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SAE Truck & Off-Highway Engineering: October 2019

Terry Costlow
  • Magazine Article
  • 19TOFHP10_03
Published 2019-10-01 by SAE International in United States

Powertrain developers who spoke at SAE COMVEC are leaving no stone unturned in their quest to trim emissions.

The push to trim engine emissions is prompting industry-wide efforts to use substitutes for diesel fuel. Alternative fuels and electrified powertrains are making significant inroads, though design teams for diesel power aren't conceding the future.

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Literature Review on Dual-Fuel Combustion Modelling

Lund University-Menno Merts, Sebastian Verhelst
Published 2019-09-09 by SAE International in United States
In the search for low greenhouse gas propulsion, the dual fuel engine provides a solution to use low carbon fuel at diesel-like high efficiency. Also a lower emission of NOx and particles can be achieved by replacing a substantial part of the diesel fuel by for example natural gas. Limitations can be found in excessively high heat release rate (combustion-knock), and high methane emissions. These limitations are strongly influenced by operating parameters and properties of the used (bio)-gas. To find the dominant relations between fuel properties, operating parameters and the heat release rate and methane emissions, a combustion model is beneficial. Such a model can be used for optimizing the process, or can even be used in real time control. As precursor for such a model, the current state of art of dual fuel combustion modelling is investigated in this work.The focus is on high speed dual fuel engines for heavy duty and marine applications, with a varying gas/diesel ratio. Modelling is limited to the closed part of the 4-stroke engine cycle. A methodology part…
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CFD Investigation of the Effects of Gas’ Methane Number on the Performance of a Heavy-Duty Natural-Gas Spark-Ignition Engine

Universita degli Studi di Perugia-Luca Ambrogi, Michele Battistoni, Lorenzo Gasbarro
West Virginia Univ.-Jinlong Liu, Cosmin Dumitrescu
Published 2019-09-09 by SAE International in United States
Natural gas (NG) is an alternative fuel for spark-ignition engines. In addition to its cleaner combustion, recent breakthroughs in drilling technologies increased its availability and lowered its cost. NG consists of mostly methane, but it also contains heavier hydrocarbons and inert diluents, the levels of which vary substantially with geographical source, time of the year and treatments applied during production or transportation. To investigate the effects of NG composition on engine performance and emissions, a 3D CFD model of a heavy-duty diesel engine retrofitted to NG spark ignition simulated lean-combustion engine operation at low speed and medium load conditions. The work investigated three NG blends with similar lower heating value (i.e., similar energy density) but different Methane Number (MN). The results indicated that a lower MN increased flame propagation speed and thus increased in-cylinder pressure and indicated mean effective pressure. In addition, a low MN increased the thermal efficiency despite the higher heat transfer to the surroundings. Also, a higher MN reduced the nitrogen-oxides emissions but increased unburned hydrocarbons (UHC) emissions. Moreover, while UHC emissions…
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Experimental and Numerical Analysis of a Dual Fuel Operation of Turbocharged Engine at Mid-High Load

Univ. of Zagreb-Darko Kozarac, Mladen Bozic, Ante Vucetic, Josip Krajnovic, Momir Sjeric
Published 2019-09-09 by SAE International in United States
In the paper the operation of a turbocharged dual fuel engine at mid-high load is investigated on a single cylinder experimental engine complemented by a full 0D/1D simulation model that provides boundary conditions for the experiment and full engine system results. When duel fuel combustion mode is used on a turbocharged engine with the variable geometry turbocharger, the mid-high load operating points can be obtained with number of different combinations of intake pressure and excess air ratio. Besides the impact on combustion, the specific combination of intake pressure - excess air ratio has also impact on the exhaust back pressure caused by the turbocharger and consequently on the obtained brake efficiency. Additionally, the dual fuel combustion is influenced by natural gas mass fraction and start of injection of diesel fuel and the search for the optimal solution could be a challenging task. The method presented here enables the use of a single cylinder experimental engine in this search, while simultaneously taking into account the influences of the effects of a full engine system. The results…
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Experimental Investigation of Combustion Characteristics in a Heavy-Duty Compression-Ignition Engine Retrofitted to Natural-Gas Spark-Ignition Operation

West Virginia University-Jinlong Liu, Cosmin Dumitrescu
Published 2019-09-09 by SAE International in United States
Recent development in hydraulic fracking made natural gas (NG) to be a promising alternative gaseous fuel for heavy-duty diesel engines. The existing compression ignition (CI) engine can be retrofitted to NG spark ignition (SI) operation by replacing the diesel injector with a spark plug and fumigating NG into the intake manifold. However, the original diesel piston geometry (flat head and bowl-in-piston chamber) was usually retained to reduce modification cost. The goal of this study was to increase the understanding of the NG lean-burn characteristics in a diesel-like, fast-burn SI combustion chamber. The experimental platform can operate in conventional (i.e., all engine parts are metal) or in optical configuration (i.e., the stock piston and cylinder block are replaced with a see-through piston and an extended cylinder block). The optical data indicated a fast-propagated flame inside the piston bowl. However, this rapid-burning process did not shorten the combustion duration, which can be explained by an important fuel mass trapped in the squish that burned slowly during the expansion stroke. Steady-state experiments that operated at the metal engine…
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Integrated CFD-Experimental Methodology for the Study of a Dual Fuel Heavy Duty Diesel Engine

Brunel University London-Vinícius Pedrozo, Hua Zhao
University of Napoli Federico II-Maria Cristina Cameretti, Roberta De Robbio, Raffaele Tuccillo
  • Technical Paper
  • 2019-24-0093
Published 2019-09-09 by SAE International in United States
This paper deals with the experimental and numerical investigation of a 2.0 litre single cylinder Heavy Duty Diesel Engine fuelled by natural gas and diesel oil in Dual Fuel mode. Due to the gaseous nature of the main fuel and to the high compression ratio of the diesel engine, reduced emissions can be obtained. An experimental study has been carried out at three different load level (25%, 50% and 75% of full engine load). Basing on experimental data, the authors recreated a 45° mesh sector of the engine cylinder and performed CFD simulations for the cases at 50% and 75% load levels. Numerical simulations were carried out on the 3D code Ansys FORTE. The aim of this work is to study combustion phenomena and, in particular, the interaction between natural gas and diesel oil, respectively represented by methane and n-dodecane. A reduced kinetic scheme for methane auto-ignition was implemented while for n-dodecane two set of reactions were utilised. The first one consisting of a one-step mechanism is compared with the far more detailed second one…
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Heavy-Duty Compression-Ignition Engines Retrofitted to Spark-Ignition Operation Fueled with Natural Gas

Universita degli Studi di Perugia-Lorenzo Gasbarro, Michele Battistoni, Luca Ambrogi
West Virginia Univ-Jinlong Liu, Cosmin Dumitrescu, Christopher Ulishney
  • Technical Paper
  • 2019-24-0030
Published 2019-09-09 by SAE International in United States
Natural gas is a promising alternative gaseous fuel due to its availability, economic, and environmental benefits. A solution to increase its use in the heavy-duty transportation sector is to convert existing heavy-duty compression ignition engines to spark-ignition operation by replacing the fuel injector with a spark plug and injecting the natural gas inside the intake manifold. The use of numerical simulations to design and optimize the natural gas combustion in such retrofitted engines can benefit both engine efficiency and emission. However, experimental data of natural gas combustion inside a bowl-in-piston chamber is limited. Consequently, the goal of this study was to provide high-quality experimental data from such a converted engine fueled with methane and operated at steady-state conditions, exploring variations in spark timing, engine speed and equivalence ratio. The results showed that a higher engine speed reduced the motoring pressure, advanced maximum brake torque timing, and reduced the power output per cycle. Moreover, advanced spark timing increased and advanced the cylinder pressure, and increased both hydrocarbon and nitrogen oxides emissions. Leaner operation retarded the flame…
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Development of a Physically/Chemically Based Approach for 2-Stage Ignition Delay Calculation in Medium Speed Dual-Fuel Engines

Technische Universität Braunschweig-Jelto Frerichs, Peter Eilts
Published 2019-09-09 by SAE International in United States
This paper presents a newly developed 2-stage ignition delay model for pilot ignited medium speed dual-fuel (DF) engines. This provides the first major step towards a new combustion model for the prediction of the DF combustion in the context of 0D/1D simulation. The combustion models known from literature are based on empirical models of a steady jet. Here in most cases the package model of Hiroyasu is used. Because in a DF engine the injection timing of the diesel fuel is very early and the injection ends before ignition, the spray behavior differs from that of a steady jet. Especially the end-of-injection transients lead to stronger entrainment and therefore affect the ignition delay. In addition, the presence of natural gas in the cylinder extends the ignition delay at the chemical level. In this paper the 1D transient spray model of Musculus and Kattke is used to describe the spray behavior. The spray model is extended with a mixing controlled evaporation model to derive the temperature distribution inside the spray. A 2-stage ignition delay model with…
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A Fundamental Study on Combustion Characteristics in a Pre-Chamber Type Lean Burn Natural Gas Engine

Waseda University-Masashi Tanamura, Shintaro Nakai, Mahoko Nakatsuka, Shota Taki, Kohei Ozawa, Beini Zhou, Ratnak Sok, Yasuhiro Daisho, Jin Kusaka
Published 2019-09-09 by SAE International in United States
Pre-chamber spark ignition technology can stabilize combustion and improve thermal efficiency of lean burn natural gas engines. During compression stroke, a homogeneous lean mixture is introduced into pre-chamber, which separates spark plug electrodes from turbulent flow field. After the pre-chamber mixture is ignited, the burnt jet gas is discharged through multi-hole nozzles which promotes combustion of the lean mixture in the main chamber due to turbulence caused by high speed jet and multi-points ignition. However, details mechanism in the process has not been elucidated.To design the pre-chamber geometry and to achieve stable combustion under the lean condition for such engines, it is important to understand the fundamental aspects of the combustion process. In this study, a high-speed video camera with a 306 nm band-pass filer and an image intensifier is used to visualize OH* self-luminosity in rapid compression-expansion machine experiment. The results show that the OH* self-luminosity is observed in outer edge of the jet, while the luminosity in the jet temporarily weakens because the turbulent jet is exposed to low temperature surrounding in the…
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Experimental Characterization of Methane Direct Injection from an Outward-Opening Poppet-Valve Injector

Istituto Motori CNR-Maurizio Lazzaro, Francesco Catapano, Paolo Sementa
Published 2019-09-09 by SAE International in United States
The in-cylinder direct injection of natural gas can be a further step towards cleaner and more efficient internal combustion engines (ICE). However, the injector design and its characterization, both experimentally and by numerical simulation, is challenging because of the complex fluid dynamics related to gas compressibility and the small length scale. In this work, the under-expanded flow of methane from an outward-opening poppet-valve injector has been experimentally characterized by high-speed schlieren imaging. The investigation has been performed at ambient temperature and pressure and different nozzle pressure ratios (NPR) ranging from 10 to 18. The gaseous jet has been characterized in terms of its macroscale parameters. A scaling-law analysis of the results has been performed. The gas-dynamic structure at the nozzle exit has been also investigated.
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