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Research

  • 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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  • Individual Cylinder Combustion Control Based on Real-Time Processing of Ion Current Signals

    Year: 2007

    Author: Nicolò Cavina, Davide Moro, Luca Poggio, Daniele Zecchetti, Riccardo Nanni, Andrea Gelmetti

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    The paper presents the main results of a research activity focused on the analysis, development, and real time implementation of a closed-loop, individual cylinder combustion control system, based on ion sensing technology.

    The innovative features of the proposed control system consist of extracting combustion quality related information from the ion current signal, and of using such information, together with pre-defined look-up-tables, for feedback control of the spark advance throughout the entire engine operating range. In particular, the ion current signal processing algorithm that is carried out in real-time, initially determines whether knocking is affecting or not the actual combustion process. Based on such evaluation, the closed-loop spark advance controller uses different signal processing algorithms to continuously determine individual cylinder spark advance deviations with respect to a pre-defined, base spark advance look up table, common to all the engine cylinders, and to store them in the Electronic Control Unit memory.

    The main result is therefore a spark advance controller that is continuously able to adapt its actuations both to engine/components variations (either due to ageing or to manufacturing component dispersion), as well as to varying external conditions (fuel quality, air temperature,…), in order to maximize torque production (or overall efficiency), cylinder by cylinder and combustion by combustion, even if the specific operating condition is affected by knock insurgence.

    The proposed control strategy has been successfully tested on a V12 6.0 liter and on a V12 6.2 liter high performance engines, and it is now part of the control system of V12 6 liter and V8 4 liter Ferrari engines.

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  • Common Rail Multi-Jet Diesel Engine Combustion Model Development for Control Purposes

    Year: 2007

    Author: Fabrizio Ponti, Enrico Corti, Gabriele Serra, Matteo De Cesare

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    Multi-jet injection strategies open significant opportunities for the combustion management of the modern diesel engine. Splitting up the injection process into 5 steps facilitates the proper design of the combustion phase in order to obtain the desired torque level, whilst attempting a reduction in emissions, particularly in terms of NOx.
    Complex 3-D models are needed in the design stage, where components such as the injector or combustion chamber shape have to be determined. Alternatively, zero-dimensional approaches are more useful when fast interpretation of experimental data is needed and an optimization of the combustion process should be obtained based on actual data. For example, zero-dimensional models allow a quick choice of optimum control settings for each engine operating condition, avoiding the need to test all the possible combinations of engine control parameters.
    In this paper a zero-dimensional model suitable for multi-jet engines with up to 4 injections is proposed, in order to synthesize the experimental results that have been obtained running a 1.3 liters multi-jet diesel engine in a test cell. The effects of Pilot injection rate on the heat release after the following injections in the same pattern are particularly emphasized: tests with different injection patterns have been run, focusing the attention on the very first part of the combustion process, where the fuel injected in the Pilot and Pre injections is burned.
    The model is finally employed to perform the optimization of the injection and intake control parameters for a single engine operating condition as an example of what has been done throughout the entire engine operating range. The optimization has been performed on the basis of the torque, noise and emission outputs obtained.

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  • Knock Indexes Thresholds Setting Methodology Technical Paper

    Year: 2007

    Author: Enrico Corti, Davide Moro

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    Gasoline engines can be affected, under certain operating conditions, by knocking combustions: this is still a factor limiting engines performance, and an accurate control is required for those engines working near the knock limit, in order to avoid permanent damage. HCCI engines also need a sophisticated combustion monitoring methodology, especially for high BMEP operating conditions.
    Many methodologies can be found in the literature to recognize potentially dangerous combustions, based on the analysis of the in-cylinder pressure signal. The signal is usually filtered and processed, in order to obtain an index that is then be compared to the knock threshold level.
    Thresholds setting is a challenging task, since usually indexes are not intrinsically related to the damages caused by abnormal combustions events. Furthermore, their values strongly depend on the engine operating conditions (speed and load), and thresholds must therefore vary with respect to speed and load.
    The knock phenomenon is associated to a steep increase in the combustion speed: some of the indexes proposed in the literature are based on the evaluation of the Rate of Heat Release (ROHR) by means of the in-cylinder pressure signal. The filtering operation, in this case, is crucial: in this paper a novel methodology for ROHR filtering is proposed, consisting in the application of a zero-dimensional model based on Wiebe functions. The observation of reconstructed Heat Release traces leads to determine whether the combustion will lead to knock or not. The methodology allows defining a knock index which is essentially dependent on the knocking-combustion rate, and therefore operating conditions-independent. This means that it can be used as a knock intensity reference for other indexes, making it possible to associate to the given index for the given operating condition a proper threshold level.

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  • Real-Time Evaluation of IMEP and ROHR-related Parameters

    Year: 2007

    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 system features a signal conditioning module allowing to plug directly VRS/Hall effect/encoder as reference sensors; the signals, thus converted to TTL level, are digitally sampled at high frequency for the crankshaft position recognition. In-cylinder pressure signals, instead, are sampled @ 100kHz. The conversion of these samples from the time domain to the angular domain is triggered by the sensor wheel signal. The algorithm used for the conversion can be time and memory consuming: the paper shows that the methodology used is crucial in order to save hardware resources, i.e. to increase the number of analyzed signals.
    As regards the hardware choice, many requirements have been taken into account: portability, sampling rate, computational power, programming language, external devices interface etc. The final solution is based on a portable Real-Time/FPGA based hardware, which allows performing all the necessary I/O functions and calculations in real time, even at high engine speed and with a high number of cylinders.

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  • Knock Indexes Normalization Methodologies

    Year: 2006

    Author: Nicolò Cavina, Enrico Corti, Giorgio Minelli, Davide Moro, Luca Solieri

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    Gasoline engines can be affected, under certain operating conditions, by knocking combustions, which can result in serious engine damage. Specific power and efficiency are influenced by factors such as compression ratio and spark advance regulation, that modify the combustion development over the crank angle: the trade-off between performance and the risk of irreversible damages is still a key factor in the design of both high-performance (racing) and low-consumption engines. New generation detection systems, especially based on ionization current technology, allow aggressive advance mapping and control, and future equipment, such as low-cost in-cylinder pressure transducers, will allow following that trend.

    Also HCCI (Homogeneous Charge Compression Ignition) engines need a sophisticated combustion monitoring methodology, since increasing BMEP levels in HCCI mode force the combustion to approach the knocking operation.

    Many methodologies can be found in the literature to recognize potentially dangerous combustions, usually based on the analysis of accelerometer, in-cylinder pressure or ionization current signals. Signals are sampled with high sample rates, then filtered, for a clear recognition of the phenomenon. Filtered signals can then be used to define damage-related indexes, by means of various types of mathematical operations. The indexes are then compared to pre-defined thresholds, for the diagnosis of dangerous combustion events.

    Thresholds setting is a challenging task, since indexes are not usually intrinsically related to the damages caused by abnormal combustion events. Furthermore, the indexes values usually strongly depend on the engine operating conditions (speed and load), and thresholds must therefore vary with respect to speed and load. It can be said that indexes generally depend on the combustion development over the crank angle, and not necessarily on the knock phenomenon. This means that the index value is also influenced by the spark advance regulation, even without knock.

    This paper shows why commonly used indexes values vary with engine running conditions, and how raw indexes can be modified in order to obtain an operating conditions independent information. In-cylinder pressure data are analyzed both in the time and frequency domains, in order to show how parameters such as window angular position and width, and band-pass filter characteristics influence the filtered in-cylinder pressure signals, and, as a consequence, knock indexes. Such parameters can affect both the signal to noise ratio and the operating condition dependence, thus they must be carefully optimized.

    Once operating conditions effects on knock indexes are known, they can be taken into account for indexes evaluation, letting emerge the plain knock effect. This compensation can be carried out in many ways: in the paper two possible methodologies are considered and compared. Both of them perform an index normalization, the first one in the time domain, the second one in the frequency domain.

    The frequency-domain normalization methodology proves to be efficient in finding operating conditions-independent knock indexes, allowing an a significant reduction of the calibration time. The time-domain methodology is more influenced by the window choice

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  • A Heat Flux Damages-Related Index

    Year: 2006

    Author: Nicolò Cavina, Enrico Corti, Luca Solieri

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    Gasoline engines can be affected, under certain operating conditions, by excessive heat flux through the combustion chamber walls, which can result in serious engine damage. Specific power and efficiency are influenced by factors such as compression ratio and spark advance regulation, that modify the combustion development over the crank angle: the trade-off between performance and the risk of irreversible damages is still a key factor in the design of both high-performance (racing) and low-consumption engines. New generation detection systems, especially based on ionization current technology, allow aggressive advance mapping and control, and future equipment, such as low-cost in-cylinder pressure transducers, will allow following that trend. Also HCCI (Homogeneous Charge Compression Ignition) engines need a sophisticated combustion monitoring methodology, since increasing BMEP levels in HCCI mode force the combustion to approach large heat-flux operation. Many methodologies can be found in the literature to recognize potentially dangerous combustions, usually based on the analysis of accelerometer, in-cylinder pressure or ionization current signals. Signals are sampled with high sample rates, than filtered, for a clear recognition of the phenomenon. Filtered signals can then be used to define damage-related indexes, by means of various types of mathematical operations. The indexes are then compared to pre-defined thresholds, for the diagnosis of dangerous combustion events. Thresholds setting is a challenging task, since most indexes are usually not intrinsically related to the damages caused by abnormal combustion events. Furthermore, the indexes values usually strongly depend on the engine operating conditions (speed and load), and thresholds must therefore vary with respect to speed and load. This paper presents a novel approach to the problem, whose objective is to define a damage-related and operating conditions-independent index. The methodology is based on the in-cylinder pressure signal, that is used for the Rate Of Heat Release evaluation. An onset condition is defined, for the dangerous phenomenon identification, and the mean thermal power released during the over-heating part of the combustion is considered as a damage intensity index. The paper shows that this parameter does not depend on the engine operating conditions, and it reaches similar values for different types of engine, under critical conditions. The index, however, must also take into account the malfunction frequency, since permanent damages are not caused by isolated events. The use of a moving average filter on the raw index is aimed at obtaining a stable output, more representative of the permanent damage risk and less influenced by the single combustion. These considerations lead to the definition of a heat flux index, strictly related to the damages caused by abnormal combustions. The diagnostic threshold value is constant over the entire operating range. Once the index is defined, it can be implemented on a control unit for real time diagnosis, or it can be used as a reference for the off-line calibration of other indexes. Examples are shown of other indexes trends and threshold calibrations over the engine operating range.

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