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Large Eddy Simulation of an Ignition Front in a Heavy Duty Partially Premixed Combustion Engine

Lund University-Christian Ibron, Hesameddin Fatehi, Mehdi Jangi, Xue-Song Bai
Published 2019-09-09 by SAE International in United States
In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in a combustion mode dominated by ignition wave propagation. 3D-CFD modeling of such a combustion mode is challenging as the rate of fuel consumption can be dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of stratification in scalar concentration (enthalpy and reactant mass fraction) due to large scale turbulence on the propagation of reaction waves in PPC combustion engines. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane). Two injection timings are investigated; start of injection at -17 CAD aTDC and -30 CAD aTDC. One-equation transported turbulence sub-grid closure is used for the unresolved momentum and scalar fluxes…
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Numerical Investigation of Methanol Ignition Sequence in an Optical PPC Engine with Multiple Injection Strategies

Birmingham University-Mehdi Jangi
Lund University-Mateusz Pucilowski, Hesameddin Fatehi, Sara Lonn, Alexios Matamis, Oivind Andersson, Mattias Richter, Xue-Song Bai
Published 2019-09-09 by SAE International in United States
Methanol is a genuine candidate on the alternative fuel market for internal combustion engines, especially within the heavy-duty transportation sector. Partially premixed combustion (PPC) engine concept, known for its high efficiency and low emission rates, can be promoted further with methanol fuel due to its unique thermo-physical properties. The low stoichiometric air to fuel ratio allows to utilize late injection timings, which reduces the wall-wetting effects, and thus can lead to less unburned hydrocarbons. Moreover, combustion of methanol as an alcohol fuel, is free from soot emissions, which allows to extend the operation range of the engine. However, due to the high latent heat of vaporization, the ignition event requires a high inlet temperature to achieve ignition event. In this paper LES simulations together with experimental measurements on an heavy-duty optical engine are used to study methanol PPC engine. After a successful calibration of the pressure trace in terms of required intake temperature and combustion model, the optical natural luminosity data is used to validate prediction of ignition kernel and vapor penetration length. Moreover, it…
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Effect of Injection Timing on the Ignition and Mode of Combustion in a HD PPC Engine Running Low Load

Lund University-Christian Ibron, Mehdi Jangi, Sara Lonn, Alexios Matamis, Oivind Andersson, Martin Tuner, Mattias Richter, Xue-Song Bai
Published 2019-04-02 by SAE International in United States
This work aims to study the effect of fuel inhomogeneity on the ignition process and subsequent combustion in a compression ignition Partially Premixed Combustion (PPC) engine using a primary reference fuel (PRF) in low load conditions. Five cases with injection timings ranging from the start of injection (SOI) at -70 crank angle degrees (CAD) to -17 CAD have been studied numerically and experimentally in a heavy duty (HD) piston bowl geometry. Intake temperature is adjusted to keep the combustion phasing constant. Three dimensional numerical simulations are performed in a closed cycle sector domain using the Reynolds Averaged Navier-Stokes (RANS) formulation with k-ϵ turbulence closure and direct coupling of finite rate chemistry. The results are compared with engine experiments. The predicted trends in required intake temperature and auto-ignition location for a constant combustion phasing are consistent with experiments. The simulations show that the auto-ignition is critically dependent on both fuel and temperature stratification. The ignition occurs in fuel-lean regions but the mixing of the fuel with the cylinder gas and the cylinder gas temperature stratification (prior…
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Effects of In-Cylinder Flow Simplifications on Turbulent Mixing at Varying Injection Timings in a Piston Bowl PPC Engine

Lund University-Christian Ibron, Mehdi Jangi, Xue-Song Bai
Published 2019-04-02 by SAE International in United States
In computational fluid dynamic simulations of partially premixed combustion engines it is common to find simplifications of the in cylinder flow conditions in order to save computational cost. One common simplification is to start the simulation at the moment of intake valve closing with an assumed initial flow condition, rather than making a full scavenging simulation. Another common simplification is the periodic sector assumption, limiting all sector cuts of the full cylinder to be identical periodic copies of each other. This work studies how such flow simplifications affect the spray injection and in turn the fuel/air mixing at different injection timings. Focus is put on the stratification of fuel concentration and gas temperature due to interaction of the spray, turbulence and piston geometry. The investigated engine setup consists of a light duty engine with a piston bowl and a five-hole injector. The simulations are performed under non-reacting conditions and utilize the large eddy simulation turbulence model. Both full cylinder mesh and sector mesh simulations are carried out to evaluate the effects of (a) turbulent vs…
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Heat Loss Analysis for Various Piston Geometries in a Heavy-Duty Methanol PPC Engine

Lund University-Mateusz Pucilowski, Mehdi Jangi, Sam Shamun, Martin Tuner, Xue-Song Bai
Published 2018-09-10 by SAE International in United States
Partially premixed combustion (PPC) in internal combustion engine as a low temperature combustion strategy has shown great potential to achieve high thermodynamic efficiency. Methanol due to its unique properties is considered as a preferable PPC engine fuel. The injection timing to achieve methanol PPC conditions should be set very close to TDC, allowing to utilize spray-bowl interaction to further improve combustion process in terms of emissions and heat losses. In this study CFD simulations are performed to investigate spray-bowl interaction for a number of different piston designs and its impact on the heat transfer and the overall piston performance. The validation case is based on a single cylinder heavy-duty Scania D13 engine with a compression ratio 15. The operation point is set to low load 5.42 IMEPg bar with SOI -3 aTDC. After satisfactory agreement with experiments in terms of combustion phasing, in-cylinder pressure and heat release rate, the effect of piston bowl geometry is investigated by performing several CFD simulations with modified piston bowl geometry while keeping the compression ratio, CA50 and injection conditions…
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Numerical Estimation of Asymmetry of In-Cylinder Flow in a Light Duty Direct Injection Engine with Re-Entrant Piston Bowl

Lund University-Christian Ibron, Mehdi Jangi, Xue-Song Bai
Politecnico di Milano-Tommaso Lucchini
Published 2017-10-08 by SAE International in United States
Partially premixed combustion (PPC) can be applied to decrease emissions and increase fuel efficiency in direct injection, compression ignition (DICI) combustion engines. PPC is strongly influenced by the mixing of fuel and oxidizer, which for a given fuel is controlled mainly by (a) the fuel injection, (b) the in-cylinder flow, and (c) the geometry and dynamics of the engine. As the injection timings can vary over a wide range in PPC combustion, detailed knowledge of the in-cylinder flow over the whole intake and compression strokes can improve our understanding of PPC combustion. In computational fluid dynamics (CFD) the in-cylinder flow is sometimes simplified and modeled as a solid-body rotation profile at some time prior to injection to produce a realistic flow field at the moment of injection. In real engines, the in-cylinder flow motion is governed by the intake manifold, the valve motion, and the engine geometry. The deviation of the real in-cylinder flow from a solid body rotation flow field varies with different piston positions. This paper reports on an CFD study of the…
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The Effect of Injection Pressure on the NOx Emission Rates in a Heavy-Duty DICI Engine Running on Methanol.

Lund University-Mateusz Pucilowski, Mehdi Jangi, Sam Shamun, Martin Tuner, Xue-Song Bai
Published 2017-10-08 by SAE International in United States
Heavy-duty direct injection compression ignition (DICI) engine running on methanol is studied at a high compression ratio (CR) of 27. The fuel is injected with a common-rail injector close to the top-dead-center (TDC) with two injection pressures of 800 bar and 1600 bar. Numerical simulations using Reynold Averaged Navier Stokes (RANS), Lagrangian Particle Tracking (LPT), and Well-Stirred-Reactor (WSR) models are employed to investigate local conditions of injection and combustion process to identify the mechanism behind the trend of increasing nitrogen oxides (NOx) emissions at higher injection pressures found in the experiments. It is shown that the numerical simulations successfully replicate the change of ignition delay time and capture variation of NOx emissions. The fuel vapor penetration length before the onset of ignition has been significantly altered at a higher injection pressure, which had an important impact on the high temperature zone and thus on the increased formation rate of NOx emissions.
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Effect of Start of Injection on the Combustion Characteristics in a Heavy-Duty DICI Engine Running on Methanol

Lund University-Mateusz Pucilowski, Mehdi Jangi, Sam Shamun, Changle Li, Martin Tuner, Xue-Song Bai
Published 2017-03-28 by SAE International in United States
Methanol as an alternative fuel in internal combustion engines has an advantage in decreasing emissions of greenhouse gases and soot. Hence, developing of a high performance internal combustion engine operating with methanol has attracted the attention in industry and academic research community. This paper presents a numerical study of methanol combustion at different start-of-injection (SOI) in a direct injection compression ignition (DICI) engine supported by experimental studies.The aim is to investigate the combustion behavior of methanol with single and double injection at close to top-dead-center (TDC) conditions. The experimental engine is a modified version of a heavy duty D13 Scania engine. URANS simulations are performed for various injection timings with delayed SOI towards TDC, aiming at analyzing the characteristics of partially premixed combustion (PPC). The simulations are based on a relatively detailed chemical kinetic mechanism and a well-stirred reactor (WSR) approach, accelerated using a so-called chemistry coordinate mapping (CCM). The injection of the fuel is treated with Lagrangian Particle Tracking (LPT) method. A baseline case with SOI of -20 after TDC (ATDC) was studied experimentally;…
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Towards the Use of Eulerian Field PDF Methods for Combustion Modeling in IC Engines

SAE International Journal of Engines

Lund University of Technology-Mehdi Jangi
Politecnico di Milano-Tommaso Lucchini, Gianluca D'Errico
  • Journal Article
  • 2014-01-1144
Published 2014-04-01 by SAE International in United States
Detailed chemistry and turbulence-chemistry interaction need to be properly taken into account for a realistic combustion simulation of IC engines where advanced combustion modes, multiple injections and stratified combustion involve a wide range of combustion regimes and require a proper description of several phenomena such as auto-ignition, flame stabilization, diffusive combustion and lean premixed flame propagation. To this end, different approaches are applied and the most used ones rely on the well-stirred reactor or flamelet assumption. However, well-mixed models do not describe correctly flame structure, while unsteady flamelet models cannot easily predict premixed flame propagation and triple flames. A possible alternative for them is represented by transported probability density functions (PDF) methods, which have been applied widely and effectively for modeling turbulent reacting flows under a wide range of combustion regimes. For IC engine simulations, the most promising ones are the Eulerian field PDF methods (SEF) whose formulation was originally proposed by Valiño and Sabel'nikov. Such models can be easily incorporated into CFD codes and are less computationally intensive with respect to Lagrangian approaches. In…
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Investigation of Chemical Kinetics on Soot Formation Event of n-Heptane Spray Combustion

Lund Univ.-Mehdi Jangi, Xue-Song Bai
Technical University of Denmark-Kar Mun Pang, Jesper Schramm
Published 2014-04-01 by SAE International in United States
In this reported work, 2-dimsensional computational fluid dynamics studies of n-heptane combustion and soot formation processes in the Sandia constant-volume vessel are carried out. The key interest here is to elucidate how the chemical kinetics affects the combustion and soot formation events. Numerical computation is performed using OpenFOAM and chemistry coordinate mapping (CCM) approach is used to expedite the calculation. Three n-heptane kinetic mechanisms with different chemistry sizes and comprehensiveness in oxidation pathways and soot precursor formation are adopted. The three examined chemical models use acetylene (C2H2), benzene ring (A1) and pyrene (A4) as soot precursor. They are henceforth addressed as nhepC2H2, nhepA1 and nhepA4, respectively for brevity. Here, a multistep soot model is coupled with the spray combustion solver to simulate the soot formation/oxidation processes. Comparison of the results shows that the simulated ignition delay times and liftoff lengths have good agreements with the experimental measurements across wide range of operating conditions when the nhepC2H2 model is implemented. The performance of this mechanism however drops in cases with low ambient temperatures. Besides, the overall…
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