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Research

  • Misfire and Partial Burn Detection based on Ion Current Measurement

    Year: 2011

    Author: Nicolo Cavina, Luca Poggio, Giovanni Sartoni

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    The paper presents the implementation of a combustion diagnosis system that integrates crankshaft speed oscillations analysis with ion current signal processing, for V8 and V12 high performance engines.
    Ion current sensing has been introduced in the last V8 and V12 Ferrari models in order to improve combustion control by implementing ion current based closed-loop spark-advance control systems, both under knocking and non-knocking conditions (respectively based on measured knocking level, and on ion current peak position control).
    Another area where ion current sensing can improve the engine controller performance is related to the ability of detecting and isolating missing and partial burn combustions. The typical approach to misfire detection (based on engine speed oscillation measurement) is in fact particularly critical for engines with a large number of cylinders, and ion current sensing provides additional information not only about presence (or absence) of combustion, but also about the causes that generated the fault. Moreover, the paper shows that real-time analysis of specific ion current signal features allows isolating incomplete and inefficient combustion events, thus providing extremely useful information to the engine control system, which can for example be used to activate multi-spark discharge ignition mode.
    The first part of the paper shows the main critical aspects of speed-measurement based misfire detection, and introduces the ion current signal main features during regular engine operation. Then, ion current signal is analyzed during abnormal combustion events: absence of combustion (both due to missing injections and missing ignitions) and partial burn cycles. It is shown how it is possible to isolate missing and incomplete combustions in a relatively straightforward way, and also how the causes that induced the fault may be isolated by integrating standard diagnostic functions with specific ion current signal processing algorithms. Finally, the performance of the diagnostic system that integrates engine speed oscillation analysis and information extracted from the ion signal has been evaluated during on-board tests, and the main results are presented at the end of the paper.

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  • Development of a Multi-Spark Ignition System for Reducing Fuel Consumption and Exhaust Emissions of a High Performance GDI Engine

    Year: 2011

    Author: Nicolo Cavina, Enrico Corti, Luca Poggio, Daniele Zecchetti

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    The paper presents the development and real-time implementation of a combustion control system based on optimal management of multiple spark discharge events, in order to increase combustion stability, reduce pollutant emissions and fuel consumption, and avoid partial or missing combustion cycles.

    The proposed approach has been developed as a cost-effective solution to several combustion-related issues that affect Gasoline Direct Injection (GDI) engines during cold start and part load operation. The problem of optimizing combustion efficiency and improving its stability during such operating modes is even more critical for high performance engines, which are designed to maximize charge efficiency especially at medium-high engine speeds.

    The main benefits that have been achieved by introducing and optimizing a multi-spark ignition mode can be summarized as follows: missing and partial burn combustions elimination, combustion variability minimization, HC emissions reduction (also due to absence of misfiring events), NOx emissions reduction (mainly due to the possibility of increasing residual gas fraction), significant specific fuel consumption reduction (especially during very low load operation - brake mean effective pressure around 0.5∼1.0 bar - and during cold start operation).

    Finally, the paper introduces the idea of extracting from ion current signals information related to combustion instability, which can be used to activate multi-spark mode, and to identify the optimal charge-discharge sequential pattern.

    The main characteristics of the rapid control prototyping system that has been developed to demonstrate the feasibility and the effectiveness of the proposed solution are synthesized in the first part of the paper, while the multi-spark pattern calibration process and the main experimental results are shown next, both during test cell and on-board operation.

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  • Model-Based Assessment of Hybrid Powertrain Solutions

    Year: 2011

    Author: Oliver Dingel, Joerg Ross PhD, Igor Trivic, Nicolo Cavina, Mauro Rioli

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    This paper shows the main results of a research activity carried out in order to investigate the impact of different hybridization concepts on vehicle fuel economy during standard homologation cycles (NEDC, FTP75, US Highway, Artemis). Comparative analysis between a standard passenger vehicle and three different hybrid solutions based on the same vehicle platform is presented. The following parallel hybrid powertrain solutions were investigated: Hybrid Electric Vehicle (HEV) solution (three different levels of hybridization are investigated with respect to different Electric Motor Generator size and battery storage/power capacity), High Speed Flywheel (HSF) system described as a fully integrated mechanical (kinetic) hybrid solution based on the quite innovative approach, and hydraulic hybrid system (HHV). In order to perform a fare analysis between different hybrid systems, analysis is also carried out for equal system storage capacities. All hybrid powertrain architectures include state-of-the-art hybrid components and are analyzed from the aspects of fuel economy related to the overall system efficiency, load point moving of the internal combustion engine due to energy flow control strategy operation, and regenerative braking (applying realistic drivability constraints). The simulations were performed within the IAV-VeLoDyn software environment. VeLoDyn (Vehicle Longitudinal Dynamics Simulation) is a modular and highly flexible Simulink-based software tool, which offers a straightforward simulation of longitudinal vehicle dynamics with special considerations on the driveline and model management functionality. In order to provide control and management of the hybrid powertrain system, a cycle-independent control strategy has been implemented into the supervisory hybrid control unit model, based on Equivalent Consumption Minimization Strategy (ECMS) approach. Due to the modular nature of the simulation tool, the control strategy was effectively implemented in all analyzed hybrid models with marginal modifications. In order to determine energy flows and validate hybrid powertrain behavior, a cycle-based energetic analysis was carried out, and the main results are presented in the paper.

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  • Development and Validation of a Methodology for Real-Time Evaluation of Cylinder by Cylinder Torque Production Non-Uniformities

    Year: 2011

    Author: Fabrizio Ponti, Matteo De Cesare, Vittorio Ravaglioli

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    Modern internal combustion engine control systems require on-board evaluation of a large number of quantities, in order to perform an efficient combustion control. The importance of optimal combustion control is mainly related to the requests for pollutant emissions reduction, but it is also crucial for noise, vibrations and harshness reduction. Engine system aging can cause significant differences between each cylinder combustion process and, consequently, an increase in vibrations and pollutant emissions. Another aspect worth mentioning is that newly developed low temperature combustion strategies (such as HCCI combustion) deliver the advantage of low engine-out NOx emissions, however, they show a high cylinder-to-cylinder variation. For these reasons, non uniformity in torque produced by the cylinders in an internal combustion engine is a very important parameter to be evaluated on board.
    This work describes a methodology that allows determining the difference between torque delivered by each cylinder and the mean value. These differences can be caused by different reasons, such as different air breathing or deposits on the injectors that do not allow injecting the desired quantity. Once the differences in cylinder to cylinder torque production have been evaluated, the engine control system can adopt the interventions that are needed to re-establish the nominal behavior.
    The methodology presented in this paper requires no additional cost, because it is based on engine speed fluctuations measurement, that can be performed using the same phonic wheel already mounted on-board. This approach has been validated on an L4 Common Rail Multi-Jet Diesel engine mounted on-board a vehicle. In order to quantify the accuracy of torque non-uniformities estimation, specifically designed tests have been performed acquiring the instantaneous engine speed and the in-cylinder pressure signals (that allow evaluating indicated torque delivered by each cylinder) simultaneously.
    The presented approach has been applied to a Common Rail Diesel engine, nevertheless this methodology is general, and it is suitable for torque non-uniformities evaluation in spark ignited engines as well.

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  • Torsional Analysis of Different Powertrain Configurations for Torque and Combustion Phase Evaluation

    Year: 2011

    Author: Vittorio Ravaglioli, Fabrizio Ponti, Federico Stola

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    This paper presents the results of several studies, performed on different powertrain configurations, aimed at analyzing the correlations existing between torque and speed frequency components in an internal combustion engine. Engine speed fluctuations depend in fact on torque delivered by each cylinder, therefore it is easy to understand how these two quantities are directly connected.
    The presented methodology allows identifying a dynamic model, expressed as a transfer function that depends only on the structure of the engine-driveline system. The identified model can be used to obtain information about torque delivered by the engine and combustion positioning within the engine cycle starting from engine speed measurement. The speed signal is picked up directly from the sensor facing the toothed wheel that is already mounted on the engine for control purposes.
    This is a methodological approach, therefore it can be applied to engines with different powertrain configurations, both Compression Ignition and Spark Ignition.
    In order to clarify all the critical aspects related to the application of the methodology, this work reports the results obtained applying it to 5 different engine - driveline configurations. Many tests were performed both on Compression Ignition and Spark Ignition engines, taking also into account one case in which combustions are not evenly spaced. After having evaluated indicated torque and its harmonic components from in-cylinder pressure signals, it was possible to identify the relationship between torque and speed frequency components for all the analyzed configurations. Influence of the type of combustion performed has been discussed, as well as the effects related to cylinder filling and firing sequence.

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  • MFB50 On-Board Evaluation Based on a Zero-Dimensional ROHR Model

    Year: 2011

    Author: Vittorio Ravaglioli, Davide Moro, Gabriele Serra, Fabrizio Ponti

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    In modern Diesel engine control strategies the guideline is to perform an efficient combustion control, mainly due to the increasing request to reduce pollutant emissions. Innovative control algorithms for optimal combustion positioning require the on-board evaluation of a large number of quantities. In order to perform closed-loop combustion control, one of the most important parameters to estimate on-board is MFB50, i.e. the angular position in which 50% of fuel mass burned within an engine cycle is reached. Furthermore, MFB50 allows determining the kind of combustion that takes place in the combustion chamber, therefore knowing such quantity is crucial for newly developed low temperature combustion applications (such as HCCI, HCLI, distinguished by very low NOx emissions). The aim of this work is to develop a virtual combustion sensor, that provides MFB50 estimated value as a function of quantities that can be monitored real-time by the Electronic Control Unit (ECU).
    Modern technologies for Common Rail Multi-Jet Diesel engines allow designing injection patterns with many degrees of freedom, due to the large number of tunable injection parameters (such as rail pressure, start and duration of each injection….). First, this paper describes a model of the combustion process developed in order to evaluate the energy release within the cylinder. A zero-dimensional approach based on the Wiebe function has been chosen, because it allows obtaining a model which is accurate enough for the analysis at a low computational cost. Once the combustion model has been developed it can be used to determine MFB50. The second section of this paper describes the existing correlations between the injection parameters and the identified Wiebe parameters. These correlations can be used for heat release and MFB50 on board estimation.
    Experimental tests have been performed running a turbocharged Common Rail Multi-Jet Diesel engine (with up to 4 injections within the same engine cycle) in order to determine the accuracy of the methodology.
    The described approach allows evaluating MFB50 as a function of the injection parameters as well as other quantities that can be monitored real-time by the ECU. Additional sensors are not necessary for this methodology, therefore it requires no extra cost.

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  • Idle Stalling Phenomena in High Performance Spark Ignition PFI Engines: an Experimental Analysis

    Year: 2011

    Author: Enrico Corti, Claudio Forte

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    High performance Spark Ignition (SI) Port-Fuel Injected (PFI) internal combustion engines are usually optimized to deliver high power output at high speed in Wide Open Throttle (WOT) conditions. However, they also have to run consistently at idle, possibly with stoichiometric Air-Fuel Ratio (AFR), in order to limit tailpipe emissions. The two requirements are sometimes conflicting, as it is difficult to match high-speed volumetric efficiency with low-speed turbulence: the intake runner size and shape are often designed for performance, meaning that usually they do not guarantee a satisfying air-fuel mixing at idle. The consequence of poor mixture formation may be high cycle-to-cycle variation or misfiring, with obvious consequences on pollutant emissions and driveability. In the worst cases, however, the consequence could be even more serious: stalling phenomena have been observed on the test bench. While running at idle, the engine suddenly stops: the event is so quick that the idle controller is not able to react.
    The paper shows a detailed experimental analysis of stalling phenomena, based on engine speed, intake pressure, in-cylinder pressure, ion current information. Intake and in-cylinder pressure data show that stalling phenomena are related to anomalous combustions taking place during the compression stroke: the negative torque generated by such combustions is able to stop the engine. Further analysis show that these phenomena are triggered by defined conditions: a partial combustion releasing little heat and leading to a constant pressure exhaust stroke seems to be a necessary condition to ignite the undesired combustion. Ion current signals show that the combustion extends during the exhaust stroke, and continues throughout the following intake and compression strokes.
    The sensitivity of the phenomenon to changes in the injection layout suggests that its origin is related to the process of mixture formation. The presence of a large amount of liquid fuel in the cylinder could lead to diffusive combustions, maintained throughout the exhaust stroke and the subsequent intake stroke, thus resulting in a backfire.
    The Rate Of Heat Release (ROHR) analysis based on in-cylinder pressure confirms that the frequency of the phenomenon is higher in the cylinder where more liquid fuel is likely to be accumulated.

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  • Real-Time Combustion Phase Optimization of a PFI Gasoline Engine

    Year: 2011

    Author: Enrico Corti, Claudio Forte

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    Combustion control is assuming a crucial role in reducing engine tailpipe emissions and maximizing performance. The number of actuations influencing the combustion is increasing, and, as a consequence, the control parameters calibrations is becoming challenging.
    One of the most effective factors influencing performance and efficiency is the combustion phasing: gasoline engines Electronic Control Units (ECU) manage the Spark Advance (SA) in order to set the optimal combustion phase. SA optimal values are usually determined by means of calibration procedures carried out on the test bench by changing SA values while monitoring Brake and Indicated Mean Effective Pressure (BMEP, IMEP), Brake Specific Fuel Consumption (BSFC) and pollutant emissions. The effect of SA on combustion is stochastic, due to the cycle-to-cycle variation: the analysis of mean values requires many engine cycles to be significant of the performance obtained with the given control setting. Usually, the optimization process is carried out off-line, based on the data sampled on the test-bench.
    This paper presents the application of a new calibration concept, with the objective of improving the robustness of performance analysis, while reducing the test time. The approach is applied to a simple calibration problem, where a single input factor (SA) is tuned taking into account two issues: IMEP maximization and knock limitation. The paper shows how the methodology can be extended to multiple objective and multi-input optimization problems.
    The methodology is based on the observation that, due to cycle-to-cycle variation, the combustion phasing, represented by the 50% Mass Fraction Burned (MFB50) parameter, changes continuously, even with a fixed SA. The IMEP changes accordingly, forming a typical parabola distribution in the plane IMEP-MFB50. The optimization could then be carried out by choosing SA values maintaining the scatter around the vertex. Unfortunately the distribution shape is slightly influenced by heat losses (i.e., by SA): this effect must be taken into account in order to avoid over-advanced calibrations.
    The synthesis of this core-concept allows giving a contribution to a cost function, used to drive SA variations; another contribution comes from the knock intensity level. The final objective is to minimize the cost function absolute value, leading to the maximum IMEP achievable with tolerable knock intensity. The optimization process is carried out with an original approach: the cost function is by all means the error input of a PID (Proportional Integer Derivative) controller that, by definition, is intended to reduce the error, i.e., the cost function, thus performing the optimization.The methodology has been developed and tested off-line using data referring to three different PFI gasoline engines, then it has been implemented in Real-Time. The combustion control system used for the implementation performs a cycle-to-cycle combustion analysis, evaluating the combustion parameters necessary to calculate the target SA; the target SA is then actuated by the ECU. The approach proved to be efficient, reducing the number of engine cycles necessary for the calibration to less than 1000 per operating condition.

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