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Two-Scale Command Shaping for Reducing NVH During Engine Shutdown

Sandia National Laboratories-Justin Wilbanks
Georgia Institute of Technology-Mohid Muneeb Khattak, Michael Leamy
  • Technical Paper
  • 2020-01-0411
To be published on 2020-04-14 by SAE International in United States
Two-scale command shaping (TSCS) is a recently proposed feedforward control method aimed at mitigating undesirable vibrations in nonlinear systems. The TSCS strategy uses a scale separation to cancel oscillations arising from nonlinear behavior of the system, and command shaping of the remaining linear problem. One promising application of TSCS is in reducing engine restart and shutdown vibrations found in conventional and in hybrid electric vehicle (HEV) powertrains equipped with start-stop features. The efficacy of the TSCS during internal combustion engine (ICE) restart has been demonstrated theoretically and experimentally in the authors’ prior works. The present article presents simulation results and describes the verified experimental apparatus used to study TSCS as applied to the ICE shutdown case. The apparatus represents a typical HEV powertrain and consists of a 1.03 L three-cylinder diesel ICE coupled to a permanent magnet alternating current electric machine (EM) through a spur gear coupling. The EM is mounted on a plate and welded frame and is used to implement a given TSCS-designed torque profile to the ICE through Controlled Area Network (CAN)…
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An Investigation of Real-Gas and Multiphase Effects on Multicomponent Diesel Sprays

Sandia National Laboratories-Stephen Busch
Wisconsin Engine Research Consultants-Federico Perini, Rolf Reitz
  • Technical Paper
  • 2020-01-0240
To be published on 2020-04-14 by SAE International in United States
Lagrangian spray modeling represents a critical boundary condition for multidimensional simulations of in-cylinder flow structure, mixture formation and combustion in diesel engines. Segregated models for injection, breakup, collision and vaporization are usually employed to pass appropriate momentum, mass, and energy source terms to the gas-phase solver. Careful calibration of each sub-model generally produces appropriate results. Yet, the predictiveness of this modeling approach has been questioned by recent experimental observations, which showed that at trans- and super-critical conditions relevant to diesel injection, classical atomization and vaporization behavior is replaced by a mixing-controlled phase transition process of a dense fluid. In this work, we assessed the shortcomings of classical spray modeling with respect to real-gas and phase-change behavior, employing a multicomponent phase equilibrium solver and liquid-jet theory. A Peng-Robinson Equation of State (PR-EoS) model was implemented, and EoS-neutral thermodynamics derivatives were introduced in the FRESCO CFD platform turbulent NS solver. A phase equilibrium solver based on Gibbs free energy minimization was implemented to test phase stability and to compute phase equilibrium. Zero-dimensional flash calculations were employed to…
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Identifying the driving processes of Diesel spray injection through mixture fraction and velocity field measurements at ECN Spray A

Sandia National Laboratories-Lyle M. Pickett
Eindhoven University of Technology-Bart Somers
  • Technical Paper
  • 2020-01-0831
To be published on 2020-04-14 by SAE International in United States
Diesel spray mixture formation is investigated at target conditions using multiple diagnostics and laboratories. High speed Particle Image Velocimetry (PIV) is used to measure the velocity field inside and outside the jet simultaneously with a new frame straddling synchronisation scheme. The PIV measurements are carried out in the Engine Combustion Network Spray A target conditions, enabling direct comparisons with mixture fraction measurements previously performed in the same conditions, and forming a unique database at diesel conditions. A 1D spray model, based upon mass and momentum exchange between axial control volumes and near-Gaussian velocity and mixture fraction profiles is evaluated against the data. The 1D spray model quantitatively predicts the main spray characteristics (average mixture fraction and velocity fields) within the measurement uncertainty for a wide range of parametric variations, verifying that a Diesel spray becomes momentum controlled and has a Gaussian profile. A required input to the model is the jet angle, which is obtained experimentally. Although an expected result for a gas jet, this is the first time that combined datasets of velocity and…
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Combined experimental/numerical study of the soot formation process in a gasoline direct-injection spray in the presence of laser-induced plasma ignition

Sandia National Laboratories-Fabien Tagliante, Hyung S. Sim, Lyle M. Pickett, Tuan Nguyen, Scott Skeen
  • Technical Paper
  • 2020-01-0291
To be published on 2020-04-14 by SAE International in United States
Gasoline engines with direct-injection systems operated in a stratified mode provide improved engine efficiency. However, in such mode the particulate emissions are increased compared to conventional spark engine due to the limited mixing between air and fuel, which results in locally rich burn zones where soot is formed. Eliminating these rich combustion events requires detailed understanding of the complex physical phenomena occurring in an engine, including a very high Reynolds number two-phase flow with a complex chemistry. This study proposed a combined experimental/numerical work to better understand the soot formation process when varying the local fuel-air mixture at the spark-ignition location. Combustion issued from an eight-hole, direct-injection spray was experimentally studied in a constant-volume pre-burn combustion vessel using simultaneous high-speed diffused backlit imaging (DBI) and OH* chemiluminescence. DBI has been employed to observe the liquid-phase of the spray and to investigate the soot formation and oxidation taking place during the combustion, while OH* chemiluminescence was used to track the high-temperature ignition and flame. In the current study, the fuel-air mixture was ignited with a plasma…
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Experimental evaluation of a custom gasoline-like blend designed to simultaneously improve φ-sensitivity, RON and octane sensitivity.

Sandia National Laboratories-Dario Lopez Pintor, John Dec, Gerald Gentz
  • Technical Paper
  • 2020-01-1136
To be published on 2020-04-14 by SAE International in United States
φ-sensitivity is a fuel characteristic that has important benefits for the operation and control of low-temperature gasoline combustion (LTGC) engines. However, regular gasoline is only weakly φ–sensitive at naturally aspirated conditions, so intake boosting is required to take advantage of this property. Thus, there is strong motivation for designing gasoline-like blends that improve φ–sensitivity and simultaneously increase RON and octane sensitivity, to improve performance for LTGC and modern SI engines. In a previous study [SAE 2019-01-0961], a 5-component regulation-compliant fuel blend (CB#1) was computationally designed; and simulations showed promising results compared to regular E10 gasoline (RD5-87). The current study experimentally evaluates CB#1 in a LTGC research engine, and the results are compared to RD5-87. For premixed naturally aspirated conditions, the intake heating required to autoignite CB#1 was similar to RD5-87, ensuring that CB#1 can operate under these conditions as easily as regular gasoline. Furthermore, similar maximum engine loads were reached with both CB#1 and RD5-87 under premixed, high-boost conditions. An independent analysis showed that the RON and octane sensitivity were increased 1.3 and 3.6 units,…
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Measurements and Correlations of Local Cylinder-Wall Heat-Flux Relative to Near-Wall Chemiluminescence across Multiple Combustion Modes

Zachary Shechtman
Sandia National Laboratories-Zheming Li, Mark Musculus
  • Technical Paper
  • 2020-01-0802
To be published on 2020-04-14 by SAE International in United States
Minimizing heat transfer (HT) losses is important for both improving engine efficiency and increasing exhaust energy for turbocharging and exhaust aftertreatment management, but engine combustion system design to minimize these losses is hindered by significant uncertainties in prediction. Empirical HT correlations such as the popular Woschni model have been developed and various attempts at improving predictions have been proposed since the 1960s, but due to variations in facilities and techniques among various studies, comparison and assessment of modelling approaches among multiple combustion modes is not straightforward. In this work, simultaneous cylinder-wall temperature and OH* chemiluminescence high-speed video are all recorded in a single heavy-duty optical engine operated under multiple combustion modes. The cylinder-wall HT is derived from the measured transient temperature and compared with Woschni HT correlation predictions using both bulk and estimated local gas-temperatures. The local Woschni correlation predictions of heat flux and the HT coefficient for spark ignition (SI) and homogeneous charge compression ignition (HCCI) match surprisingly well with measurements. Uncertainty analysis shows that the modeled results falls in the measurements uncertainty. For…
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Transient internal nozzle flow in transparent multi-hole diesel injector

Sandia National Laboratories-Joonsik Hwang, Lyle M. Pickett
Argonne National Laboratory-Brandon Sforzo, Katarzyna Matusik, Christopher F. Powell
  • Technical Paper
  • 2020-01-0830
To be published on 2020-04-14 by SAE International in United States
An accurate prediction of internal nozzle flow in fuel injector offers the potential to improve predictions of spray computational fluid dynamics (CFD) in and engine, providing a coupled internal-external calculation or by defining better rate of injection (ROI) profile and spray angle information for Lagrangian parcel computations. Previous research has addressed experiments and computations in transparent nozzles, but less is known about realistic multi-hole diesel injectors compared to single axial-hole fuel injectors. In this study, the transient injector opening and closing is characterized using a transparent multi-hole diesel injector, and compared to that of a single axial hole nozzle (ECN Spray D shape). A real-size five-hole acrylic transparent nozzle was mounted in a high-pressure, constant-flow chamber. Internal nozzle phenomena such as cavitation and gas exchange were visualized by high-speed long-distance microscopy. Through optical observation, we find that the initial sac condition is mostly occupied by gas, and the gas remains relatively long after the start of injection, even longer than the case from a single axial hole, thereby affecting the ramp-up in ROI. Also, pronounced…
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Numerical investigation of near nozzle flash-boiling spray in an axial-hole transparent nozzle

Sandia National Laboratories-Joonsik Hwang, Marco Arienti, Lyle M. Pickett
Hino Motors, Ltd.-Koji Yasutomi
  • Technical Paper
  • 2020-01-0828
To be published on 2020-04-14 by SAE International in United States
Understanding and predicting flash-boiling spray behavior in gasoline direct-injection (GDI) engines remains a challenge. In this study, computational fluid dynamics (CFD) simulations using homogeneous relaxation model (HRM) for not only internal nozzle flow but also external spray were evaluated using CONVERGE software and compared to experimental data. High-speed extinction imaging experiments were carried out in a real-size axial-hole transparent nozzle installed at the tip of machined GDI injector fueled with n-pentane under various ambient pressure conditions (Pa/Ps=0.07-1.39). The width of the spray during injection was assessed by means of projected liquid volume, but the structure and timing for boil-off of liquid within the sac of the injector was also assessed after the end of injection, including cases with different designed sac volumes. Compared to the experiment, the default HRM model produces a more narrow liquid width, and a longer boil-off period, suggesting that the evaporation process is underestimated. When varying the HRM model constant to smaller values to promote evaporation, some level of improvement in predictions was observed, but the spray radial width and boil-off…
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On the Role of Nitric Oxide for the Knock-Mitigation Effectiveness of EGR in a DISI Engine Operated with Various Gasoline Fuels

SAE International Journal of Advances and Current Practices in Mobility

Sandia National Laboratories-Magnus Sjöberg, David Vuilleumier, Namho Kim
Toyota Motor Corporation-Nozomi Yokoo, Terutoshi Tomoda, Koichi Nakata
  • Journal Article
  • 2019-01-2150
Published 2019-12-19 by SAE International in United States
The knock-suppression effectiveness of exhaust-gas recirculation (EGR) can vary between implementations that take EGR gases after the three-way catalyst and those that use pre-catalyst EGR gases. A main difference between pre-and post-catalyst EGR gases is the level of trace species like NO, UHC, CO and H2. To quantify the role of NO, this experiment-based study employs NO-seeding in the intake tract for select combinations of fuel types and compression ratios, using simulated post-catalyst EGR gases as the diluent. The four investigated gasoline fuels share a common RON of 98, but vary in octane sensitivity and composition. To enable probing effects of near-zero NO levels, a skip-firing operating strategy is developed whereby the residual gases, which contain trace species like NO, are purged from the combustion chamber.Overall, the effects of NO-seeding on knock are consistent with the differences in knock limits for preand post-catalyst EGR gases. This suggests that for a majority of the conditions studied here, variations in NO concentration dominate the autoignition-influencing role of trace species that are present in pre-and post-catalyst EGR gases.…
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Piston Bowl Geometry Effects on Combustion Development in a High-Speed Light-Duty Diesel Engine

Sandia National Laboratories-Stephen Busch, Kan Zha
Ford Motor Company-Eric Kurtz
Published 2019-09-09 by SAE International in United States
In this work we studied the effects of piston bowl design on combustion in a small-bore 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 Sandia single-cylinder optical engine facility, with a medium-load, mild-boosted operating condition featuring a pilot+main injection strategy. CFD simulations were carried out with the FRESCO platform featuring full-geometric body-fitted mesh modeling of the engine and 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 it would in 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. Details of the local in-cylinder flow are also more crucial than injection parameters in igniting the main injection’s premixed fuel, as it…
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