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Development of a CFD Solver For Primary Diesel Jet Atomization in FOAM-Extend

King Abdullah Univ of Science & Tech-Hong Im
Universita degli Studi di Perugia-Michele Battistoni
  • Technical Paper
  • 2019-24-0128
To be published on 2019-09-09 by SAE International in United States
High fidelity CFD framework for the simulation of primary atomization of a high pressure diesel jet is presented in this work. The numerical model is based on a second order accurate, polyhedral Finite Volume method implemented in foam-extend, a community driven fork of the OpenFOAM software. A geometric VOF method isoAdvector is used for accurate interface advection, while the Ghost Fluid Method (GFM) is used to handle the discontinuity of the pressure and the pressure gradient at the interface between the two phases: n-dodecane and air in the combustion chamber. The discontinuities are a direct consequence of different densities and viscosities, and surface tension effects between the phases. In order to obtain highly resolved interface while minimizing computational time, an Adaptive Mesh Refinement (AMR) strategy for arbitrary polyhedral cells is employed in order to refine the parts of the mesh near the interface and within the nozzle. The developed numerical framework is tested on the Spray D geometry. The unstructured, mostly hexahedral mesh is used with the base cell size of 40 micrometres. Five refinement…
 

Novel Geometry Reaching High Efficiency for Multiple Injector Concepts

King Abdullah University of Science & Technology-Gustav Nyrenstedt, Hong Im, Bengt Johansson
Volvo Global Truck Tech Powertrain Eng-Arne Andersson
Published 2019-04-02 by SAE International in United States
Heat losses are known to decrease the efficiency of CI engines largely. Here, multiple injectors have been suggested to shrink these losses through reduction of spray wall impingement. Studies on multiple injectors have proven the concept’s heat transfer reduction but also highlighted the difficulty of using a standard piston bowl. This study proposes a two-injector concept combined with a flat bowl to reduce heat losses further. To change the spray pattern, the two injectors are injecting in a swirling motion while placed at the rim of the bowl. Four injection timings have been investigated using Reynolds-Averaged Navier-Stokes simulations. This computational method quantified the amount of heat loss reduction possible. A conventional single injector concept is compared to two injector concepts with a standard and flat bowl. A Double Compression Expansion Engine (DCEE) concept, based on a modified Volvo D13 single-cylinder engine, was the base for all simulations. The DCEE can re-use the residual exhaust energy for a second expansion meaning increased importance of reduced heat losses. Heat release effects were discarded in the evaluation as…
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Large-Eddy Simulation of Turbulent Dispersion Effects in Direct Injection Diesel and Gasoline Sprays

King Abdullah University of Science & Technology-Hong Im, Francisco Hernandez Perez
University of Wisconsin Madison-Hongjiang Li, Christopher Rutland
Published 2019-04-02 by SAE International in United States
In most large-eddy simulation (LES) applications to two-phase engine flows, the liquid-air interactions need to be accounted for as source terms in the respective governing equations. Accurate calculation of these source terms requires the relative velocity “seen” by liquid droplets as they move across the flow, which generally needs to be estimated using a turbulent dispersion model. Turbulent dispersion modeling in LES is very scarce in the literature. In most studies on engine spray flows, sub-grid scale (SGS) models for the turbulent dispersion still follow the same stochastic approach originally proposed for Reynolds-averaged Navier-Stokes (RANS). In this study, an SGS dispersion model is formulated in which the instantaneous gas velocity is decomposed into a deterministic part and a stochastic part. The deterministic part is reconstructed using the approximate deconvolution method (ADM), in which the large-scale flow can be readily calculated. The stochastic part, which represents the impact of the SGS flow field, is assumed to be locally homogeneous and isotropic and, therefore, governed by a Langevin-type equation. The model is applied to the spray G…
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CFD Study of Heat Transfer Reduction Using Multiple Injectors in a DCEE Concept

King Abdullah University of Science & Technology-Gustav Nyrenstedt, Tariq Alturkestani, Hong Im, Bengt Johansson
Published 2019-01-15 by SAE International in United States
Earlier studies on efficiency improvement in CI engines have suggested that heat transfer losses contribute largely to the total energy losses. Fuel impingement on the cylinder walls is typically associated with high heat transfer. This study proposes a two-injector concept to reduce heat losses and thereby improve efficiency. The two injectors are placed at the rim of the bowl to change the spray pattern. Computational simulations based on the Reynolds-Averaged Navier-Stokes approach have been performed for four different fuel injection timings in order to quantify the reduction in heat losses for the proposed concept. Two-injector concepts were compared to reference cases using only one centrally mounted injector. All simulations were performed in a double compression expansion engine (DCEE) concept using the Volvo D13 single-cylinder engine. In the DCEE, a large portion of the exhaust energy is re-used in the second expansion, thus increasing the thermodynamic efficiency. To isolate the heat losses associated with the changed spray pattern of the two-injector concept, effects of the heat release are excluded during the analysis. Results showed that the…
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A Computational Study of Lean Limit Extension of Alcohol HCCI Engines

King Abdullah University of Science & Tech.-Mohammed Jaasim Mubarak Ali, Balaji Mohan, Hong Im
Shanghai Jiao Tong University-Qiyan Zhou, Xing-Cai Lu
Published 2018-09-10 by SAE International in United States
The purpose of present numerical study was to extend the operating range of alcohol (methanol and ethanol) fueled Homogeneous Charge Compression Ignition (HCCI) engine under low load conditions. Ignition of pure methanol and ethanol under HCCI mode of operation requires high intake temperatures and misfires at low loads are common in HCCI engines. Three methods have been adapted to optimize the use of methanol and ethanol for HCCI operation without increasing the intake temperature. First, blending methanol and ethanol with ignition improver, namely di-methyl ether (DME) and di-ethyl ether (DEE), was used to increase the cetane number and ignitability of premixed charge. Second, based on the blended fuels, the spark assistance was used to reduce required intake temperature for auto-ignition. Third, DME and DEE were directly injected to methanol and ethanol operated HCCI engine, in the form of Reactivity Controlled Compression Ignition (RCCI) combustion. Negligible improvement in reducing intake temperature was observed in spark-assisted HCCI combustion due to the slow flame propagation speed under the lean premixed condition with blended fuels. In all three methods,…
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Probabilistic Approach to Predict Abnormal Combustion in Spark Ignition Engines

King Abdullah University of Science & Tech.-Mohammed Jaasim Mubarak Ali, Minh Bau Luong, Aliou Sow, Francisco Hernandez Perez, Hong Im
Published 2018-09-10 by SAE International in United States
This study presents a computational framework to predict the outcome of combustion process based on a given RANS initial condition by performing statistical analysis of Sankaran number, Sa, and ignition regime theory proposed by Im et al. [1]. A criterion to predict strong auto-ignition/detonation a priori is used in this study, which is based on Sankaran-Zeldovich criterion. In the context of detonation, Sa is normalized by a sound speed, and is spatially calculated for the bulk mixture with temperature and equivalence ratio stratifications. The initial conditions from previous pre-ignition simulations were used to compute the spatial Sa distribution followed by the statistics of Sa including the mean Sa, the probability density function (PDF) of Sa, and the detonation probability, PD. Sa is found to be decreased and detonation probability increased significantly with increase of temperature. The statistic mean Sa calculated for the entire computational domain and the predicted Sa from the theory were found to be nearly identical. The predictions based on the adapted Sankaran-Zel’dovich criterion and detonation probability agree well with the results of…
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Compression Ignition of Low Octane Gasoline under Partially Premixed Combustion Mode

King Abdullah University of Science & Tech.-Yanzhao An, Mohammed Jaasim Mubarak Ali, R Vallinayagam, Abdullah AlRamadan, Hong Im, Bengt Johansson
Saudi Aramco-Jaeheon Sim, Junseok Chang
Published 2018-09-10 by SAE International in United States
Partially premixed combustion (PPC) is an operating mode that lies between the conventional compression ignition (CI) mode and homogeneous charge compression ignition (HCCI) mode. The combustion in this mixed mode is complex as it is neither diffusion-controlled (CI mode) nor governed solely by chemical kinetics (HCCI mode). In this study, CFD simulations were performed to evaluate flame index, which distinguishes between zones having a premixed flame and non-premixed flame. Experiments performed in the optical engine supplied data to validate the model. In order to realize PPC, the start of injection (SOI) was fixed at −40 CAD (aTDC) so that a required ignition delay is created to premix air/fuel mixture. The reference operating point was selected to be with 3 bar IMEP and 1200 rpm. Naphtha with a RON of 77 and its corresponding PRF surrogate were tested. The simulations captured the general trends observed in the experiments well. The flame index was noted to be an indicator to evaluate and quantify the in-cylinder combustion development under PPC engine operating condition. The evolution of premixed flames…
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Effects of Injection Rate Profiles on Auto-Ignition in Ignition Quality Tester

King Abdullah University of Science & Tech.-Mohammed Jaasim Mubarak Ali, Hong Im
Shanghai Jiao Tong University-Yueqi Luo, Zhen Huang
Published 2018-09-10 by SAE International in United States
Ignition quality tester (IQT) is a standard experimental device to determine ignition delay time of liquid fuels in a controlled environment in the absence of gas exchange. The process involves fuel injection, spray breakup, evaporation and mixing, which is followed by auto-ignition. In this study, three-dimensional computational fluid dynamics (CFD) is used for prediction of auto-ignition characteristics of diethyl ether (DEE) and ethanol. In particular, the sensitivity of the ignition behavior to different injection rate profiles is investigated. Fluctuant rate profile derived from needle lift data from experiments performs better than square rate profile in ignition delay predictions. DEE, when used with fluctuant injection rate profile resulted in faster ignition, while for ethanol the situation was reversed. The contrasting results are attributed to the difference in local mixing. The fluctuant injection profile yields larger spray velocity variations promoting fuel evaporation and local turbulent mixing. The suitable ignition conditions were reached earlier for DEE with fluctuant injection profile, whereas ethanol exhibits pseudo-homogeneous mixing due to its lower cetane number. Ignition was faster for square rate profile…
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Investigation of Premixed and Diffusion Flames in PPC and CI Combustion Modes

King Abdullah University of Science & Technology-Yanzhao An, Mohammed Jaasim Mubarak Ali, R Vallinayagam, S Vedharaj, Francisco Hernandez Perez, Hong Im, Bengt Johansson
Saudi Aramco-Jaeheon Sim, Junseok Chang
Published 2018-04-03 by SAE International in United States
The experimental in-cylinder combustion process was compared with the numerical simualtion for naphtha fuel under conventional compression ignition (CI) and partially premixed combustion (PPC) conditions. The start of injection timing (SOI) with the single injection strategy was changed from late of −10 CAD aTDC to early of −40 CAD aTDC. The three-dimensional full cycle engine combustion simulation was performed coupling with gas phase chemical kinetics by the CFD code CONVERGE™. The flame index was used for evaluating the combustion evolution of premixed flame and diffusion flame. The results show that the flame index could be used as an indicator for in-cylinder homogeneity evaluation. Hydroperoxyl shows a similar distribution with the premixed combustion. Formaldehyde could be used as an indicator for low temperature combustion.
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A Computational Study of Abnormal Combustion Characteristics in Spark Ignition Engines

SAE International Journal of Engines

King Abdullah University of Science & Technology-Mohammed Jaasim Mubarak Ali, Francisco Hernandez Perez, Aliou Sow, Hong Im
  • Journal Article
  • 2018-01-0179
Published 2018-04-03 by SAE International in United States
Super-knock that occurs in spark ignition (SI) engines is investigated using two-dimensional (2D) numerical simulations. The temperature, pressure, velocity, and mixture distributions are obtained and mapped from a top dead center (TDC) slice of full-cycle three-dimensional (3D) engine simulations. Ignition is triggered at one end of the cylinder and a hot spot of known temperature was used to initiate a pre-ignition front to study super-knock. The computational fluid dynamics code CONVERGE was used for the simulations. A minimum grid size of 25 μm was employed to capture the shock wave and detonation inside the domain. The Reynolds-averaged Navier-Stokes (RANS) method was employed to represent the turbulent flow and gas-phase combustion chemistry was represented using a reduced chemical kinetic mechanism for primary reference fuels. A multi-zone model, based on a well-stirred reactor assumption, was used to solve the reaction terms. Hot spots introduced inside the domain at various initial temperatures initiated a pre-ignition front, which resulted in super-knock due to detonation of the end gas. The detonation was induced for temperatures greater than 1000 K during…
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