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Model Reduction of Diesel Mean Value Engine Models

The University of Melbourne-Timothy Broomhead, Chris Manzie, Michael Brear
DSTO-Peter Hield
Published 2015-04-14 by SAE International in United States
In the literature, a wide range of Mean Value Engine Models are used in the simulation and control of reciprocating engines. These models are often underpinned by a number of implicit assumptions, which determine the model structure and system states. Systematic model reduction approaches have been developed to avoid these assumptions, where high order models are reduced using singular perturbation techniques, eliminating states operating on irrelevant time-scales. While this framework allows the elimination of states based on sufficiently small perturbation parameters, a systematic method of identifying non-dimensional perturbation parameters has not yet been proposed. The development of a rigorous method to identify non-dimensional time scales present in the model is a natural and powerful extension to the existing approach.In this work, starting from a calibrated, high-order physics based non-linear mean value model of a diesel engine, non-dimensional analysis is used to identify system states on relevant time-scales. Singular perturbation techniques are then used to isolate the identified states. The resulting boundary layer is then approximated before the impact of linearising the state and output equations…
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The Effect of Charge Cooling on the RON of Ethanol/Gasoline Blends

SAE International Journal of Fuels and Lubricants

The University of Melbourne-Tien Mun Foong, Kai J. Morganti, Michael J. Brear, Gabriel da Silva, Yi Yang
Princeton University-Frederick L. Dryer
  • Journal Article
  • 2013-01-0886
Published 2013-04-08 by SAE International in United States
This paper examines the effect of charge cooling on the Research Octane Number (RON) of ethanol/gasoline blends. While gasoline is fully vaporized prior to entry into the engine in a standard RON test, significant charge cooling is observed for blends with high ethanol content, with the presence of a near-saturated and potentially two-phase air-fuel mixture during induction. Thus, the relative significance of the charge cooling and the autoignition chemistry cannot be determined from the standard RON test.In order to better delineate the effects of charge cooling and autoignition chemistry, a so-called ‘modified RON’ test is therefore devised in which the temperature of the air-fuel mixture entering the engine is fixed and representative of that observed for primary reference fuels (PRFs). Thermodynamic modeling of this modified RON test suggests the mixture is always fully vaporized prior to compression, and that the modified RON test maintains much more constant temperatures during compression, regardless of the enthalpy of vaporization. The modified RON test thus appears to be a more practical means of examining the significance of autoignition chemistry…
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High-Bandwidth Clamp Force Control for an Electromechanical Brake

SAE International Journal of Passenger Cars - Electronic and Electrical Systems

The University of Melbourne-Chih Feng Lee, Chris Manzie
  • Journal Article
  • 2012-01-1799
Published 2012-09-17 by SAE International in United States
A controller that fully utilizes the available motor capacity of an electromechanical brake to achieve high closed-loop bandwidth is proposed. The controller is developed based on the time-optimal switching curve derived from Pontryagin's Maximum Principle. The control input is scheduled using a switching surface based on the current motor velocity and position offset. Robustness to modeling errors is achieved by introducing a boundary layer in vicinity of the switching curve, reminiscent of a high gain controller. A flexible tuning procedure is also developed to aid in practical implementation, allowing a balanced choice between tracking speed and energy usage. The controller is implemented on a production-ready prototype EMB, and tested over different braking scenarios to assess the performance and robustness relative to the benchmark controllers. It is demonstrated that significant improvements in step response and dynamic tracking are obtained using the proposed approach.
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Adaptive Brake Torque Variation Compensation for an Electromechanical Brake

SAE International Journal of Passenger Cars - Electronic and Electrical Systems

The University of Melbourne-Chih Feng Lee, Chris Manzie
  • Journal Article
  • 2012-01-1840
Published 2012-09-17 by SAE International in United States
A novel method for attenuation of brake judder directly at the source is proposed, utilizing an electromechanical brake to actively compensate for the variation in brake torque that causes judder. Taking advantage of the high-bandwidth closed-loop clamp force tracking performance offered by an electromechanical brake, an adaptive compensator is designed to estimate the brake torque variation (BTV), and to produce a compensating clamp force command to cancel it. The compensator is tested over fixed and varying BTV frequencies by employing a production-ready prototype EMB. It is demonstrated that significant BTV attenuation is obtained using the proposed approach.
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Modeling Alternative Prechamber Fuels in Jet Assisted Ignition of Gasoline and LPG

The University of Melbourne-Elisa Toulson, Harry C. Watson, William P. Attard
Published 2009-04-20 by SAE International in United States
Gas assisted jet ignition is a prechamber combustion initiation system for conventional spark ignition engines. With the system, a chemically active turbulent jet is used to initiate combustion in lean fuel mixtures enabling reliable combustion over a much broader range of air-fuel ratios. The extended range is due to the distributed ignition source provided by the jet, which can overcome the problems of poorly mixed main chamber charges and slower burning fuels. In addition, the ability to reliably ignite lean mixtures improves the thermal efficiency and enables ultra low emission levels.Experiments together with flame propagation modeling completed using STAR-CD with CHEMKIN Kinetics were done in order to examine the effects of numerous prechamber fuels on the ignition of the main fuel, which consisted of either liquefied petroleum gas (LPG) or gasoline. The modeling and experimental results showed similar trends, with the modeling results giving insight into the physicochemical process by which main fuel combustion is initiated in the jet ignition process.Both the modeling and experimental results indicate that the level of ignition enhancement provided by…
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Control Oriented Modeling of Turbocharged (TC) Spark Ignition (SI) Engine

The University of Melbourne-R. Sharma, D. Nesic, C. Manzie
Published 2009-04-20 by SAE International in United States
This paper proposes a new systematic procedure for model reduction of TC SI engines. The technique is based on the identification of time scale separation within the dynamics of various engine state variables. The model reduction is performed in two stages. First stage is to use dynamic properties of the engine states to obtain reduced order slow and fast time scale subsystems. Then in the second stage, physical characteristics are considered to isolate fast pressures. As a result a library of the control oriented engine models is obtained. The limitation of the reduced order models as a true representation of original model is first gauged qualitatively by the application of perturbation theory and then characterized quantitatively by means of simulations. Various assumptions under which these model reductions are applicable are presented and their validity in the context of the engine are discussed.
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Mixture Preparation Effects on Gaseous Fuel Combustion in SI Engines

SAE International Journal of Engines

The University of Melbourne-Mohammad Ali Khan, Harry C. Watson, Paul Baker
  • Journal Article
  • 2009-01-0323
Published 2009-04-20 by SAE International in United States
This paper presents a comparison of the influence of different mixture preparation strategies on gaseous fuel combustion in SI engines. Three mixture preparation strategies are presented for a dedicated LPG fuelled engine, showing varying results - gaseous phase port injection (PFI-G), liquid-phase port injection (PFI-L) and gaseous-phase throttle-body injection (TBI-G). Previous work by the authors has shown considerable differences in emissions and thermal efficiency between different fuelling strategies. This paper extends this work to the area of combustion characteristics and lean limit operation and closer analyses the differences between these systems.A dedicated LPG in-line six cylinder engine with compression ratio increased to 11.7:1 (up from the standard 9.65:1) was tested over a range of speed/torque conditions representing most of the steady-state parts of the Euro drive-cycle for light duty-vehicles. The air-fuel ratio was varied from lambda 1.0 to the lean limit. Cylinder-to-cylinder measurements of air/fuel ratio and emissions were conducted. Additionally, sweeps of lambda at five important engine operating points were undertaken for each configuration and results of COV of IMEP, thermal efficiency, HC, NOx…
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Numerical Study of a Turbocharged, Jet Ignited, Cryogenic, Port Injected, Hydrogen Engine

The University of Melbourne-Alberto A. Boretti, Harry C. Watson
Published 2009-04-20 by SAE International in United States
Favorable and unfavorable properties of hydrogen as a combustion engine fuel have been accommodated in a design of a fuel efficient and clean engine providing similar to gasoline maximum torque and power. The advanced H2ICE being developed is a turbocharged engine fitted with cryogenic port hydrogen fuel injection and the hydrogen assisted jet ignition (HAJI). The combustion chamber is designed to produce a high compression ratio and therefore high thermal efficiency. A waste gated turbocharger provides pressure boosting for an increased power density running ultra lean for SULEV operation without after treatment. Thanks to the combustion properties of hydrogen further enhanced by the HAJI system, the engine load is mainly controlled throttle-less decreasing the fuel-to-air equivalence ratio from ultra lean ϕ=0.43 to ultra-ultra lean ϕ=0.18. The computational model developed for addressing the major design issues and the predicted engine performance and efficiency maps are included.
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The Lean Limit and Emissions at Near-Idle for a Gasoline HAJI System with Alternative Pre-Chamber Fuels

The University of Melbourne-Elisa Toulson, Harry C. Watson, William P. Attard
Published 2007-09-16 by Consiglio Nazionale delle Ricerche in Italy
Hydrogen assisted jet ignition (HAJI) is a pre-chamber ignition system for otherwise standard gasoline fueled spark ignition engines that involves the use of a chemically active turbulent jet to initiate combustion in lean fuel mixtures. HAJI burns the lean main charge rapidly and with almost no combustion variability, which allows for low hydrocarbon emissions and almost zero NOx, due to lower peak temperatures.This paper focuses on the effects of different pre-chamber fuels on combustion stability, lean limit and emissions in a single cylinder, HAJI equipped, CFR engine under a worst case, light load condition. Results indicate that the choice of pre-chamber fuel affects the main chamber lean limit but that emissions are not largely affected before this lean limit is reached. The lean limit was extended furthest, to λ = 2.5 with hydrogen, followed by λ = 2.35 with LPG, λ = 2.25 with CNG and λ = 2.15 with carbon monoxide.
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The Effects of Hot and Cool EGR with Hydrogen Assisted Jet Ignition

The University of Melbourne-Elisa Toulson, Harry C. Watson, William P. Attard
Published 2007-08-05 by SAE International in United States
Hydrogen assisted jet ignition (HAJI) is a pre-chamber ignition system for standard gasoline fueled engines that involves the use of a chemically active turbulent jet to initiate combustion in lean fuel mixtures. HAJI burns the lean main charge rapidly and with almost no combustion variability, which allows for low hydrocarbon emissions and almost zero NOx, due to lower peak temperatures.This paper focuses on the effects of internal and cooled external exhaust gas recirculation (EGR) on combustion parameters, emissions and thermal efficiency in a single cylinder HAJI equipped CFR engine. Experimental results indicate that replacing air with EGR in λ=2 mixtures can shift the lean limit at which NOx is negligible to mixtures as rich as λ=1.3, without a large penalty in hydrocarbon emissions and thermal efficiency.
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