NEWAC SP6 “Innovative Combustor” Editorial by Salvatore Colantuoni (Avio S.p.A.)

It’s a very interesting experience, as SP6 Leader, to manage since May 2006 the strong and fruitful research technical cooperation between ten European Partners in the frame of NEWAC: with three teams of engineers and technicians of AVIO, RRD and TM aero-engine companies, scientists and researchers from Karlsruhe, Florence and Graz Universities, the ONERA, DLR and DGA Experimental Centres and the SME Enginsoft.

Our objectives in SP6 are to develop and validate lean fuel injection technology up to TRL 5-6 demonstrating 60% to 70% reduction of NOX emissions in the LTO cycle versus the CAEP/2 limit. The NOX reduction targets are set assuming that emissions of CO, un-burnt hydrocarbons, and soot/smoke remain at least unchanged on the level of year 2000 technology.

Let’s remind that lean combustion technology operates with an excess of air to significantly lower flame temperatures and consequently reduce NOX formation. Up to 70% of the total combustor air flow has to be premixed with the fuel, before entering the reaction zone within the combustor module. The optimisation of homogeneous fuel-air mixtures is the key factor to achieve lower flame temperatures and hence lower thermal NOX formation. Depending on the size and thrust range of the particular engine application, three different fuel injector technologies have been considered by SP6 teams (fig. 1):

[Begleittext / Subline: Fig 1 – Application of different fuel injector technologies depending on engine OPR ]

• LP(P) (Lean Pre-vaporizing Pre-mixing) (fig 2) is based on the action of two air flows, one devoted to the fuel atomisation and the second dedicated to the mixing and fuel evaporation. Their combination acts as promoter for the flame stabilisation in the combustion chamber.

• PERM (Partial Evaporation and Rapid Mixing) (fig 3) is based on swirler technology development and is addressed to achieve partial evaporation and rapid mixing within the combustor, optimising the location of the flame and the stability of the lean lystem;

• LDI (Lean Direct Injection) (fig 4) has a controlled premixing: concentric internally staged fuel injection, with optimised pilot and main stage flame structure, to control their interaction for low NOx and weak extinction stability.

[Begleittext / Subline: Fig 2 – LPP concept ]

[Begleittext / Subline: Fig 3 – PERM concept ]

[Begleittext / Subline: Fig 4 – LDI concept ]

In SP6 all partners are following the route of implementing novel fuel injection technologies on single annular combustors with very advanced cooling schemes.

WP6.2 – Advanced Injection System & Fuel spray technology development

In the WP6.2 the innovative injection systems concepts have been defined and their design optimised through a combined approach of intensive CFD and detailed experimental investigations. WP6.2 technical result is the validation at TRL 4 of three injection systems for a wide range of OPR over 40, from -60 to -70% NOX vs. CAEP/2.

The fuel injector configurations have been tested (2008-2009) within low (fig. 5, 6) and high pressure single sector rigs (fig. 7, 8) to validate the overall performance. In particular high pressure single sector tests (from 10 up to 40 bar) give indications of the pollutants emissions (NOX, CO, UHC) and of their thermo-acoustic behaviour.

[Begleittext / Subline: Fig 5 - KIT Rig (AP, LP tests on PERM) ]

[Begleittext / Subline: Fig 6 - TM Rig (LP tests on LPP) ]

[Begleittext / Subline: Fig. 7 - ONERA Rig (HP tests on LPP, PERM) ]

[Begleittext / Subline: Fig 8 - DLR Rig (HP Tests on LDI) ]

Detailed flow-field and combustion investigations have been supported by advanced laser optical diagnostics techniques, that give insight into the fuel preparation, fuel placement, the initial combustion flame front of both pilot and main combustion zones (Fig. 9, 10, 11). These tests, under finalization by the end of 2010, have substantiated the design and triggered further modifications with subsequent CFD work.

[Begleittext / Subline: Fig. 9 - DLR Rig (LDI) ]

[Begleittext / Subline: Fig. 10 - ONERA Toulouse (LPP) ]

[Begleittext / Subline: Fig. 11 - TUG Rig (LPP) ]

WP6.3 – Ultra Low NOx Combustor chamber design

In the WP6.3 the design or redesign of three Ultra Low NOx combustor chambers has been done (Fig.12,13,14), focusing on the optimisation of Single Annular Combustor architecture and on other lean combustion technologies, like advanced cooling systems, fuel control systems and fuel staging concepts.

[Begleittext / Subline: Fig 12 - LPP Combustor (TM) ]

[Begleittext / Subline: Fig. 13 - PERM Combustor (AVIO) ]

[Begleittext / Subline: Fig. 14 - LDI Combustor (RRD) ]

In particular the PERM Combustor design been optimized by an extensive experimental test investigation on effusion cooling system (Fig. 15) and by detailed CFD analysis (Fig 16).

[Begleittext / Subline: Fig 15 – Test rig and Liquid Crystals technique (UNIFI) ]

[Begleittext / Subline: Fig 16 – CFD Analysis on PERM (ES) ]

WP6.4 – ULN combustor technology validation

The validation of the ULN combustion technology up to TRL 5/6 is now well on-going: three test-articles have been manufactured and instrumented, to be tested in full annular combustor rigs, simulating engine environment, through test campaigns in a wide range of operating conditions, from sub-atmospheric, to ambient pressure up to high pressures.

Two HP test campaigns on LDI combustor have been done up to 15 bar, exploring air pressure, temperature, Fuel-Air-Ratio, pilot/main fuel split effect (Fig 17). Based on first analysis of 2nd test results (July 2010), NOx improvement for all NEWAC high OPR cycles have been obtained. Altitude relight test has been completed with Light-around achieved (30 kft altitude simulation).

[Begleittext / Subline: Fig 17 – FANN LDI Combustor (RRD) ]

Ignition and Lean Blow-Out characterization tests have been completed on PERM Combustor (LP conditions) at AVIO Pomigliano experimental Centre (Fig. 18) early in 2010. Then the PERM Test-Article has been reassembled in the HP Combustor rig configuration to be installed in the K11 Test-bench at DGA (Fig. 18). HP Test campaign started in October and is actually on-going.

[Begleittext / Subline: Fig 18 – FANN PERM Combustor LP Rig (AVIO) ]

[Begleittext / Subline: Fig 19 – FANN PERM Combustor HP Rig (DGA) ]

Regarding the LPP FANN Combustor, the Test-Unit prepared by TM has been sent to ONERA to be installed in the M1 Test-cell in Palaiseau (Fig. 19). During the 1Q 2010 the aerodynamic investigations (without combustion) confirmed the air split between LPP injectors and combustor and LBO limits characterisations achieved for Pilot and LPP injectors.

Emission levels and temperature field characterisations at the combustor exit plane have been completed up to 8.1 bar and 570K for the 2 Pilot injector configurations. The test campaign restarted in October and will be completed in November 2010 reaching the maximum pressure operating conditions of 20 bar.

[Begleittext / Subline: Fig 20 – FANN LPP Combustor HP Rig (TM, ONERA) ]

SP6 full annular combustor test programs actually are well on going and detailed analysis of the results will be completed early in 2011. On the basis of the SP6 successful validation:

• The injection systems improved through several iterations from TRL 2 to TRL 4

• The combustion systems validated at TRL 5 in terms of pollutant emissions and operability

• The NOx emissions evaluated for NEWAC engine cycles and assessed versus target

I believe that NEWAC SP6 results we are consolidating in the next six months will demonstrates the capabilities to reach significant results in the design/development and validation of lean burn technologies up to TRL 5, as a specific step-forward contribution reaching the ACARE 2020 target.