Robert Meier

Evaluation of Advanced Two-Phase Flow and Combustion Models for Predicting Low Emission Combustors

The development of low emission aero engine combustors strongly depends on the availability of accurate and efficient numerical models. The prediction of the interaction between two-phase flow and chemical combustion is one of the major objectives of the simulation of combustor flows. In this paper, predictions of a swirl stabilized model combustor are compared to experimental data. The computational method is based on an Eulerian two-phase model in conjunction with an Eddy Dissipation (ED) and a presumed-shapePDF (JPDF) combustion model. The combination of an Eulerian two-phase model with a JPDF combustion model is a novelty. It was found to give good agreement to the experimental data.

Low-NOx Combustor Development pursued within the scope of the Engine 3E German national research program in a cooperative effort among engine Manufacturer MTU, University of Karlsruhe and DLR German Aerospace Research Center

Abstract MTU Aero Engines, the University of Karlsruhe and the DLR Aerospace Research Centre co-operated within the scope of the German national aeronautical research program Engine 3E. The program was focused on improving high-bypass turbofan engines. As a part of this program, a low-emission single-annular combustor was developed. The NOx emissions of this combustor are significantly reduced by using the rich-lean combustion concept. The basic idea of this concept is to avoid stoichiometric combustion conditions by splitting the combustion domain into a fuel-rich zone (low-oxygen zone) and a fuel-lean (low temperature zone). The NOx reduction capability of a combustor of this type scales with the homogeneity of the mixture in the rich zone and the time interval needed for the transition from the rich to the lean zone. Based on the insights gained from this cooperative research, an annular combustor was developed and tested at pressures up to 20 bar and inlet temperatures up to 800 K. The tested annular combustor was found to have NOx emissions of about 40% of the ICAO 96 standard. The carbon monoxide and unburned hydrocarbon emissions of the combustor are of about the same levels as present state of the art combustors.

Combined “Fluorescence” LDV (FLDV) and PDA Technique for Non‐ambiguous Two Phase Measurements Inside the Spray of a SI‐Engine

Laser velocimetry measurements in the vicinity of reflecting surfaces are still a major problem in many fluid mechanical applications such as measuring close to walls or wall film surfaces, respectively. Moreover, in any kind of two phase flow an unambiguous separation of the gas and the liquid phase is of particular interest. Commonly used techniques like Phase Doppler Analyzers (PDA) with size discrimination are limited to two phase flows where the smallest particle of the dispersed phase is significantly larger than the seeding particles. This condition can rarely be fulfilled in technically relevant spray/air systems for instance in automobile engines or gas turbines. One of the most promising approaches to overcome this problem is a correct phase discrimination using fluorescent tracer particles for the gas phase. In this paper different laser based velocimeters have been compared using the spray of a gasoline injection nozzle as a typical example. The working principle of the “fluorescence” LDV (FLDV) will be explained in detail. Moreover, the quality of the fluorescence signals and of the standard bursts received from Mie-scattering particles will be compared. Finally, the capabilities of combined FLDV and PDA measurements inside the spray of a SI-engine at unsteady conditions will be presented. The pros and cons of this technique will be discussed against the background of discriminatory two phase PIV measurements applied to the same spray.

Visualization and phase doppler particle analysis measurements of oscillating spray propagation of an airblast atomizer under typical engine conditions.

Abstract: Propagation of a kerosene spray formed by a prefilming airblast atomizer within a pulsating flame has been investigated. The measurements were performed in a 400 kW single combustor rig at typical engine conditions of up to 0.8 MPa inlet pressure and 673 K inlet temperature. The homogeneity of the fuel spray propagation in the reacting zone substantially influences the local temperature distribution in the reaction zone and, therefore, the formation of thermal NOχ. Phase locked visualization of the spray propagation and the flame luminescence was applied to the pulsating combustion process in order to analyze the complex interaction between the time dependent flow field, the spray propagation, and the combustion process. The spray characteristic was additionally investigated by means of time resolved PDPA measurements in the reacting flow.

Phase discrimination inside a spray: LDV measurements using fluorescent seeding particles (FLDV)

Laser Velocimetry measurements in the vicinity of reflecting surfaces are still a major problem in many fluid mechanical applications such as measuring close to walls or wall film surfaces, respectively. Moreover, in any kind of two phase flow an unambiguous separation of the gas and the liquid phase is of particular interest. Commonly used techniques like Phase Doppler Analysers (PDA) with size discrimination are limited to two phase flows where the smallest particle of the dispersed phase is significantly larger than the seeding particles. This condition can rarely be fulfilled in technically relevant spray/air systems. One of the most promising approaches is a phase discrimination using fluorescent tracer particles for the gas phase. In this paper the working principle of the “fluorescent” LDV (FLDV) will be explained. Moreover, the applicability of different fluorescent dyes will be discussed. Finally, a comparison between PDA results using size discrimination and FLDV results inside a hollow cone spray will be presented.

EFFECT OF THE SHEAR DRIVEN LIQUID WALL FILM ON THE PERFORMANCE OF PREFILMING AIRBLAST ATOMIZERS

Advanced prefilming airblast atomizers are widely used for low emission combustors since they deliver a fine spray almost independently of the fuel flow rate. The droplet spectrum produced by this type of atomizer results from the aerodynamic forces at the atomizer edge and from the fuel properties prior to the film disintegration. Therefore, the wall film temperature is an important parameter affecting the fuel properties and in turn the atomization quality. Even though this atomizer type became well investigated (Lefebvre 1989, Rizk et al. 1987, Sattelmayer et al. 1989), still no general quantitative relationship between atomizer design and spray quality could be established since the fuel state at the atomizer edge cannot be precisely predicted yet.In extending earlier experimental and theoretical work on airblast atomizers (Sattelmayer et al. 1989, Himmelsbach et al. 1994, Willmann et al. 1997) and recent advances in the numerical modeling of wall film flows (Rosskamp et al. 1997a), this paper presents a numerical approach to judge the effect of fuel mass flow, air flow and the film length (i. e. length of atomizer lip) on the temperature of the liquid at the atomizer edge. The computer code developed provides detailed information on the wall film flow and the nozzle wall temperature. For the prediction of heat transfer to the film a new model has been developed which is based on measurements of the internal film flow (Elsaser et al 1997).This new numerical approach can serve as a design tool to evaluate the effects of design modifications during atomizer development with view to their effect on atomization performance. The paper includes the theory for two-phase flow modeling and a generic parameter study that points out that the liquid loading and the length of the atomizer lip are important parameters in atomizer design. The calculations presented in the paper emphasize the necessity of coupled two-phase flow calculations because the film strongly interacts with the gas phase and the predicted atomizer performance is sensitive to changes in the air flow.Copyright