Evaluation of Blow-Off Dynamics in Aero-Engine Combustors Using Recurrence Quantification Analysis

The lean blow-out performance of an engine and the ability to re-ignite the flame, especially at high-altitude conditions, are important aspects for the safe operability of airplanes. The operability margins of the engine could be extended if it was possible to predict the occurrence of flame blowout from in-flight measurements and take actions to dynamically control the flame behaviour before complete extinction. In this work, the use of Re-currence Quantification Analysis (RQA), an established tool for the analysis of non-linear dynamical systems, is explored to reconstruct and study the blow-off dynamics starting from pressure measurements taken from blow-off experiments of an engine rig. It is shown that the dynamics of the combustor exhibit chaotic characteristics far away from blow-off and that the dynamics become more coherent as the blow-off condition is approached. The degree of determinism and recurrence rate are studied during the entire combustor’s dynamics, from stable flame to flame extinction. It is shown that the flame extinction is anticipated by an increase of the degree of determinism and recurrence rate at all investigated conditions, which indicates intermittent behavior of the combustor before the blow-off condition is reached. Therefore, in the configuration investigated here, the determinism and the recurrence rate of the system could be good predictors of blow-off occurrence and could potentially enable control actions to avoid flame extinction. This study opens up new possibilities for engine control and operability. The development of real-time RQA should be addressed in future research.

Computational and Experimental Analysis of a Compact Combustor Integrated into a JetCat P90 RXi

Ultra Compact Combustors (UCC) look to reduce the overall combustor length and weight in modern gas turbine engines. Previously, a UCC achieved self-sustained operation at sub-idle speeds in a JetCat P90 RXi turbine engine with a length savings of 33% relative to the stock combustor. However, that combustor experienced flameout as reactions were pushed out of the primary zone before achieving mass flow rates at the engine's idle condition. A new combustor that utilized a bluff body flame stabilization with a larger combustor volume looked to keep reactions in the primary zone within the same axial dimensions. This design was investigated computationally for generalized flow patterns, pressure losses, exit temperature profiles, and reaction distributions at three engine power conditions. The computational results showed the validity of this new Ultra Compact Combustor, with a turbine inlet temperature of 1080 K and a pattern factor of 0.67 at the cruise condition. The combustor was then built and tested in the JetCat P90 RXi with rotating turbomachinery and gaseous propane fuel. The combustor maintained a stable flame from ignition through the 36,000 RPM idle condition. The engine ran self-sustained from 25,000 to 36,000 RPM with an average exit gas temperature of 980 K, which is comparable to the stock engine.

Combustibility of lightweight foam concrete based on natural protein foaming agent

There is an experimental study of samples of monolithic foam concrete “SOVBI” with a density of 205 kg /m3 (grade D200) for combustibility. The evaluation criteria are the following values of combustion characteristics: temperature increment in the furnace, duration of the stable flame burning, sample mass loss. The experimental results show the following values for foam concrete: temperature increment in the furnace of 2 °C, duration of the stable flame burning of 0 s, and sample mass of 24.4%. Thus, monolithic foam concrete with a density of 205 kg/m3 is noncombustible material. It is proposed to use monolithic foam concrete and other lightweight monolithic cellular foam concrete, as a structural fire protection for lightweight steel concrete structures. It, in turn, can increase the fire resistance of external walls and floor structure with the steel frame of cold-formed zinc-coated profiles.

Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner with Central Bluff Body

Lean premixed gas turbulent flames stabilized in the flow generated by an industrial swirl burner with a central bluff body are experimentally found to behave bi-stable. This bi-stable behaviour, which can be triggered via a small change in some of the controlling parameters, for example the bulk equivalence ratio, consists in a rather sudden transition of the flame from completely lifted to well attached to the bluff body. While several experimental investigations exist on this topic, numerical analysis is limited. The present work is therefore also of numerical nature, with a two-fold scope: a) simulation and validation with experiments of the bi-stable flame behaviour via Computational Fluid Dynamics (CFD) in the form of Large Eddy Simulation (LES) and b) analysis of CFD results to shed light on the flame stabilization properties. LES results, in case of the lifted flame, show that the vortex core is sharply precessing at a given frequency. Phase averaging these results at the frequency of precession clearly indicates a counter-intuitive and unexpected presence of reverse flow going all the way through the flame apex and the bluff body tip. A simple one-dimensional flame stabilization model is applied to explain the bi-stable flame behaviour.

Characterizing Premixed Syngas Combustion and Flame Dynamics in Micro Scales

Syngas can potentially replace most of conventional fuels, due to its lower emission rates in the case of lean combustion with acceptable energy densities, and can be used in small-scale combustion-related devices. However, with various constituents having various burning characteristics, syngas combustion at micro scales can be more complicated than that of conventional gaseous fuels. It is therefore highly important to understand syngas combustion characteristics. In this work, premixed syngas combustion in a horizontal, two-dimensional microchannel of length 20 mm and width 2 mm is simulated with detailed chemistry, with axisymmetric boundary condition on the lower wall of the computational domain and a fixed temperature gradient on the upper wall to account for the conjugate heat transfer. The simulations are run with varying inlet velocities ranging from 0.1 m/s to 3.0 m/s. The flame shape and dynamics were similar for all the cases, however, not all cases resulted in a stable flame. Two different types of results, i.e., (i) stable flame and (ii) flames with repetitive ignition and extinction (FRIE) are observed. The ignition, extinction, and FRIE events have been characterized in various cases. In addition, the FRIE phenomenon is analyzed by investigating the FRIE periods (the time intervals between the two consecutive ignitions). Similar to the ignition delays, the FRIE periods are found to be dependent on the inlet velocity. The loci of ignition and of a stabilized flame (in stable cases) are found to be further away from the inlet as the inlet velocity increases.

Experimental Study of Kerosene Ignition and Flame Stabilization in a Supersonic Combustor

A supersonic kerosene ignition and flame stabilization experiments were conducted on a directly connected supersonic combustion test bench. The kerosene fuel was jetted by wall jet at Ma 2.5 airflow. High-speed photography was used to record the CH* emission during ignition, extinguishing and evolution of the flame. Experiments of different equivalence ratios were performed. The processes of ignition, flame holding, and extinguishing were observed as well. The experiment showed the characteristics of ignition core initiation and extension. The time of ignition increased with the increase of equivalence ratios. Flame stability during the process of Ma 2.5 at the entrance of the combustion chamber was also studied. An equilibrium flame pattern of shock wave and flame was discovered in the experiment. In the stable flame state, shock waves near the kerosene jet orifice promote atomization and blending, and the combustion chamber pressure with stable flame makes the shock waves stable near the kerosene jet orifice, thus forming the flame stability model. The whole process and characteristics of kerosene ignition, flame holding and extinguishing are revealed in the experiment.