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Research

  • Exhaust Gas Turbocharger Speed Measurement Via Acoustic Emission Analysis

    Year: 2008

    Author: Nicolò Cavina, Davide Moro, Matteo De Cesare, Gabriele Serra

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    The paper presents a non-intrusive, indirect and low-cost methodology for a real time on-board measurement of an automotive turbocharger rotational speed. In the first part of the paper the feasibility to gather information on the turbocharger speed trend is demonstrated by comparing the time-frequency analysis of the acoustic signal with the direct measurement obtained by an optical sensor facing the compressor blades, mounted in the compressor housing of a spark ignited turbocharged engine. In the second part of the paper, a real time algorithm, to be implemented in the engine control unit, is proposed. The algorithm is able to tune on the turbocharger revolution frequency and to follow it in order to extract the desired speed information. The frequency range containing the turbocharger acoustic frequency can be set utilizing a raw estimation of the compressor speed, derived by its characteristic map. Different tests have been performed on a turbocharged Diesel engine and encouraging results have been achieved, since a satisfactory turbocharger speed reconstruction has been obtained.

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  • Development of Model-Based OBDII-Compliant Evaporative Emissions Leak Detection Systems

    Year: 2008

    Author: Nicolò Cavina, Enrico Corti, Stefano Sgatti, Luca Guidotti, Filippo Cavanna

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    The paper presents the main results obtained by developing and critically comparing different evaporative emissions leak detection diagnostic systems.

    Three different leak detection methods have been analyzed and developed by using a model-based approach: depressurization, air and fuel vapor compression, and natural vacuum pressure evolution. The methods have been developed to comply with the latest OBD II requirement for 0.5 mm leak detection. Detailed grey-box models of both the system (fuel tank, connecting pipes, canister module, engine intake system) and the components needed to perform the diagnostic test (air compressor or vacuum pump) have been used to analyze in a simulation environment the critical aspects of each of the three methods, and to develop “optimal” diagnostic model-based algorithms. Experiments have been initially carried out in a laboratory environment to identify both the main model unknown parameters and the main disturbances, and to acquire data that could be used to validate the simulation results. During a subsequent phase of the project, a prototype vehicle has been setup with various sensors and actuators, and several experiments have been conducted to test the three leak detection model-based methods, while varying environmental and in-vehicle conditions. The critical aspects of each methodology have thus been isolated and compared, also by taking into account actual and possibly future European and North American on-board diagnostic regulations.

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  • Powertrain Torsional Model Development or On-Board Indicated Torque Estimation

    Year: 2008

    Author: Fabrizio Ponti, Gabriele Serra, Savino Lupo

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    Effective and precise torque estimation is a great opportunity to improve actual torque-based engine management strategies. Modern ECU often already implement algorithms to estimate on-board the torque that is being produced by the engine, even if very often these estimation algorithms are based on look-up tables and maps and cannot be employed for example for diagnostic purposes.
    The indicated torque estimation procedure presented in this paper is based on the measurement of the engine speed fluctuations, and is mainly based on two separated steps.
    As a first step a torsional behavior model of the powertrain configuration is developed. The engine-driveline torsional model enables to estimate the indicated torque frequency component amplitude from the corresponding component of the instantaneous engine speed fluctuation. This estimation can be performed cycle by cycle and cylinder by cylinder.
    As a second step the analysis of the relationship between the indicated torque mean value over an engine cycle and the amplitude of its frequency components, allowed defining the final estimation algorithm that reconstructs the indicated torque mean value starting from the instantaneous engine speed fluctuation analysis.
    The developed approach has been applied with success to a diesel engine mounted on-board a vehicle. The obtained precision is compatible with on-board application like for example torque-based engine management strategies.

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  • Measurement Errors in Real-Time IMEP and ROHR Evaluation

    Year: 2008

    Author: Enrico Corti, Davide Moro, Luca Solieri

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    Combustion control is one of the key factors to obtain better performance and lower pollutants emissions, for diesel, spark ignition and HCCI engines. This paper describes a real-time indicating system based on commercially available hardware and software, which allows the real-time evaluation of Indicated Mean Effective Pressure (IMEP) and Rate of Heat Release (ROHR) related parameters, such as 50%MFB, cylinder by cylinder, cycle by cycle. This kind of information is crucial for engine mapping and can be very important also for rapid control prototyping purposes.
    The project objective is to create a system able to process in-cylinder pressure signals in the angular domain without the need for crankshaft encoder, for example using as angular reference the signal coming from a standard equipment sensor wheel. This feature can be useful both for test bench and on-board tests. In order to gain reliable results or acceptable precision on ROHR-related parameters (ROHR peak & 50%MFB, for example) a high sampling rate is required for the in-cylinder pressure. Since the angular reference signal can have low angular resolution (6 degrees with a typical sensor wheel), the in-cylinder pressure signal sampling rate must be higher than the crankshaft signal frequency. The choice for this application has been to use a high sample rate on a time base for the cylinder pressure signal, performing the transformation from the time domain to the angular domain (necessary in order to evaluate the indicating parameters) by means of an interpolation algorithm.
    The use of standard automotive crankshaft position referencing sensors (and sensor wheels), however, increases the risk of angular errors in the conversion from the time to the angular domain: transducers intrinsic delay, analog filters delay, TDC referencing error could cause large errors on RHOR and IMEP. Furthermore, if the in-cylinder pressure signal mean value is reconstructed by means of the Polytropic Index Pressure Referencing methodology, errors on the pressure samples angular position would lead to a wrong estimation of the pressure signal mean value. This would introduce an offset in the pressure trace, affecting ROHR results.
    The paper shows how these considerations can be taken into account in the implementation of the algorithm of IMEP and RHOR evaluation. In order to correct IMEP and ROHR calculations, some parameters need to be identified: the position sensor delay, the TDC actual position and the sensor wheel teeth unevenness. Algorithms implementing these functions have been integrated within the main application. Once the correction-parameters are estimated, they are directly used for IMEP and RHOR evaluation.

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  • Fast Prototyping of a Racing Diesel Engine Control System

    Year: 2008

    Author: Enrico Corti, Giulio Cazzoli, Matteo Rinaldi, Luca Solieri

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    This paper shows how Rapid Control Prototyping (RCP) and Computational Fluid Dynamics (CFD) techniques have been applied to design and implement an engine control system for a common rail diesel engine. The project aim is to setup a high performance engine in order to participate to the Italian Tractor Pulling Championship (Prostock category).
    The original engine is a John Deere 6081 Tier2 model, already equipped with a common rail system. Engine performance is substantially determined by the control system, which is in charge of limiting engine speed, boost pressure and Air to Fuel Ratio (AFR). Given that typically the information and equipment needed to change control parameters are not accessible to customers, the first step of the project has been to replace the original control system, while maintaining injectors and pumps. This solution can guarantee the best performance, but it requires time to design the new control system, both in terms of hardware and software. The challenge of setting up a new control system in a three months time is even more demanding if the control parameters cannot be tuned on the test bench. As it is well known, a common rail system requires the calibration of many parameters (rail pressure, injection timing and splitting, boost pressure, minimum AFR, etc.). This demands for intensive testing, which is expensive and time-consuming; moreover, tests must be carried out in racing conditions (i.e., high engine speed, high boost pressure, low AFR), affecting engine durability. Cost reduction is a key factor in this type of competition, therefore Computational Fluid Dynamics (CFD) simulations were used to assess a range of control parameters setting that could be used as a decent starting point for a fine optimization on the test bench.
    The time constraints oriented the hardware choice toward an RCP (Rapid Control Prototyping) system, programmable by means of object oriented software. Computational power, harsh environment compatibility, availability of third party products (such as power modules for the injectors) were taken into account in order to chose the hardware-software package. The ECU has been finally implemented on a National Instruments cRIO 9074 equipped with a 400 MHz controller, 2 Mgate FPGA and Analog-digital I/O modules.
    The control system was designed to guarantee performance, driveability and easy access: it was equipped with an easy-to-use interface, allowing the user to change crucial control parameters, and to manage data logging, that can be used to monitor the engine performance after the race.

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  • Combined experimental and numerical analysis of the influence of air-to-fuel ratio on cyclic variation of high performance engines

    Year: 2008

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

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    The Cycle by Cycle Variation (CCV) of a SI engine is analyzed by combining experimental tests and numerical investigations. The quantification of CCV is based on the evaluation of the Coefficient of Variance (COV) of IMEP. The analysis of the experimental pressure data shows an increase in CCV towards leaner mixture conditions. The evaluation of the Heat Release Rate from the in-cylinder pressure traces reveals the strong influence of the early stages of combustion on the variability of the flame evolution. In order to evaluate the influence on CCV of local air equivalence ratio cycle-to-cycle variability and mixture homogeneity in the chamber, a numerical CFD methodology for the simulation of the combustion process has been proposed. The results reproduce with reasonable accuracy the increase in CCV with leaner combustions and put the basis for a deeper insight into the complex phenomena involved in the combustion process by the use of parametric analysis.

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