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Computational Chemistry Consortium: Surrogate Fuel Mechanism Development, Pollutants Sub-Mechanisms and Components Library

Convergent Science Inc.-Kuiwen Zhang, Mandhapati Raju, Peter Kelly Senecal
Lawrence Livermore National Lab-Scott Wagnon, William Pitz
Published 2019-09-09 by SAE International in United States
The Computational Chemistry Consortium (C3) is dedicated to leading the advancement of combustion and emissions modeling. The C3 cluster combines the expertise of different groups involved in combustion research aiming to refine existing chemistry models and to develop more efficient tools for the generation of surrogate and multi-fuel mechanisms, and suitable mechanisms for CFD applications. In addition to the development of more accurate kinetic models for different components of interest in real fuel surrogates and for pollutants formation (NOx, PAH, soot), the core activity of C3 is to develop a tool capable of merging high-fidelity kinetics from different partners, resulting in a high-fidelity model for a specific application. A core mechanism forms the basis of a gasoline surrogate model containing larger components including n-heptane, iso-octane, n-dodecane, toluene and other larger hydrocarbons. Moreover, poly-aromatic hydrocarbon modules are developed in addition to a NOx formation module. This work describes the challenges and approach for merging the different modules, discussing and analyzing the results from the model, obtained by comparing with experimental targets typically used for model validation…
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Identification and Characterization of Steady Spray Conditions in Convergent, Single-Hole Diesel Injectors

Convergent Science Inc.-Priyesh Srivastava, P.K. Senecal
Argonne National Laboratory-Katarzyna Matusik, Christopher F. Powell
Published 2019-04-02 by SAE International in United States
Reduced-order models typically assume that the flow through the injector orifice is quasi-steady. The current study investigates to what extent this assumption is true and what factors may induce large-scale variations. Experimental data were collected from a single-hole metal injector with a smoothly converging hole and from a transparent facsimile. Gas, likely indicating cavitation, was observed in the nozzles. Surface roughness was a potential cause for the cavitation. Computations were employed using two engineering-level Computational Fluid Dynamics (CFD) codes that considered the possibility of cavitation. Neither computational model included these small surface features, and so did not predict internal cavitation. At steady state, it was found that initial conditions were of little consequence, even if they included bubbles within the sac. They however did modify the initial rate of injection by a few microseconds. Though the needle was never stationary, the mass discharge by the nozzle remained constant for most of the injection. The momentum discharge was more sensitive to lower needle lifts than the mass flow rate. An annular jet, that may follow either…
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Accelerating Accurate Urea/SCR Film Temperature Simulations to Time-Scales Needed for Urea Deposit Predictions

Convergent Science Inc.-Daniel Maciejewski, Parvez Sukheswalla, Chu Wang, Scott A. Drennan, Xiaochuan Chai
Published 2019-04-02 by SAE International in United States
Urea water solution-based Selective Catalytic Reduction (SCR) of NOx emissions from vehicular diesel engines is now widely used world-wide to meet strict health and environmental protection regulations. While urea-based SCR is proven effective, urea-derived deposits often form near injectors, on mixers and pipes, and on the SCR catalyst face. Further understanding of these deposit-formation processes is needed to design aftertreatment system hardware and control systems capable of avoiding severe urea-derived deposits. Computational Fluid Dynamics (CFD) is widely used in SCR aftertreatment design. Film formation, movement, solid wall cooling and deposit initiation/growth time-scales are in the range of minutes to hours, but traditional CFD simulations take too long to reach these time-scales. Here, we propose and demonstrate the frozen flow approach for pulsed sprays and conjugate heat transfer to reduce computation time while maintaining accuracy of key physics. The motivation and assumptions of frozen flow are discussed and the experiments of Birkhold et al. are simulated for validation. Simulations up to 200 seconds are completed in several days computation time, including every injection event and continuous…
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Validation of a Species-Based Extended Coherent Flamelet Model (SB-ECFM) in a Spark Ignition Engine

Convergent Science Inc.-Yang Gao, Mingjie Wang
Published 2019-04-02 by SAE International in United States
The Extended Coherent Flamelet Model (ECFM) is limited to lower order upwinding schemes to minimize the numerical discrepancy between species and tracers, which can lead to inaccurate estimates of the progress variable and consequently negative conditional mass fractions in the burned gases after ignition. The recently developed Species-Based ECFM (SB-ECFM) removes the species tracers from the definition of the progress variable, and allows the use of higher order schemes. In this study, SB-ECFM is coupled with the Imposed Stretch Spark Ignition Model (ISSIM) to simulate a spark-ignition engine, the transparent combustion chamber (TCC) engine. To examine the spatial discretization effect and demonstrate the improvement due to using higher order schemes, Reynolds-Averaged-Navier-Stokes (RANS) simulations performed with a first-order upwinding scheme and a second-order central differencing scheme are compared. In addition, with second-order scheme, the effect of grid refinement around the spark plug on the predicted cycle-to-cycle variability (CCV) is investigated. To efficiently simulate multiple engine cycles, concurrent engine cycles are run following the parallel perturbation method (PPM). The simulation results are compared to experimental data. Three…
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Towards Quantitative Prediction of Urea Thermo-Hydrolysis and Deposits Formation in Exhaust Selective Catalytic Reduction (SCR) Systems

Convergent Science Inc.-Shaoping Quan, Scott Drennan
IFP Energies Nouvelles-Chaouki Habchi, Julien Bohbot
Published 2019-04-02 by SAE International in United States
In order to assist in fast design cycle of Diesel engines selective catalytic reduction (SCR) exhaust systems, significant endeavor is currently being made to improve numerical simulation accuracy of urea thermo-hydrolysis. In this article, the achievements of a recently developed urea semi-detailed decomposition chemical scheme are assessed using three available databases from the literature.First, evaporation and thermo-hydrolysis of urea-water solution (UWS) single-droplets hanged on a thin thermocouple ring (127 μm) as well as on a thick quartz (275 μm), have been simulated at ambient temperature conditions ranging from 473K to 773K. It has been shown that the numerical results, in terms of evaporation rate and urea gasification, as well as droplet temperature history are very close to the experiments if the heat flux coming from the droplet support is properly accounted for. Indeed, an additional conduction flux has proved to be necessary in the evaporation model in order to account for the droplet heating coming from the support (i.e. thermocouple ring or quartz bead). This additional heat conduction flux has shown more critical for droplets…
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CFD-Guided Combustion System Optimization of a Gasoline Range Fuel in a Heavy-Duty Compression Ignition Engine Using Automatic Piston Geometry Generation and a Supercomputer

SAE International Journal of Advances and Current Practices in Mobility

Convergent Science Inc.-Daniel Probst
Aramco Research Center - Detroit-Yuanjiang Pei, Yu Zhang, Michael Traver, David Cleary
  • Journal Article
  • 2019-01-0001
Published 2019-01-15 by SAE International in United States
A computational fluid dynamics (CFD) guided combustion system optimization was conducted for a heavy-duty diesel engine running with a gasoline fuel that has a research octane number (RON) of 80. The goal was to optimize the gasoline compression ignition (GCI) combustion recipe (piston bowl geometry, injector spray pattern, in-cylinder swirl motion, and thermal boundary conditions) for improved fuel efficiency while maintaining engine-out NOx within a 1-1.5 g/kW-hr window. The numerical model was developed using the multi-dimensional CFD software CONVERGE. A two-stage design of experiments (DoE) approach was employed with the first stage focusing on the piston bowl shape optimization and the second addressing refinement of the combustion recipe. For optimizing the piston bowl geometry, a software tool, CAESES, was utilized to automatically perturb key bowl design parameters. This led to the generation of 256 combustion chamber designs evaluated at several engine operating conditions. The second DoE campaign was conducted to optimize injector spray patterns, fuel injection strategies and in-cylinder swirl motion for the best performing piston bowl designs from the first DoE campaign. This comprehensive…
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FSI - MRF Coupling Approach For Faster Turbocharger 3D Simulation

SAE International Journal of Advances and Current Practices in Mobility

Convergent Science Inc.-Jasim Sadique, Yunliang Wang
Southwest Research Institute-Zainal Abidin, Andrew Morris, Jason Miwa
  • Journal Article
  • 2019-01-0007
Published 2019-01-15 by SAE International in United States
Fluid-Structure Interaction (FSI) simulation approach can be used to simulate a turbocharger. However, this predictive 3D simulation encounters the challenge of a long computational time. The impeller speed can be above 100,000 rpm, and generally a CFD solver limits the maximum movement of the impeller surface per time step. The maximum movement must be a fraction (~0.3) of the cell length, thus the time step will be very small. A Multiple Reference Frame (MRF) approach can reduce computational time by eliminating the need to regenerate the mesh at each time-step to accommodate the moving geometry. A static local reference zone encompassing the impeller is created and the impact of the impeller movement is modeled via a momentum source. However, the MRF approach is not a predictive simulation because the impeller speed must be given by the User. A new simulation approach was introduced that coupled the FSI and MRF approach. Like in the FSI approach, the total moment of the impeller was calculated based on the resultant force acting over the impeller surface. This calculation…
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Gas Turbine Blade Cooling

Convergent Science Inc.-Chaitanya D. Ghodke
  • Progress In Technology (PT)
  • PT-196
Published 2018-12-10 by SAE International in United States

Gas turbines play an extremely important role in fulfilling a variety of power needs and are mainly used for power generation and propulsion applications. The performance and efficiency of gas turbine engines are to a large extent dependent on turbine rotor inlet temperatures: typically, the hotter the better.

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Modeling the Dynamic Coupling of Internal Nozzle Flow and Spray Formation for Gasoline Direct Injection Applications

Convergent Science Inc.-Priyesh Srivastava, Shaoping Quan, P. K. Senecal, Eric Pomraning
Argonne National Laboratory-Sibendu Som
Published 2018-04-03 by SAE International in United States
A numerical study has been carried out to assess the effects of needle movement and internal nozzle flow on spray formation for a multi-hole Gasoline Direct Injection system. The coupling of nozzle flow and spray formation is dynamic in nature and simulations with pragmatic choice of spatial and temporal resolutions are needed to analyze the sprays in a GDI system. The dynamic coupling of nozzle flow and spray formation will be performed using an Eulerian-Lagrangian Spray Atomization (ELSA) approach. In this approach, the liquid fuel will remain in the Eulerian framework while exiting the nozzle, while, depending on local instantaneous liquid concentration in a given cell and amount of liquid in the neighboring cells, part of the liquid mass will be transferred to the Lagrangian framework in the form of Lagrangian parcels. Such approach requires solving an additional transport equation apart from the conservation equations of mass, momentum, species, energy, and turbulence in Eulerian framework. This additional equation is termed as the Σ equation. Σ represents the liquid-gas interfacial area per unit volume in a…
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Urea Deposit Predictions on a Practical Mid/Heavy Duty Vehicle After-Treatment System

Convergent Science Inc.-Scott Drennan
Isuzu Advanced Engineering Center, Ltd.-Keiko Shibata
Published 2018-04-03 by SAE International in United States
Urea/SCR systems have been proven effective at reducing NOx over a wide range of operating conditions on mid/heavy duty diesel vehicles. However, design changes due to reduction in the size of modern compact Urea/SCR systems and lower exhaust temperature have increased the possibility of urea deposit formation. Urea deposits are formed when urea in films and droplets undergoes undesirable secondary reactions and generate by-products such as ammelide, biuret and cyanuric Acid (CYA). Ammelide and CYA are difficult to decompose which lead to the formation of solid deposits on the surface. This phenomenon degrades the performance of the after treatment system by decreasing overall mixing efficiency, lowering de-NOx efficiency and increasing pressure drop. Therefore, mitigating urea deposits is a primary design goal of modern diesel after-treatment systems. The purpose of current study is to introduce the Computational Fluid Dynamics (CFD) approach to predict urea deposit formation in the Isuzu exhaust system using detailed urea decomposition mechanism. Conjugate Heat Transfer (CHT) is used along with the advanced splashing and film evaporation models to correctly predict the film…
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