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Final Report Summary - NEWAC (New aero engine core concepts)

NEWAC focus was on thermal efficiency to further reduce carbon dioxide (CO2) emissions and fuel consumption. For a conventional gas turbine cycle the thermal efficiency is mainly a function of the overall pressure ratio and the turbine entry temperature. A further increase of overall pressure ratio and turbine entry temperature is limited by maximum material temperatures and increasing nitrogen oxides (NOx) emissions. The first step towards higher thermal efficiency without increasing temperatures is to improve the efficiency of the components. Thus in the NEWAC project new innovative technologies such as active systems (active core) and flow control technologies (flow controlled core) to increase efficiency were investigated. Another possibility is to integrate an intercooler to a core (intercooled core). It is an enabler for very high overall pressure ratios, which leads to fuel burn improvements. A big step forward is to use an exhaust gas heat exchanger in order to exploit the heat of the engine exhaust gas. Therewith the thermal efficiency increases at a low overall pressure ratio, which is good for low NOx emissions.

Commercial aviation has an impressive history of success, having become a means of mass transportation that carries in excess of two billion passengers a year. Breathtaking technological improvements have occurred in the past on economical and ecological fronts alike. Air traffic nonetheless faces novel challenges in the wake of diminishing energy supplies and worsening climate changes. In the past, air traffic grew some 5 % a year, and the outlook for the future is much the same. Technological improvements have indeed appreciably reduced specific fuel consumption (per passenger kilometre), yet fast-paced traffic growth keeps increasing fuel consumption and hence CO2 emissions of the world's aircraft fleet by about 3 % annually.

NEWAC aimed and provided through its research and intensive validation activities the following technological achievements:
- For the intercooled recuperative aero engine configuration, an optimised recuperator arrangement, ducts with reduced pressure losses and a radial compressor optimised for the actual IRA core engine specification has been validated with rig tests.
- For an intercooled core configuration, a compact and efficient intercooler with an aggressive ducting has been validated in rig tests and an advanced compressor with improved transient behaviour that can be integrated into an intercooled engine has been validated in rig test.
- For an active core configuration, a new type of casing treatment for the compressor rear stages has been developed. Here, the goal was not only to improve the full speed surge margin, but also the design point efficiency by lowering the tip clearance sensitivity of the rear stages by the casing treatment. Such a type of casing-treatment - together with a semi-active clearance control system - competed with the above mentioned ACC system for rear stages and was tested in a compressor rig.
- For a flow controlled core, outer flow-path control technologies from casing, an air aspiration concept applied on blades or vanes, a new advanced 3D compressor aerodynamic design and a robust and tight rotor/stator clearance management has been validated in model and a compressor rig test.
- For the different core configurations innovative combustors as LP(P) technology applied for low OPR engines (IRA), Partially evaporated rapid mixing (PERM) technology for medium OPR engines (active or flow controlled core) and Lean direct injection (LDI) technology for medium to high OPR engines (intercooled core) has been validated in model tests, atmospheric rig test and full annular high pressure tests.

All new configurations investigated in NEWAC were compared and assessed regarding their benefits and contributions to the global project targets. Detailed specifications were provided based on the global project target for all innovative core configurations. Analytical studies compared the different environmental and economic impact. As a result, NEWAC identified the technology routes to environmentally friendly and economic propulsion solutions. The developed components further resulted in optimised engine designs based on the NEWAC technologies but also in combination with the results of the EEFAE, Silencer and VITAL programmes. To be able to exceed the ACARE 2020 objectives also even more innovative core configurations were investigated and benchmarked with the engine specification mentioned above.

The project was structured into specific sub-projects, as follows:
- Sub-project 0 - NEWAC coordination and technical management
- Sub-project 1 - Whole engine integration
- Sub-project 2 - Intercooled recuperative core
- Sub-project 3 - Intercooled core
- Sub-project 4 - Active core
- Sub-project 5 - Flow controlled core
- Sub-project 6 - Innovative combustor.

Due to the fact that the engines are operated in very different applications like short/long range or low / high thrust, different approaches are needed to optimise the emission reduction. Four approaches were undertaken to reduce the CO2 emissions:
- the increase of the thermal efficiency by heat management;
- the introduction of active systems;
- the high power density core engine to enable very high bypass ratio engines;
- more efficient core components.

To reduce the NOX emissions, the following three options were utilised in NEWAC:
- The reduction of fuel burn related to the above mentioned CO2 reductions result in an equivalent decrease of the produced NOX, provided that the combustion temperature is unchanged.
- The reduction of the combustion temperature leads to lower NOX emissions.
- The combustor technology itself exhibits potential for NOX reductions.

As the related technologies could not be tested in one validator, different test vehicles were envisaged. In all cases, the test vehicles and experimental data for the baseline geometry already existed so that this approach was cost-effective. Furthermore, this approach allowed for a more precise evaluation of the investigated concepts and technologies, in comparison to an integrated validator. It is a matter of fact that the high pressure compressor is the most critical engine component concerning complexity, development risk and engine operability. For that reason, changes in the engine layout always require an adaptation of the HPC, to ensure that this sensitive component still guarantees an appropriate performance and operability. The four approaches even had extremely strong implications and demands on the HPC, for example the additional volumes of heat exchangers and ducting in the compression system, the variable need of cooling air mass flow, or the demand of very high aerodynamic loading. Consequently, besides the combustor technology and the heat exchanger and ducting technology, a further focus of NEWAC was the HP compressor. Besides the above mentioned near and medium term approaches, in NEWAC also studies on highly innovative core configurations were undertaken, which originally had a TRL of 1. The goal of the studies was to pick up ideas available in the research field and identify those, which show high improvement potential using real engine specifications and therefore may be developed in the farer future. By this, NEWAC also generated basic concepts to close upcoming technology gaps and opened up a long-term perspective of further improvements.

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