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Safety assurance concepts for automated driving systems

University of Melbourne-Stuart Ballingall, Majid Sarvi, Peter Sweatman
  • Technical Paper
  • 2020-01-0727
To be published on 2020-04-14 by SAE International in United States
Automated Driving Systems (ADSs) for road vehicles are being developed that can perform the entire dynamic driving task without a human driver in the loop. However, current regulatory frameworks for assuring vehicle safety may restrict the deployment of ADSs that can use machine learning to modify their functionality while in service. A review was undertaken to identify and assess key initiatives and research relevant to the safety assurance of adaptive safety-critical systems that use machine learning, and to highlight assurance concepts that could benefit from further research. The primary objective was to produce findings and recommendations that can inform policy and regulatory reform relating to ADS safety assurance. Due to the almost infinite number and combination of scenarios that an ADS could encounter, the review found much support for concepts that involve the use of simulation data as virtual evidence of safety compliance, with suggestions of a need to assure simulation tools and models. Real-world behavioural competency testing was also commonly proposed, although noting this concept has its limitations. The concept of whole-of-life assurance was…
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An Optical and Numerical Characterization of Directly Injected Compressed Natural Gas Jet Development at Engine-Relevant Conditions

University of Melbourne-Joshua Lacey, Marie Meulemans, Michael Brear
Continental-Mike Hornby, Doug Cosby, Perry Czimmek
Published 2019-04-02 by SAE International in United States
Compressed natural gas (CNG) is an attractive, alternative fuel for spark-ignited (SI), internal combustion (IC) engines due to its high octane rating, and low energy-specific CO2 emissions compared with gasoline. Directly-injected (DI) CNG in SI engines has the potential to dramatically decrease vehicles’ carbon emissions; however, optimization of DI CNG fueling systems requires a thorough understanding of the behavior of CNG jets in an engine environment.This paper therefore presents an experimental and modeling study of DI gaseous jets, using methane as a surrogate for CNG. Experiments are conducted in a non-reacting, constant volume chamber (CVC) using prototype injector hardware at conditions relevant to modern DI engines. The schlieren imaging technique is employed to investigate how the extent of methane jets is impacted by changing thermodynamic conditions in the fuel rail and chamber.Post-processing of these optical results presents challenges because of the similarity between the density of methane and the background nitrogen. A methodology to interpret the jet extent in the high-speed movies is therefore proposed and used to quantify methane jet propagation and structure. The…
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Effects of Engine Speed on Spray Behaviors of the Engine Combustion Network “Spray G” Gasoline Injector

University of Melbourne-Joshua Lacey, Michael Brear
Robert Bosch LLC-Mohammad Fatouraie
Published 2018-04-03 by SAE International in United States
Non-reacting spray behaviors of the Engine Combustion Network “Spray G” gasoline fuel injector were investigated at flash and non-flash boiling conditions in an optically accessible single cylinder engine and a constant volume spray chamber. High-speed Mie-scattering imaging was used to determine transient liquid-phase spray penetration distances and observe general spray behaviors. The standardized “G2” and “G3” test conditions recommended by the Engine Combustion Network were matched in this work and the fuel was pure iso-octane. Results from the constant volume chamber represented the zero (stationary piston) engine speed condition and single cylinder engine speeds ranged from 300 to 2,000 RPM. As expected, the present results indicated the general spray behaviors differed significantly between the spray chamber and engine. The differences must be thoughtfully considered when applying spray chamber results to guide spray model development for engine applications. Overall, increases in engine speed correlated well with enhanced vaporization, loss of distinct plume structure, and enhanced spray collapse which led to reductions in wetted-footprint area. Furthermore, while loss of distinct plume structures appeared to be strongly dependent…
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The Direct Transition of Fuel Sprays to theDense-Fluid Mixing Regime in the Contextof Modern Compression Ignition Engines

University of Melbourne-Joshua Lacey, Michael Brear, Robert Gordon
Georgia Institute of Technology-Farzad Poursadegh
Published 2018-04-03 by SAE International in United States
Fuel supercriticality has recently received significant attention due to the elevated pressures and temperatures that directly-injected (DI) fuel sprays encounter in modern internal combustion (IC) engines. This paper presents a theoretical examination of conventional and alternative DI fuels at conditions relevant to the operation of compression ignition (CI) engines. The focus is to identify the conditions under which the injected liquid fuel can bypass the atomization process and directly transition to a diffusional mixing regime with the chamber gas. Evaluating the microscopic length-scales of the phase boundary associated with the injection of liquid nitrogen into its own vapor, it is found that the conventional threshold based on the interfacial Knudsen number (i.e. Kn = 0.1) does not adequately quantify the direct transition between sub- and supercriticality. Instead, a threshold that is an order of magnitude smaller is more appropriate for this purpose. Extending the analysis to a range of diesel fuel surrogates (e.g. n-heptane and n-dodecane), and alternative engine fuels that can be blended for use in CI engines (e.g. dimethyl ether and propane), it is then…
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A Comparison of Four Methods for Determining the Octane Index and K on a Modern Engine with Upstream, Port or Direct Injection

University of Melbourne-Zhenbiao Zhou, Yi Yang, Michael Brear, Joshua Lacey
Ford Motor Company-Thomas G. Leone, James E. Anderson, Michael H. Shelby
Published 2017-03-28 by SAE International in United States
Combustion in modern spark-ignition (SI) engines is increasingly knock-limited with the wide adoption of downsizing and turbocharging technologies. Fuel autoignition conditions are different in these engines compared to the standard Research Octane Number (RON) and Motor Octane Numbers (MON) tests. The Octane Index, OI = RON - K(RON-MON), has been proposed as a means to characterize the actual fuel anti-knock performance in modern engines. The K-factor, by definition equal to 0 and 1 for the RON and MON tests respectively, is intended to characterize the deviation of modern engine operation from these standard octane tests. Accurate knowledge of K is of central importance to the OI model; however, a single method for determining K has not been well accepted in the literature.This paper first examines four different methods for determining K, using literature results from a modern SI engine operating with direct injection (DI), port fuel injection (PFI) and homogeneous, upstream fuel injection (UFI). The test fuels were ethanol-gasoline blends spanning a wide range of RON and MON, together with isooctane as a reference. The…
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Optical Characterization of Propane at Representative Spark Ignition, Gasoline Direct Injection Conditions

University of Melbourne-Joshua Lacey, Farzad Poursadegh, Michael Brear
Ford Motor Company of Australia-Charles Lakey, Steve Ryan, Brendan Butcher
Published 2016-04-05 by SAE International in United States
The focus of internal combustion (IC) engine research is the improvement of fuel economy and the reduction of the tailpipe emissions of CO2 and other regulated pollutants. Promising solutions to this challenge include the use of both direct-injection (DI) and alternative fuels such as liquefied petroleum gas (LPG).This study uses Mie-scattering and schlieren imaging to resolve the liquid and vapor phases of propane and iso-octane, which serve as surrogates for LPG and gasoline respectively. These fuels are imaged in a constant volume chamber at conditions that are relevant to both naturally aspirated and boosted, gasoline direct injection (GDI) engines. It is observed that propane and iso-octane have different spray behaviors across these conditions. Iso-octane is subject to conventional spray breakup and evaporation in nearly all cases, while propane is heavily flash-boiling throughout the GDI operating map. This severe flashing behavior has major implications for the design and calibration of LPG DI injection systems and engines.
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Modeling of Trace Knock in a Modern SI Engine Fuelled by Ethanol/Gasoline Blends

University of Melbourne-Hao Yuan, Tien Mun Foong, Zhongyuan Chen, Yi Yang, Michael Brear
Ford Motor Co.-Thomas Leone, James E. Anderson
Published 2015-04-14 by SAE International in United States
This paper presents a numerical study of trace knocking combustion of ethanol/gasoline blends in a modern, single cylinder SI engine. Results are compared to experimental data from a prior, published work [1]. The engine is modeled using GT-Power and a two-zone combustion model containing detailed kinetic models. The two zone model uses a gasoline surrogate model [2] combined with a sub-model for nitric oxide (NO) [3] to simulate end-gas autoignition.Upstream, pre-vaporized fuel injection (UFI) and direct injection (DI) are modeled and compared to characterize ethanol's low autoignition reactivity and high charge cooling effects. Three ethanol/gasoline blends are studied: E0, E20, and E50. The modeled and experimental results demonstrate some systematic differences in the spark timing for trace knock across all three fuels, but the relative trends with engine load and ethanol content are consistent. Possible reasons causing the differences are discussed. Finally, the influence of NO on autoignition is investigated, yielding results that are consistent with prior works. Overall, the same, two-zone kinetic model appears to capture both the UFI and DI autoignition similarly well.…
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An Integrated Model of Energy Transport in a Reciprocating, Lean Burn, Spark Ignition Engine

SAE International Journal of Engines

University of Melbourne-Peter A. Dennis, Michael J. Brear, Harry C. Watson, Pedro J. Orbaiz, Payman Abbasi Atibeh
  • Journal Article
  • 2015-01-1659
Published 2015-04-14 by SAE International in United States
This paper presents a combined experimental and numerical method for analysing energy flows within a spark ignition engine. Engine dynamometer data is combined with physical models of in-cylinder convection and the engine's thermal impedances, allowing closure of the First Law of Thermodynamics over the entire engine system. In contrast to almost all previous works, the coolant and metal temperatures are not assumed constant, but rather are outputs from this approach. This method is therefore expected to be most useful for lean burn engines, whose temperatures should depart most from normal experience.As an example of this method, the effects of normalised air-fuel ratio (λ), compression ratio and combustion chamber geometry are examined using a hydrogen-fueled engine operating from λ = 1.5 to λ = 6. This shows large variations in the in-cylinder wall temperatures and heat transfer with respect to λ. In keeping with our other works, thermal efficiency also appears to be limited by in-cylinder heat transfer on the rich side of optimum λ, and diminishing combustion quality on the lean side.By comparing different compression…
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The Psychological and Accident Reconstruction “Thresholds” of Drivers' Detection of Relative Velocity

University of Melbourne-Errol Hoffmann
Accident Research Specialists PLLC-Aaron Kiefer
Published 2014-04-01 by SAE International in United States
Relative velocity detection thresholds of drivers are one factor that determines their ability to avoid rear-end crashes. Laboratory, simulator and driving studies show that drivers could scale relative velocity when it exceeded the threshold of about 0.003 rad/sec. Studies using accident reconstruction have suggested that the threshold may be about ten times larger. This paper discusses this divergence and suggests reasons for it and concludes that the lower value should be used as a true measure of the psychological threshold for detection of relative velocity.
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Bio-Ketones: Autoignition Characteristics and Their Potential as Fuels for HCCI Engines

SAE International Journal of Fuels and Lubricants

University of Melbourne-Yi Yang
Sandia National Laboratories-John E. Dec
  • Journal Article
  • 2013-01-2627
Published 2013-10-14 by SAE International in United States
This paper studies autoignition characteristics and HCCI engine combustion of ketone fuels, which are important constituents of recently discovered fungi-derived biofuels. Two ketone compounds, 2,4-dimethyl-3-pentanone (DMPN) and cyclopentanone (CPN), are systematically investigated in the Sandia HCCI engine, and the results are compared with conventional gasoline and neat ethanol. It is found that CPN has the lowest autoignition reactivity of all the biofuels and gasoline blends tested in this HCCI engine. The combustion timing of CPN is also the most sensitive to intake-temperature (Tin) variations, and it is almost insensitive to intake-pressure (Pin) variations. These characteristics and the overall HCCI performance of CPN are similar to those of ethanol. In contrast, DMPN shows multi-faceted autoignition characteristics. On the one hand, DMPN has strong temperature-sensitivity, even at boosted Pin, which is similar to the low-reactivity ethanol and CPN. On the other hand, DMPN shows much stronger pressure-sensitivity than ethanol and CPN. This pressure-sensitivity reduces the Tin requirement for DMPN as Pin increases, in a manner similar to gasoline, and it allows the same Tin = 60°C for…
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