Occurrence Of Combustion Instabilities Research Articles

Influence of flame-holder temperature on the acoustic flame transfer functions of a laminar flame

The occurrence of combustion instabilities in high-performance engines such as gas turbines is often affected by the thermal state of the engine. For example, strong bursts of pressure fluctuations may occur at cold start for operating conditions that are stable once the engine reaches thermal equilibrium. This observation raises the question of the influence of material temperature on the response of flames to acoustic perturbations. In this study, we assess the influence of the temperature of the flame holder for a laminar flame. Both experiments and numerical simulations show that the Flame Transfer Function (FTF) is strongly affected by the flame-holder temperature. The key factors driving the evolution of the FTF are the flame-root location as well as the modification of the flow, which affects its stability. In the case of the cooled flame-holder, the formation of a recirculation zone is identified as the main impact on the FTF.

SI1-3: Experimental analysis of the effect of Tumble motion on ignition and instabilities(SI: Spark-Ignition Engine Combustion,General Session Papers)

Many studies have already been conducted in order to improve knowledge on impacts of tumble motion on combustion processes. Furthermore, many studies have also been performed to study the links between flame kernel behaviour and combustion stability. But only a few experimental studies have concentrated on the links between local conditions during the ignition, including the spark itself, and flame kernel. With this study we aim at specifying the occurrence of combustion instabilities, as well as their key factors connected to air flow motion. Thus the current paper presents a study led on 4-valve spark ignition optical single cylinder engine. Different operating conditions were characterized using several optical and non optical diagnostics. The diagnostics used were PIV measurement in the combustion chamber, direct visualizations of the spark and flame visualizations. Additionally, recordings of the intensity and the voltage of the secondary side of the ignition coil, as well as in-cylinder pressure were acquired. The provided analysis confirmed the importance of the link existing between air flow motion prior to spark and combustion stability. Regarding the impact of tumble motion on combustion, it has been showed that the more velocity is obtained at the vicinity of the spark plug, the more cyclic fluctuation of air flow motion occurs. Nevertheless, analyses confirmed that stronger tumble motion is favourable to decrease in the ignition delay by convection of the spark and consecutive flame kernels further from spark plug electrodes, which is directly linked to the resulting ignition duration. Thus the air flow needed at the ignition timing has to be optimized for higher flow velocity, rather than higher flow reproducibility with lower flow velocity.

Modelling the Nonlinear Dynamics of Combustion Instabilities in Gas Turbines Towards Active Control

A main obstacle to the use of premixed flames in gas turbine combustors is the occurrence of combustion instabilities. In this paper, we propose a model for the description of the coupling between the acoustic field and the heat release process. While the gasdynamics is modelled by means of transcendental transfer functions, the flame description, worked out on physical basis, is a nonlinear lumped parameter system. The developed model is intended for active control, and it accounts for the limit-cycle phenomenon.