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Numerical investigations on strong knocking combustion under compression ignition conditions

State Key Lab of Engines-Jiaying Pan
Tianjin University-Lin Chen, Jianfu Zhao
  • Technical Paper
  • 2020-01-1137
To be published on 2020-04-14 by SAE International in United States
Homogeneous charge compression ignition (HCCI) combined with high compression ratio is an effective way to improve engines’ thermal efficiency. However, the severe thermodynamic conditions at high load may induce knocking combustion thus damage engine body. In this study, compression ignition knocking characteristics were parametrically investigated through RCM experiments and simulation analysis. First, the knocking characteristics were optically investigated. The experimental results show that there even exists detonation when the knock occurs thus the combustion chamber is damaged. Considering both safety and costs, the effects of different initial conditions were numerically investigated and the results show that knocking characteristics is more related to initial pressure other than initial temperature. The initial pressure have a great influence on peak pressure and knock intensity while initial temperature on knock onset. Further analysis shows that knock intensity is mainly related to the energy density of the in-cylinder mixture and energy density is higher under higher pressure conditions. Then the effects of different cylinder wall temperature on the local auto-ignition thus knocking characteristics were further discussed. The results show that…
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The Prospect and Benefits of Using the Partial-Averaged Navier-Stokes Method for Engine Flows

AVL LIST GmbH-Branislav Basara, Zoran Pavlovic
Texas A&M University-Sharath Girimaji
  • Technical Paper
  • 2020-01-1107
To be published on 2020-04-14 by SAE International in United States
This paper presents calculations of engine flows by using the Partially-Averaged Navier-Stokes (PANS) method [1]. The PANS is a scale-resolving turbulence computational approach designed to resolve large scale fluctuations and model the remainder with appropriate closures. Depending upon the prescribed cut-off length (filter width) the method adjusts seamlessly from the Reynolds-Averaged Navier-Stokes (RANS) to the Direct Numerical Solution (DNS) of the Navier-Stokes equations. In the conventional well-established PANS, the unresolved to total kinetic energy ratio fk known as the cut-off control parameter, is calculated from the grid spacing and the computed integral turbulence length scale. Several formulations have been derived up to now. In most of these formulations, fk is obtained by summing up the resolved turbulence, while the unresolved motion is computed from the modelled equation. The PANS method was successfully used on large number applications but mainly on static geometries, e.g. [2]; [3]. This is due to calculations of the resolved kinetic energy which is obtained by suitably averaging of the resolved field. Such averaging process is expensive and impractical for engines as…
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LES Modeling Study on Cycle-to-Cycle Variations in a DISI Engine

Honda R&D Co., Ltd.-Hiroyoshi Taniguchi
RWTH Aachen University-Tobias Falkenstein, Marco Davidovic, Antonio Attili, Mathis Bode, Hongchao Chu, Heinz Pitsch
  • Technical Paper
  • 2020-01-0242
To be published on 2020-04-14 by SAE International in United States
The reduction of cycle-to-cycle variations (CCV) is a prerequisite for the development and control of spark-ignition engines with increased efficiency and reduced engine-out emissions. To this end, Large-Eddy Simulations can improve the understanding of stochastic in-cylinder phenomena during the engine design process, if the employed modeling approach is sufficiently accurate. To assess the predictive capabilities of the turbulent combustion model used in this work, an engine-relevant Direct Numerical Simulation (DNS) dataset of premixed flame propagation in homogeneous isotropic turbulence is considered for a-posteriori investigations. LES predictions using the Flame Front / Progress Variable Equation Model are demonstrated to be in good agreement with the DNS results. Integral flame propagation results are shown to be unaffected by the choice of two eddy viscosity models, although some differences in the SFS velocity distributions near the flame front exist between the Dynamic Smagorinsky Model (DSM) and the Coherent Structure Model (CSM). The validated combustion model has been applied to investigate CCV in a direct-injected spark ignition (DISI) engine under fuel-lean conditions with respect to a stoichiometric baseline operating…
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Acoustic performance analysis of automotive HVAC duct designs using a Lattice-Boltzmann based method and correlation with Semi-anechoic chamber.

Dassault Systemes-Prasad Sivakumar, Adrien Mann, Minsuk Kim
FCA Engineering India Pvt., Ltd.-Sivaji Pasupuleti
  • Technical Paper
  • 2020-01-1263
To be published on 2020-04-14 by SAE International in United States
Acoustic comfort of automotive cabins has progressively become one of the key attributes of vehicle design, with wind noise and HVAC noise being two of the key contributors to noise levels heard inside the car. With the increasing prevalence of hybrid technologies and electrification and the associated reduction in powertrain noise levels, the industry has seen an increasing focus on understanding HVAC noise, as it is a main source of noise in the cabin if not the single one when the vehicle is stopped. The complex turbulent flow path through the ducts, combined with acoustic resonances can potentially lead to significant noise generation, both broadband and tonal. In order to avoid time consuming and expensive late stage design changes, or avoid being hit by low consumer rating ignoring the issues, it is important to identify potential problems early in the design process and take appropriate measures to rectify them. In this study, the noise characteristics of three HVAC duct designs are studied using a commercial CFD code based on the Lattice-Boltzmann method. The noise spectra…
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A Quasi-Dimensional SI Burn Rate Model for Predicting the Effects of Changing Fuel, Air-Fuel-Ratio, EGR and Water Injection

FKFS-Michael Grill
IVK, University of Stuttgart-Sebastian Hann, Michael Bargende
  • Technical Paper
  • 2020-01-0574
To be published on 2020-04-14 by SAE International in United States
As a result of the shifted R&D focus from internal combustion engines to electrified powertrains, resources for the development of internal combustion engines are restricted more and more. With that, the importance of highly efficient engine development tools is increased. In this context, 0D/1D engine simulation offers the advantage of low computational effort and fast engine model set-up. To ensure a high predictive ability of the engine simulation, a reliable combustion model is needed. Considering the increasing interest in alternative fuels, the aspect of predicting the fuel influence on combustion is of special importance. To reach these targets, the change of engine combustion characteristics with changing fuels and changing air-fuel-ratios is investigated systematically in a first step. For this purpose, engine test bed data is compared with expected fuel-dependent flame wrinkling trends based on Markstein / Lewis-number theory. Furthermore, the possibility of influences caused by the Darrieus-Landau instability is evaluated. Based on these comparisons, an existing combustion model is improved by adapting the sub-models for laminar and turbulent flame speed as well as the approach…
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Wake study on isolated, detailed and rotating car wheels

Audi AG-Lukas Haag, Vincent Zander
Technische Universitat Munchen-Jan Reiß, Jonas Sebald, Thomas Indinger
  • Technical Paper
  • 2020-01-0686
To be published on 2020-04-14 by SAE International in United States
Wheels on passenger vehicles cause about 25% of the aerodynamic drag. The interference of rims and tires in combination with the rotation result in strongly turbulent wake regions with complex flow phenomena. This wake structures interact with the flow around the vehicle. To understand the wake structures of wheels and their aerodynamic impact on the aerodynamic drag of the vehicle, the complexity was reduced by investigating a standalone tire in the windtunnel. Besides the influence of geometry changes on the acting forces, the wake region behind the wheel is investigated via Particle Image Velocimetry (PIV). The average flow field behind the investigated wheels is captured with this method and offers insight into the flow field. The investigation of the wake region allows to attribute changes in the flow field to the change of tires and rims. Due to increased calculation performance sophisticated CFD simulations can capture detailed geometries like the tire tread and the movement of the rim. Therefore, the wake investigation via PIV is a usable basis to compare it to results of such…
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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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Experimental and computational study on helical coil and flat type sub-cooled condenser for air conditioner in automobile vehicle

Keihin Corporation-Junya Washiashi, Jun Liu
Sophia University-Hardeep Singh, Mitsuhisa Ichiyanagi, Edtya Dzieminska, Takashi Suzuki
  • Technical Paper
  • 2020-01-1246
To be published on 2020-04-14 by SAE International in United States
Due to the compact structure, large heat transfer area, and high heat transfer capability, this paper provides the importance of helical coil sub-cooled condenser as comparing to flat type sub-cooled condenser in the automobile vehicle. By improving the coefficient of performance of the air-conditioning (A/C) system, the reduction in vehicular emission can be possible. Because A/C unit is the most power consumption unit after the engine. Previous studies explain that there is a generation of secondary flow inside the fluid in circular cross-section of the helical coil. By using the effect of secondary flow generation, the author’s tried to enhance the heat transfer rate as it leads to heterogeneous temperature distribution across the periphery of the tube and causes a higher heat transfer. During the studies, a prototype with square cross-sectional 2.7mm X 2.7mm channel with flat fins towards outer side has been constructed. Experimentally, heat transfer characteristics for the square channel helical coil cub-cooled condenser has been evaluated and then compared with CFD analysis. During the bench test, the Calorimeter was used to obtain…
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A numerical study on the ignition of lean CH4/air mixture by a pre-chamber-initiated turbulent jet

King Abdullah University of Science & Technology-Sangeeth Sanal, Mickael Silva, Ponnya Hlaing, Bengt Johansson, Hong G. Im
Saudi Aramco-Emre Cenker
  • Technical Paper
  • 2020-01-0820
To be published on 2020-04-14 by SAE International in United States
Ultra-lean combustion in a spark-ignited (SI) engine is one of the most promising methods explored to reduce the nitrogen oxides (NOx) emissions and increases engine efficiency by decreasing the peak combustion temperature. However, this leads to an increase in combustion instabilities, hence emissions of unburned hydrocarbons (UHC). A spark ignited stratified pre-chamber combustion system has been demonstrated to overcome the obstacles related to ultra-lean combustion. However, the ignition mechanism of the ultra-lean mixture is not well studied. For that, the turbulent jet forced out of the pre-chamber through the nozzles needs to be well understood. The turbulent jet ignition can be either flame ignition (hot active radicals) or jet ignition (hot combustion products), depending on the pressure gradient and nozzle diameter. This hot jet determines the combustion characteristics of the lean main-chamber mixture and engine performance. Converge CFD code was used in this study, and the model used were validated against the measurements performed in-house. To elucidate the main-chamber ignition mechanism, the spark plug location and the spark timing were varied, resulting in different pressure…
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High-fidelity simulation of primary breakup of a "spray G" gasoline jet with an adaptive mesh refinement and volume-of-fluid method

Baylor University-Yue Ling, Bo Zhang
  • Technical Paper
  • 2020-01-0826
To be published on 2020-04-14 by SAE International in United States
Efficient atomization of a gasoline jet is essential to the performance of gasoline direct injection (GDI) engines. This paper presents a numerical investigation of the primary breakup of a gasoline surrogate jet. The fuel properties and injection condition are chosen based on the X-ray experiment performed at Argonne National Lab (Duke et al, Exp. Therm. Fluid Sci., 88:608-621, 2017). The surrogate fuel has a low volatility and thus no phase change occurs in the atomization process. The nozzle geometry and operation conditions are similar to the Engine Combustion Network (ECN) ``Spray G". We focus the present study on the near field where inter-jet interaction is of secondary importance. Therefore, we have considered only one of the eight jets in the original Spray G injectors. The liquid is injected from the inlet into a chamber with stagnant gas. To mimic the internal liquid flow in the original injector, an angle is introduced between the liquid inflow and the inner hole axis. A parametric study on the inlet angle is carried out. The adaptive multiphase flow solver,…