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Research

  • Guidelines for Integration of Kinetic Energy Recovery System (KERS) based on Mechanical Flywheel in an Automotive Vehicle Technical Paper 05/05/2010 D

    Year: 2010

    Author: Davide Moro, Nicolò Cavina, Igor Trivić, Vittorio Ravaglioli

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    In order to increase overall energy efficiency of road vehicles, new systems that are able to recover vehicle's kinetic energy usually lost in dissipating process of frictional braking are being developed. This study was done to look at the effects of integrating Mechanical Flywheel-based Kinetic Energy Recovery System (KERS) into an automotive vehicle. Possible system architectures, due to different connection point of the KERS into the vehicle driveline, were proposed and investigated. Interaction of the system main components (IC engine, vehicle Gearbox, KERS subsystems) was analyzed and explained. In particular, three plots are proposed to introduce a graphical representation that can help the project manager to understand the effect of different parameter values related to the main system components on the overall system behavior during energy transfer from the vehicle to KERS and back.

    Thermal Management Strategies for SCR After Treatment Systems
    Technical Paper
    08/09/2013
    Nicolo Cavina, Giorgio Mancini, Enrico Corti, Davide Moro, Matteo De Cesare, Federico Stola
    While the Diesel Particulate Filter (DPF) is actually a quasi-standard equipment in the European Diesel passenger cars market, an interesting solution to fulfill NOx emission limits for the next EU 6 legislation is the application of a Selective Catalytic Reduction (SCR) system on the exhaust line, to drastically reduce NOx emissions.

    In this context, one of the main issues is the performance of the SCR system during cold start and warm up phases of the engine. The exhaust temperature is too low to allow thermal activation of the reactor and, consequently, to promote high conversion efficiency and significant NOx concentration reduction. This is increasingly evident the smaller the engine displacement, because of its lower exhaust system temperature (reduced gross power while producing the same net power, i.e., higher efficiency).

    The proposal of the underlying work is to investigate and identify optimal exhaust line heating strategies, to provide a fast activation of the catalytic reactions on SCR. The main constrain is to limit the potential fuel consumption increase, and possibly to even increase global efficiency, and the chosen application is a small EU5-compliant diesel engine.

    After an initial investigation, the research has been focused on main combustion control parameters, rather than on post-oxidation processes associated with late injections, in an effort to reduce eventual fuel penalties. The effect of each relevant engine control parameter has been analyzed on the test bench, observing the results in terms of exhaust system temperature and fuel efficiency. After this preliminary identification phase, different calibration strategies have been tested on the vehicle, executing several NEDC cycles. The most relevant comparisons are illustrated and critically discussed in the paper.

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  • Common Rail Multi-Jet Diesel Engine Combustion Development Investigation for MFB50 On-board Estimation

    Year: 2010

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

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    Proper design of the combustion phase has always been crucial for Diesel engine control systems. Modern engine control strategies' growing complexity, mainly due to the increasing request to reduce pollutant emissions, requires on-board estimation of a growing number of quantities. In order to feedback a control strategy for optimal combustion positioning, one of the most important parameters to estimate on-board is the angular position where 50% of fuel mass burned over an engine cycle is reached (MFB50), because it provides important information about combustion effectiveness (a key factor, for example, in HCCI combustion control).
    In modern Diesel engines, injection patterns are designed with many degrees of freedom, such as the position and the duration of each injection, rail pressure or EGR rate. In this work a model of the combustion process has been developed in order to evaluate the energy release within the cylinder as a function of the injection parameters. In this case a zero-dimensional approach has been chosen, because it allows obtaining a model accurate enough for the analysis, with a low computational cost. Once the combustion model has been developed, it can be used to evaluate the cumulated heat release and, consequently, MFB50.
    MFB50 can also be evaluated using in-cylinder pressure sensors, nevertheless they would account for a relevant part of the whole engine control system's cost. On the contrary, if MFB50 is evaluated as a function of the injection parameters, the methodology does not require any additional cost. Therefore, the aim of this work is to develop a zero-dimensional combustion model, and verify if the level of accuracy obtained in MFB50 evaluation is compatible with engine management requirements.

     

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

    Year: 2010

    Author: Nicolò Cavina, Enrico Corti, Davide Moro

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    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.

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  • A statistical approach to spark advance mapping

    Year: 2010

    Author: Enrico Corti, Claudio Forte

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    Engine performance and efficiency are largely influenced by combustion phasing. Operating conditions and control settings influence the combustion development over the crankshaft angle; the most effective control parameter used by electronic control units to optimize the combustion process for spark ignition engines is spark advance (SA). SA mapping is a time-consuming process, usually carried out with the engine running in steady state on the test bench, changing SA values while monitoring brake mean effective pressure, indicated mean effective pressure (IMEP), and brake specific fuel consumption (BSFC). Mean values of IMEP and BSFC for a test carried out with a given SA setting are considered as the parameters to optimize. However, the effect of SA on IMEP and BSFC is not deterministic, 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. Finally, other elements such as engine or components aging, and disturbances like air-to-fuel ratio or air, water, and oil temperature variations could affect the tests results; this facet can be very significant for racing engine testing. This paper presents a novel approach to SA mapping with the objective of improving the performance analysis robustness while reducing the test time. The methodology is based on the observation that, for a given running condition, IMEP can be considered a function of the combustion phasing, represented by the 50% mass fraction burned (MFB50) parameter. Due to cycle-to-cycle variation, many different MFB50 and IMEP values are obtained during a steady state test carried out with constant SA. While MFB50 and IMEP absolute values are influenced by disturbance factors, the relationship between them holds, and it can be synthesized by means of the angular coefficient of the tangent line to the MFB50-IMEP distribution. The angular coefficient variations as a function of SA can be used to feed a SA controller, able to maintain the optimal combustion phasing. Similarly, knock detection is approached by evaluating two indexes; the distribution of a typical knock-sensitive parameter (maximum amplitude of pressure oscillations) is related to that of CHRNET (net cumulative heat release), determining a robust knock index. A knock limiter controller can then be added in order to restrict the SA range to safe values. The methodology can be implemented in real time combustion controllers; the algorithms have been applied offline to sampled data, showing the feasibility of fast and robust automatic mapping procedures.

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  • Validation of a lagrangian ignition model in si engine simulations

    Year: 2010

    Author: Claudio Forte, Gian Marco Bianchi, Enrico Corti

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    Ignition process plays a key role in flame kernel formation and heavily affects further combustion development. The paper aim is to present a 1D lagrangian ignition model and to validate it against real engine configurations. A lump model for the electrical circuit of the spark plug is used to compute breakdown and glow energy. At the end of shock wave and very first plasma expansion, a spherical kernel is deposited inside the gas flow at spark plug location. A simple model allows computing initial flame kernel radius and temperature based on physical mixture properties and spark plug characteristics. The sphere surface of the kernel is discretized by triangular elements which move radially according to a lagrangian approach. Expansion velocity is computed accounting for both heat conduction effect at the highest temperatures and thermodynamic energy balance at relatively lower temperatures. Turbulence effects and thermodynamic properties of the air-fuel mixture are accounted for. Restrikes are possible depending on gas flow velocity and mixture quality at spark location. CFD solver and 1D/lagrangian ignition model are closely coupled at each time step. The model proves to strongly reduce the grid sensitivity. The CFD model validation phase is crucial for a correct representation of both kernel formation and combustion development: the operation has been carried out by means of an accurate statistical analysis of experimental in-cylinder pressure data in real engine configurations.

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