The mean value engine model (MVEM) is a mathematical model derived from basic physical principles such as conservation of mass and energy equations. Although the MVEM is based on some simplified assumptions and time averaged combustion engine parameters, it models the engine with a reasonable approximation and gives a satisfactory amount of information about the physics of the fluid energy passing through an engine system. MVEM can predict an engine’s main external variables such as crankshaft speed and manifold pressure, and important internal variables, such as volumetric and thermal efficiencies. Usually, the differential equations used in MVEM will predict fuel film flow, manifold pressure, and crankshaft speed. Because of its simplicity and short simulation time, the MVEM is widely used for engine control development. A mean value engine based on mathematical and parametric equations has recently been developed in the new MapleSim software. The model consists of three main components: the throttle body, the manifold, and the engine. The new MVEM uses combinations of causal and acausal components along with lookup tables and parametric equations. Adjusting the parameters allows the model to be used for new engines of interest. The model is forward-looking and so benefits from both Maple’s powerful mathematical tool and Modelica’s modern equation-based language. A set of throttle angle and mass flow data is used to find the throttle angle function, and to validate the throttle mass flow rates obtained from the model and the experiment.

The automotive industry has long been searching for efficient ways to improve vehicle performance such as drivability, fuel consumption, and emissions. Researchers in the automotive industry have tried to develop methods to improve fuel consumption and reduce the emission gases of a vehicle, while satisfying drivability and ride comfort issues. Today, by developing computer/software technologies, automotive manufacturers are moving more and more towards modelling a real component (prototype) in a software domain (virtual prototype). For instance, modelling the components of a vehicle's powertrain (driveline) in the software domain helps the designers to iterate the model for different operating conditions and scenarios to obtain better performance without any cost of making a real prototype. The objective of this research is to develop and validate physics-based powertrain models with sufficient fidelity to be useful to the automotive industry for rapid prototyping. Developing a physics-based powertrain model that can accurately simulate real phenomenon in the powertrain components is of great importance. For instance, a high-fidelity simulation of the combustion phenomenon in the internal combustion (IC) engine with detailed physical and chemical reactions can be used as a virtual prototype to estimate physical prototype characteristics in a shorter time than it would take to build a physical prototype. Therefore, the powertrain design can be explored and validated virtually in the software domain to reduce the cost and time of product development. The main focus of this thesis is on development of an internal combustion engine model, four-cylinder spark ignition engine, and a hydrodynamic torque converter model. Then, the models are integrated along with the rest of a powertrain's components (e.g. vehicle longitudinal dynamics model) through acausal connections, which represents a more feasible physics-based powertrain model for model-based control design. The powertrain model can be operated at almost all operating conditions (e.g. wide range of the engine speeds and loads), and is able to capture some transient behaviour of the powertrain as well as the steady state response. Moreover, the parametric formulation of each component in the proposed powertrain model makes the model more efficient to simulate different types of powertrain (e.g. for a passenger car or truck).

Internal combustion engine emissions are currently a major source of air pollution. The harmful impact of engine emissions can be reduced when engines are fuelled by alternatives to petrol and diesel such as natural gas. The use of lean burn technology in spark-ignition engines has been dominant; however, the lean burn technique can not economically satisfy the increasingly restricted future emission standards particularly for NOx emissions. In this thesis, the use of the stoichiometric air-fuel mixture with exhaust gas recirculation (EGR) technique in a spark ignition natural gas engine is investigated. The aim of the research is to optimize the key engine operating conditions in order to obtain the lowest NO emissions accompanied with low fuel consumption and high power. This is achieved via both experimental and computer simulation research. / PhD Doctorate

The losses in an internal combustion engine are dominated by thermal and parasitic sources. The latter arises from mechanical inefficiencies inherent within the system, particularly friction in load bearing conjunctions such as the piston assembly. During idle and at low engine speeds, frictional losses are the major contributor to the overall engine losses as opposed to the dominant contribution of thermal losses under other driving conditions. Given the relatively small size and simple structure of the top compression ring, it has a disproportionate contribution to the total frictional losses. This suggests further analysis would be required to understand the underlying causes of compression ring behaviour throughout the engine cycle. The available literature on tribological analyses of compression rings does not account for the transient ring elastodynamics. They usually assume a rigid ring for film thickness and power loss predictions, which is not representative of the ring's dynamic response. A combined study of ring elastodynamic behaviour and its tribological conjunction is a comprehensive approach.

[pt] É realizado um estudo teórico experimental sobre motores a combustão interna operando com taxa de compressão variável. É feita uma análise teórica sobre determinado mecanismo que permite variar a taxa de compressão. Para tal foi utilizado um programa de simulação para motores com ignição por centelha. No presente trabalho o modelo de simulação foi aprimorado, com a inclusão de previsão de detonação, de emissão de hidrocarbonetos, do cálculo da potencia de atrito, assim como a inclusão do dispositivo do mecanismo de taxa de compressão variável, entre outras alterações. Uma parte experimental foi também realizada, como o objetivo de validar os resultados do modelo teórico e de quantificar os benefícios proporcionados pelo mecanismo em questão. Para tal um motor de pesquisa de combustível – motor CFR – foi utilizado. Uma comparação dos resultados teóricos e experimentais obtidos no presente trabalho com os de outros pesquisadores é também apresentada. / [en] The present work is concerned with a theoretical and expererimental study of variable compression ratio spark ignition internal combustion engines. A theoretical analysis of the engine, operating with a mechanism allows for variable compression ratio, is carried out. For that a simulation program is utilized. In the present work the simulation model was updated with the inclusion of friction, knocking and hidrocarbon emission models, among other things. An experimental work was also carried out, with a CFR engine. The objective was a wo-fold to validade the results of the theoretical model and to assens the benefits of running an engine with variable compression ratio. A comparison is also made between the rrsults of the present work and those from other authors.

Pre-Chamber combustion systems are gaining popularity in Internal Combustion Engines (ICE) with the increasing emissions regulations due to their advantages in improving fuel economy by increasing the lean limit and cutting emission, especially NOx. In pre-chamber Combustion, flame jets shoot out from the pre-chamber orifices into the main chamber and generates several ignition points that promote a rapid burn rate of the lean mixture (air-excess ratio (λ) >1) in the main chamber. This work focused on studying two different fuels in the main chamber, lean limit, combustion efficiency (ηc), and emissions. A single-cylinder heavy-duty engine equipped with a narrow throat active pre-chamber was used. Two fuels were tested in the main chamber, Methane (CH4) and Ethanol (C2H5OH), the first fuel is used as a baseline, while keeping the pre-chamber fueled by Methane only. The engine was operated at a fixed speed, intake pressure, and spark-timing. The amount of fuel injected was varied to attain different global λ, then at each global λ; the amount of fuel injected to the Pre-chamber was varied to observe the effect of the pre-chamber λ. Different air intake temperatures were tested to see the effect on combustion efficiency. Results from the study showed an increase in the lean-limit using Ethanol in the main chamber compared to using only Methane in both chambers. However, lower ηc than that of the Methane was reported; this is due to a combination of the narrow-throat feature and the high heat of vaporization of Ethanol, ηc showed improvement when the air intake temperature increased.

This thesis discusses the thermoeconomic modeling and simulation of micro-CHP systems powered by various prime movers. Micro Cooling, Heating, and Power (micro-CHP) is becoming an increasingly important energy option as the demand for electrical power as well as heating and cooling for buildings increases worldwide. Micro-CHP has the potential to increase the total energy efficiency for cooling, heating, and powering residences, offices, and other relatively small buildings by using waste thermal energy from electricity production to deliver heating and cooling. Calculation methodologies are presented for the different components of micro CHP systems using thermodynamic cycles and mass and energy balances. System performance characteristics are calculated and compared for different prime movers using various fuels. Performance characteristics that are compared include fuel consumption, monthly energy savings, and system energy efficiencies.

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For an engine running at a constant speed, both exhaust and intake processes are periodic in nature. This inspires the muffler designer to go for the much easier and faster frequency domain modeling. But analogous to electrical filter, as per Thevenin’s theorem, the acoustic filter or muffler requires prior knowledge of the load-independent source characteristics (acoustic pressure and internal impedance), corresponding to the open circuit voltage and internal impedance of an electrical source. Studies have shown that it is not feasible to evaluate these source characteristics making use of either the direct measurement method or the indirect evaluation method. Hence, prediction of the radiated exhaust or intake noise has been subject to trial and error. Making use of the fact that pressure perturbation in a duct is a superposition of the forward moving wave and the reflected wave, a simple hybrid approach has been proposed making use of an interrelationship between progressive wave variables of the linear acoustic theory and Riemann variables of the method of characteristics. Neglecting the effect of nonlinearities, reflection of the forward moving wave has been duly incorporated at the exhaust valve. The reflection co-efficient of the system downstream of the exhaust valve has been calculated by means of the transfer matrix method at each of the several harmonics of the engine firing frequency. This simplified approach can predict exhaust noise with or without muffler for a naturally aspirated, single cylinder engine. However, this proves to be inadequate in predicting the exhaust noise of multi-cylinder engines. Thus, estimation of radiated noise has met only limited success in this approach. Strictly speaking, unique source characteristics do not exist for an IC engine because of the associated non-linearity of the time-varying source. Yet, a designer would like to know the un-muffled noise level in order to assess the required insertion loss of a suitable muffler. As far as the analysis and design of a muffler is concerned, the linear frequency-domain analysis by means of the transfer matrix approach is most convenient and time saving. Therefore, from a practical point of view, it is very desirable to be able to evaluate source characteristics, even if grossly approximate. If somehow it were possible to parameterize the source characteristics of an engine in terms of basic engine parameters, then it would be possible to evaluate the un-muffled noise before a design is taken up as a first approximation. This aspect has been investigated in detail in this work. A finite-volume CFD (one dimensional) model has been used in conjunction with the two-load or multi-load method to evaluate the source characteristics at a point just downstream of the exhaust manifold for the exhaust system, and upstream of the air filter (dirty side) in the case of the intake system. These source characteristics have been extracted from the pressure time history calculated at that point using the electro-acoustic analogy. Systematic parametric studies have yielded approximate empirical expressions for the source characteristics of an engine in terms of the basic engine parameters like engine RPM, capacity (swept volume or displacement), air-fuel ratio, and the number of cylinders. The effect of other parameters has been found to be relatively insignificant. Unlike exhaust noise, the intake system noise of an automobile cannot be measured because of the proximity of the engine at the point of measurement. Besides, the intake side is associated with turbocharger (booster), intercooler, cooling fan, etc., which will make the measurement of the intake noise erroneous. From the noise radiation point of view, intake noise used to be considered to be a minor source of noise as compared to the exhaust noise. Therefore, very little has been done or reported on prediction of the intake noise as compared to the exhaust noise. But nowadays, with efficient exhaust mufflers, the un-muffled intake noise has become a contributing factor to the passenger compartment noise level as a luxury decisive factor. Therefore, in this investigation both the intake and the exhaust side source characteristics have been found out for the compression ignition as well as the spark ignition engines. Besides, in the case of compression ignition engines, typical turbocharged as well as naturally aspirated engines have been considered. One of the inputs to the time-domain simulation is the intake valve and exhaust valve lift histories as functions of crank angle. It is very cumbersome and time-consuming to measure and feed these data into the program. Sometimes, this data is not available or cannot be determined easily. So, a generalized formula for the valve lift has been developed by observing the valve lift curves of various engines. The maximum exhaust valve lift has been expressed as a function of the swept volume of the cylinder. This formulation is not intended for designing a cam profile; it is for the purpose of determining approximate thermodynamic quantities to help a muffler designer for an initial estimation. It has also been observed during the investigation that from the acoustic point of view, sometimes it is better to open the exhaust valve a little earlier, but very slowly and smoothly, and keep it open for a longer time. Although the exact source characteristics for an automobile engine cannot be determined precisely, yet the values of source characteristics calculated using this methodology have been shown to be reasonably good for approximate prediction of the un-muffled noise as well as insertion loss of a given muffler. The resultant empirical expressions for the source characteristics enable the potential user to make use of the frequency-domain cum-transfer matrix approach throughout; the time consuming time-domain simulation of the engine exhaust source is no longer necessary. Predictions of the un-muffled sound pressure level of automotive engines have been corroborated against measured values as the well as the full scale time-domain predictions making use of a finite-volume software.

<p>Biomass is one of the main natural resources in Sweden.Increased utilisation of biomass for energy purposes incombined heat and power (CHP) plants can help the country meetits nuclear phase-out commitment. The present low-CO2 emissioncharacteristics of the Swedish electricity production system(governed by hydropower and nuclear power) can be retained onlyby expansion of biofuels in the CHP sector. Domestic Swedishbiomass resources are vast and renewable, but not infinite.They should be utilised as efficiently as possible in order tomeet the conditions for sustainability in the future.Application of efficient power generation cycles at low cost isessential for meeting this challenge. This applies also tomunicipal solid waste (MSW) incineration with energyextraction, which is to be preferred to landfilling.</p><p>Modern gas turbines and internal combustion engines firedwith natural gas have comparatively low installation costs,good efficiency characteristics and show reliable performancein power applications. Environmental and source-of-supplyfactors place natural gas at a disadvantage as compared tobiofuels. However, from a rational perspective, the use ofnatural gas (being the least polluting fossil fuel) togetherwith biofuels contributes to a diverse and more secure resourcemix. The question then arises if both these fuels can beutilised more efficiently if they are employed at the samelocation, in one combined cycle unit.</p><p>The work presented herein concentrates on the hybriddual-fuel combined cycle concept in cold-condensing and CHPmode, with a biofuel-fired bottoming steam cycle and naturalgas fired topping gas turbine or engine. Higher electricalefficiency attributable to both fuels is sought, while keepingthe impact on environment at a low level and incorporating onlyproven technology with standard components. The study attemptsto perform a generalized and systematic evaluation of thethermodynamic advantages of various hybrid configurations withthe help of computer simulations, comparing the efficiencyresults to clearly defined reference values.</p><p>Results show that the electrical efficiency of hybridconfigurations rises with up to 3-5 %-points in cold-condensingmode (up to 3 %-points in CHP mode), compared to the sum of twosingle-fuel reference units at the relevant scales, dependingon type of arrangement and type of bottoming fuel. Electricalefficiency of utilisation of the bottoming fuel (biomass orMSW) within the overall hybrid configuration can increase withup to 8-10 %-points, if all benefits from the thermalintegration are assigned to the bottoming cycle and effects ofscale on the reference electrical efficiency are accounted for.All fully-fired (windbox) configurations show advantages of upto 4 %-points in total efficiency in CHP mode with districtheating output, when flue gas condensation is applied. Theadvantages of parallel-powered configurations in terms of totalefficiency in CHP mode are only marginal. Emissions offossil-based CO2 can be reduced with 20 to 40 kg CO2/MWhel incold-condensing mode and with 5-8 kg CO2 per MWh total outputin CHP mode at the optimum performance points.</p><p>Keywords: Biomass, Municipal Solid Waste (MSW), Natural Gas,Simulation, Hybrid, Combined Cycle, Gas Turbine, InternalCombustion Engine, Utilization, Electrical Efficiency, TotalEfficiency, CHP.</p>