DSpace Collection:
https://dspace.lboro.ac.uk/2134/5807
Tue, 28 Mar 2017 19:38:12 GMT2017-03-28T19:38:12ZEngine thermal management with model predictive control
https://dspace.lboro.ac.uk/2134/24274
Title: Engine thermal management with model predictive control
Authors: Abdul-Jalal, Rifqi I.
Abstract: The global greenhouse gas CO2 emission from the transportation sector is very significant.To reduce this gas emission, EU has set an average target of not more than 95 CO2/km for new passenger cars by the year 2020. A great reduction is still required to achieve the CO2 emission target in 2020, and many different approaches are being considered. This thesis focuses on the thermal management of the engine as an area that promise significant improvement of fuel efficiency with relatively small changes.
The review of the literature shows that thermal management can improve engine efficiency through the friction reduction, improved air-fuel mixing, reduced heat loss, increased engine volumetric efficiency, suppressed knock, reduce radiator fan speed and reduction of other toxic emissions such as CO, HC and NOx. Like heat loss and friction, most emissions can be reduced in high temperature condition, but this may lead to poor volumetric efficiency and make the engine more prone to knock. The temperature trade-off study is conducted in simulation using a GT-SUITE engine model coupled with the FE in-cylinder wall structure and cooling system. The result is a map of the best operating temperature over engine speed and load. To quantify the benefit of this map, eight driving styles from the legislative and research test cycles are being compared using an immediate application of the optimal temperature, and significant improvements are found for urban style driving, while operation at higher load (motorway style driving) shows only small efficiency gains. The fuel consumption saving predicted in the urban style of driving is more than 4%.
This assess the chance of following the temperature set point over a cycle, the temperature reference is analysed for all eight types of drive cycles using autocorrelation, lag plot and power spectral density. The analysis consistently shows that the highest volatility is recorded in the Artemis Urban Drive Cycle: the autocorrelation disappears after only 5.4 seconds, while the power spectral density shows a drop off around 0.09Hz. This means fast control action is required to implement the optimal temperature before it changes again.
Model Predictive Control (MPC) is an optimal controller with a receding horizon, and it is well known for its ability to handle multivariable control problems for linear systems with input and state limits. The MPC controller can anticipate future events and can take control actions accordingly, especially if disturbances are known in advance. The main difficulty when applying MPC to thermal management is the non-linearity caused by changes in flow rate. Manipulating both the water pump and valve improves the control authority, but it also amplifies the nonlinearity of the system.
Common linearization approaches like Jacobian Linearization around one or several operating points are tested, by found to be only moderately successful. Instead, a novel approach is pursued using feedback linearization of the plant model. This uses an algebraic transformation of the plant inputs to turn the nonlinear systems dynamics into a fully or predominantly linear system. The MPC controller can work with the linear model, while the actual control inputs are found using an inverse transformation.
The Feedback Linearization MPC of the cooling system model is implemented and testing using MathWork Simulink®. The process includes the model transformation approach, model fitting, the transformation of the constraints and the tuning of the MPC controller. The simulation shows good temperature tracking performance, and this demonstrates that a MPC controller with feedback linearization is a suitable approach to thermal management. The controller strategy is then validated in a test rig replicating an actual engine cooling system.
The new MPC controller is again evaluated over the eight driving cycles. The average water pump speed is reduced by 9.1% compared to the conventional cooling system, while maintaining good temperature tracking. The controller performance further improves with future disturbance anticipation by 20.5% for the temperature tracking (calculated by RMSE), 6.8% reduction of the average water pump speed, 47.3% reduction of the average valve movement and 34.0% reduction of the average radiator fan speed.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Fri, 01 Jan 2016 00:00:00 GMThttps://dspace.lboro.ac.uk/2134/242742016-01-01T00:00:00ZBrittle mixed-mode cracks between linear elastic layers
https://dspace.lboro.ac.uk/2134/24177
Title: Brittle mixed-mode cracks between linear elastic layers
Authors: Wood, Joseph D.
Abstract: Original analytical theories are developed for partitioning mixed-mode fractures on rigid interfaces in laminated orthotropic double cantilever beams (DCBs) based on 2D elasticity by using some novel methods. Note that although the DCB represents a simplified case, it provides a deep understanding and predictive capability for real applications and does not restrict the analysis to a simple class of fracture problems. The developed theories are generally applicable to so-called 1D fracture consisting of opening (mode I) and shearing (mode II) action only with no tearing (mode III) action, for example, straight edge cracks, circular blisters in plates and shells, etc. A salient point of the methods is to first derive one loading condition that causes one pure fracture mode. It is conveniently called the first pure mode. Then, all other pure fracture modes can be determined by using this pure mode and the property of orthogonality between pure mode I modes and pure mode II modes. Finally, these 2D-elasticity-based pure modes are used to partition mixed-mode fractures into contributions from the mode I and mode II fracture modes by considering a mixed-mode fracture as the superposition of pure mode I and mode II fractures. The partition is made in terms of the energy release rate (ERR) or the stress intensity factor (SIF).
An analytical partition theory is developed first for a DCB composed of two identical linear elastic layers. The first pure mode is obtained by introducing correction factors into the beam-theory-based mechanical conditions. The property of orthogonality is then used to determine all other pure modes in the absence of through-thickness-shear forces. To accommodate through-thickness shear forces, first two pure through-thickness-shear-force pure modes (one pure mode I and one pure mode II) are discovered by extending a Timoshenko beam partition theory. Partition of mixed-mode fractures under pure through-thickness shear forces is then achieved by using these two pure modes in conjunction with two thickness-ratio-dependent correction factors: (1) a shear correction factor, and (2) a pure-mode-II ERR correction factor. Both correction factors closely follow a normal distribution around a symmetric DCB geometry. The property of orthogonality between all pure mode I and all pure mode II fracture modes is then used to complete the mixed-mode fracture partition theory for a DCB with bending moments, axial forces and through-thickness shear forces.
Fracture on bimaterial interfaces is an important consideration in the design and application of composite materials and structures. It has, however, proved an extremely challenging problem for many decades to obtain an analytical solution for the complex SIFs and the crack extension size-dependent ERRs, based on 2D elasticity. Such an analytical solution for a brittle interfacial crack between two dissimilar elastic layers is obtained in two stages. In the first stage the bimaterial DCB is under tip bending moments and axial forces and has a mismatch in Young s modulus; however, the Poisson s ratios of the top and bottom layers are the same. The solution is achieved by developing two types of pure fracture modes and two powerful mathematical techniques. The two types of pure fracture modes are a SIF-type and a load-type. The two mathematical techniques are a shifting technique and an orthogonal pure mode technique. In the second stage, the theory is extended to accommodate a Poisson s ratio mismatch. Equivalent material properties are derived for each layer, namely, an equivalent elastic modulus and an equivalent Poisson s ratio, such that both the total ERR and the bimaterial mismatch coefficient are maintained in an alternative equivalent case. Cases for which no analytical solution for the SIFs and ERRs currently exist can therefore be transformed into cases for which the analytical solution does exist. It is now possible to use a completely analytical 2D-elasticity-based theory to calculate the complex SIFs and crack extension size-dependent ERRs.
The original partition theories presented have been validated by comparison with numerical simulations. Excellent agreement has been observed. Moreover, one partition theory is further extended to consider the blister test and the adhesion energy of mono- and multi-layered graphene membranes on a silicon oxide substrate. Use of the partition theory presented in this work allows the correct critical mode I and mode II adhesion energy to be obtained and all the experimentally observed behaviour is explained.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Sun, 01 Jan 2017 00:00:00 GMThttps://dspace.lboro.ac.uk/2134/241772017-01-01T00:00:00ZFrictionally induced, self excited vibrations in a disc brake system
https://dspace.lboro.ac.uk/2134/23868
Title: Frictionally induced, self excited vibrations in a disc brake system
Authors: North, M.R.
Abstract: This work describes an investigation into the frictionally induced, self excited vibrations which occur in braking systems and
are generally known as squeal. The.work is largely theoretical, but measurements made on a rig are used to correlate the predictions of
the theory with a practical brake system.
Following an historical review, the theoretical behaviour of
a brake disc is examined and adapted to predict the approximate natural frequencies and nodal spacings of an annular disc for a range of masses added to the disc to represent the pads and caliper.
Knowing the disc behaviour, it is then possible to propose an eight degree of freedom model which describes the caliper, pads and a lumped model of the disc in the immediate vicinity of the caliper. From this model it can be shown how self excited vibrations can arise in such a system, and squeal frequencies and mode shapes can be predicted.
The effects of stiffness non-linearity in the system are then investigated and it is shown that limit cycles will occur; conditions for obtaining mode shapes at the limit cycle are defined.
An experimental rig is described and measurements made on
the rig are given in some detail. Parameter values are inserted in
the mathematical models and mode shapes and natural frequencies are computed. These are compared with the measured mode shapes and
natural frequencies to give an assessment of correlation between the theory and the actual vibrational behaviour.
Despite the simple nature of the model used to represent the brake system, and the fact that a number of parameters are only known within wide limits,.correlation between the measured mode shape and squeal frequency and the calculated mode shapes and frequencies can be made good by the choice of suitable parameter values within the defined limits. For example, a 26% reduction in the caliper stiffness altered the mode of the disc vibration and hence caused a large change in squeal frequency, but insertion of the new parameter values into the equations showed that a corresponding instability was predicted at the correct frequency.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Sat, 01 Jan 1972 00:00:00 GMThttps://dspace.lboro.ac.uk/2134/238681972-01-01T00:00:00ZOn the combustion of premixed natural gas/gasoline dual fuel blends in SI engines
https://dspace.lboro.ac.uk/2134/23547
Title: On the combustion of premixed natural gas/gasoline dual fuel blends in SI engines
Authors: Petrakides, Sotiris
Abstract: The continuous update of challenging emission legislations has renewed the interest for the use of alternative fuels. The low carbon content, the knocking resistance, and the abundance reserves, have classified natural gas as one of the most promising alternative fuels. The major constituent of natural gas is methane. Historically, the slow burning velocity of methane has been a major concern for its utilisation in energy efficient combustion applications.
As emphasized in a limited body of experimental literature, a binary blend of methane and gasoline has the potential to accelerate the combustion process in an SI engine, resulting in a faster combustion even to that of gasoline. The mechanism of such effects remains unclear. This is partially owned to the inadequate prior scientific understanding of the fundamental combustion parameters, laminar burning velocity (Su0) and Markstein length (Lb), of a gasoline-natural gas Dual Fuel (DF) blend. The value of Lb characterises the sensitivity of the flame to stretch. The flame stretch is induced by aerodynamic straining and/or flame curvature.
The current research study has therefore being concerned on understanding the combustion mechanism of premixed gasoline - natural gas DF blends both on a fundamental as well as practical SI engine level. The understanding on the contribution of Su0 and Lb to the velocity of a stretched laminar propagating flame has been extended through numerical analysis. A conceptual analysis of the laminar as compared to the SI engine combustion allowed further insights on the effect of turbulence to the mass burning rate of the base fuels.
On a fundamental level, the research contribution is made through the quantification of the response of Su0 and Lb with the ratio of methane to PRF95 (95%volliq iso-octane and 5%volliq n-heptane) in a DF blend. Methane has been used as a surrogate for natural gas and PRF95 as a surrogate for gasoline. Constant volume laminar combustion experiments have been conducted in a cylindrical vessel at equivalence ratios of 0.8, 1, 1.2, initial pressures of 2.5, 5, 10 Bar, and a constant temperature of 373 K. Methane was added to PRF95 in three different energy ratios 25%, 50% and 75%. Spherically expanding flames visualised through schlieren photography were used to derive the values of Lb and Su0. It has been concluded that for pressures relevant to SI engine operation (>5bar) and stoichiometric to lean Air Fuel Ratios (AFRs), there is a positive synergy for blending methane to PRF95 due to the convergence of Lb of the blended fuel towards that of pure gas and Su0 towards that of pure liquid.
In an SI engine environment, the research contribution is made through the characterisation and scientific understanding of the mechanism of DF combustion, and the importance of flame-stretch interactions at various engine operating conditions. Optical diagnostics have been integrated with in-cylinder pressure analysis to investigate the mechanism of flame velocity and stability with the addition of natural gas to gasoline in a DF blend, under a sweep of engine load (Manifold Absolute Pressure = 0.44, 0.51. 0.61 Bar), speed (1250, 2000, 2750 RPM) and equivalence ratio (0.8, 0.83, 1, 1.25). Consisted with the constant volume experiments, natural gas was added to gasoline in energy ratios of 25%, 50% and 75%. It has been concluded that within the flamelet combustion regime the effect of Lb is dominating the lean burn combustion process both from a flame stability and velocity prospective. The effect of Su0 on the combustion process gradually increases as the AFR shifts from stoichiometric to fuel rich values.
For stoichiometric to fuel lean mixtures, the effect of turbulence on the increase of the mass burning rate is on average 13% higher for natural gas as compared to gasoline. The higher turbulence sensitivity of natural gas is attributed to its lower Lb value.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Fri, 01 Jan 2016 00:00:00 GMThttps://dspace.lboro.ac.uk/2134/235472016-01-01T00:00:00Z