Fabio Chiara

A review of energy consumption, management, and recovery in automotive systems, with considerations of future trends:

In response to the current and future energy and environment challenges, the automotive industry is strongly focusing on improving the fuel efficiency of vehicles. Although the electrification of automotive powertrains is clearly the principal path towards sustainable transportation, many opportunities still exist to improve the fuel economy of conventional vehicles. However, some of the technical solutions representing the state of the art in research and advanced development are difficult to benchmark in terms of their potential benefits for fuel consumption improvement. A greater understanding of the fuel energy utilization on the vehicle (here intended as a ‘system’ ) is therefore necessary in order to identify the readily available opportunities for efficiency improvements and, ultimately, to develop automobiles which are more fuel efficient. To this extent, this paper presents a review of the state of the art and technology trends in the field of energy management and recovery for automotive systems, with the primary focus on conventional powertrains. An understanding of the fuel energy utilization and dissipation associated with the vehicle subsystems (the engine, transmission, and chassis) is provided, as well as an overview of the opportunities and potential challenges in improving the fuel economy through system-level energy management, recovery, and harvesting. Finally, an overview of the most important solutions for managing energy dissipation, energy recovery, and harvesting is presented, discussing their potential for fuel economy improvement, technical readiness, and challenges. Wherever possible, projections on fuel economy improvements, based on either experimental data or simulations, are reported to provide opportunity for the assessment and comparison of current and future technologies.

Development and experimental validation of a control-oriented Diesel engine model for fuel consumption and brake torque predictions

This article describes the development and experimental validation of a control-oriented, real-time capable, Diesel engine instantaneous fuel consumption and brake torque model under warmed-up conditions with only two inputs: torque request and the engine speed and no other measurements. Such a model, with the capability of reliably and computationally efficiently estimating the aforementioned variables at both steady-state and transient engine-operating conditions, can be utilized in the context of real-time control and optimization of hybrid power train systems. Although Diesel engine dynamics are highly non-linear and very complex, by considering the Diesel engine and its control system, that is, engine control unit together as an entity, it becomes possible to predict the engine instantaneous fuel consumption and torque based on only those two inputs. A synergy between different modelling methodologies including physically based grey-box and data-driven black-box approaches were integrated in the Diesel engine model. The fuelling and torque predictions have been validated by means of experimental data from a medium-duty Diesel engine at both steady-state and transient operations, including engine start-ups and shutdowns.

An exhaust manifold pressure estimator for a two-stage turbocharged Diesel engine

The exhaust manifold pressure is a crucial variable for turbocharged Diesel engines, affecting the torque production and the emissions through variations in the EGR mass flow and in the residual mass fraction in the cylinder. This variable is therefore considered very relevant for closed-loop EGR and turbocharger control. However, in production applications, the cost of the pressure sensor and the particularly harsh environment where this must work are practical barriers to its actual implementation. Therefore, the need for a rapid, reliable and robust estimation of this variable from low-cost production sensors is strong, above all, in the contest of advanced engine powertrains. This work describes the development of an estimator for the exhaust manifold pressure in a turbocharged Diesel engine with two-stage turbocharger. The approach proposed relies on a feed-forward scheme based on the inversion of a two-stage turbocharger model, which includes the radial turbines, nozzles and valves. Calibration and validation results of the estimator are presented in both steady-state and transient operating conditions.

DYNAMICS AND CONTROL OF DI AND HCCI COMBUSTION IN A MULTI-CYLINDER DIESEL ENGINE

Abstract Homogeneous Charge Compression Ignition (HCCI) is a new combustion concept that, in the last few years, has attracted more and more attention for its potential to reduce NOx and PM emissions without penalizing the engine efficiency. HCCI is a viable technology that combines the advantages of both compression ignition and spark ignition engines to meet future stringent emissions regulations. It can be accomplished using both gasoline and Diesel fuels, and it is based on the combustion of a homogeneous charge without using external ignition devices. Because of the great complexity of the control issues related to this process, further investigation is still required to apply the technology to automotive engines. The present work deals with a novel engine concept based of integrating the traditional Common Rail direct injection with an innovative external injection based on a highly effective atomization device. An optimized control of these injection strategies allows the engine to run in pure HCCI mode at low loads, with a consistent reduction of exhaust emissions, as well as in conventional DI mode at high loads without compromising performance. In addition, the possibility of simultaneously controlling both injection modes allows an operating range where the advantages of HCCI can be extended to medium loads. The paper presents an experimental analysis that proves the effectiveness of this new concept and constitutes a valid reference for further modeling and control studies.

System analysis and optimization of Variable Geometry Compressor for turbocharged diesel engines

Variable Geometry Compressors (VGC) have been recently considered as a solution for downsized, turbocharged engines to improve the stability of the compressor and increase its efficiency at low engine speed without compromising the operation at peak loads. This paper presents a system analysis of the air path dynamics of an automotive Diesel engine equipped with exhaust gas recirculation (EGR) variable geometry turbine (VGT) and VGC system. Starting from a validated model of the engine air path dynamics, a reduced-order model is designed to facilitate system analysis and control design. Then, a study of the steady-state and dynamic response of the air path system is conducted to understand the combined influence of the EGR-VGT-VGC actuators on the performance and transient behavior of the system. Finally, a multivariable optimization is performed to define a simple open-loop control strategy for the air path system. The work shown in this paper is intended as a preliminary study for the design of feedback control algorithms, which coordinate the available actuators to optimize the engine performance and the stability of the compressor.

Experimental Validation for Control-Oriented Modeling of Multi-Cylinder HCCI Diesel Engines

Homogeneous Charge Compression Ignition (HCCI) is a combustion process based on a lean, homogeneous, premixed charge reacting and burning uniformly throughout the mixture volume. This principle leads to a consistent decrease in NOx and PM emissions, while the combustion efficiency remains comparable to traditional Compression Ignition Direct Injection (CIDI) engines at low and mid-load operations. However, understanding and controlling the combustion process is still extremely difficult, as well as finding a proper method for the fuel introduction. A viable method consists of premixing the charge by applying a proper fuel atomization device in the intake port, thus decoupling the HCCI mixture formation from the traditional in-cylinder injection. This avoids the traditional drawbacks associated to external Diesel mixture preparation, such as high intake heating, low compression ratio, wall wetting, and soot formation. The system, previously developed and tested on a single-cylinder engine, has been successfully applied to multi-cylinder Diesel engine for automotive applications. Building on previous modeling and experimental work, the paper reports a detailed experimental analysis of HCCI combustion with external mixture formation. In the considered testing setup, the fuel atomizer has been applied to a four-cylinder turbo-charged Common Rail Diesel engine equipped with a cooled EGR system. In order to extend the knowledge on the process and to provide a large base of data for the identification of Control-Oriented Models, Diesel-fueled HCCI combustion has been characterized over different values of loads, EGR dilution and boost pressures. The data collected were then used for the validation of a HCCI Diesel engine model that was previously built for steady state and transient simulation and for control purposes. The experimental results obtained, especially considering the emission levels and efficiency, suggest that the technology developed for external mixture formation is a feasible upgrade for automotive Diesel engines without introducing additional design efforts or constraints on the DI combustion and injection system.Copyright

Surge index and compressor efficiency estimation for Diesel engines with variable geometry compressor system

Variable geometry turbochargers are a well established technology for Diesel engine systems to optimize the energy recovery over a large operating range. More recently, Variable Geometry Compressors (VGC) systems are being considered as a further improvement of automotive turbochargers for their potential of providing a more direct control over the stability margin and the efficiency of the compressor. In particular, a direct control on the stability margin allows to size the compressor more aggressively to obtain better peak performances. When such an aggressive design is adopted the control of the VGC to prevent surging becomes essential and a reliable Surge Index (SI) estimator needs to be included in the control algorithm. This paper presents two estimator designs for an automotive Diesel engine equipped with a variable geometry compressor. The estimators aim at tracking the value of two important performance variables, namely the Surge Index and the compressor efficiency. The first estimator design relies on an open-loop scheme that is based on the analytical inversion of a grey-box model for the prediction of the compressor flow and efficiency maps. The second estimator is a Kalman filter observer that allows to improve estimation performances when sensor measurements are corrupted by noise. Simulation results are provided in steady-state and transient conditions to verify the accuracy and robustness of the estimators and compare their performances.

Set-Point Generation Using Kernel-Based Methods for Closed-Loop Combustion Control of a CIDI Engine

Closed-loop control of diesel combustion is of great interest for improving conventional Diesel engine combustion as well as facilitating new combustion modes such as Homogenous Charge Compression Ignition and other low NOx regimes. Most generalized feedback control systems that can be applied to this problem require a reference or set-point which the control attempts to achieve. Diesel engines are well known for having many degrees of freedom which poses a problem in generating valid set-points for all possible conditions encountered in practice. This problem is compounded by the fact that these set-points are usually determined in steady state operation further limiting the space where set-points can be defined. Kernel-based methods are applied to this problem as a method of generating valid setpoints when operating in regions outside of the space where set-points are defined. This is most useful during transient conditions where conditions such as exhaust gas recycle level, manifold air flow, and fuel mass are far from the steady state values.© 2009 ASME

Optimal Performance of Cylinder-by-Cylinder and Fuel Bank Controllers for a CIDI Engine

At present, Diesel engine combustion in most production engines is controlled via open-loop control. Increasing pressure from tightening emissions standards and on-board diagnosis requirements has made closed-loop combustion a possibility for production engines in the near future. For new combustion concepts, such as Homogeneous Charge Compression Ignition and other low NOx regimes, the need for closed-loop combustion control is very strong. In this work, the applicability of closed-loop combustion control for controlling the variability between cylinders in conventional Diesel combustion is explored through the use of a high-fidelity engine model. The problem is formulated such that the optimal performance of two different closed-loop control concepts can be evaluated through optimization rather than via control design. It is found that, for the types of disturbances occurring in a non-faulty engine, that control of individual cylinders leads to small performance gains compared to fuel bank control.Copyright

Energy-Based Modeling of Alternative Energy Storage Systems for Hybrid Vehicles

Alternative energy storage systems (AESS) are receiving considerable interest today for low-cost mild-hybrid vehicles where the electrical system is substituted with mechanical or hydraulic energy storage. As these technologies are being explored, simulation tools become helpful to predict the behavior of the energy storage system during vehicle use, as well as to conduct comparative studies evaluating the energy and power density, fuel economy improvement, system weight and costs. This paper presents an energy-based modeling approach to characterize the low-frequency dynamic behavior of alternative energy storage systems for hybrid vehicle applications, with the ability to predict the energy flows and sources of energy loss during driving operations. The model aims at evaluating the potential, in terms of efficiency and fuel economy improvement, offered by non-electrified energy storage systems, such as mechanical (flywheels) or hydraulic (accumulators). The modeling tool developed is able to provide a characterization of the performance of each of the two systems starting from a characterization of the components energy conversion behavior. The paper includes a simulation study where the performance of a mechanical and hydraulic energy storage system are compared on a forward-oriented hybrid vehicle simulator, with the objective of characterizing and comparing the energy recuperation process and the energy efficiency of the two systems.Copyright