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Effects of Stepped-Lip Combustion System Design and Operating Parameters on Turbulent Flow Evolution in a Diesel Engine

SAE International Journal of Engines

Ford Motor Company, USA-Eric Kurtz
USA-Stephen Busch
  • Journal Article
  • 03-13-02-0016
Published 2020-01-16 by SAE International in United States
Interactions between fuel sprays and stepped-lip diesel piston bowls can produce turbulent flow structures that improve efficiency and emissions, but the underlying mechanisms are not well understood. Recent experimental and simulation efforts provide evidence that increased efficiency and reduced smoke emissions coincide with the formation of long-lived, energetic vortices during the mixing-controlled portion of the combustion event. These vortices are believed to promote fuel-air mixing, increase heat-release rates, and improve air utilization, but they become weaker as main injection timing is advanced nearer to the top dead center (TDC). Further efficiency and emissions benefits may be realized if vortex formation can be strengthened for near-TDC injections. This work presents a simulation-based analysis of turbulent flow evolution within a stepped-lip combustion chamber. A conceptual model summarizes key processes in the evolution of turbulent flow for main injections starting after TDC. Differences in turbulent flow evolution are described for a near-TDC main injection, and potential variations in combustion system design and operating parameters to enhance vortex formation under these conditions are hypothesized. The parametric studies executed to…
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Investigating the engine behavior of a hybrid vehicle and its impact on regulated emissions during on-road testing.

Beijing Institute of Technology, China-Xin Wang, Yunshan Ge
University of Leeds, UK-Daisy Thomas, Hu Li, Karl Ropkins
  • Technical Paper
  • 2019-01-2199
Published 2019-12-19 by SAE International in United States
This paper presents the emissions results and operational behavior of two hybrid vehicles over EU legislative Real Driving Emissions (RDE) and other on-road testing cycles. The behavior of one hybrid vehicle during real world driving is investigated, including analyses of air-fuel ratio and catalyst temperature changes, in order to elucidate the reasons for the emissions results seen in the other hybrid vehicle over an RDE cycle. It was observed that the catalyst cooled down over time when the hybrid vehicle SI (Spark Ignition) engine was turned off, meaning that when the engine restarted the catalyst efficiency was decreased until it was able to light-off once again. This leads to increases in the tailpipe emissions of CO, NOx and hydrocarbons after the engine restarts. In addition to this problem, the engine restarts demanded fuel enrichment, which resulted in incomplete combustion and further increases in CO and PN emissions. Finally, the rate of catalyst temperature decrease during engine-off and increase during engine start/restart were also investigated and quantified for one of the hybrid vehicles.
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Comparing Knock between the CFR Engine and a Single Cylinder Research Engine

Southwest Research Institute-Andre Swarts, Garrett L. Anderson, Julian M. Wallace
  • Technical Paper
  • 2019-01-2156
Published 2019-12-19 by SAE International in United States
The confluence of increasing fuel economy requirements and increased use of ethanol as a gasoline blend component has led to various studies into the efficiency and performance benefits of higher octane numbers and high ethanol content fuels in modern engines. As part of a comprehensive study of the autoignition of different fuels in both the CFR octane rating engine and a modern, direct injection, turbocharged spark ignited engine, a series of fuel blends were prepared with varying composition, octane numbers and ethanol blend levels. The paper reports on the second part of this study where cylinder pressures were recorded for fuels under knocking conditions in both a single cylinder research engine (SCRE), utilizing a GM LHU head and piston, as well as the CFR engines used for octane ratings. In the SCRE, spark timing and air-fuel ratios were adjusted to achieve a consistent level of knock based on peak-to-peak values of the filtered cylinder pressures, over a range of engine speeds and manifold air pressures. The CFR engines were operated at standard RON and MON…
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Experimental Proof-of-Concept of HiL Based Virtual Calibration for a Gasoline Engine with a Three-Way-Catalyst

FEV Europe GmbH-Pietro Gardini, Thomas Scheel, Vitali Walter, Jaykumar Kansagara Raul Tharmakulasingam, Marius Böhmer, Martin Nijs
Institute for Combustion Engines, RWTH Aachen University-Feihong Xia, Frank Dorscheidt, Stefan Lücke, Jakob Andert
  • Technical Paper
  • 2019-01-2301
Published 2019-12-19 by SAE International in United States
The increasing complexity of modern combustion engines together with the substantial variability of hybrid electric powertrains, lead to new challenges in function development, system integration and vehicle calibration processes. Hardware-in-the-Loop (HiL) simulations have been introduced to front-load part of the testing and calibration tasks from the vehicle to a virtual environment. With this approach, the simulation quality and the cost-benefit ratio are strongly dependent on the accuracy of the plant modelling and the computational effort.This paper introduces a novel HiL simulation platform for an engine control unit (ECU) with a crank-angle resolved real-time model (GT-Power) for a gasoline engine with direct fuel injection, single stage turbocharging and a three-way catalyst. By simplifying the fluid dynamics simulation model from the concept phase, a good compromise between model accuracy and computation speed can be achieved with relatively low effort. The coupling of the engine model and the hardware ECU has been implemented using a realtime workstation with a co-simulation platform (xMOD) coupled to a HiL-simulator with the necessary I/O boards (dSPACE). The closed-loop boost pressure and the…
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1D Numerical and Experimental Investigations of an Ultralean Pre-chamber Engine

SAE International Journal of Engines

Business Unit Gasoline Powertrains FEV Europe GmbH in Aachen, Germany-Christoph Müller, Knut Habermann
Universita degli Studi di Napoli Federico II Dipartimento di Ingegneria Industriale, Italy-Vincenzo De Bellis
  • Journal Article
  • 03-13-02-0012
Published 2019-11-19 by SAE International in United States
In recent years, lean-burn gasoline Spark-Ignition (SI) engines have been a major subject of investigations. With this solution, in fact, it is possible to simultaneously reduce NOx raw emissions and fuel consumption due to decreased heat losses, higher thermodynamic efficiency, and enhanced knock resistance. However, the real applicability of this technique is strongly limited by the increase in cyclic variation and the occurrence of misfire, which are typical for the combustion of homogeneous lean air/fuel mixtures. The employment of a Pre-Chamber (PC), in which the combustion begins before proceeding in the main combustion chamber, has already shown the capability of significantly extending the lean-burn limit. In this work, the potential of an ultralean PC SI engine for a decisive improvement of the thermal efficiency is presented by means of numerical and experimental analyses. The SI engine is experimentally investigated with and without the employment of the PC with the aim to analyze the real gain of this innovative combustion system. For both configurations, the engine is tested at various speeds, loads, and air-fuel ratios. A…
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Knock and Pre-Ignition Limits on Utilization of Ethanol in Octane-on-Demand Concept

King Abdullah Univ. of Science & Tech.-Eshan Singh, Robert Dibble
Saudi Aramco-Kai Morganti
Published 2019-09-09 by SAE International in United States
Octane-on-Demand (OoD) is a promising technology for reducing greenhouse emissions from automobiles. The concept utilizes a low-octane fuel for low and mid load operating conditions, and a high-octane additive is added at high load operating conditions. Researchers have focused on the minimum ethanol content required for operating at high load conditions when the low-octane fuel becomes knock limited. However, it is also widely known that ethanol has a high tendency to pre-ignite, which has been linked with its high laminar flame speed and surface ignition tendency. Moreover, ethanol has a lower stoichiometric air-fuel ratio, requiring a larger injected fuel mass per cycle. A larger fuel mass increases the potential for oil dilution by the liquid fuel, creating precursors for pre-ignition. Hence, the limits on ethanol addition owing to pre-ignition also need consideration before the technology can be implemented. In this regard, experiments were performed using light naphtha (RON 68) and ethanol in direct and port-fuel injection configuration, respectively. The engine load was parametrically swept by simultaneously increasing the intake air and fuel quantity until the…
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Large Eddy Simulation of Ignition and Combustion Stability in a Lean SI Optical Access Engine

Università degli Studi di Perugia-Jacopo Zembi, Francesco Mariani, Michele Battistoni
  • Technical Paper
  • 2019-24-0087
Published 2019-09-09 by SAE International in United States
Large-Eddy simulations (LES) are becoming an engineering tool for studying internal combustion engines (ICE) thanks to their ability to capture cycle-to-cycle variability (CCV) resolving most of the turbulent flow structures. ICEs can operate under lean combustion conditions to maximize efficiency. However, instabilities associated with lean combustion may cause problems, such as excessive levels of CCV or even misfires. In this context, the energy released by the spark during the ignition and its interaction with the flow field are fundamental parameters that affect ignition stability and how combustion takes place and develops. The aim of this paper is the characterization of the combustion stability in a SI optical access engine, by means of multicycle LES simulations, using CONVERGE software. Sub-grid-scale turbulence is modeled with a viscous one-equation model. Two different combustion approaches are used combined with local adaptive mesh refinement (AMR): G-equation combustion model and the perfectly stirred reactor (PSR) combustion model with a skeletal kinetic mechanism for primary reference fuel (PRF). First, a mesh sensitivity study was carried out comparing three different resolutions and discussing…
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Development of a Dedicated CNG Three-Way Catalyst Model in 1-D Simulation Platforms

FPT Industrial SpA-Stefano Golini, Francesco Giovanni Rutigliano
Istituto Motori CNR-Carlo Beatrice, Valentina Fraioli
Published 2019-09-09 by SAE International in United States
A growing interest towards heavy-duty engines powered with NG, dictated by stringent regulations in terms of emissions, has made it essential to study a specific Three-Way Catalyst (TWC). Oxygen storage phenomena characterize the catalytic converter efficiency under real world driving operating conditions and, consequently, during strong dynamics in Air-to-Fuel ratio (AFR).A numerical “quasi-steady” model has been set-up to simulate the chemical process inside the reactor. A dedicated experimental campaign has been performed in order to evaluate the catalyst response to a defined λ variation, thus providing the data necessary for the numerical model validation. In fact, goal of the present research activity was to investigate the effect of very fast composition transitions of the engine exhaust typical of the mentioned driving conditions (including fuel cutoffs etc.) on the catalyst performance and on related emissions.A surface reactions kinetic mechanism, representing CH4, CO, H2 oxidation and NO reduction, has been appropriately calibrated in steady-state operation, using a step-by-step procedure all over the engine operating conditions at different AFRs. Then transient conditions were numerically reproduced, through cyclical and…
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Inner-Insulated Turbocharger Technology to Reduce Emissions and Fuel Consumption from Modern Engines

BorgWarner Turbo Systems-Jürgen Werner
Ricardo UK Ltd-Joshua Dalby
Published 2019-09-09 by SAE International in United States
Reducing emissions from light duty vehicles is critical to meet current and future air quality targets. With more focus on real world emissions from light-duty vehicles, the interactions between engine and exhaust gas aftertreatment are critical. For modern engines, most emissions are generated during the warm-up phase following a cold start. For Diesel engines this is exaggerated due to colder exhaust temperatures and larger aftertreatment systems. The De-NOx aftertreatment can be particularly problematic. Engine manufacturers are required to take measures to address these temperature issues which often result in higher fuel consumption (retarding combustion, increasing engine load or reducing the Diesel air-fuel ratio).In this paper we consider an inner-insulated turbocharger as an alternative, passive technology which aims to reduce the exhaust heat losses between the engine and the aftertreatment. Firstly, the concept and design of the inner-insulated turbocharger is presented. A transient 3D CFD/FEM (Computation Fluid Dynamics/Finite Element Modelling) simulation is conducted and predicts that external heat losses will be reduced by 70% compared to a standard turbocharger, i.e. non-insulated turbocharger. A 1D modelling methodology…
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Back-Pressure and Fuel Type Effects on Exhaust Gas Oxygen Sensor Readings for a Single Cylinder Spark Ignition Engine Running on Gasoline and Ethanol

Istituto Motori CNR-Adrian Irimescu
  • Technical Paper
  • 2019-24-0046
Published 2019-09-09 by SAE International in United States
Application of more and more complex control strategies in spark ignition (SI) engines is required for ensuring high conversion efficiency and effective emissions reduction. Closed loop fuel injection is being implemented on an ever wider scale in small size SI units that generally feature single cylinder architecture. For such systems the readings from the exhaust gas oxygen sensor are essential for controlling air-fuel ratio and indirectly combustion. The present study looked at the influence of pressure oscillations on the values given by the sensor, for different equivalence ratio settings in wide open throttle conditions for an experimental SI unit. As expected, the readings were found to be influenced by pressure oscillations in the exhaust line during lean operation, while with stoichiometric and rich fueling the effects were minimal. Fuel type was also found to be an important aspect. Gasoline was compared to ethanol, and the latter underlined the effect of combustion efficiency on how the sensor readings need to be interpreted. Quasi-dimensional simulation using the GT-Power software was also used to provide further insight into…
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