Aviation's environmental impact must be reduced to allow sustainable growth to benefit European industry and society. This is captured in ACARE's 2020 goals of reducing CO2 by 50%, NOx by 80% and in SRA1/2 proposed reductions in soot and development of alternative fuels.
Computational Fluid Dynamics (CFD) tools are essential to design combustors for emissions, soot, thermo-acoustic noise, flame stability, cooling and the outlet temperature profile. The two most significant gaps in today's CFD capability are fuel injector spray and soot modelling.
FIRST will deliver key enabling technologies for combustion emission reduction by developing improved design tools and techniques for modelling and controlling fuel sprays and soot.
The fuel injector is critical to the design of low emission combustors. By understanding and controlling the complex physics of fuel atomisation and mixing, the emissions performance can be directly improved. CFD simulations have for many years relied upon over-simplistic definition of the fuel spray. The availability of methods developed in the automotive industry and faster computers make their application to aero-engines timely.
The FIRST project will deliver a step change in the detail and accuracy of the fuel spray boundary conditions, through novel physics based modelling techniques, advanced diagnostic measurements and the derivation of sophisticated correlations. CFD computations of the combustion system also provide the information needed to allow soot emissions to be controlled and minimised. These calculations require the improved fuel spray boundary condition described but also need higher fidelity physical and chemical models describing the soot production and consumption processes. FIRST will deliver improved CFD soot models, enabling the reduction of soot in aero-engine combustors.
The design of future alternative fuels will be enhanced by FIRST by performing predictions and measurements of both fuel sprays and soot across a number of alternative fuels.
New tools to model combustion and fuels
Developments in aircraft engines should go hand in hand with advanced technologies that aim to reduce aviation impact on citizens and the environment. EU-funded scientists developed critical new tools for optimising engine combustion systems for green and sustainable air transport.
The fuel injector is critical to the design of low-emission combustors. By understanding and controlling the complex physics of fuel atomisation, there is great potential for minimising harmful emissions. Until now, simulations have been relying on over-simplistic definitions of the fuel spray. In addition, current soot models are not sufficiently accurate to support the design of new environmentally friendly combustors. The two modelling areas are closely related as the spray characteristics set the boundary conditions for soot modelling.
The http://www.first-fp7project.eu/ (FIRST) (Fuel injector research for sustainable transport) project delivered a step change in detail and accuracy of predicting spray break-up and soot emissions through advanced physics-based modelling techniques, diagnostics measurements and derivation of sophisticated correlations.
Development of a virtual injector numerical tool and soot formation predictive techniques requires extensive validation databases with quantitative measurement results. Detailed atomisation and spray experimental measurements were performed using advanced state-of-the-art diagnostics methods across a range of geometries to validate both the physics- and phenomenological-based modelling approaches. For atomisation, researchers investigated three different levels of experimental complexity: fundamental configurations, idealised injector configurations and industrial injector configurations. For soot measurements, several modern measurement techniques were tested and applied to provide comprehensive data sets for soot model validation.
Work on numerical models of the atomisation process included small-domain direct numerical simulations of the Navier-Stokes equations, computational fluid dynamic calculations of combustor geometry and phenomenological models. The newly developed spray break-up and soot models were incorporated into project partners' design tools. These tools were then used to predict the spray and emissions performance of state-of-the-art low-emission combustion systems.
Through improved measurement and modelling tools both in fuel spray and in soot formation, the FIRST project’s outcomes accelerate development of affordable, cleaner and reliable engine products. These new developments will help the aviation industry move a step closer to achieving the Advisory Council for Aviation Research and Innovation in Europe (ACARE) goals for preserving the environment.