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Ra, Youngchul
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Numerical Parametric Study of a Six-Stroke Gasoline Compression Ignition (GCI) Engine Combustion

Hyundai Motor Co.-Kyoung-Pyo Ha
Michigan Technological University-Oudumbar Rajput, Youngchul Ra
Published 2019-04-02 by SAE International in United States
Numerical investigation of engine performance and emissions of a six-stroke gasoline compression ignition (GCI) engine combustion at low load conditions is presented. In order to identify the effects of additional two strokes of the six-stroke engine cycle on the thermal and chemical conditions of charge mixtures, an in-house multi-dimensional CFD code coupled with high fidelity physical sub-models along with the Chemkin library was employed. The combustion and emissions were calculated using a reduced chemical kinetics mechanism for a 14-component gasoline surrogate fuel. Two power strokes per cycle were achieved using multiple injections during compression strokes.Parametric variations of injection strategy viz., individual injection timing for both the power strokes and the split ratio that enable the control of combustion phasing of both the power strokes were explored. The computational results suggest that the operability limit of GCI combustion can be effectively expanded by controlling the mixture thermodynamic conditions and achieving optimum mixture stratification. It was uniquely found that the charge mixtures could burn in the mixing-controlled mode during the second power stroke with the injection timing…
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A Combustion Model for Multi-Component Fuels Based on Reactivity Concept and Single-Surrogate Chemistry Representation

Korea Institute of Machinery & Materials-Wonah Park, Gyubaek Cho
Michigan Technological University-Arash Jamali, Youngchul Ra
Published 2018-04-03 by SAE International in United States
High fidelity engine simulation requires realistic fuel models. Although typical automotive fuels consist of more than few hundreds of hydrocarbon species, researches show that the physical and chemical properties of the real fuels could be represented by appropriate surrogate fuel models. It is desirable to represent the fuel using the same set of physical and chemical surrogate components. However, when the reaction mechanisms for a certain physical surrogate component is not available, the chemistry of the unmatched physical component is described using that of a similar chemical surrogate component at the expense of accuracy.In order to reduce the prediction error while maintaining the computational efficiency, a method of on-the-fly reactivity adjustment (ReAd) of chemical reaction mechanism along with fuel re-distribution based on reactivity is presented and tested in this study.The method is applied to simulate engine combustion with multi-component fuel sprays and its performance is compared to that of simulations with a reaction mechanism that considers the full set of physical/chemical surrogate components. The results show that the ReAd method improves the accuracy of combustion…
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Development of a Reduced Chemical Mechanism for Combustion of Gasoline-Biofuels

CNR - Istituto Motori-Michela Costa
CNR- Istituto Motori-Vittorio ROCCO
Published 2017-09-04 by SAE International in United States
Bio-derived fuels are drawing more and more attention in the internal combustion engine (ICE) research field in recent years. Those interests in use of renewable biofuels in ICE applications derive from energy security issues and, more importantly, from environment pollutant emissions concerns.High fidelity numerical study of engine combustion requires advanced computational fluid dynamics (CFD) to be coupled with detailed chemical kinetic models.This task becomes extremely challenging if real fuels are taken into account, as they include a mixture of hundreds of different hydrocarbons, which prohibitively increases computational cost. Therefore, along with employing surrogate fuel models, reduction of detailed kinetic models for multidimensional engine applications is preferred.In the present work, a reduced mechanism was developed for primary reference fuel (PRF) using the directed relation graph (DRG) approach. The mechanism was generated from an existing detailed mechanism. The adjustment of reaction rate constants of selected reactions was performed and the present reduced mechanism was validated against experiments in terms of ignition delay times, flame speed and HCCI combustion. Employing similar procedures, reduced reaction mechanisms for ethanol and…
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An Efficient Level-Set Flame Propagation Model for Hybrid Unstructured Grids Using the G-Equation

SAE International Journal of Engines

Michigan Technological University-Youngchul Ra
Mitsubishi Heavy Industries Ltd.-Kenji Hiraoka, Kazutoshi Nomura, Akihiro Yuuki, Yuji Oda
  • Journal Article
  • 2016-01-0582
Published 2016-04-05 by SAE International in United States
Computational fluid dynamics of gas-fueled large-bore spark ignition engines with pre-chamber ignition can speed up the design process of these engines provided that 1) the reliability of the results is not affected by poor meshing and 2) the time cost of the meshing process does not negatively compensate for the advantages of running a computer simulation. In this work a flame propagation model that runs with arbitrary hybrid meshes was developed and coupled with the KIVA4-MHI CFD solver, in order to address these aims. The solver follows the G-Equation level-set method for turbulent flame propagation by Tan and Reitz, and employs improved numerics to handle meshes featuring different cell types such as hexahedra, tetrahedra, square pyramids and triangular prisms.Detailed reaction kinetics from the SpeedCHEM solver are used to compute the non-equilibrium composition evolution downstream and upstream of the flame surface, where chemical equilibrium is instead assumed. A generalized least-squares gradient reconstruction algorithm is employed to evaluate spatial derivatives with arbitrary node and cell connectivities, instead of the original ENO scheme. Finally, a new, extended version…
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Use of Multiple Injection Strategies to Reduce Emission and Noise in Low Temperature Diesel Combustion

Ford Forschungszentrum Aachen GmbH-Werner Willems
Ford Motor Co-Eric Kurtz
Published 2015-04-14 by SAE International in United States
The low temperature combustion concept is very attractive for reducing NOx and soot emissions in diesel engines. However, it has potential limitations due to higher combustion noise, CO and HC emissions. A multiple injection strategy is an effective way to reduce unburned emissions and noise in LTC. In this paper, the effect of multiple injection strategies was investigated to reduce combustion noise and unburned emissions in LTC conditions. A hybrid surrogate fuel model was developed and validated, and was used to improve LTC predictions. Triple injection strategies were considered to find the role of each pulse and then optimized. The split ratio of the 1st and 2nd pulses fuel was found to determine the ignition delay. Increasing mass of the 1st pulse reduced unburned emissions and an increase of the 3rd pulse fuel amount reduced noise. It is concluded that the pulse distribution can be used as a control factor for emissions and noise.
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Experimental and Computational Assessment of Inlet Swirl Effects on a Gasoline Compression Ignition (GCI) Light-Duty Diesel Engine

Univ. of Wisconsin-Paul Loeper, Youngchul Ra, David E. Foster, Jaal Ghandhi
Published 2014-04-01 by SAE International in United States
The light-medium load operating regime (4-8 bar net IMEP) presents many challenges for advanced low temperature combustion strategies (e.g. HCCI, PPC) in light-duty, high speed engines. In this operating regime, lean global equivalence ratios (Φ<0.4) present challenges with respect to autoignition of gasoline-like fuels. Considering this intake temperature sensitivity, the objective of this work was to investigate, both experimentally and computationally, gasoline compression ignition (GCI) combustion operating sensitivity to inlet swirl ratio (Rs) variations when using a single fuel (87-octane gasoline) in a 0.475-liter single-cylinder engine based on a production GM 1.9-liter high speed diesel engine.For the first part of this investigation, an experimental matrix was developed to determine how changing inlet swirl affected GCI operation at various fixed load and engine speed operating conditions (4 and 8 bar net IMEP; 1300 and 2000 RPM). Here, experimental results showed significant changes in CA50 due to changes in inlet swirl ratio. For example, at the 4 bar net IMEP operating condition at 1300 RPM, a reduction in swirl ratio (from 2.2 to 1.5) caused a 6…
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A Surrogate Fuel Formulation Approach for Real Transportation Fuels with Application to Multi-Dimensional Engine Simulations

SAE International Journal of Fuels and Lubricants

Univ. of Wisconsin-Xingyuan Su, Youngchul Ra, Rolf D. Reitz
  • Journal Article
  • 2014-01-1464
Published 2014-04-01 by SAE International in United States
Real transportation fuels, such as gasoline and diesel, are mixtures of thousands of different hydrocarbons. For multidimensional engine applications, numerical simulations of combustion of real fuels with all of the hydrocarbon species included exceeds present computational capabilities. Consequently, surrogate fuel models are normally utilized. A good surrogate fuel model should approximate the essential physical and chemical properties of the real fuel. In this work, we present a novel methodology for the formulation of surrogate fuel models based on local optimization and sensitivity analysis technologies. Within the proposed approach, several important fuel properties are considered. Under the physical properties, we focus on volatility, density, lower heating value (LHV), and viscosity, while the chemical properties relate to the chemical composition, hydrogen to carbon (H/C) ratio, and ignition behavior. An error tolerance is assigned to each property for convergence checking. In addition, a weighting factor is given to each property indicating its individual importance among all properties considered; the overall quality of the surrogate fuel model is controlled by a weighted error tolerance. It is observed that the…
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Improved Chemical Kinetics Numerics for the Efficient Simulation of Advanced Combustion Strategies

SAE International Journal of Engines

University of Wisconsin-Federico Perini, Bishwadipa Das Adhikary, Jae Hyung Lim, Xingyuan Su, Youngchul Ra, Hu Wang, Rolf D. Reitz
  • Journal Article
  • 2014-01-1113
Published 2014-04-01 by SAE International in United States
The incorporation of detailed chemistry models in internal combustion engine simulations is becoming mandatory as local, globally lean, low-temperature combustion strategies are setting the path towards a more efficient and environmentally sustainable use of energy resources in transportation. In this paper, we assessed the computational efficiency of a recently developed sparse analytical Jacobian chemistry solver, namely ‘SpeedCHEM’, that features both direct and Krylov-subspace solution methods for maximum efficiency for both small and large mechanism sizes. The code was coupled with a high-dimensional clustering algorithm for grouping homogeneous reactors into clusters with similar states and reactivities, to speed-up the chemical kinetics solution in multi-dimensional combustion simulations. The methodology was validated within the KIVA-ERC code, and the computational efficiency of both methods was evaluated for different, challenging engine combustion modeling cases, including dual fuel, dual direct-injection and low-load, multiple-injection RCCI, direct injection gasoline compression ignition (GDICI), and HCCI engine operation using semi-detailed chemistry representations. Reaction mechanisms of practical applicability in internal combustion engine CFD simulations were used, ranging from about 50 up to about 200 species. Computational…
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Experimental Investigation of Light-Medium Load Operating Sensitivity in a Gasoline Compression Ignition (GCI) Light-Duty Diesel Engine

General Motors Company-Russ Durrett
Univ. of Wisconsin Madison-Paul Loeper, Youngchul Ra, Cory Adams, David E. Foster, Jaal Ghandhi, Michael Andrie, Roger Krieger
Published 2013-04-08 by SAE International in United States
The light-medium load operating range (4-7 bar net IMEP) presents many challenges for advanced low temperature combustion strategies utilizing low cetane fuels (specifically, 87-octane gasoline) in light-duty, high-speed engines. The overly lean overall air-fuel ratio (Φ≺0.4) sometimes requires unrealistically high inlet temperatures and/or high inlet boost conditions to initiate autoignition at engine speeds in excess of 1500 RPM. The objective of this work is to identify and quantify the effects of variation in input parameters on overall engine operation. Input parameters including inlet temperature, inlet pressure, injection timing/duration, injection pressure, and engine speed were varied in a ~0.5L single-cylinder engine based on a production General Motors 1.9L 4-cylinder high-speed diesel engine.With constraints of combustion efficiency, noise level (pressure rise rate) and emissions, engine operation sensitivity due to changes in inlet temperature between 50-90C was first examined for fixed fueling rates. This experiment was then repeated at different inlet pressures and engine speeds. Finally, constant load experiments were performed in which perturbations in injection strategies (timing, duration, and pressure) were executed to assess overall system sensitivity.…
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Numerical Optimization of a Light-Duty Compression Ignition Engine Fuelled With Low-Octane Gasoline

Bishwadipa Das Adhikary
Argonne National Laboratory-Stephen Ciatti
Published 2012-04-16 by SAE International in United States
In automotive industry it has been a challenge to retain diesel-like thermal efficiency while maintaining low emissions. Numerous studies have shown significant progress in achieving low emissions through the introduction of common-rail injection systems, multiple injections and exhaust gas recirculation and by using a high octane number fuel, like gasoline, to achieve adequate premixing. On the other hand, low temperature combustion strategies, like HCCI and PCCI, have also shown promising results in terms of reducing both NOx and soot emissions simultaneously. With the increasing capacity of computers, multi-dimensional CFD engine modeling enables a reasonably good prediction of combustion characteristics and pollutant emissions, which is the motivation behind the present research. The current research effort presents an optimization study of light-duty compression ignition engine performance, while meeting the emission regulation targets. A numerical optimization study was carried out on a light-duty, single-cylinder, compression ignition engine, fueled with a PRF87 gasoline surrogate, at a full load operating condition. The simulations were performed using a Non-dominated Sorting Genetic Algorithm II (NSGAII) code coupled to a multi-dimensional CFD code,…
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