Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E26: Reacting Flows: Multiphase |
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Chair: Ann Karagozian, University of California, Los Angeles Room: E146 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E26.00001: Periodic Partial Extinction Regime in Acoustically Coupled Fuel Droplet Combustion Miguel Plascencia Quiroz, John Bennewitz, Andres Vargas, Hyung Sub Sim, Owen Smith, Ann Karagozian This experimental study investigates the response of burning liquid fuel droplets exposed to standing acoustic waves, extending prior studies quantifying mean and temporal flame response to moderate acoustic excitation\footnote{Sevilla, et al., Comb. Flame \textbf{161}, pp. 1604-1619, 2014}. This investigation explores alternative fuels exposed to a range of acoustic forcing conditions (frequencies and amplitudes), with a focus on ethanol and JP-8. Three fundamental flame regimes are observed: sustained oscillatory combustion, periodic partial extinction and reignition (PPER), and full extinction. Phase-locked OH* chemiluminescence imaging and local temporal pressure measurements allow quantification of the combustion-acoustic coupling through the local Rayleigh index $G$. As expected, PPER produces negative $G$ values, despite having clear flame oscillations. PPER is observed to occur at low-frequency, high amplitude excitation, where the acoustic time scales are large compared with kinetic/reaction times scales for diffusion-limited combustion processes. These quantitative differences in behavior are determined to depend on localized fluid mechanical strain created by the acoustic excitation as well as reaction kinetics. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E26.00002: Effects of Particle Additives on Acoustically Coupled Fuel Droplet Combustion Hyung Sub Sim, Miguel Plascencia Quiroz, Andres Vargas, John Bennewitz, Owen Smith, Ann Karagozian Addition of nanoscale particulates to liquid hydrocarbon fuels is suggested to have numerous benefits for combustion systems, although aggregation of metal nanoparticles can produce deleterious effects. The present experiments explore the effect of nano Aluminum (nAl) additives on the combustion of single liquid fuel droplets, with and without exposure of the droplets to standing acoustic waves. Building on prior studies\footnote{Sevilla, et al., Comb. Flame \textbf{161}, pp. 1604-1619, 2014}, the present experiments quantify variations in the burning rate constant $K$ for ethanol droplets with increasing concentrations of nAl in a quiescent environment. Burning fuel droplets that are continuously fed via a capillary as well as suspended (non-fed) droplets are examined. Nano Al is observed to create ejections of both particles and vapor toward the end of the burning period for non-fed droplets; this phenomenon is delayed when the droplet is replenished via continuous fuel delivery. Yet for the majority of conditions explored, increasing concentrations of nAl tend to reduce $K$. When ethanol droplets with nAl are exposed to standing waves, acoustic perturbations appear to delay particulate agglomeration, sustaining combustion for a longer period of time and increasing $K$. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E26.00003: Characterization of transcritical and supercritical droplet vaporization regimes using computations Pavan Govindaraju, Daniel Banuti, Peter Ma, Muralikrishna Raju, Matthias Ihme Mixing of liquid fuel with ambient gases plays an important role in engine combustion efficiency and emissions. The situation of cold liquid fuel injected into gas at very high pressure and temperature conditions creates special challenges for prediction of combustion characteristics. Among them, the important question is how the interface between cold liquid fuel and hot ambient responds at the pressures and temperatures specific to engines. The presentation will elaborate on the computational procedure used to simulate the injection of n-dodecane into $N_{2}$ and comparing interface characteristics with experimental data. This requires robust tools for predicting droplet evaporation, real fluid properties and molecular-dynamic simulations for validating surface tension characteristics. The effect of pyrolysis in the gas phase is considered and the influence of surface tension is examined. Finally, a comparison between theory, experiments and simulations is presented for transition in vaporization regimes. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E26.00004: Computational Analysis of End-of-Injection Transients and Combustion Recession Dorrin Jarrahbashi, Sayop Kim, Benjamin W. Knox, Caroline L. Genzale Mixing and combustion of ECN Spray A after end of injection are modeled with different chemical kinetics models to evaluate the impact of mechanism formulation and low-temperature chemistry on predictions of combustion recession. Simulations qualitatively agreed with the past experimental observations of combustion recession. Simulations with the Cai mechanism show second-stage ignition in distinct regions near the nozzle, initially spatially separated from the lifted diffusion flame, but then rapidly merge with flame. By contrast, the Yao mechanism fails to predict sufficient low-temperature chemistry in mixtures upstream of the diffusion flame and combustion recession. The effects of the shape and duration of the EOI transient on the entrainment wave near the nozzle, the likelihood of combustion recession, and the spatiotemporal development of mixing and chemistry in near-nozzle mixtures are also investigated. With a more rapid ramp-down injection profile, a weaker combustion recession occurs. For extremely fast ramp-down, the entrainment flux varies rapidly near the nozzle and over-leaning of the mixture completely suppresses combustion recession. For a slower ramp-down profile complete combustion recession back toward the nozzle is observed. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E26.00005: Numerical Simulation of Condensation of Sulfuric Acid and Water in a Large Two-stroke Marine Diesel Engine J. H. Walther, N. Karvounis, K. M. Pang We present results from computational fluid dynamics simulations of the condensation of sulfuric acid ($\mathrm{H_{2}S_{O4}}$) and water ($\mathrm{H_{2}O}$) in a large two-stroke marine diesel engine. The model uses a reduced n-heptane skeletal chemical mechanism coupled with a sulfur subset to simulate the combustion process and the formation of $\mathrm{SO_{x}}$ and $\mathrm{H_{2}S_{O4}}$. Condensation is modeled using a fluid film model coupled with the Eulerian in-cylinder gas phase. The fluid film condensation model is validated against both experimental and numerical results. % The engine simulations reveal that the fluid film has a significant effect on the sulfuric acid gas phase. A linear correlation is found between the fuel sulfur content and the sulfuric acid condensation rate. The initial in-cylinder water content is found not to affect the sulfuric acid condensation but it has a high impact on water condensation. The scavenging pressure level shows an inverse correlation between pressure and condensation rate due to change in the flame propagation speed. Finally, increasing the cylinder liner temperature significantly decreases water condensation but has a negligible influence on the condensation of sulfuric acid. [Preview Abstract] |
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