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KIAI
Knowledge for Ignition, Acoustics and Instabilities

Tags: Air

State of the Art - Background

The engine emissions issue is addressed by the evolution of the relevant international regulations (e.g. ICAO CAEP2 standards) and by ambitious technological objectives agreed by the European aeronautics industry described in Vision 2020 of the 2nd version of the ACARE Strategic Research Agenda (SRA2).

The availability of clean engines not only has a huge environmental impact, but it is now vital that every manufacturer tries to maintain a position within world competition for the sustainable growth of aviation transport.

For the time being, the European engine industry does not have the methodologies adapted to predict behaviour of low NOx combustors. Consequently, and in order to be able to set up the development of low NOx technologies, KIAI will deliver unstationary Computational Fluid Dynamics (CFD) tools which will allow a deeper comprehension of unsteady phenomena.

Results from previous European projects on conventional and lean combustion technologies are the basis of the KIAI project. They have adapted CFD methodologies to design conventional combustors and are now preparing for paths to deal with low NOx combustors.

Objectives

The main objective of the KIAI project is to provide reliable methodologies to predict the stability of industrial low NOx combustors, as well as their ignition process from spark to annular combustion. When used at an early stage in the conception cycle of low NOx combustors, KIAI CFD methodologies will play a key role and accelerate the delivery process of lean combustion technology considerably with a proven capability to reach the 80% NOx emission reduction required for introduction into service before 2020 with the necessary reliability, safety and economical viability.

As already demonstrated by past and ongoing studies and European projects, low NOx technologies lead to crucial unsteady phenomena that are neither controlled nor predictable at the moment.

Directly linked to a better understanding and prediction of these unsteady phenomena, the scientific objectives of KIAI are:

- To predict the coupling between the acoustics and the flame;

- To determine the acoustic boundary conditions of multi-perforated plates surrounding the combustion chamber;

- To account for non-premixed spray flows in the combustion process;

- To explore aerodynamic unsteadiness in strutted pre-diffusers adapted to high mass flow injectors and develop a liquid film break-up model for an injector;

- To evaluate the sensitivity of Large Eddy Simulation (LES) predictors to small technological variations of geometry.

Description of Work

To address the weaknesses introduced by the lean low Nox combustion technology, KIAI is structured into four main technical sub-projects (SPs):

- SP2: Prediction method for thermoacoustics.

The main implication of low NOx technologies is an increased sensitivity to combustion instabilities. These instabilities come from a tight coupling between pressure fluctuations introduced by the flame and the backward influence of the acoustics of the chamber. In SP2, KIAI will integrate the impact of the flame on the thermoacoustic behaviour of combustors.

- SP3: Multiperforated plates issue in industrial combustors.

The knowledge of acoustic boundary conditions is essential to determine the correct acoustic behaviour of combustors. In SP3, KIAI will determine the influence of multi-perforated plates to incident acoustic waves.

- SP4: Ignition and re-ignition.

For evident operational and safety reasons, ignition and especially altitude re-ignition are essential issues for aeronautical gas turbine applications. The early propagation of the flame from spark to the combustion chamber, and then from one sector to the totality of the annular combustor is a complex, unsteady process. In SP4, KIAI will work on the flame itself by considering tabulated chemistry descriptions, re-circulated burnt gases, two phase flows and high altitude conditions.

- SP5: Unsteady aero-dynamics in injection.

When dealing with low NOx combustors, the upstream flow conditions can greatly influence the unsteady behaviour of the flame. Thus, pre-diffusers and injectors become instability sources that have to be controlled. In SP5, KIAI will shed light on spray atomisation as well as on the unsteady flows generated by pre-diffusers and injectors.

Sustaining the four aforementioned technical subprojects, the additional subproject SP1 - KIAI Coordination will focus on the project monitoring, dissemination and exploitation of project results.

Expected Results

The main expected outputs of KIAI are:

- Acoustic tools able to provide stability maps of the combustors including the influence of the flame;

- An acoustic description of multi-perforated plates widely encountered in combustion chambers;

- A tabulated chemical description of non-premixed spray combustion;

- A liquid film break up model;

- An estimation of the reliability of LES with respect to its capacity to account for small technological variations of geometry for both isothermal and reactive flows.

KIAI will secure the innovative developments emerging from technologically orientated projects like the TECC-AE FP7 project. When used at an early stage in the conception cycle of low NOx combustors, KIAI CFD methodologies will play a key role and considerably accelerate the delivery process of lean combustion technology with a proven capability to reach the 80% NOx emissions reduction required for introduction into service before 2020 as well as the necessary reliability, safety and economic viability needed.

State of the art of methodologies addressing processes for low NO combustion
State of the art of methodologies addressing processes for low NO combustion

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