Anders Karlström

Compensation method for attenuated planar laser images of optically dense sprays

We present a method for compensating laser attenuation in optically dense sprays, in particular for use in combustion engine research. Images of the fuel sprays are produced by planar laser imaging, where Mie scattered light from a cross section of the spray is imaged onto a CCD camera. The compensation scheme is based on the Beer-Lambert law, which is used here to sum up the loss of light along the path of the laser in the image, and to compensate iteratively, pixel by pixel, for this loss.

Realisation and estimation of piecewise-linear output-error models

Piecewise-linear systems in input/output form can have different switching schedules. In this article, two categories, instant and delayed switching, are analysed. Even though a general piecewise-linear state-space model cannot be converted into input/output form, it is shown that it is possible to find state-space models representing instant and delayed switching. In addition, a prediction-error minimisation (PEM) method for piecewise-linear output-error predictors is derived and it is concluded that the instant-switching model candidate is not necessarily the most suitable for the parameter estimation procedure.

Considerations on Engine Design and Fuelling Technique Effects on Qualitative Combustion in Alcohol Diesel Engines

The paper depicts the main topics of the experimental investigation on alcohol engine development field, aiming at the engineering targets for the emission levels. The first part of this study was focused on engine design optimization for running on ethanol mexed with poly-ethylene glycol (PEG) as ignition improver. It was shown that some design changes in compression ratio, turbine casing, injector nozzle configuration and exhaust pressure governor (EPG) activation, lead to a better engine thermodynamics and thermochemistry. The second objective of this study was the investigation of engine performance and enmission levels, when the ignition improver diethyl ether (DEE) would be generated on board via catalyticallly dehydration of ethanol, and used directly as soluble mixture or separately fumigated. Both alternatives: ether fumigation technique and dissolved ether in alcohol fuel application were conceptually analyzed, and a stand up system based on DEE fumigation was used to determine the optimum DEE-ethanol ratio at any engine operating range. The heat release investigation, when the engine was run on neat ethanol and optimum fumigated DEE, has been indicated earlier combustion, and very short ignition delay. Verified possibilities for using DEE as ignition improver, would lead to a proper version of the on board ether reactor design, which would bring to another solution for ethanol fuelled engines.

Refining models for control purposes

Many studies have been carried out with the goal of improving pulp quality control in TMP refining processes without a deeper understanding about the physical conditions inside the refining zone. The refiner is thereby considered as a black box where the chips are defibrated to fibers. In this paper, a non-linear model for the estimation of thermodynamic and defibration/fibrillation work is presented. It is shown that the model requires temperature measurements to span the energy balances and obtain reliable pressure gradients inside the refining zone. Based on process data from a single disc refiner, it is shown that the defibration/fibrillation work varies substantially along the radius of the refining segments, even though the total work, i.e. the motor load, is almost the same over the specific time sequences. This is a consequence of variations in the concentration of the fiber pad built up inside the refining zone. Moreover, it is shown that the commonly used control concept, where the traditional specific energy is used as a control variable should be reconsidered. Besides a deeper analysis about the assumptions made in the refiner modeling procedure, obtained results regarding estimated fiber concentration along the radius, consistency and steam efficiency are discussed.

Direction-dependent system modeling approaches exemplified through an electronic nose system

The modeling of processes exhibiting direction-dependent behavior is considered. Depending on the application, different models may be suitable. This brief is concerned with the use of Wiener models and piecewise-linear (PWL) models. These approaches are applied to data from an electronic nose system, for which knowledge of the physical principles is combined with system identification methods. Both models are found to provide close approximations to the behavior of the system itself.

Controllability of direction-dependent processes

In a direction-dependent process, the dynamic response depends on the input or output direction. In this paper, controllability analysis of these processes investigates the ability to govern the output in any direction, even though the input signal is bounded. A sufficient condition for the controllability of single-input, single-output, direction-dependent processes is stated and proven.

Using multi-rate filter banks to detect internal combustion engine knock

The wavelet transform is used in the analysis of the cylinder pressure trace and the ionic current trace of a knocking, single-cylinder, spark ignition engine. Using the wavelet transform offers a significant reduction of mathematical operations when compared with traditional filtering techniques based on the Fourier transform. It is shown that conventional knock analysis in terms of average energy in the time domain (AETD), corresponding to the signals energy content, and maximum amplitude in the time domain (MATD), corresponding to the maximum amplitude of the bandpass filtered signal, can be applied to both the reconstructed filtered cylinder pressure and the wavelet coefficients. The use of the filter coefficients makes possible a significant additional reduction in calculation effort in comparison with filters based on the windowed Fourier transform. A knock classification system based on the duration of the knocking process, defined as the time during which the signal exceeds an energy threshold, is presented using different scales. An advantage of this method is that the relation of the duration between different frequency bands can be used to draw conclusions about the presence of multiple knock.

Piecewise-Linear Output-Error Models

Abstract Piecewise-linear systems in input/output form can have different switching schemes. In this paper two categories, instant and delayed switching, are analysed. Even though a general piecewise-linear state-space model cannot be converted into input/output form, it is shown that it is possible to find state-space models representing instant as well as delayed switching. In addition, a prediction-error minimisation (PEM) method for piecewiselinear output-error predictors is derived and it is concluded that the instant-switching model candidate is not necessarily the most suitable for the parameter estimation procedure.

Control strategies for refiners Part I: Soft sensors for CD-refiner control

Abstract Internal variables in (C)TMP-refining processes (e. g. temperature, consistency, fiber residence time, backward flowing steam and forces acting upon the chips and pulp) are defined as physical states obtained in different parts of the refining zones. In short, they differ from the traditional external variables (e. g. dilution water feed rate and specific energy) which are not obtained from measurements or physical models of the process in the refining zone. The internal variables are the backbone of physical models and are used in this paper as soft sensors for advanced process control. Besides the shape of the temperature profile, the position of the maximum temperature and the shape of the consistency profiles inside the refining zones are important to control as they are directly linked to the development of different pulp and handsheet properties. To illustrate the capability when using combined modeling and control strategies, the concept is applied on a full scale CD82 refiner. This means both temperature and consistency control in the flat zone and the conical zone, together with an overall estimator for fiber development. Finally, in this paper it is shown that the production can be increased significantly without changing the refiner motor load nor violating the pulp property specification.

Refiner optimization and control Part IV: Long term follow up of control performance in TMP processes

This paper focuses on three important issues; Process understanding in relation to control of nonlinear processes; Natural decoupling by using internal state measurement devices; Long term follow up procedures of process control investments. As an example, a new control system for Thermo Mechanical Pulp (TMP) refiners is used, based on a cascaded control structure. The internal states, in this case the refining zone temperature profiles, are controlled in the inner loop whereas the outer loop handles pulp properties. The characteristics of the temperature profile dynamics makes it possible to introduce a decoupling scheme where the anti-diagonal elements in the transfer function matrix describing the process, can be eliminated naturally. The system can handle several pulp propertied simultaneously but in this study mean fiber length (MFL) is the target variable. The process is followed about 200 days in manual mode control and 200 days in automatic mode. It is shown that the standard deviations in the pulp property variables freeness (CSF) and MFL were decreased about 40 and 60%, respectively. Significant reductions in variability of shives and a motor load standard deviations was achieved. On top of this, an increased production was obtained and the control system runnability was raised from 50% to 98%, levels that are far from commercial MPC-control concepts in TMP refining control.