Nicolò Cavina

Residual Gas Fraction Estimation: Application to a GDI Engine with Variable Valve Timing and EGR

The paper presents an original review and extension of existing mathematical models for on-line residual gas fraction estimation. The resulting model has first of all been extended to take into account also the presence of externally recirculated exhaust gas (external EGR), and then critically analyzed to highlight the importance of a correct Intake Valve Opening and Exhaust Valve Closing effective position identification. As shown in the paper, such quantities may be evaluated by using experimental data, either acquired in the test-cell or on a valve flow bench. The main objective is to obtain a simple and reliable model (that could be run in real time within the engine control unit) also in presence of Variable Valve Timing (VVT, both on intake and exhaust valves) and external Exhaust Gas Recirculation (EGR) systems. In fact, the two main contributions to residual gas fraction (backflow of the burned gas during the valve overlap period, and amount of gas trapped within the cylinder) are strongly affected by intake and exhaust valves timing, and EGR flow should be taken into account in order to determine the total exhaust gas mass within the cylinder at IVC. Therefore, real time estimation of residual gas mass and composition is crucial for designing VVT and EGR management strategies that allow an optimal control of the combustion process. The new model has been applied to experimental data acquired on a 3.2 liter V6 GDI engine, equipped with intake and exhaust Variable Valve Timing systems. Tests were performed throughout the engine operating range for different combinations of intake and exhaust valve timings, while varying EGR flow. Model results are in good agreement with other measured quantities (such as Spark Advance angle and NO x emissions), and the proposed approach therefore represents a powerful tool for on-board optimal combustion control.

Closed-loop individual cylinder air–fuel ratio control via UEGO signal spectral analysis

The paper presents the development and real time application of an original closed-loop individual cylinder AFR control system, based on a spectral analysis of the lambda sensor signal. The observation that any type of AFR disparity between the various cylinders is reflected in a specific harmonic content of the AFR signal spectrum, represents the starting point of the project. The results observed on a 4 cylinder Spark Ignition engine are encouraging, since in the investigated engine operating conditions the controller is able to reduce AFR inequality below 0.01 lambda. The paper also shows how the proposed controller can be applied to other engine configurations.

Analysis of a Dual Mass Flywheel System for Engine Control Applications

Dual Mass Flywheel (DMF) systems are today widely adopted in compression ignition automotive powertrains, due to the well-known positive effects on vehicle drivability and fuel consumption. This work deals with the analysis of undesirable effects that the installation of a DMF may cause to engine and transmission dynamics, with the objective of understanding the causes and of determining possible solutions to be adopted. The main results of an experimental and simulation analysis, focused on the rotational dynamics of a powertrain equipped with a DMF system, are presented in the paper. A mathematical model of the physical system has been developed, validated, and used to investigate, in a simulation environment, the anomalous behavior of the powertrain that had been experimentally observed under specific conditions. Particular attention has been devoted to two aspects that are considered critical: ○ engine cranking phase; ○ interactions between powertrain dynamics and idle speed control. Experimental tests have initially been carried out in a laboratory environment, to characterize the performance (both static and dynamic) of the DMF system under study. On-board tests have subsequently been performed on a vehicle whose powertrain is equipped with the same DMF. During on-board tests, signals preprocessed by the Electronic Control Unit have been recorded together with analog signals sampled at higher frequency with an external device.

A methodology for increasing the signal to noise ratio for the misfire detection at high speed in a high performance engine

Abstract The paper presents a methodology for pre-processing the combustion time intervals, that is the basic signal used in misfire detection strategies, with the aim of increasing the signal-to-noise ratio to enable a more efficient misfire diagnosis, especially when the engine is running at high speeds and low loads. The performance of the basic misfire detection algorithm shows that in those engine operating conditions the background noise amplitude has approximately the same value of the information related to the misfire presence, thus hiding the misfire event that may not be detected. The proposed methodology is based on the correction of the combustion time signal cycle-by-cycle, using a vector of data that take into account the specific behavior of every cylinder. The vector of data for the combustion time correction is stored in a map inside the control unit and could be continuously updated with an auto-adaptive learning technique.

Full Load Performance Optimization Based on Turbocharger Speed Evaluation via Acoustic Sensing

Turbocharger performance optimization on passenger car engines is particularly challenging, especially in case of severe engine downsizing and downspeeding.On high performance engines (e.g., heavy duty truck applications) turbocharger speed measurement is usually performed with the aim of maximizing engine power and torque, limiting turbocharger over-speed, which is harmful for its durability and reliability. This solution is too expensive for passenger cars, and the turbocharger speed sensor is typically not available.In this work, an innovative and low cost sensing chain for the rotational speed evaluation of the turbocharger is applied. With this information, obtained via an acoustic sensor, a new turbocharger control architecture has been developed to optimize turbocharger performance, in order to improve engine output torque under full load conditions.After a brief description of the new sensing chain and of the electronic components developed to manage this kind of information, the paper shows the new control architecture that takes advantage of the turbocharger speed information.Moreover, experimental results on a small turbocharged Diesel engine for passenger car applications are presented, demonstrating the achieved benefits.Copyright

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

Abstract 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.

A framework for the iterative dynamic optimisation of diesel engines: numerical methods, experimental setup, and first results

Owing to the many degrees of freedom provided by current engine systems and to the need to consider transientoperation,derivingan engine calibration has become a tedioustask. Controltrajectoriesresultingfromthesolutionof anoptimal-control problem provide a guideline to the calibration engineer, serve as a benchmark, and might be used for a partial automation of the calibration procedure. The common approach to dynamic optimisation consists of solving a single optimal-control problem. However, this approach requires the availability of models that are valid throughout the whole engine operating range and actuator ranges. In addition, the result of the optimisation is meaningful only if the model is very accurate. We propose a methodology to circumvent those demanding requirements: an iteration between transient measurements to refine a purpose-built model and a dynamic optimisationwhich is constrainedto themodel-validityregion.This paper presents all numerical methods required to implement this procedure. The crucial steps are analysed in detail, and the most important caveats are indicated. Finally, an experimental validation demonstrates the applicability of the method and reveals the components that require further development.

Wind-Hydro-Gas Turbine Unit Commitment to Guarantee Firm Dispatchable Power

The randomness and intermittence of wind power require additional reserves provided by thermal generators. This creates difficult scheduling of generation, causing thermal generators to start up or shut down frequently, or to operate at low efficiency and high fuel consumption state. If not, some wind power will be curtailed and wasted. This paper examines the operation of a hybrid system made up of a wind farm, a pump storage hydro and conventional thermal generation units consisting in a combination of a heavy-duty and an aeroderivative gas turbines.In order to seek an optimal approach to deal with the uncertainty of increasing wind power and ensure both the efficient operation of thermal generators and full use of wind energy, two different control strategies have been proposed and compared: (i) a “custom” in house developed strategy and (ii) an “optimal” strategy based on Dynamic Programming.Using actual generation data of a wind farm, the operation of hydro power plant and gas turbines are obtained with the aim of compensating differences between actual wind generation and load demanded. Natural gas fuel consumption and average gas turbine efficiencies during the analyzed time period are calculated along with number of units starts-up.© 2014 ASME

Diesel Engine Combustion Sensing Methodology Based on Vibration Analysis

The increasing request for pollutant emissions reduction spawned a great deal of research in the field of combustion control and monitoring. As a matter of fact, newly developed low temperature combustion strategies for Diesel engines allow obtaining a significant reduction both in particulate matter and NOx emissions, combining the use of high EGR rates with a proper injection strategy. Unfortunately, due to their nature, these innovative combustion strategies are very sensitive to in-cylinder thermal conditions. Therefore, in order to obtain a stable combustion, a closed-loop combustion control methodology is needed.Many works demonstrate that a closed-loop combustion control strategy can be based on real-time analysis of in-cylinder pressure trace, that provides important information about the combustion process, such as start of combustion, center of combustion and torque delivered by each cylinder. Nevertheless, cylinder pressure sensors on-board installation is still uncommon, due to problems related to unsatisfactory measurement long term reliability and cost.This paper presents a newly developed approach that allows extracting information about combustion effectiveness through the analysis of engine vibrations. In particular, the developed methodology can be used to obtain an accurate estimation of the indicated quantities of interest combining the information provided by engine speed fluctuations measurement and by the signals coming from acceleration transducers mounted on the engine.This paper also reports the results obtained applying the whole methodology to a light-duty turbocharged Common Rail Diesel engine.Copyright

Numerical model for hybrid rocket internal ballistic

In order to predict the propulsion characteristic of an hybrid rocket, the knowledge of its internal ballistic is essential. The purpose of this work is to write a numerical code, in FORTRAN environment, in order to predict and analyze the propulsion characteristics of the rocket itself. The thermo-fluid dynamics is performed using a zero-dimension non steady model and it is coupled with a mono-dimensional quasi-steady one. In contrast with other codes, in this, one a moving combustion surface is used, in order to better model the internal fluid-dynamic during all the simulation itself. Even though, due to the high complexity level, some approximation are used. Finally the code is validate and set, with good final results, using some real tests having GOX and HTPB as oxidizer and fuel.