Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E02: Spray Combustion |
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Chair: Marcus Herrmann, Arizona State University Room: Georgia World Congress Center B203 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E02.00001: Lean blow-out mechanism in a swirl-stabilized turbulent spray combustion in a realistic gas turbine combustor Veeraraghava Raju Hasti, Prithwish Kundu, Sibendu Som, Jay P. Gore The present study involves identification of lean blow-out mechanism in a swirl-stabilized turbulent spray combustion in a realistic gas turbine combustor using large eddy simulation. A modified Cartesian cut-cell technique and a gradient-adaptive mesh refinement are employed. Combustion is modeled using a finite rate chemistry approach with compact kinetic models for fuel chemistry. The subgrid stress tensor in the filtered momentum equation is evaluated by solving a transport equation for subgrid kinetic energy. Subgrid turbulence-chemistry interactions are accounted using a partially stirred reactor closure. The multiphase spray is modeled with discrete injections of droplets in a Lagrangian framework to simulate an air-blast atomizer. Injection droplet diameter distributions are derived from experiments. Lean blow-out calculations are carried out by the gradual reduction in the fuel flow rate. These results are further utilized to understand the physics of the lean blow-out process by studying the coupled interactions between fluid dynamics and combustion. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E02.00002: Direct Numerical Simulation of Spray Flame-Wall Interaction under Compression-Ignition Engine Relevant Conditions Abhishek L. Pillai, Takuya Murata, Takato Ikedo, Ryo Masuda, Ryoichi Kurose Development of compression-ignition (CI) engines with higher thermal efficiencies and reduced CO2 emissions warrants the accurate prediction of wall heat loss. In this work, Direct Numerical Simulation (DNS) is used to predict heat flux through chamber-wall during spray flame-wall interaction process, inside a constant volume chamber under CI engine relevant conditions. The simulations employ an Eulerian-Lagrangian framework. The fuel droplets are assumed to be single-component n-decane, whose combustion is modeled using a 2-step chemical scheme designed to predict ignition delay time and burnt gas temperature, for a wide range of equivalence ratio and fresh gas temperature. DNSs are performed for varying fuel injection pressure yielding varying fuel injection velocity. The spray combustion fields are used to analyze the relationship between Nusselt and Reynolds numbers corresponding to wall heat transfer, along with the dependence of representative velocity on heat transfer coefficient. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E02.00003: Comparison of imaging techniques for measurement of diesel combustion lift-off length. Boni Yraguen, Farzad Poursadegh, Caroline Genzale The extent of soot formation in direct injection compression ignition engines has been found to correlate with the charge quality upstream of the corresponding reaction zone. Lift-off length (LOL) is a widely-accepted quantity used to infer the amount of air entrainment into the fuel stream which effects the local equivalence ratio at the onset of ignition. Hence, it serves as an important marker investigating soot emissions in Diesel engines. This work therefore compares two imaging techniques used for determining the LOL of a diesel spray, i.e. Broadband natural luminosity and OH* chemiluminescence to discuss the advantages and challenges of each. To this end, data taken at simulated engine-relevant conditions in an state-of-the-art spray facility at Georgia Tech is used. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E02.00004: Acoustically-Driven Combustion Dynamics and Extinction in Burning Nanofuel Droplets Hyung Sub Sim, Andres Vargas, Miguel A Plascencia Quiroz, Ann Karagozian This study investigates combustion of liquid fuel droplets containing energetic aluminum nanoparticles (nAl) in an acoustic waveguide, extending prior studies on ethanol to examine the nature of extinction as well as the impact of nAl on sooting hydrocarbon liquids such as dodecane and Fischer–Tropsch (FT) synthetic fuel. The addition of nAl to ethanol alters flame dynamics close to extinction, with attendant effects on estimated extinction strain rates. For sooting hydrocarbons, surfactant (Span80) is required to maintain a uniform dispersion of nanoparticles, and this in and of itself causes increases in the burning rate constant (K) with increasing surfactant concentration. Both Span80 and nAl concentrations impact droplet combustion behavior, with and without the application of acoustic excitation. As with nAl additives to ethanol, acoustically-perturbed, sooting droplets can burn for much longer periods of time than in the absence of particle additives, demonstrating continuous oscillatory combustion as enhanced particle dispersion takes place within the liquid. These studies are relevant to other acoustically-coupled reactive systems, such as gaseous jet flames, also currently under exploration. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E02.00005: Microexplosions in Multicomponent Fuel Droplets Tony Yau, Pavan Govindaraju, Matthias Ihme Certain blends of multicomponent fuel droplets containing compounds with large differences in volatility have a tendency to experience violent combustion, which is known as microexplosions. The preferential evaporation of the more volatile component at the surface of the droplet creates a liquid phase concentration gradient when there is little internal circulation. At high temperatures such as those experienced in combustion, this allows the interior of the droplet to become superheated. It is postulated that when the temperature at the center of the droplet reaches the limit of superheat for the mixture composition at that point, the droplet will microexplode. A computational model is developed to predict conditions under which a multicomponent droplet undergoes microexplosion. Simulations are performed and results are compared with measurements to rationalize the transition between stable, weakly disruptive puffing, and microexplosion modes. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E02.00006: Characterizing polydispersity in counterflow spray flames Pavan Govindaraju, Matthias Ihme Counterflow spray flames offer a canonical representation of combustion-physical phenomena that are of relevance to practical applications. An important feature of the spray is the polydisperse character of the droplet distribution arising from the atomization. To examine the effect of polydispersed droplet disribution on the combustion, multi-dimensional counterflow simulations in liminar and turbulent regimes are performed using a Lagrangian particle-tracking approach. The results are compared with existing analytical models for polydisperse counterflow spray flames along with characterizing the effect of droplet distribution on the flame structure. Regimes based on the standard deviation of the droplet distribution in comparison to the Sauter Mean diameter are identified at various strain rates relative to extinction. |
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