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Research

  • A Control-Oriented Knock Intensity Estimator

    Year: 2017

    Author: Enrico Corti, Claudio Forte, Gian Marco Bianchi, Lorenzo Zoffoli

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    The performance optimization of modern Spark Ignition engines is limited by knock occurrence: heavily downsized engines often are forced to work in the Knock-Limited Spark Advance (KLSA) range. Knock control systems monitor the combustion process, allowing to achieve a proper compromise between performance and reliability. Combustion monitoring is usually carried out by means of accelerometers or ion sensing systems, but recently the use of cylinder pressure sensors is also becoming frequent in motorsport applications. On the other hand, cylinder pressure signals are often available in the calibration stage, where SA feedback-control based on the pressure signal can be used to avoid damages to the engine during automatic calibration.
    A predictive real-time combustion model could help optimizing engine performance, without exceeding the allowed knock severity. Several knock models are available in the literature: most of those proposed for real-time applications are single zone or two-zone models, grounded on more complex CFD simulations. However, since the knock phenomenon is influenced by several factors, the real-time determination of KLSA requires the model to be adapted to the engine actual behavior. The approach proposed in the present paper, is based on the constant adaptation of a two-zone model to measured cylinder pressure data: typical results of the indicating analysis, available cycle-by-cycle and cylinder-by-cylinder, are used as inputs for the model, with the aim of predicting KLSA for the current running condition, without exceeding the maximum allowed knock intensity.
    The approach has been applied to indicating data referring to non-knocking, light and heavy knocking conditions, showing a good prediction capability.

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  • Investigation of Water Injection Effects on Combustion Characteristics of a GDI TC Engine

    Year: 2017

    Author: Nicolo Cavina, Nahuel Rojo, Andrea Businaro, Alessandro Brusa, Enrico Corti, Matteo De Cesare

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    This paper presents simulation and experimental results of the effects of intake water injection on the main combustion parameters of a turbo-charged, direct injection spark ignition engine. Water injection is more and more considered as a viable technology to further increase specific output power of modern spark ignition engines, enabling extreme downsizing concepts and the associated efficiency increase benefits. The paper initially presents the main results of a one-dimensional simulation analysis carried out to highlight the key parameters (injection position, water-to-fuel ratio and water temperature) and their effects on combustion (in-cylinder and exhaust temperature reduction and knock tendency suppression). The main results of such study have then been used to design and conduct preliminary experimental tests on a prototype direct-injection, turbocharged spark ignition engine, modified to incorporate a new multi-point water injection system in the intake runners. The experiments allowed to validate the model results, demonstrating the effectiveness of the proposed technology, and to further investigate on the mechanisms that allow controlling thermal load and knocking tendency by varying the water-to-fuel ratio.

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  • Zero-Dimensional Model for Dynamic Behavior of Engineered Rubber in Automotive Applications

    Year: 2017

    Author: L. Zoffolia, E. Corti, D. Moro, F. Ponti, V. Ravagliolia

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    This paper presents a zero-dimensional model for the simulation of the mechanical behavior of automotive engineered rubber components, such as flexible couplings. The objective is to develop a real-time-capable model, able to simulate the behavior of a driveline containing elastomer components: the engineered rubber model has to correlate stretch to stress, the mechanical behavior being represented by means of a hysteresis cycle. The study presents the implementation of Maxwell and Voigt models, showing their limits in the representation of the material behavior: elastomers present a nonlinear response in the relationship stress-strain. A combination of Maxwell and Voigt models, with stiffness and damping variable according to the stress and strain rate, to represent nonlinear material responses, is coupled to a relaxation model, in order to represent the Mullins effect (the rubber mechanical behavior also depends on load history).

    Experimental tests have been carried out with different pre-load settings, stress amplitudes and stress frequencies. Tests results have been used to calibrate the parameters defining the simulation model, comparing the model outputs to experimental data: an optimization algorithm has been applied, with the aim of minimizing the results discrepancy with respect to experimental results. The optimization tool has been also used to reduce the number of parameters defining the model, in order to simplify the required computational power, avoiding at the same time over-parametrization.

    In the second section of the paper, the model is used for the simulation of a different rubber component, whose behavior is identified using quasi-static load ramps, frequency and amplitude sweeps, steps and random cycles. An alternative model formulation, minimizing the degrees of freedom is then applied to the new dataset. The model parameters are separately optimized using different tests, in order to capture the specific mechanical behavior. Finally, the identified parameters are used to simulate the elastomer response in random tests, comparing the results to experimental data, to evaluate the simulation quality in terms of RMSE.

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  • Investigation of Knock Damage Mechanisms on a GDI TC Engine

    Year: 2017

    Author: Cavina, N., Rojo, N., Ceschini, L., Balducci, E. et al

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    The recent search for extremely efficient spark-ignition engines has implied a great increase of in-cylinder pressure and temperature levels, and knocking combustion mode has become one of the most relevant limiting factors. This paper reports the main results of a specific project carried out as part of a wider research activity, aimed at modelling and real-time controlling knock-induced damage on aluminium forged pistons. The paper shows how the main damage mechanisms (erosion, plastic deformation, surface roughness, hardness reduction) have been identified and isolated, and how the corresponding symptoms may be measured and quantified. The second part of the work then concentrates on understanding how knocking combustion characteristics affect the level of induced damage, and which parameters are mainly responsible for piston failure. For this purpose, steady-state tests have been conducted controlling different and constant levels of knock intensity (i.e., pressure waves oscillation amplitude) and thermal load (i.e., average temperature and pressure levels inside the combustion chamber). Since these parameters are strictly interrelated for a given engine operating condition and for a given fuel, fuels with different knock resistance (i.e., RON number) have been employed, to allow a clearer understanding of the damage distribution in the knock intensity-thermal load domain.

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  • Individual Cylinder Air-Fuel Ratio Control for Engines with Unevenly Spaced Firing Order

    Year: 2017

    Author: Nicolo Cavina, Francesco Ranuzzi, Matteo De Cesare, Enrico Brugnoni

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    The most recent European regulations for two- and three-wheelers (Euro 5) are imposing an enhanced combustion control in motorcycle engines to respect tighter emission limits, and Air-Fuel Ratio (AFR) closed-loop control has become a key function of the engine management system also for this type of applications.
    In a multi-cylinder engine, typically only one oxygen sensor is installed on each bank, so that the mean AFR of two or more cylinders rather than the single cylinder one is actually controlled. The installation of one sensor per cylinder is normally avoided due to cost, layout and reliability issues. In the last years, several studies were presented to demonstrate the feasibility of an individual AFR controller based on a single sensor. These solutions are based on the mathematical modelling of the engine air path dynamics, or on the frequency analysis of the lambda probe signal.
    This work presents a novel approach that has been developed specifically for engines with big-bang (or unevenly spaced) firing order, which is typically adopted in motorcycle applications with either V (all of them) or in-line cylinder configuration. This approach is much simpler if compared to previously published solutions, because it doesn’t require a mathematical model of the air path dynamics, it doesn’t need high computational resources, and it is reliable and robust up to high engine speeds, which are often reached in motorcycle engines.
    The control algorithm was developed, designed and tested in a simulation environment, by means of a 1-D model of a twin-cylinder motorcycle engine, and then real-time implemented and experimentally validated on the vehicle.

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  • Model Based Control of Intake Air Temperature and Humidity on the Test Bench

    Year: 2017

    Author: E. Corti, M.Taccioli, L. Marogna, N. Cavina, V. Ravaglioli

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    Engine test benches are crucial instruments to perform tests on internal combustion engines. Possible purposes of these tests are to detect the engine performance, check the reliability of the components or make a proper calibration of engine control systems managing the actuations. Since many factors affect tests results in terms of performance, emissions and components durability, an engine test bench is equipped with several conditioning systems (oil, water and air temperature, air humidity, etc.).

    One of the most important systems is the HVAC (Heating, Ventilating and Air Conditioning), that is essential to control the conditions of the intake air. Intake air temperature, pressure and humidity should be controllable test parameters, because they play a key role on the combustion development. In fact, they can heavily affect the performance detected, such as power and specific consumption, and, in some cases, they may promote knock occurrence.

    This work presents an HVAC model-based control methodology, where each component of the air treatment system (humidifier, pre-heating and post-heating resistors, chiller and fan) is managed coupling open-loop and closed-loop controls. Each branch of the control model is composed of two parts, the first one to evaluate the target for the given HVAC component, based on the system physical model, the second one is a PID controller based on the difference between the set-point and the feedback values.

    The control methodology has been validated on an engine test bench where the automation system has been developed on an open software Real-Time compatible platform, allowing the integration of the HVAC control with all other functionalities concerning the test management. The paper shows the plant layout, details the control strategy and finally analyzes experimental results obtained on the test bench, highlighting the benefits of the proposed HVAC management approach.

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  • Combustion and Intake/Exhaust Systems Diagnosis Based on Acoustic Emissions of a GDI TC Engine

    Year: 2016

    Author: Nicolò Cavina, Andrea Businaro, Nahuel Rojo, Matteo De Cesare, Luigi Paiano, Alberto Cerofolini

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    Due to increasingly stringent emission regulations and the need for more efficient powertrains, engine control systems that have been developed during the recent years have become more and more sophisticated. Obtaining accurate information about the combustion process and about all the subsystems that compose the engine can be considered key to reach the maximum overall performance. Low-cost in-cylinder pressure and turbo speed sensors are being developed, but they still present long-term reliability issues, and represent a considerable part of the entire engine management system cost. Sound emissions represent an extremely rich information source about the operating conditions of all the subsystems that comprise the entire engine. The paper shows how it is possible to extract fundamental information regarding the combustion process (such as knock and misfire), turbo speed, and air path fault at the same time, by performing an appropriate analysis of the engine acoustic emissions acquired from the very same microphone, which can thus be considered as an innovative, multifunction, and low-cost sensor for automotive applications.

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  • Analysis of Pre-ignition Combustions Triggered by Heavy Knocking Events in a Turbocharged GDI Engine

    Year: 2016

    Author: Nicolò Cavina, Nahuel Rojo, Andrea Businaro, Lorella Ceschini, Eleonora Balducci, Alberto Cerofolini

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    In this paper, a pre-ignition sequence with detrimental effects on the engine has been analysed and described, with the aim of identifying the main parameters involved in damaging the combustion chamber components. The experiment was carried out in a wider research context, focused on knock damage mechanisms in turbocharged GDI engines. The pre-ignition sequence was a consequence of a high knock condition, induced at high load at 4500 rpm. The abnormal thermal load due to knock caused overheating of the whole combustion chamber, until the spark plug electrodes became a “hot spot”, resulting in premature flame initiation in the following cycles, with a self-sustaining mechanism. Slight cylindrical differences, mainly in terms of volumetric efficiency, allowed comparisons and correlations between indicated parameters, pre-ignition sequence and damage. The main responsible in damaging the engine, in this case and for this engine, is the extremely high heat transferred to the walls in the pre-ignited cycles, characterized by higher mean temperatures. Heavy knock triggered the pre-ignited combustions but progressively reduced its intensity as the spontaneous ignition advance increased, thus having a secondary role in damaging directly the combustion chamber.

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