G. Cabot

Laser-Induced Spark Ignition of Premixed Confined Swirled Flames

Optimization of the ignition location is of crucial importance for many combustion systems and requires advanced knowledge of the ignition process for both fundamental and applied configurations. In this article, a premixed swirl burner was designed to experimentally study the impact of the spark location on successful ignition and to detail the scenario from ignition to flame stabilization. Two swirl numbers were investigated to evaluate their impact on the ignition process. Particular attention was paid to providing accurate data on cold flow velocity field statistics (obtained by stereoscopic particle image velocimetry) as well as on ignition conditions. Ignition probability maps were obtained for a constant level of deposited energy. Contrary to previous studies, no correlation between local turbulent kinetic energy and ignition probability was observed, and a deeper analysis of the temporal evolution of the flame kernel within the combustion chamber is required. Coupling fast flame visualization with the corresponding pressure signal demonstrated that the efficiency of the ignition location was not only controlled by the local flow properties, but also by the early flame kernel development, linked by its typical trajectories within the combustion chamber.

Experimental Study of Aeronautical Ignition in a Swirled Confined Jet-Spray Burner

Aeronautical gas turbine ignition is still not well understood and its management and control is mandatory for new lean-burner designs. The fundamental aspects of swirled confined two-phase flow ignition are addressed in the present work. Two facilities enable the analysis of two characteristic phases of the process. The KIAI-Spray single-injector burner was investigated in terms of local flow properties, including the air velocity and droplet fuel (n-heptane) size-velocity characterization by phase Doppler anemometry (PDA), and the study of local equivalence ratio by means of planar laser induced fluorescence (PLIF) on a tracer (toluene). The initial spark location inside the chamber is vital to ensure successful ignition. An ignition probability map was elaborated varying the location of a 532 nm laser-induced spark in the chamber under ultra-lean nominal conditions (phi=0.61). The outer recirculation zone (ORZ) was found to be the best region for placing a spark and successfully igniting the mixture. A strong correlation was found between the ignition probability field and the airflow turbulent kinetic energy and velocity fields. Local equivalence ratio enhances the importance of the ORZ. Once a successful ignition is accomplished on one injector, the injector-to-injector flame propagation must be examined. Highspeed visualization through two synchronized perpendicular cameras was applied on the KIAI-Spray linear multi-injector burner. Four different injector-to-injector distances and four fuels of different volatilities (n-heptane, n-decane, n-dodecane and jet-A1 kerosene) were evaluated. Spray branches and inter injector regions changed with the inter-injector distance. Two different flame propagation mechanisms were identified: the direct radial propagation and the arc propagation mode. Ignition delay times were modified with the injector-to-injector distance and with the different fuels.

Study of Experimental and Calculated Flame Speed of Methane/Oxygen-Enriched Flame in Gas Turbine Conditions As a Function of Water Dilution: Application to CO2 Capture by Membrane Processes

A solution for CCS (Carbon Dioxide Capture and Sequestration of CO2) is oxycombustion. Due to the high cost of pure O2 production, however, other approaches recently emerged such as post-combustion coupled with Oxygen Enhanced Air (OEA). This is the solution studied in this paper, which presents an innovative gas turbine cycle, the Oxygen Enriched Air Steam Injection Gas Turbine Cycle (OEASTIG). The OEASTIG cycle is composed of Methane combustion with OEA (Oxygen Enhanced Air), EGR (Exhaust Gas Recirculation) and H2O coming from a STIG (Steam Injection Gas Turbine). CO2 capture is achieved by a membrane separator. The final aim of this work is to predict NO and CO emissions in the gas turbine by experimental and numerical approaches. Before carrying out this study, the validation of a reaction mechanism is mandatory. Moreover, this new gas turbine cycle impacts on the combustion zone and it is therefore necessary to understand the consequences of H2O and CO2 dilution on combustion parameters. While a large number of papers deal with CO2 dilution, only a few papers have investigated the impact of water dilution on methane combustion. A study of the influence of H2O dilution on the combustion parameters by experimental and numerical approaches was therefore carried out and is reported in the present paper. The paper is divided in three parts: i) description of the innovative gas turbine (OEASTIG) cycle and determination of the reactive mixtures compatible with its operation; ii) validation of the reaction mechanism by comparing laminar methane flame velocity measurements performed in a stainless steel spherical combustion chamber with calculations carried out in a freely propagating flame using the Chemical Workbench v.4.1. Package in conjunction with the GRIMech3.0 reaction mechanism; iii) Extrapolation to gas turbine conditions by prediction of flame velocities and determination of the feasible conditions from a gas turbine point of view (flame stability). In particular, mixtures (composed of CH4/O2/N2/H2O or CO2) leading to the same adiabatic temperature were investigated. Lastly, the influence of oxygen enrichment and H2O dilution (compared to CO2 dilution) were investigated.

EFFECT OF CO2 CAPTURE ON COMBINED CYCLE GAS TURBINE EFFICIENCY USING MEMBRANE SEPARATION, EGR AND OEA EFFECTS ON COMBUSTION CHARACTERISTICS

In an energetic world of fossil fuel, there is a need to reduce the CO2 emission released to the atmosphere. CO2 Capture and Sequestration (CCS) is one of the solutions.To optimize the CO2 capture cost, thermodynamic cycles of power plants have to be modified, and resulting new designs inevitably lead to new combustion modes [1][2][3]. CO2 capture of post combustion gases can be performed using membrane processes, but its efficiency is interesting only if the CO2 concentration in the combustion process exhaust gases is higher than 30% [4]. Unfortunately, in classical combustion processes (e.g. gas turbine), diluted Exhaust Gases (EG) contain no more than 5 % of CO2 because combustion products are strongly diluted in air. Our objective consists in increasing the EG CO2 concentration, by using both Oxygen-Enriched Air (OEA) combustion and exhaust gas recirculation (EGR). Our approach is based on numerical simulations and on experimental work. First, operating parameters which minimize the CO2 capture cost are calculated and compared with the reference capture cost [5] (achieved by amine absorption of CO2). In parallel, experiments and additional calculations are performed in order to check the quality and the operability of such combustion mode.This paper is organized as follows: the first part presents the optimization of a new thermodynamic GTCC cycle, using OEA and EGR to increase EG CO2 concentration and capturing it in post-combustion with membrane separator. The effects of pressure and membrane selectivity will be studied in terms of CO2 capture cost, avoided CO2, implemented membrane surface, EGR rate and OEA quality.The second part is dedicated to the experimental and calculation [6] studies of combustion met in this type of configuration. A premixed swirl flame is fed first with Air, CH4 and CO2, then with OEA, CH4 and EGR. To neglect the thermal aspect of NOx production, measurements are performed at constant adiabatic flame temperature. The flame structure, combustion instability and pollutant emissions are presented as a function of the EGR rate dilution.Copyright