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Piston Bowl Geometry Effects on Combustion Development in a High-Speed Light-Duty Diesel Engine

University of Wisconsin-Madison-Federico Perini, Rolf Reitz
Ford Motor Company-Eric Kurtz
  • Technical Paper
  • 2019-24-0167
To be published on 2019-09-09 by SAE International in United States
In this work, we studied the effects of piston bowl design on combustion in a light-duty direct-injection diesel engine. Two bowl designs were compared: a conventional, omega-shaped bowl and a stepped-lip piston bowl. Experiments were carried out in the SNL single-cylinder optical engine facility, with a medium-load, mild-boosted operating condition featuring a pilot+main injection strategy. CFD simulations carried out with the FRESCO platform featuring full-geometric modeling of the engine, were validated against measured in-cylinder performance as well as soot natural luminosity images. Differences in combustion development were studied using the simulation results, and sensitivities to in-cylinder flow field (swirl ratio) and injection rate parameters were also analyzed. In-cylinder mixture formation analysis showed that ignition of the pilot injection mixture develops nearly as a homogeneous adiabatic reactor, being mostly advected, not mixed, by the bowl’s swirling motion, while its timing is influenced by the local flow field. Local in-cylinder flow is also more crucial than injection parameters to igniting the main injection’s premixed fuel, as it determines the relative overlap with the high-temperature pilot ignited mixture.…

Bowl Geometry Effects on Turbulent Flow Structure in a Direct Injection Diesel Engine

University of Wisconsin-Madison-Federico Perini
Ford Motor Company-Eric Kurtz
Published 2018-09-10 by SAE International in United States
Diesel piston bowl geometry can affect turbulent mixing and therefore it impacts heat-release rates, thermal efficiency, and soot emissions. The focus of this work is on the effects of bowl geometry and injection timing on turbulent flow structure. This computational study compares engine behavior with two pistons representing competing approaches to combustion chamber design: a conventional, re-entrant piston bowl and a stepped-lip piston bowl. Three-dimensional computational fluid dynamics (CFD) simulations are performed for a part-load, conventional diesel combustion operating point with a pilot-main injection strategy under non-combusting conditions. Two injection timings are simulated based on experimental findings: an injection timing for which the stepped-lip piston enables significant efficiency and emissions benefits, and an injection timing with diminished benefits compared to the conventional, re-entrant piston.While the flow structure in the conventional, re-entrant combustion chamber is dominated by a single toroidal vortex, the turbulent flow evolution in the stepped-lip combustion chamber depends more strongly on main injection timing. For the injection timing at which faster mixing controlled heat release and reduced soot emissions have been observed experimentally,…
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Autonomous Vehicles in the Cyberspace: Accelerating Testing via Computer Simulation

University of Wisconsin-Madison-Dan Negrut, Radu Serban, Asher Elmquist, Dylan Hatch
Mandli Communications Inc-Eric Nutt, Phil Sheets
Published 2018-04-03 by SAE International in United States
We present an approach in which an open-source software infrastructure is used for testing the behavior of autonomous vehicles through computer simulation. This software infrastructure is called CAVE, from Connected Autonomous Vehicle Emulator. As a software platform that allows rapid, low-cost and risk-free testing of novel designs, methods and software components, CAVE accelerates and democratizes research and development activities in the field of autonomous navigation. CAVE is (a) heterogeneous and multi-agent, in that it supports the simulation of heterogeneous traffic scenarios involving conventional, assisted, and autonomous vehicles as well as pedestrians and cyclists; (b) open platform, as it allows any client that subscribes to a standard application programming interface (API) to remotely plug into the emulator and engage in multi-participant traffic scenarios that bring together autonomous agents from different solution providers; (c) vehicle-to-vehicle (V2V) communication emulation ready, owing to its ability to simulate the V2V data exchange enabled in real-world scenarios by ad-hoc dedicated short range communication (DSRC) protocols; and (d) open-source, as the software infrastructure will be available under a BSD3 license in a…
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On Simulating Sloshing in Vehicle Dynamics

University of Wisconsin-Madison-Dan Negrut, Hammad Mazhar, Radu Serban, Milad Rakhsha
Published 2018-04-03 by SAE International in United States
We present an approach in which we use simulation to capture the two-way coupling between the dynamics of a vehicle and that of a fluid that sloshes in a tank attached to the vehicle. The simulation is carried out in and builds on support provided by two modules: Chrono::FSI (Fluid-Solid Interaction) and Chrono::Vehicle. The dynamics of the fluid phase is governed by the mass and momentum (Navier-Stokes) equations, which are discretized in space via a Lagrangian approach called Smoothed Particle Hydrodynamics. The vehicle dynamics is the solution of a set of differential algebraic equations of motion. All equations are discretized in time via a half-implicit symplectic Euler method. This solution approach is general - it allows for fully three dimensional (3D) motion and nonlinear transients. We demonstrate the solution in conjunction with the simulation of a vehicle model that performs a constant radius turn and double lane change maneuver. We also present results for a vehicle operating on deformable terrain.
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Divided Exhaust Period Implementation in a Light-Duty Turbocharged Dual-Fuel RCCI Engine for Improved Fuel Economy and Aftertreatment Thermal Management: A Simulation Study

SAE International Journal of Engines

University of Wisconsin-Madison-Anand Nageswaran Bharath, Rolf Reitz, Christopher Rutland
  • Journal Article
  • 2018-01-0256
Published 2018-04-03 by SAE International in United States
Although turbocharging can extend the high load limit of low temperature combustion (LTC) strategies such as reactivity controlled compression ignition (RCCI), the low exhaust enthalpy prevalent in these strategies necessitates the use of high exhaust pressures for improving turbocharger efficiency, causing high pumping losses and poor fuel economy. To mitigate these pumping losses, the divided exhaust period (DEP) concept is proposed. In this concept, the exhaust gas is directed to two separate manifolds: the blowdown manifold which is connected to the turbocharger and the scavenging manifold that bypasses the turbocharger. By separately actuating the exhaust valves using variable valve actuation, the exhaust flow is split between two manifolds, thereby reducing the overall engine backpressure and lowering pumping losses. In this paper, results from zero-dimensional and one-dimensional simulations of a multicylinder RCCI light-duty engine equipped with DEP are presented. It is shown that while DEP helped reduce pumping penalty at medium and high loads, the pumping benefit was negated by crankshaft power consumption from a mechanical supercharger which made up for the boost deficit as the…
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Comparison of Linear, Non-Linear and Generalized RNG-Based k-epsilon Models for Turbulent Diesel Engine Flows

University of Wisconsin-Madison-Federico Perini, Rolf Reitz
Sandia National Laboratories-Kan Zha, Stephen Busch
Published 2017-03-28 by SAE International in United States
In this work, linear, non-linear and a generalized renormalization group (RNG) two-equation RANS turbulence models of the k-epsilon form were compared for the prediction of turbulent compressible flows in diesel engines. The object-oriented, multidimensional parallel code FRESCO, developed at the University of Wisconsin, was used to test the alternative models versus the standard k-epsilon model.Test cases featured the academic backward facing step and the impinging gas jet in a quiescent chamber. Diesel engine flows featured high-pressure spray injection in a constant volume vessel from the Engine Combustion Network (ECN), as well as intake flows in a high-swirl diesel engine. For the engine intake flows, a model of the Sandia National Laboratories 1.9L light-duty single cylinder optical engine was used. An extensive experimental campaign provided validation data in terms of ensemble averages of planar PIV measurements at different vertical locations in the combustion chamber, for different swirl ratio configurations during both the intake and the compression strokes.The generalized RNG k-epsilon model provided the best accuracy trade-off for both swirl and shear flows, thanks to the polynomial…
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Investigating Air Handling Requirements of High Load Low Speed Reactivity Controlled Compression Ignition (RCCI) Combustion

University of Wisconsin-Madison-Chaitanya Kavuri, Sage Kokjohn
Published 2016-04-05 by SAE International in United States
Past research has shown that reactivity controlled compression ignition (RCCI) combustion offers efficiency and NOx and soot advantages over conventional diesel combustion at mid load conditions. However, at high load and low speed conditions, the chemistry timescale of the fuel shortens and the engine timescale lengthens. This mismatch in timescales makes operation at high load and low speed conditions difficult. High levels of exhaust gas recirculation (EGR) can be used to extend the chemistry timescales; however, this comes at the penalty of increased pumping losses. In the present study, targeting the high load - low speed regime, computational optimizations of RCCI combustion were performed at 20 bar gross indicated mean effective pressure (IMEP) and 1300 rev/min. The two fuels used for the study were gasoline (low reactivity) and diesel (high reactivity). The effects of intake pressure and EGR on combustion and emissions were studied using a full factorial design of experiments of genetic algorithm optimizations. The optimizations were setup for three values of EGR (30%, 45% and 55%) and equivalence ratios (0.8, 0.9 and 1.0).…
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Simultaneous Reduction of Soot and NOX Emissions by Means of the HCPC Concept: Complying with the Heavy Duty EURO 6 Limits without Aftertreatment System

University of Wisconsin-Madison-Rolf D. Reitz
Universita degli Studi di Pisa-Riccardo Rossi, Ettore Musu, Stefano Frigo, Roberto Gentili
Published 2013-09-08 by SAE International in United States
Due to concerns regarding pollutant and CO2 emissions, advanced combustion modes that can simultaneously reduce exhaust emissions and improve thermal efficiency have been widely investigated. The main characteristic of the new combustion strategies, such as HCCI and LTC, is that the formation of a homogenous mixture or a controllable stratified mixture is required prior to ignition. The major issue with these approaches is the lack of a direct method for the control of ignition timing and combustion rate, which can be only indirectly controlled using high EGR rates and/or lean mixtures.Homogeneous Charge Progressive Combustion (HCPC) is based on the split-cycle principle. Intake and compression phases are performed in a reciprocating external compressor, which drives the air into the combustor cylinder during the combustion process, through a transfer duct. A transfer valve is positioned between the compressor cylinder and the transfer duct. The compressor runs with a fixed phase delay with respect to the combustor. As a consequence, during the combustion process, air moves from the compressor cylinder to the combustor cylinder. Contemporary with the air…
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A Quasi-Dimensional NOx Emission Model for Spark Ignition Direct Injection (SIDI) Gasoline Engines

University of Wisconsin-Madison-Jian Gong, Christopher Rutland
Published 2013-04-08 by SAE International in United States
A fundamentally based quasi-dimensional NOx emission model for spark ignition direct injection (SIDI) gasoline engines was developed. The NOx model consists of a chemical mechanism and three sub-models. The classical extended Zeldovich mechanism and N₂O pathway for NOx formation mechanism were employed as the chemical mechanism in the model. A characteristic time model for the radical species H, O and OH was incorporated to account for non-equilibrium of radical species during combustion. A model of homogeneity which correlates fundamental dimensionless numbers and mixing time was developed to model the air-fuel mixing and inhomogeneity of the charge. Since temperature has a dominant effect on NOx emission, a flame temperature correlation was developed to model the flame temperature during the combustion for NOx calculation.Measured NOx emission data from a single-cylinder SIDI research engine at different operating conditions was used to validate the NOx model. The effects of fuel injection timing, injection pressure, spark timing, overall engine AFR, and intake temperature on NOx emission were examined and well captured by the model. Comparison of all the NOx emission…
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A Computational Investigation of the Effects of Swirl Ratio and Injection Pressure on Mixture Preparation and Wall Heat Transfer in a Light-Duty Diesel Engine

University of Wisconsin-Madison-Federico Perini, Adam Dempsey, Rolf D. Reitz
Ford Motor Company-Benjamin Petersen
Published 2013-04-08 by SAE International in United States
In a recent study, quantitative measurements were presented of in-cylinder spatial distributions of mixture equivalence ratio in a single-cylinder light-duty optical diesel engine, operated with a non-reactive mixture at conditions similar to an early injection low-temperature combustion mode. In the experiments a planar laser-induced fluorescence (PLIF) methodology was used to obtain local mixture equivalence ratio values based on a diesel fuel surrogate (75% n-heptane, 25% iso-octane), with a small fraction of toluene as fluorescing tracer (0.5% by mass). Significant changes in the mixture's structure and composition at the walls were observed due to increased charge motion at high swirl and injection pressure levels. This suggested a non-negligible impact on wall heat transfer and, ultimately, on efficiency and engine-out emissions. In this work, the extensive and quantitative local information provided by the PLIF experiments was used as the reference for assessing the accuracy of the CFD modeling of the engine. The KIVA3V-ERC code was used, with a sector mesh featuring high spatial resolution (about 0.1 cm). A compressible model for the extended piston and connecting rod…
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