experts on future technologies, have also been commissioned by Derwent to create an aircraft performance assessment model for hybrid aircraft.