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Development and validation of SI combustion models for natural-gas heavy-duty engines

Politecnico di Milano-Lorenzo Sforza, Tommaso Lucchini, Giovanni Gianetti, Gianluca D'Errico
  • Technical Paper
  • 2019-24-0096
To be published on 2019-08-15 by SAE International in United States
Flexible, reliable and consistent combustion models are necessary for the improvement of the next generation spark-ignition engines. Different approaches have been proposed and widely applied in the past. However, the complexity of the process involving ignition, laminar flame propagation and transition to turbulent combustion need further investigations. Purpose of this paper is to compare two different approaches describing turbulent flame propagation. The first approach is the one-equation flame wrinkling model by Weller, while the second is the Coherent Flamelet Model (CFM). Ignition is described by a simplified deposition model while the correlation from Herweg and Maly is used for the transition from the laminar to turbulent flame propagation. Validation of the proposed models was performed with experimental data of a natural-gas, heavy duty engine running at different operating conditions. To deeply analyze main differences between Weller and CFM models, a detailed comparison of computed and experimental data was performed in terms of cylinder pressure, heat release rate, wall heat transfer, distribution of progress variable and flame surface density.

Possibilities of wall heat transfer measurements at a supercharged Euro IV heavy-duty Diesel engine with high EGR-rates, an in-cylinder peak pressure of 250 bar and injection pressure up to 2500 bar

Daimler AG-Christian HENNES, Jürgen Lehmann
KIT Karlsruhe Institute Of Technology-Thomas Koch
  • Technical Paper
  • 2019-24-0171
To be published on 2019-08-15 by SAE International in United States
A raise of efficiency is, especially for CV, the strongest selling point concerning the TCO. Accompanied by legislations, with contradictive development demands, satisfying solutions have to be found. The analysis of energy losses in modern engines shows three influencing parameters. The losses resulting from taking real gas properties and non-ideal combustion into account have only a limited potential for gains, wall heat losses are currently believed to have the highest optimization potential. Critical for the occurrence of these losses is the wall heat transfer, which can be described by coefficients. To reduce WHT accompanying losses a decrease of energy transfer between combustion gas and combustion chamber wall is necessary. A measurement of heat fluxes is needed to determine the WHT relations at the combustion chamber of an engine. Methods to reduce the WHT can be developed and their effectiveness can be evaluated. As this is not done before for a heavy-duty engine, with peak pressures up to 250 bar, an increased in-cylinder turbulence and high EGR-rates is presented the following. The different methods to determine…

A Review of Spark-Assisted Compression Ignition (SACI) Research in the Context of Realizing a Production SACI Strategy

Clemson Univ-Robert Prucka
Clemson Univ.-Dennis Robertson
  • Technical Paper
  • 2019-24-0027
To be published on 2019-08-15 by SAE International in United States
Low temperature combustion (LTC) strategies have been a keen interest in the automotive industry for over four decades since they offer improved fuel efficiency compared to conventional spark-ignition (SI) engines. LTC strategies use high dilution to keep combustion temperatures below about 2000 K to reduce heat transfer losses while avoiding locally rich in-cylinder regions that produce high soot. High dilution also enables an efficiency improvement from reduced pumping work and improved thermodynamic properties, though it requires high ignition energy. Combustion can be achieved by triggering autoignition from compression energy. High compression ratios are typically required to produce this level of ignition energy, which further improves fuel efficiency. The timing of the autoignition event is influenced by fuel properties and mixture composition, and is exponentially sensitive to temperature. Control of autoignition timing is difficult without a direct actuator, and has been a significant obstacle for realizing LTC in production. Spark-assisted compression ignition (SACI) addresses this challenge by using a spark plug to initiate chemical reactions that trigger autoignition. The combustion chamber is slightly stratified to promote…

Experimental investigation on the use of Argon to improve FMEP determination through motoring method

Jaguar & Land Rover-Gilbert Sammut
Univ of Malta-Carl Caruana, Mario Farrugia
  • Technical Paper
  • 2019-24-0141
To be published on 2019-08-15 by SAE International in United States
Mechanical friction is still one of the current topics in internal combustion engine research and development. In the ever increasing challenge of developing more efficient and less polluting engines, friction reduction is of significant importance; whose investigation needs an accurate and reliable measurement technique. The Pressurized Motoring method is one of the techniques used for both friction and heat transfer measurements in internal combustion engines. This method is able to simulate mechanical loading on the engine components similar to the fired conditions. It also allows measurement of friction mean effective pressure (FMEP) with a much smaller uncertainty as opposed to that achieved from a typical firing setup. Despite its advantages, this method of FMEP determination is usually criticized over the fact that the thermal conditions imposed in pressurized motoring are far detached from those seen in fired conditions, hence not able to simulate the complete effects on FMEP. The authors have put forward a modification to the method, employing Argon in place of Air as pressurization medium (SAE paper 2019-01-0930). Due to the higher heat…

CFD Modeling of Compact Heat Exchangers for I.C. Engine Oil Cooling

Politecnico di Milano-Augusto Della Torre, Gianluca Montenegro, Angelo Onorati
UFI Filters-Roberto Icarelli
  • Technical Paper
  • 2019-24-0179
To be published on 2019-08-15 by SAE International in United States
In the last years, the increase of the specific power of the modern engines has required a parallel improvement of the performances of the cooling system. In this context, also the control of the oil temperature has become an important issue, leading to the introduction of dedicated cooling circuits (air-cooled or liquid-cooled). Among the two, the liquid-cooled solution results in a more compact installation in which the oil-to-liquid heat exchanger is directly mounted on the engine block and integrated in the engine cooling system. It is clear that, in a liquid-cooled solution, the design of the heat exchanger represents an issue of extreme concern, which requires a compromise between different objectives: high compactness, low pressure drop, high heat-transfer efficiency. In this work, a computational framework for the CFD simulation of compact oil-to-liquid heat exchangers, including offset-strip fins as heat transfer enhancer (turbolator), has been developed. The main problem is represented by the need of considering different scales in the simulation, ranging from the characteristic size of the turbolator geometry (tipically µm – mm) to the…

A novel 1D co-simulation framework for the prediction of tailpipe emissions under different IC engine operating conditions.

Aristotle University of Thessaloniki-Zissis Samaras, Grigorios Koltsakis
EMPA-Patrik Soltic, Panayotis Dimopoulos Eggenschwiler, Viola Papetti, Jakub Rojewski PhD
  • Technical Paper
  • 2019-24-0147
To be published on 2019-08-15 by SAE International in United States
The prediction of the pollutants emitted by internal combustion engines during driving cycles has been a challenge since the introduction of the emission regulation legislation. During the last decade, along with the more tightening limits and increased public concern about the matter of air quality, the possibility of simulating various driving tests with cost effective computing facilities has become a key feature for modern simulation codes. Many 1D simulation tools are available on the market, offering real time models capable of achieving the simulation of any driving cycle in limited time frames. These approaches are based on the extreme simplification of the engine geometry and on the adoption of engine maps, which, for any engine operating condition, give the engine output in terms of power, or torque, and of exhaust gas composition. Specific fluid dynamic models are used to track the composition along the exhaust system and, with the aid of ad-hoc modules, to evaluate the conversion efficiency of after-treatment devices, such as TWC, GPF, DPF, DOC, SCR and so on. This work is based…

Performance and emissions of an advanced multi-cylinder SI engine operating in ultra-lean conditions

Renault SA-Cédric LIBERT
Univ of Naples-Fabio Bozza, Luigi Teodosio, Vincenzo De Bellis
  • Technical Paper
  • 2019-24-0075
To be published on 2019-08-15 by SAE International in United States
Along the design process of a new engine, the calibration phase at the test bench usually involves a relevant percentage of the overall time-to-market. Each control variable, in fact, needs to be properly selected to optimize the performance and emissions, complying with thermal and mechanical stresses limits of the engine. This issue is still more critical for advanced engine architectures, which include additional control variables, such as valve phasing, turbocharger control, EGR level, etc. The aim of this work is the development of a numerically performed calibration procedure, applied to a prototype multi-cylinder Spark Ignition (SI) engine, designed to operate at very lean mixtures. To this aim, an active Pre-Chamber ignition system is considered. The required air flow rate is indeed provided by a Low-Pressure (LP) variable geometry turbocharger group, coupled to a high-pressure e-compressor. A Variable Valve Timing (VVT) device is also selected to reduce pumping losses at low load and for knock control at high-load. For the above engine, seven control variables have to be fixed in each operating condition, namely the Air/Fuel…

Validation of heat losses prediction using Conjugate Heat Transfer simulation for an internal combustion engine

Universitat Politecnica de Valencia-Alberto Broatch, Xandra Margot, Jorge Garcia-Tiscar, Johan Escalona
  • Technical Paper
  • 2019-24-0091
To be published on 2019-08-15 by SAE International in United States
New technologies are required to improve engine thermal efficiency. For this it is necessary to use all the tools available nowadays, in particular computational tools, which allow testing the viability of different solutions at reduced cost. In addition, numerical simulations often provide more complete and precise information than experimental tests. Such is the case for the study of the heat transfer through the walls of an engine. Conjugate Heat Transfer (CHT) simulations permit precise calculations of the heat transfer rate from gas to walls throughout the whole engine cycle, and thus it is possible to know such details as the instantaneous heat losses and wall temperature distribution on the walls, which no experiment can give. Nevertheless, it is important to validate CHT calculations, either with some experimental measurements or with some other reliable tool, such as 0D-1D modelling known to work well. The proposed work is based on the CHT simulation of the heat transfer to the walls of an engine piston during an entire cycle to determine the parameters that permit obtaining good results.…

Development of a hybrid power unit for Formula SAE application: packaging optimization and thermomechanical design of the electric motor case

University of Modena and Reggio Emilia-Valerio Mangeruga, Matteo Giacopini, Saverio Giulio Barbieri, Fabio Berni
  • Technical Paper
  • 2019-24-0197
To be published on 2019-08-15 by SAE International in United States
This paper presents the development of a parallel hybrid power unit for Formula SAE application. In particular, the system is made up of a brand new, single-cylinder 480 cc internal combustion engine developed on the basis of the Ducati “959 Superquadro” V90 2-cylinder engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The performance of the ICE has been optimized through CFD-1D simulation (a review of this activity is reported in a parallel paper). The main design goal is to get the maximum amount of mechanical energy from the fuel, considering the car typical usage: racing on a windy track. The Ducati “959 Superquadro” engine is chosen because of its high power-to-weight ratio, as well as for its V90 2-cylinder layout. In fact, the vertical engine head is removed and it is subsequently replaced by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. The mechanical behaviour of the original chain is investigated for…

A coupled Lattice Boltzmann-Finite Volume method for the thermal transient modeling of an air-cooled Li-ion battery module for electric vehicles

Univ. Tor Vergata-Gino Bella
Univ. di Roma Niccolo Cusano-Daniele Chiappini, Laura Tribioli
  • Technical Paper
  • 2019-24-0207
To be published on 2019-08-15 by SAE International in United States
Due to their ability to store higher electrical energy, lithium ion batteries are the most promising candidates for electric and hybrid electric vehicles, whose market share is growing fast. Heat generation during charge and discharge processes, frequently undergone by these batteries, causes temperature increase and thermal management is indispensable to keep temperature in an appropriate level. In this paper, a coupled Lattice Boltzmann-Finite Volume model for the three-dimensional transient thermal analysis of an air-cooled Li-ion battery module is presented. As it has already been successfully used to deal with several fluid dynamics problems, the Lattice Boltzmann method is selected for its simpler boundary condition implementation and complete parallel computing, which make this approach promising for such applications. The standard Lattice Boltzmann method, here used only for the fluid-dynamic evolution, is coupled with a Finite Volume approach for solving the energy equation and recovering the temperature field throughout the whole domain (air, aluminum and battery). This coupled approach allows having a fully reliable control of the transient phase in conjugate heat transfer problems without introducing any…