The impacts of three flamelet burning regimes in nonlinear combustion dynamics

Abstract

Axisymmetric simulations of a liquid rocket engine are performed using a delayed detached-eddy-simulation (DDES) turbulence model with the Compressible Flamelet Progress Variable (CFPV) combustion model. Three different pressure instability domains are simulated: completely unstable, semi-stable, and fully stable. The different instability domains are found by varying the combustion chamber and oxidizer post length. Laminar flamelet solutions with a detailed chemical mechanism are examined. The β Probability Density Function (PDF) for the mixture fraction and Dirac δ PDF for both the pressure and the progress variable are used. A coupling mechanism between the volumetric Heat Release Rate (HRR) and the pressure in an unstable cycle is demonstrated. Local extinction and reignition is investigated for all the instability domains using the full S-curve approach. A monotonic decrease in the amount of local extinctions and reignitions occurs when pressure oscillation amplitude becomes smaller. The flame index is used to distinguish between the premixed and nonpremixed burning mode in different stability domains. An additional simulation of the unstable pressure oscillation case using only the stable flamelet burning branch of the S-curve is performed. Better agreement with experiments in terms of pressure oscillation amplitude is found when the full S-curve is used.

Mixing and combustion in a laminar shear layer with imposed counterflow

“…diffusion) flames and subject to flow strain. Nguyen, Popov & Sirignano (2018) and Nguyen & Sirignano (2018) employed the Pierce–Moin flamelet approach in the simulation of a single-injector rocket engine. They showed the importance of flamelets subject to high strain rates.…”

Research of Combustion Modes During Layer-Burning of Shubarkul Coal on the Fire Grate With the Hand Furnace of the KSVR-0.43 Hot Water Boiler

“…The ascending part of the flue behind the boiler is made with a three-fold increase in cross-section for collecting ash. In front of the chimney, a smoke exhaust was installed in parallel with a bypass to the main gas flue duct to ensure the reliable operation of the boiler and in natural draft mode (Nguyen and Sirignano, 2018). A chimney with a 325 mm diameter and a height of 12 m, preheated by the operation of the boiler in the nominal mode without a smoke exhauster, provided a vacuum of up to 100-150 Pa.…”

Physics-Aware Neural Network Flame Closure for Combustion Instability Modeling in a Single-Injector Engine

“…represented through a set of tables, is implemented in the baseline simulations discussed in this work, and which are extensively analyzed in [27,29,30]. Utilization of the flamelet model helps to avoid the need for very short computational time steps determined by chemical kinetics.…”

“…To take a step closer toward this goal, in this work, we train the NNs on CFD data, which only observes parts of the flamelet space, and verify our model by testing the NNs on a number of different simulations. The designed NNs are also tested on the whole flamelet table library, which includes the unobserved parts as well as the training data.The Continuously Variable Resonance Combustor (CVRC) experiment of Purdue University[25,26] is a well studied configuration that is the selected testbed in this work following the previous work in our group on longitudinal combustion instability in LPREs[27,28,29,30]. This fundamental single injector/oxidizerpost rocket combustor produces different stability behaviors for different oxidizer post lengths.…”