Gaetano Continillo

Numerical study of premixed laminar flame propagation in a closed tube with a full navier-stokes approach

This paper describes a numerical study of the dynamics of the propagation of gas flames in enclosures. The proposed model is based on a primitive-variable, pseudocompressible flow approach, with a projection method to derive an elliptic equation for the perturbation pressure. Finite-rate combustion chemistry is taken into account. The numerical solution of the model equations is conducted by means of a method, developed by the authors, based on an explicit formulation for the time-dependent balance equations, and a direct, band matrix LU solver for the pressure elliptic equation. The use of high-order upwind schemes makes it possible to keep numerical diffusion to a minimum. The model was applied to the study of the transient development of a laminar methane-air flame in a closed cylinder. Detailed numerical results are presented and analyzed to investigate aspects of flame-flow interactions. Issues addressed include the role of location and shape of the ignition zone, the influence of the tube aspect ratio on flame propagation, and the effect of wall friction in the onset of a tulip-shaped flame.

Coal dust explosions in a spherical bomb

Abstract Results of coal dust explosion experiments obtained by means of the Barknecht-Siwek 20 litre sphere are presented and discussed. Several coal dusts have been tested at ambient conditions. The oxygen mass fraction and the initial pressure have been varied to test their influence. The data collected lead to an extension of the hazard limits for coal dusts with respect to data in the current literature. The maximum explosion overpressure depends linearly on the partial pressure of atmospheric oxygen. The ‘optimum’ dust concentration depends linearly on the oxygen concentration in the suspending atmosphere. This has led to a useful non-dimensional representation of the results: in the new variables, maximum explosion overpressure data for a coal dust at various values of the initial oxygen partial pressure are correlated by a single curve for all tests in which most of the oxygen is consumed. Differences in the maximum explosion overpressure exhibited by different coals could not be related to chemical parameters due to the prevailing effect of non-adiabatic explosions in this apparatus at such low rates of pressure rise. The maximum rate of pressure rise has been found generally to increase with the standard volatile matter content and with the hydrogen content in the coal.

Construction of approximate inertial manifold by decimation of collocation equations of distributed parameter systems

Abstract A collocation method is adopted as a numerical framework to develop approximate inertial manifolds (AIMs) in the case of partial differential problems (e.g. reaction/diffusion models) containing non-polynomial nonlinearities. The spatial discretization, based on the collocation approach, is the starting point for the alternative construction of AIMs by means of a renormalization/decimation approach naturally derived from the incremental unknown method developed by Temam in a finite difference framework.

Wavelet-like collocation method for finite-dimensional reduction of distributed systems

Abstract A wavelet-like collocation method is proposed to approach the reduction of dissipative distributed systems, expressed by means of partial differential equations, applying the methods of inertial manifold theory. The collocation method proposed, based on localized trial functions, provides a convenient numerical framework to develop approximate inertial manifolds in the case of partial differential problems (e.g. reaction/diffusion models) containing nonpolynomial nonlinearities. The collocation method is based on the interpolation of concentration/temperature fields by means of Gaussian–sinc functions. As model systems, we consider reaction diffusion schemes such as the non-isothermal model for stockpile ignition and the Elezgaray–Arneodo diffusion model.

Reduced order modelling of chemical reactors with recycle by means of POD-penalty method

Abstract Spectral method based on POD are an effective approach for model reduction but variable boundary conditions are often a problem, since basis functions must satisfy boundary conditions at all times. In this work we introduce weak imposition of boundary conditions by means of a penalty method and apply the method to develop reduced order models of two different chemical reactors. A quantitative analysis shows that, by changing the values of the penalty parameters, arbitrary accuracy can be achieved at the expense of increasing CPU time. Computations can be reduced by a factor 50 at least, by maintaining still acceptable accuracy. Performance parameters of the approach appear to be model dependent.

Computation of frequency locking regions for a discontinuous periodically forced reactor

The interaction between an external periodic forcing and the natural frequencies of a reactor or system of reactors can give rise to an interesting dynamic behaviour. Particularly, the system may develop subharmonic regimes (also called resonant regimes, where the periods are exact multiples of the period of the forcing), quasi-periodic regimes and chaos. In this work, frequency locking phenomena, that is transitions between quasi-periodic regimes and resonant regimes are studied for a reactor with discontinuously and periodically forced feed. In the parameter space, regions containing resonant regimes (Arnold tongues) can be detected by means of automatic parameter continuation. The difficulties related to the discontinuous nature of the forcing are overcome by applying continuation algorithms to the (smooth) Poincare map of the system. The relationship between Floquet multipliers and rotation number of the corresponding resonant regimes is exploited to readily locate the cusps of resonance regions in a two-parameter space.

Bifurcation analysis of periodically forced systems via continuation of a discrete map

Publisher Summary This chapter explains how it is possible to reconstruct systematically the regime behavior of periodically forced systems, by applying robust continuation algorithms to an associated discrete-time system, properly constructed and implemented numerically, starting from a Poincare section of the underlying continuous time system. The approach proposed permits to identify bifurcations and to automatically trace solution branches stemming from pitchfork bifurcations. Future applications include larger systems, such as those obtained by reducing distributed parameter systems. The bifurcation study was conducted by considering as bifurcation parameter both the time of flow reversal (Zp) and the Damkohler number (Da). The continuation results are presented in the form of solution diagrams; such diagrams report a suitable norm or seminorm of the state variables versus the parameter. The chapter discusses a system of two continuous stirred-tank reactors with heat exchange between reactors and surroundings and with a periodically inverted feed. The model without feed-inversion is written in terms of mass and energy balances, and is given in dimensionless form.

ANN-based Virtual Sensor for On-line Prediction of In-cylinder Pressure in a Diesel Engine

Abstract This study presents the process design and tune-up of robust artificial neural networks (ANN) to be used as virtual sensors for the diagnosis of a three-cylinder Diesel engine operating at various conditions. Particularly, a feed-forward neural network based on radial basis functions (RBF) is employed. The use of different radial basis functions, and their relevant parameters, is investigated in detail, with their effect on the network accuracy. The RBF network is validated using data not included in training, showing good correspondence between measured and reconstructed pressure signal. The accuracy of the predicted pressure signals is analyzed in terms of mean square error and in terms of a number of pressure-derived parameters. Results are promising in terms of performance and accuracy, both for the predicted pressure signals and for the pressure-derived engine parameters that can be used in a closed loop engine control system.

Analysis of flame kinematics and cycle variation in a Port Fuel Injection Spark Ignition Engine

ABSTRACT This paper reports on the analysis of flame kinematics and cycle variation in port fuel injection (PFI) spark ignition (SI) engine. The engine was equipped with a four-valve head and with an external boost device. Different operating conditions were considered. Cycle-resolved digital imaging was used to investigate flame motion and the effects of an abnormal combustion due to the firing of fuel deposition near the intake valves and on the piston surface. Various algorithms are applied to the acquired images. Coefficients of Proper Orthogonal Decomposition (POD) were computed and used for a statistical analysis of cycle variability. The advantage is that the analysis can be run on a small number of scalar coefficients rather than on the full data set of pixel valued luminosity. POD modes are then discriminated by means of normality tests, to separate the mean from the coherent and the incoherent parts of the fluctuation of the luminosity field, in a non truncated representation of the data.

Dynamic behavior of a reaction/diffusion system: wavelet-like collocations and approximate inertial manifolds

This article develops a simple collocation method based on a non-polynomial choice of the trial functions (corresponding to localized sinc functions), and applies it in the construction of approximate inertial manifolds of a typical reaction/diffusion scheme containing non-polynomial nonlinearities.