1,721,090 research outputs found
Robust Modeling for Optimal Control of Parallel Hybrids With Dynamic Programming
Full text linkThe aim of this work is to provide insight and guidelines for engineers and researchers when developing hybrid
powertrain models to be employed in a dynamic programming optimal control algorithm. In particular, we focus on the advantages and disadvantages of the various control sets that can be used to characterize the power flow (e.g. the engine torque or a
torque-split coefficient).
Dynamic programming is the reference optimal control technique for hybrid electric vehicles. However, its practical implementation is not exempt from numerical issues which may hamper its accuracy. Amongst these, some are directly related to the different modeling choices that can be made when defining the system dynamics of the powertrain.
To treat these issues, we first define four relevant evaluation criteria: control bounds definition, numerical efficiency, model complexity and interpretability. Then, we introduce eight different control sets and we discuss and compare them in light of these criteria. This discussion is supported by an extensive set of numerical experiments on a p2 parallel hybrid. Finally, we revisit our analysis and simulation results to draw modeling recommendations
Driveability Constrained Models for Optimal Control of Hybrid Electric Vehicles
Full text linkThis work investigates the effect of three different driveability constraints on the optimal energy management strategy for a p2 parallel hybrid. Two of these constraints are used to prevent frequent gear shifting and engine start/stops, while the third is used to increase the sportiness of the vehicle by maximizing the available torque reserve at all times. The constraints are imposed by reformulating them as penalty terms to be added to the base running cost of the control strategy, which is fuel consumption. Dynamic programming, a popular optimal control technique, is then used to design the energy management strategy that minimizes the total cost. A case study is developed for a p2 parallel hybrid and simulated on a combination of the Artemis driving cycles. The impact of each driveability constraint is analyzed with respect to a set of relevant features of the control strategy, such as the choice of engine operating points and the gear shift pattern. The resulting discussion provides some useful insight for the design of real-time, rule-based control strategies
Development and assessment of a new methodology for end of combustion detection and its application to cycle resolved heat release analysis in IC engines
No full textThe heat release analysis has proved to be a powerful diagnostic tool for the analysis of the combustion process in spark ignition engines. Still, a fine tuning of the heat transfer correlations embedded in the heat release models is necessary for a correct diagnostic analysis of the pressure signal. To that end, a new methodology has been developed and assessed to properly locate the end of combustion on the basis of the heat release intensity. The results produced by the proposed method have been compared to those obtained by applying different methodologies available in the literature. The newly developed method has proved to be accurate and consistent and has allowed a reliable estimation of the end of combustion on a cycle-by-cycle basis. An extensive burn rate analysis has also been accomplished by means of a heat release model previously developed and purposely modified to embed the new end of combustion detection procedure. The main combustion related quantities have been considered for the experimental investigation to appropriately quantify the engine cyclic variability as a function of the relative air-to-fuel ratio. The experimental tests have been performed on a naturally aspirated 2L engine featuring a fast-burn combustion chamber and running on gasoline and natural gas as well as on a 1.2L turbocharged natural gas engine displaying a disk shaped combustion chamber. The diagnostic tool has proved to properly match the nonlinear behavior of the quantities related to the combustion duration in the cycle-resolved analysis and a general good agreement with previous works has emerged as far as the coefficient of variations of the main combustion parameters are concerned. Moreover, thanks to the automatic facet the proposed methodology retains, it is strongly recommended when an extensive cycle-by-cycle and cylinder-to-cylinder analysis needs to be performed. Finally, regardless of the considered fuel, the heat release model embedding the EOC detection procedure proved to be capable of properly detecting the combustion features induced by a fast-burn combustion chamber with respect to a traditional one. As a matter of fact, smaller Δθ10-90% values and an overall reduced cyclic dispersion were highlighted for the 2L engin
Development of a method for the estimation of the behavior of a CNG engine over the NEDC cycle and its application to quantify for the effect of hydrogen addition to methane operations
No full textThe current pollutant regulations and policies have set the need to consider the use of alternative fuels capable of complying with the emission limits still retaining appreciable engine performance. Natural gas has been considered as an effective alternative to gasoline but the drawbacks connected to its use forced the researchers to investigate into fuel additives, dual fuel solutions and innovative engine control strategies. The present work analyzes the use of hydrogen as an additive to CNG for a natural gas production engine of a C-segment vehicle and carries out a thorough investigation into the engine response over a selection of operating key points. The actual focus is set on the investigation into the vehicle as well as into the engine response and performance over driving cycles. Still, the simulation of real driving conditions would set the need to properly quantify for the effect of the hydrogen enriched blends on the full engine map over varying powers and speeds within the vehicle driving cycle. Such an approach often turns out to be too demanding in terms of time and costs and an alternative solution has been hereafter proposed by properly selecting a reduced number of operating points on the basis of the correspondent residence time and frequency over the NEDC. The selection has been performed by matching the actual engine map to the readings from the NEDC vehicle testing. Different selections have been considered and compared so as to assess for the one embedding the minimum number of working points. The key points are not meant to substitute the accomplishment of the NEDC cycle but are to be used as driving factors in the engine design so as to allow for detecting the optimal hardware and ECU configurations. The so considered engine key points have hence been extensively studied by reproducing the engine performance at the test bench and by performing a detailed heat release analysis. Different composition of the hydrogen-methane blends have been considered up to a 25% by volume of hydrogen in the mixture and specific attention has been paid to the main combustion parameters and to their optimization. As a matter of fact, such a study would allow for detecting major trends in the engine design and control strategies to compensate for the poor behavior of some of the considered points. As an example, low load and speed operations assessed for the need of a better control of the engine parameters to diminish the cylinder-to-cylinder as well as the cycle-to-cycle variabilit
Development and application of a method for characterizing mixture formation in a port-injection natural gas engine
Full text linkNatural gas has been identified as one of the most promising alternative fuels. Port injection of natural gas, due to
its advantages of costs, manufacturing complexity and mixture homogeneity, is relevant to the current and future
engine development. The present work aims to provide a comprehensive characterization of gas fuel injection
and mixing process, by developing a modeling method for the injector and the engine as a whole serving as a
diagnostic tool for further expounding on the basis of experimental results. The injector is modeled by the source
cell approach that allows for cost-efficient and physics-consistent description of the underexpanded gas jet, by
which a set of fuel injection timings is investigated and then compared with a conventional premixed case. Two
mechanisms peculiar to gas port injection are characterized, being firstly the two-stage mixing process that involves immediate induction of the residual fuel from the previous engine cycle and delayed induction of the fuel
injected in the current cycle, and secondly the limited fuel penetration speed along the intake ports with associated delay of charge induction. Additional information on volumetric efficiency, mixture quality, coherent flow
motion and turbulence level is highlighted. It is concluded that the otherwise intuitive correlation between injection timing and mixture homogeneity for port injection is complicated by those two mechanisms, and,
depending on specific engine design and operating point, differences resulted from modeling the engine operation with fuel injection and with premixed charge may prove combustion-significant. The method and the
underlying mechanisms found herein are equally applicable to other combustion systems involving port injection
of gaseous fuels
DynaProg: Deterministic Dynamic Programming solver for finite horizon multi-stage decision problems
Full text linkDynaProg is an open-source MATLAB toolbox for solving multi-stage deterministic optimal decision
problems using Dynamic Programming. This class of optimal control problems can be solved with
Dynamic Programming (DP), which is a well-established optimal control technique suited for highly
non-linear dynamic systems. Unfortunately, the numerical implementation of Dynamic Programming
can be challenging and time consuming, which may discourage researchers from adopting it. The
toolbox addresses these issues by providing a numerically fast DP optimization engine wrapped in
a simple interface that allows the user to set up an optimal control problem in a straightforward yet
flexible environment, with no restrictions on the controlled system’s simulation model. Therefore, it
enables researchers to easily explore the usage of Dynamic Programming in their fields of expertise.
Thorough documentation and a set of step-by-step examples complete the toolbox, thus allowing for
easy deployment and providing insight of the optimization engine. Finally, the source code’s classoriented
design allows researchers experienced in Dynamic Programming to extend the toolbox if
needed
Development and validation of a semi-empirical model for the estimation of particulate matter in diesel engines
No full textA semi-empirical correlation for the estimation of PM (particulate matter) emissions in diesel engines, as a function of significant engine operating variables, has been developed and validated on a GM (General Motors) Euro 5 diesel engine. The experimental data used in the present study have been acquired at the dynamic test bench of ICEAL-PT (Internal Combustion Engine Advanced Laboratory at the Politecnico di Torino), in the frame of a research activity with GMPT-E (General Motors PowerTrain-Europe) for the calibration of a Euro 5 prototype 2.0 liter diesel engine equipped with a twin-stage turbine and a piezo-driven Common Rail injection system. The experimental data were acquired for six key-points representative of the engine working conditions over a NEDC (New European Driving Cycle). The experimental tests have been carried out according to the Design of Experiment approach and for each point several variation lists of the main engine variables have been considered. As a first step, the main engine variables which are expected to be related to the formation and oxidation of PM have been identified. An exponential mathematical model has then been introduced and a detailed statistical analysis has been carried out for each key-point in order to identify the most robust combination of the input variables among all the possible ones. It was verified that PM emissions are correlated to a great extent to the value of the chemical heat release at the end of the injection of the main pulse. This quantity is in fact related to the mass of burned gases which is generated by the oxidation of the pilot pulses that precede the main injection. Such a mass can have a large impact on the local oxygen concentration and temperature of the charge in which the fuel of the main pulse is injected, with a consequent effect on PM formation. Additional quantities have also been considered in the investigation: the relative air-to-fuel ratio k, the intake charge oxygen concentration, the accumulated fuel mass, the equivalence ratio of the spray at the main pulse start of combustion and some combustion metrics related to the heat release rate. At the end of the statistical analysis, the most influencing parameters have been selected and a semiempirical model to predict the in-cylinder formed PM mass has been developed. The model has hence been tested under both steady-state and transient condition
Numerical Analysis of a Flow Control System for High-Pressure Turbine Vanes Subject to Highly Oscillating Inflow Conditions
Full text linkUnder the prism of introducing pioneering technologies in the propulsive field, the Rotating Detonation Engine (RDE) continuously attracts the Gas Turbine (GT) research community. However, how to effectively couple an RDE with High Pressure Turbine (HPT) stages is still debated. In fact, time dependent flow conditions from the RDE greatly affect turbine performance, thus reducing the positive impact of Pressure Gain Combustion (PGC) on the overall cycle efficiency. The present numerical work aims at analysing both the impact of a pulsating inflow on the performance of a newly designed high pressure turbine vane and the effectiveness of a flow control system in governing the oscillations within the vane passage. First, a baseline vane capable to ingest high enthalpy flow at an inlet Mach number of 0.6 is introduced. A total number of 297 samples are generated by varying the 18 geometrical parameters that characterize the vane endwalls and airfoil profile with the help of Latin Hypercube sampling method. Then, an optimization strategy is performed using steady inflow conditions allows for minimizing vane loss coefficient, thus providing the final geometry of the new vane. In the second part of the work, a flow control system is proposed by placing a series of holes in the endwalls of the vane. Air at constant stagnation conditions is injected upstream of vane leading edge. Unsteady calculations with and without flow control, including similar pulsating conditions from the RDE provide an insight to the generation and evolution of the secondary flow structures inside of the passage. The main outcome of this analysis is that the flow control system intensifies the passage vortices providing less oscillating flow at the vane exit section, which is beneficial for the aerodynamic performance of a subsequent blade row
MPC-Based Cooperative Longitudinal Control for Vehicle Strings in a Realistic Driving Environment
No full textThis paper deals with the energy efficiency of cooperative cruise control technologies when considering vehicle strings in a realistic driving environment. In particular, we design a cooperative longitudinal controller using a state-of-the-art model predictive control (MPC) implementation. Rather than testing our controller on a limited set of short maneuvers, we thoroughly assess its performance on a number of regulatory drive cycles and on a set of driving missions of similar length that were constructed based on real driving data. This allows us to focus our assessment on the energetic aspects in addition to testing the controller’s robustness. The analyzed controller, based on linear MPC, uses vehicle sensor data and information transmitted by the vehicle driving the string to adjust the longitudinal trajectory of the host vehicle to maintain a reduced inter-vehicular distance while simul- taneously optimizing energy efficiency. To keep our controller
as close as possible to a real-life deployable technology, we also consider passenger comfort in our MPC design, which is a relevant aspect that is often a conflicting objective with respect
to energy efficiency. Our simulation scenario is characterized by a homogeneous string of three battery electric vehicles and was modelled in a MATLAB/Simulink environment. An extensive set of simulation experiments forms the basis for our discussion on the energy-saving potential of cooperative driving automation systems
- …
