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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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Effect of Mixture Formation and Injection Strategies on Stochastic Pre-Ignition

King Abdullah University of Science & Tech.-Eshan Singh, Mohammed Jaasim Mubarak Ali, Adrian Ichim, Robert Dibble
Saudi Aramco-Kai Morganti
Published 2018-09-10 by SAE International in United States
Stochastic pre-ignition remains one of the major barriers limiting further engine downsizing and down-speeding; two widely used strategies for improving the efficiency of spark-ignited engines. One of the most cited mechanisms thought to be responsible for pre-ignition is the ignition of a rogue droplet composed of lubricant oil and fuel. This originates during mixture formation from interactions between the fuel spray and oil on the cylinder liner. In the present study, this hypothesis is further examined using a single cylinder supercharged engine which employs a range of air-fuel mixture formation strategies. These strategies include port-fuel injection (PFI) along with side and central direct injection (DI) of an E5 gasoline (RON 97.5) using single and multiple injection events. Computational fluid dynamic (CFD) calculations are then used to explain the observed trends. Overall, this study reinforces that interactions between the fuel spray and oil on the cylinder liner can be an important contributor towards stochastic pre-ignition. The occurrence of pre-ignition, as shown by CFD calculations, is successful after completion of two stages. The first stage involves the…
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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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Auto-Ignition and Spray Characteristics of n-Heptane and iso-Octane Fuels in Ignition Quality Tester

King Abdullah University of Science & Technology-Mohammed Jaasim Mubarak Ali, Ayman Elhagrasy, Mani Sarathy, Sukho Chung, Hong G. Im
Published 2018-04-03 by SAE International in United States
Numerical simulations were conducted to systematically assess the effects of different spray models on the ignition delay predictions and compared with experimental measurements obtained at the KAUST ignition quality tester (IQT) facility. The influence of physical properties and chemical kinetics over the ignition delay time is also investigated. The IQT experiments provided the pressure traces as the main observables, which are not sufficient to obtain a detailed understanding of physical (breakup, evaporation) and chemical (reactivity) processes associated with auto-ignition. A three-dimensional computational fluid dynamics (CFD) code, CONVERGE™, was used to capture the detailed fluid/spray dynamics and chemical characteristics within the IQT configuration. The Reynolds-averaged Navier-Stokes (RANS) turbulence with multi-zone chemistry sub-models was adopted with a reduced chemical kinetic mechanism for n-heptane and iso-octane. The emphasis was on the assessment of two common spray breakup models, namely the Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) and linearized instability sheet atomization (LISA) models, in terms of their influence on auto-ignition predictions. Two spray models resulted in different local mixing, and their influence in the prediction of auto-ignition was investigated. The relative importance…
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Numerical Simulations of High Reactivity Gasoline Fuel Sprays under Vaporizing and Reactive Conditions

King Abdullah University of Science & Technology-Balaji Mohan, Mohammed Jaasim Mubarak Ali, Ahfaz Ahmed, Francisco Hernandez Perez, William Roberts, Mani Sarathy, Hong Im
Saudi Aramco-Jaeheon Sim
Published 2018-04-03 by SAE International in United States
Gasoline compression ignition (GCI) engines are becoming more popular alternative for conventional spark engines to harvest the advantage of high volatility. Recent experimental study demonstrated that high reactivity gasoline fuel can be operated in a conventional mixing controlled combustion mode producing lower soot emissions than that of diesel fuel under similar efficiency and NOx level [1]. Therefore, there is much interest in using gasoline-like fuels in compression ignition engines. In order to improve the fidelity of simulation-based GCI combustion system development, it is mandatory to enhance the prediction of spray combustion of gasoline-like fuels. The purpose of this study is to model the spray characteristics of high reactivity gasoline fuels and validate the models with experimental results obtained through an optically accessible constant volume vessel under vaporizing [2] and reactive conditions [3]. For reacting cases, a comparison of PRF and KAUST multi-component surrogate (KMCS) mechanism was done to obtain good agreement with the experimental ignition delay. From this study, some recommendations were proposed for GCI combustion modelling framework using gasoline like fuels.
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Cycle to Cycle Variation Study in a Dual Fuel Operated Engine

Convergent Science Inc.-Sameera Wijeyakulasuriya
GE, Global Research Center-ShyamSundar Pasunurthi, Ravichandra Jupudi, Sreenivasa Rao Gubba, Roy Primus, Adam Klingbeil
Published 2017-03-28 by SAE International in United States
The standard capability of engine experimental studies is that ensemble averaged quantities like in-cylinder pressure from multiple cycles and emissions are reported and the cycle to cycle variation (CCV) of indicated mean effective pressure (IMEP) is captured from many consecutive combustion cycles for each test condition. However, obtaining 3D spatial distribution of all the relevant quantities such as fuel-air mixing, temperature, turbulence levels and emissions from such experiments is a challenging task. Computational Fluid Dynamics (CFD) simulations of engine flow and combustion can be used effectively to visualize such 3D spatial distributions. A dual fuel engine is considered in the current study, with manifold injected natural gas (NG) and direct injected diesel pilot for ignition. Multiple engine cycles in 3D are simulated in series like in the experiments to investigate the potential of high fidelity RANS simulations coupled with detailed chemistry, to accurately predict the CCV.Cycle to cycle variation (CCV) is expected to be due to variabilities in operating and boundary conditions, in-cylinder stratification of diesel and natural gas fuels, variation in in-cylinder turbulence levels…
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