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Research

  • Ethanol to Gasoline Ratio Detection via Time-Frequency Analysis of Engine Acoustic Emission

    Year: 2012

    Author: Nicolo Cavina, Davide Moro, Stefano Sgatti, Filippo Cavanna

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    In order to reduce both polluting emissions and fuel costs, many countries allow mixing ethanol to gasoline either in fixed percentages or in variable percentages. The resulting fuel is labeled E10 or E22, where the number specifies the ethanol percentage.

    This operation significantly changes way the stoichiometric value, which is the air-to-fuel mass ratio theoretically needed to completely burn the mixture. Ethanol concentration must be correctly estimated by the Engine Management System to optimally control exhaust emissions, fuel economy and engine performance. In fact, correct fuel quality recognition allows estimating the actual stoichiometric value, thus allowing the catalyst system to operate at maximum efficiency in any engine working point. Moreover, also other essential engine control functions should be adapted in real time by taking into account the quality of the fuel that is being used. An example is the Spark Advance management, which may benefit from correct fuel quality recognition for example in terms of knock detection and control.

    Many possible solutions are currently available in mass production vehicles to evaluate the percentage of ethanol in fuel, all of them ranging from indirect measurements based on the use of standard lambda sensors, to the use of dedicated sensors to be installed in the fuel line. The present work shows an innovative solution to the problem of detecting ethanol percentage in fuel, based on the analysis of the acoustic signal measured by installing a microphone in the engine compartment.

    The paper initially presents the main criteria to choose the best sensor as a trade-off between cost and performance. Then the signals coming from sensors installed in different positions with respect to the engine will be analysed to demonstrate how to perform the best choice. Finally, it will be shown that starting from signal frequency spectrum analysis it is possible to develop a fuel quality recognition index based on combustion frequency amplitude and its higher-order harmonics. The index is then compared with a threshold depending on the actual working point, to detect whether the engine is running on gasolina (E22) or pure ethanol (E100).

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  • UEGO-based Exhaust Gas Mass Flow Rate Measurement

    Year: 2012

    Author: Nicolo Cavina, Alberto Cerofolini, Matteo De Cesare, Federico Stola

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    New and upcoming exhaust emissions regulations and fuel consumption reduction requirements are forcing the development of innovative and particularly complex intake-engine-exhaust layouts. Especially in the case of Compression Ignition (CI) engines, the HC-CO-NOx-PM after-treatment system is becoming extremely expensive and sophisticated, and the necessity to further reduce engine-out emission levels, without significantly penalizing fuel consumption figures, may lead to the adoption of intricate and challenging intake-exhaust systems configurations. The adoption of both long- and short-route Exhaust Gas Recirculation (EGR) systems is one example of such situation, and the need to precisely measure (or estimate) mass flow rates in the various elements of the gas exchange circuit is one of the consequences. Within this context, the paper presents an innovative solution for real-time estimation of the exhaust gas mass flow rate of a modern Turbo-Diesel Engine, equipped with Variable Geometry Turbine (VGT), Diesel Particulate Filter (DPF), and EGR.

    The proposed methodology is based on the measurement of standard operating parameters of the UEGO sensor incorporated heater, such as the applied voltage and the sensing tip temperature, which are normally available to the Engine Control Unit (ECU), and on the measurement (or estimation) of exhaust gas pressure and temperature levels, in the same location where the linear oxygen sensor is installed.

    The model for mass flow rate estimation has been developed starting from the consideration that the UEGO sensing element must be kept at constant temperature for optimal operation, thus allowing the development of physical laws similar to those used for anemometers. As shown in the paper, this approach leads to the determination of physical correlations between calculated convection coefficients and estimated velocity of the gas inside the probe. Dimensional analysis and similarity concepts may then be applied to directly estimate exhaust gas mass flow rate. Finally, the intake air mass flow rate may be evaluated via direct AFR measurement, taking also into consideration dynamic transport delays.

    Such a model may be identified for any oxygen sensor type and installation layout, and it may be applied both to Spark Ignition (SI) and CI engines, the latter being the test case used for demonstrating the feasibility of the proposed approach.

    Several experimental tests have been conducted to identify unknown parameters, and to evaluate the model performance. The results presented in this work show that a satisfying accuracy level may be reached on a wide range of flow rate values, and alternative approaches (such as Mass Air Flow sensors based or Speed-Density based) have been considered as benchmarks to evaluate the proposed methodology accuracy.

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  • Virtual GDI Engine as a Tool for Model-Based Calibration

    Year: 2012

    Author: Rita Di Gioia, Domenico Papaleo, Fabio Massimo Vicchi, Nicolo Cavina

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    Recent and forthcoming fuel consumption reduction requirements and exhaust emissions regulations are forcing the development of innovative and particularly complex intake-engine-exhaust layouts. In the case of Spark Ignition (SI) engines, the necessity to further reduce fuel consumption has led to the adoption of direct injection systems, displacement downsizing, and challenging intake-exhaust configurations, such as multi-stage turbocharging or turbo-assist solutions. Further, the most recent turbo-GDI engines may be equipped with other fuel-reduction oriented technologies, such as Variable Valve Timing (VVT) systems, devices for actively control tumble/swirl in-cylinder flow components, and Exhaust Gas Recirculation (EGR) systems. Such degree of flexibility has a main drawback: the exponentially increasing effort required for optimal engine control calibration. Even if extremely efficient and statistically-based experiments have recently been introduced as standard protocols during test-cell calibration activity, the time and the instrumentation required for a fully-validated test-cell calibration dataset has been steeply increasing during the last few years.

    The methodology proposed in this paper is based on computing technologies, and deeper understanding of physical phenomena, which have been accessible only in very recent times. If the availability of dimensional models fast enough to be used in an iterative loop (aimed at the optimization of pre-designed cost or goal functions) allows the introduction of virtual-engine based calibration techniques, the challenge is to identify the best way to take advantage of them.

    One necessary step is the reduction of fully 1-D engine models to simpler (and faster to resolve) but still-dimensional engine thermo-fluid-dynamics representations. One of the outcomes of this work is the demonstration that fully-automatic geometry simplifications (to reduce the computational effort) may still not guarantee model consistency, the main reasons being the assignment of inadequate boundary parameters (such as imposed wall temperatures) resulting after merging various elements, in an effort to reduce model complexity.

    The second and most important phase is the definition of the calibration scheme. As it always happens with model-based design, the goals of the overall activity should be closely related to the accuracy of the simulation tool. The present project demonstrates the possibility of using simulation tools in a new environment, which is somehow in-between desktop design-oriented simulation (1-D and 3-D models) and real-time model-based control (0-D). The model reliability, and therefore the geometry reduction consistency, has been carefully checked to limit significant accuracy loss, especially for the variables being used for virtual calibration. Also, in the paper the limits of the model are introduced and taken into account, and the definition of cost functions and constraints (related to emissions limitation, fuel consumption reduction, and components protection criteria) is discussed.

    Finally, the paper shows the application of the overall virtual-engine based calibration methodology to a Gasoline Direct Injection (GDI) turbocharged engine, equipped with tumble-flaps and Variable Valve Timing (VVT) systems. Simulation (and corresponding look-up-tables calibration) results are compared to experimentally measured ones (with similar sets of calibration parameters), demonstrating the potential of adopting the proposed methodology as an intermediate step between engine development and calibration-related test cell (and on-board) activities.

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  • Diesel Engine Acoustic Emission Analysis for Combustion Control

    Year: 2012

    Author: Fabrizio Ponti, Vittorio Ravaglioli, Davide Moro, Matteo De Cesare

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    Future regulations on pollutant emissions will impose a drastic cut on Diesel engines out-emissions. For this reason, the development of closed-loop combustion control algorithms has become a key factor in modern Diesel engine management systems. Diesel engines out-emissions can be reduced through a highly premixed combustion portion in low and medium load operating conditions. Since low-temperature premixed combustions are very sensitive to in-cylinder thermal conditions, the first aspect to be considered in newly developed Diesel engine control strategies is the control of the center of combustion. In order to achieve the target center of combustion, conventional combustion control algorithms correct the measured value varying main injection timing.
    A further reduction in engine-out emissions can be obtained applying an appropriate injection strategy. Modern Diesel engine injection systems allow designing injection patterns with many degrees of freedom, due to the large number of tuneable injection parameters (such as start and duration of each injection). Each variation of the injection parameters will affect and alter the whole combustion process and, consequently, pollutant emissions production. Furthermore, injection parameters variations have a strong influence on other quantities that are related to combustion process effectiveness, such as noise radiated by the engine.
    This work discusses the correlations existing between in cylinder pressure and the acoustic emission radiated by the engine. In order to set up the correlations that allow noise prediction starting from in-cylinder pressure measurement, several experimental tests have been performed, both in steady state and transient conditions, on a Diesel engine mounted in a test cell. Each operating condition was run both activating and deactivating pre-injections. As it is well known, in several low load conditions, pre-injections deactivation produces a decrease in pollutant emissions production (especially in particulate matter) and a simultaneous increase in engine noise. The investigation of the correlation between combustion process and engine noise can be used to set up a closed-loop algorithm for optimal combustion control based on engine noise prediction.

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  • Multicycle Simulation of the Mixture Formation Process of a PFI Gasoline Engine

    Year: 2012

    Author: Claudio Forte, Gian Marco Bianchi, Enrico Corti

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    The mixture composition heavily influences the combustion process of Port Fuel Injection (PFI) engines. The local mixture air-index at the spark plug is closely related to combustion instabilities and the cycle-by-cycle Indicated Mean Effective Pressure (IMEP) Coefficient of Variation (CoV) well correlates with the variability of the flame kernel development. The needs of reducing the engine emissions and consumption push the engine manufactures to implement techniques providing a better control of the mixture quality in terms of homogeneity and variability.
    Simulating the mixture formation of a PFI engine by means of CFD techniques is a critical issue, since involved phenomena are highly heterogeneous and a two phase flow must be considered. The aim of the paper is to present a multi-cycle methodology for the simulation of the injection and the mixture formation processes of high performance PFI engine, based on the validation of all the main physical sub-models involved.
    A semi-empirical methodology for the correct initialization of the Lagrangian spray is presented in the paper. The spray-wall interaction sub-models are usually based on semi-empirical correlation. In this paper the Kuhnke model was tuned by means of experimental data, chosen coherently with the spray phenomena taking place in the considered engine. Since the liquid wall film plays a key role in the mixture formation of PFI engines, an accurate representation of the wall film dynamics was enforced by the solution of the liquid film momentum equation. The gas flow dynamics in the intake port strongly interact with the liquid fuel evolution and droplet breakup, thus in this work a multi-cycle methodology for the evaluation of the mixture inside the cylinder was proposed. In order to validate the simulation results, an optical access has been created on the engine airbox, allowing to use a fast camera to capture images of the actual injection process. The comparison of simulated and acquired images confirmed that both the gas and liquid fuel dynamics have been correctly reproduced.
    The evaluation of the injection timing influence on the engine performance was finally accomplished.

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  • Development of a Dual Clutch Transmission Model for Real-Time Applications

    Year: 2012

    Author: Nicolo Cavina, Davide Olivi, Enrico Corti, Luca Poggio, Francesco Marcigliano

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    The paper presents the main features of a control-oriented model of a Dual Clutch Transmission (DCT) system that has been designed to support model-based development of the DCT controller. The model represents an innovative attempt to reproduce the fast dynamics of the hydraulic circuit while maintaining a simulation step size large enough for real time application. The model includes a detailed physical description of clutches, synchronizers and gears, and a simplified model of the vehicle and of the internal combustion engine, in order to simulate the behavior of the entire system. As the oil circulating in the system has a large bulk modulus, the pressure dynamics are very fast, possibly causing instability in a real time simulation; the same challenge involves the servo valves dynamics, due to the very small masses of the moving elements. Therefore, the hydraulic circuit model has been modified and simplified without losing physical validity, in order to adapt it to the real time simulation requirements. The results of offline simulations are compared to on board measurements to verify the validity of the developed model for real time Hardware In the Loop (HIL) applications.

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  • Multi-Cycle Simulation of the Mixture Formation Process of an High Performance Engine at Part Load Condition

    Year: 2012

    Author: Claudio Forte, Gian Marco Bianchi, Enrico Corti, Stefano Fantoni

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    Transient operation of engines leads to air fuel (A/F) ratio excursions, which can increase engine emissions. These excursions have been attributed to the formation of fuel films in the intake port, which are caused by a portion of the intake fuel impinging and adhering on the relatively cool port surface. These films act as a source or sink which cause the AF variations depending upon the transient condition. Gaining a fundamental understanding of the nature and quantity of such films may assist in future fuel mixture preparation designs that could aid in emission reductions, yet would not require overly expensive nor complicated systems.
    The control of air to fuel ratio is a critical issue for high performance engines: due to the low stroke-to-bore ratio the maximum power is reached at very high regimes, letting little time to the fuel to evaporate and mix with air. The injector located upstream the throttle causes a lot of fuel to impinge the throttle and intake duct walls, slowing the dynamics of mixture formation in part load conditions.
    The aim of this work is to present a CFD methodology for the evaluation of mixture formation dynamics applied to a Ducati high performance engine under part load conditions.
    The phenomena involved in the process are highly heterogeneous, and particular care must be taken to the choice of CFD models and their validation. In the present work all the main models involved in the simulations are validated against experimental tests available in the literature, selected based on the similarity of physical conditions of those of the engine configuration under analysis.
    The multi-cycle simulation methodology here presented reveals to be a useful tool for the evaluation of the mixture dynamics and for the evaluation of injection wall film compensator models.

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