Dissertations / Theses on the topic 'Exhaust gas recirculation'

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis. Page 145 blank.
Includes bibliographical references (pages 131-134).
The societal demand for vehicles with high efficiency and low emissions has spurred considerable changes to the automotive internal combustion engine within the past decade. Reductions in the displacement volume and increases in maximum output per unit of displacement are among the characteristics adopted to meet the fuel economy targets of world governments. However, the extent to which these changes in engine configuration may be pursued in search of efficiency is limited by several fundamental phenomena. The intent of this research project is to investigate the modeling of one of these phenomena - the autoignition of an unburned portion of the air-fuel mixture - and a potential strategy intended to delay the occurrence of this frequently damaging type of combustion reaction. The autoignition abatement approach studied entails the recirculation of burned exhaust gasses which serve to dilute the air-fuel mixture and reduce maximum unburned gas temperatures Experimental testing was performed on two different types of exhaust gas recirculation (EGR) system - one which extracts exhaust gases from upstream of the catalytic converter and another which extracts gases from downstream - in order to determine if the changes in composition that occur across the catalyst affect the autoignition abatement characteristics of the recirculated exhaust. This testing indicated that differences between the alternative installations are dominated by changes in the flow dynamics of the exhaust system, with no definite changes attributable to compositional differences. An empirical method of predicting the occurrence of autoignition using experimental data was then developed based on an approach originally proposed by Livengood and Wu. Ignition delay correlations were developed that provide accurate autoignition prediction over a range of speeds, loads, air-fuel equivalence ratios and dilution rates. Additionally, a new statistical model for autoignition is proposed that captures the cycle-to-cycle variation in autoignition intensity and relates these variations to the thermodynamic state of the charge.
by Jacob Elijah McKenzie.
Ph. D.

Selective Exhaust Gas Recirculation (S-EGR) consists of selectively transferring CO2 from the exhaust gas stream of a gas-fired power plant into the air stream entering the gas turbine compressor. Unlike in “non-selective” Exhaust Gas Recirculation (EGR) technology, recirculation of, principally, nitrogen does not occur, and the gas turbine still operates with a large excess of air. Two configurations are proposed: one with the CO2 transfer system operating in parallel to the post-combustion carbon capture (PCC) unit; the other with the CO2 transfer system operating downstream of, and in series to, the PCC unit. S-EGR allows for higher CO2 concentrations in the flue gas of approximately 13-14 vol%, compared to 6.6 vol% with EGR at 35% recirculation ratio. The oxygen levels in the combustor are approximately 19 vol%, well above the minimum limit of 16 vol% with 35% EGR reported in literature. At these operating conditions, process model simulations show that the current class of gas turbine engines can operate without a significant deviation in the compressor and the turbine performance from the design conditions. Compressor inlet temperature and CO2 concentration in the working fluid are critical parameters in the assessment of the effect on the gas turbine net power output and efficiency. A higher turbine exhaust temperature allows the generation of additional steam which results in a marginal increase in the combined cycle net power output of 5% and 2% in the investigated configurations with S-EGR in parallel and S-EGR in series, respectively. With aqueous monoethanolamine scrubbing technology, S-EGR leads to operation and cost benefits. S-EGR in parallel operating at 70% recirculation, 97% selective CO2 transfer efficiency and 96% PCC efficiency results in a reduction of 46% in packing volume and 5% in specific reboiler duty, compared to air-based combustion CCGT with PCC, and of 10% in packing volume and 2% in specific reboiler duty, compared to 35% EGR. S-EGR in series operating at 95% selective CO2 transfer efficiency and 32% PCC efficiency results in a reduction of 64% in packing volume and 7% in specific reboiler duty, compared to air-based, and of 40% in packing volume and 4% in specific reboiler duty, compared to 35% EGR. An analysis of key performance indicators for selective CO2 transfer proposes physical adsorption in rotary wheel systems as an alternative to selective CO2 membrane systems. A conceptual design assessment with two commercially available adsorbent materials, activated carbon and Zeolite X13, shows that it is possible to regenerate the adsorbent with air at near ambient temperature and pressure. Yet, a significant step change in adsorbent materials is necessary to design rotary adsorption systems with dimensions comparable to the largest rotary gas/gas heat exchanger used in coal-fired power plants, i.e. approximately 24 m diameter and 2 m height. An optimisation study provides guidelines on the equilibrium parameters for the development of materials. Finally, a technical feasibility study of configuration options with rotary gas/gas heat exchangers shows that cooling water demand around the post-combustion CO2 capture system can be drastically reduced using dry cooling systems where gas/gas heat exchangers use ambient air as the cooling fluid. Hybrid cooling configurations reduce cooling and process water demand in the direct contact cooler of a wet cooling system by 67% and 35% respectively, and dry cooling configurations eliminate the use of process and cooling water and achieve adequate gas temperature entering the absorber.

The exhaust gas recirculation (EGR) system has been widely used to reduce nitrogen oxide (NOx) emission, improve fuel economy and suppress knock by using the characteristics of charge dilution. However, previous studies have shown that as the EGR rate at a given engine operating condition increases, the combustion instability increases. The combustion instability increases cyclic variations resulting in the deterioration of engine performance and increasing hydrocarbon emissions. Therefore, the optimum EGR rate should be carefully determined in order to obtain the better engine performance and emissions. A thermodynamic cycle simulation of the four-stroke spark-ignition engine was used to determine the effects of EGR on engine performance, emission characteristics and second law parameters, considering combustion instability issues as EGR level increases. A parameter, called 'Fuel Fraction Burned,' was introduced as a function of the EGR percentage and used in the simulation to incorporate the combustion instability effects. A comprehensive parametric investigation was conducted to examine the effects of variations in EGR, load and speed for a 5.7 liter spark-ignition automotive engine. Variations in the thermal efficiencies, brake specific NOx emissions, average combustion temperature, mean exhaust temperature, maximum temperature and relative heat transfer as functions of exhaust gas recycle were determined for both cooled and adiabatic EGR configurations. Also effects of variations in the load and speed on thermal efficiencies, relative heat transfers and destruction of availability due to combustion were determined for 0% EGR and 20% EGR cases with both cooled and adiabatic configurations. For both EGR configurations, thermal efficiencies first increase, reach a maximum at about 16% EGR and then decrease as the EGR level increases. Thermal efficiencies are slightly higher for cooled EGR configuration than that for adiabatic configuration. Concentration of nitric oxide emissions decreases from about 2950 ppm to 200 ppm as EGR level increases from 0% to 20% for cooled EGR configuration. The cooled EGR configuration results in lower nitric oxide emissions relative to the adiabatic EGR configuration. Also second law parameters show the expected trends as functions of EGR. Brake thermal efficiency is higher for the 20% EGR case than that for the no EGR case over the range of load (0 to WOT) and speed (600 rpm to 6000 rpm). Predictions made from the simulation were compared with some of the available experimental results. Predicted thermal efficiencies showed a similar trend when compared to the available experimental data. Also, percentage of unused fuel availability increases as the EGR level increases, and it can be seen as one of the effects of deteriorating combustion quality as the EGR level increases.

The member states of European Union aim to promote the reduction of harmful emissions. Emissions from combustion processes cause effects on human health and pose environmental issues, for example by increasing greenhouse effect. There are two ways to reduce emissions; one is to promote renewable energy sources and the other to utilize more effectively the available fossil fuels until a long-term solution is available. Hence, it is necessary to strive for CO2 mitigation technologies applied to fossil fuels. Low natural gas prices together with high energy efficiency have made gas turbines popular in the energy market. But, gas turbine fired with natural gas come along with emissions of CO2, NOx and CO. However, these disadvantages can be eliminated by using gas turbine with precombustion CO2 capture, separating carbon from the fuel by using fuel reforming process and feeding pure hydrogen as a fuel. Hydrogen fired gas turbines are used in two applications such as a gas turbine with pre-combustion CO2 capture and for renewable power plants where hydrogen is stored in case as a backup plan. Although the CO2 emissions are reduced in a hydrogen fired gas turbine with a pre-combustion CO2 capture, there are still several challenges such as high flame temperatures resulting in production of thermal NOx. This project suggests a method for application of hydrogen fired gas turbine, using exhaust gas recirculation to reduce flame temperature and thus reducing thermal NOx. A NOx emission model for a hydrogen-fired gas turbine was built from literature data and used to select the best operating conditions for the plant. In addition, the economic benefits of switching from natural gas to pure hydrogen are reported. For the techno-economic analysis, investment costs and operating costs were taken from the literature, and an economic model was developed. To provide sensitivity analysis for the techno-economic calculation, three cases were studied. Literature review was carried out on several journal articles and websites to gain understanding on hydrogen and natural gas fired gas turbines. Results showed that, in the current state, pure hydrogen has high delivery cost both in the US and Europe. While it’s easy to access natural gas at low cost, therefore in the current state gas turbine fired with natural gas are more profitable than hydrogen fired gas turbine. But, if targeted hydrogen prices are reached while fuel reforming process technology are developed in the coming future the hydrogen fired gas turbine will compete seriously with natural gas.

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xv, 178 p.; also includes graphics (some col.). Includes bibliographical references (p. 153-158). Available online via OhioLINK's ETD Center

Modern Diesel engines fulfil challenging requirements for emission limits, fuel consumption and ride comfort by numerous modular combinable components and mechatronical actuators. These components are utilised for precondition and aftertreatment of air, fuel and exhaust gas, which is involved in the combustion process. In this dissertation a methodology for a model-based function development with semi-physical engine models for control of air path quantities of an exemplary Diesel engine with high-pressure (HP-EGR) and low-pressure exhaust gas recirculation (LP-EGR) is developed. In this framework for function development black-box models for stationary and dynamical emission formation are utilised to optimise reference values for the air path control and to rate the developed control scheme with regard to the cumulated driving cycle emissions of the new European driving cycle (NEDC). A combination of HP-EGR and LP-EGR represents a novel approach to significantly lower the particulate and NOx emissions of Diesel engines. A semi-physical mean value engine model with lumped parameters is the base to analyse the system properties of the complex air path. In doing so, the additional LP-EGR shows only minor influences to the quantities charge air pressure and HP-EGR, while there are significant influences of these quantities on the LP-EGR mass flow rate. Furthermore, the LP-EGR is characterised by significant gas propagation times in the intake and exhaust system. These delays are modelled by a gas composition model, which is incorporated into the control scheme. NOx and particulate emissions as well as engine torque are stationary modelled by local polynomial models with input quantities of the combustion process. These quantities are air mass flow rate, charge air pressure, intake temperature and crank angle of 50% mass fraction burned. A bilinear interpolation between engine speed and injection quantity transforms local polynomial models into global models. Models for the dynamical emission formation are given by considering the combustion as a batch process. Consequently all dynamics are included in the quantities of the cylinder charge at intake valve closing and the emission measurement dynamics. Thus, a combination of a dynamical gas composition model, stationary emission models and models for the emission measurement dynamics yield the dynamical course of the engine emissions. The investigated system properties and the emission models deliver the control variables charge air pressure, air content and intake temperature for the engine with VGT-turbocharger, HP- and LP-EGR. A stationary optimisation with regard to emissions and engine torque delivers reference values for the air path control and further shows the potential of the LP-EGR to lower the emissions. Due to the multi-variable characteristics of the air path with different dynamics, there are increased dynamical emissions at engine transients. These dynamical emissions are lowered by dynamical optimised reference values for the air path control. Generally, the air path is a strongly nonlinear process and the multitude of engine variants and engine operation modes result in a trade-off between achievable control quality, control robustness and number of control parameter sets. A semi-physical feedforward control, which is based upon parameterised model relationships of the mean value engine model delivers a good response to setpoint changes. Thus, the disturbance rejection can be achieved by relatively simple controllers. This results in an significantly lower application effort of control parameters and allows by its modular structure to exchange engine components without the drawback to completely re-parameterise the control parameters. A reference value transformation with modelled states of the gas composition model compensates long gas propagation times in the intake and exhaust system and delivers an optimal air content in the cylinder charge. All control concepts are validated with measurements at the engine test bench. Finally, the derived control concepts for the LP-EGR are compared to the classical HP-EGR control with regard to the cumulated driving cycle emissions. In this investigation the proportion of stationary and dynamical emissions is clearly quantified. In a nutshell this dissertation is an important contribution for model-based optimisation and function development for the air path control of Diesel engines. The given combination of models for dynamical emission formation, dynamically optimised reference values for the air path control and semi-physical control design are a holistic framework to master the complexity and variance of future Diesel and gasoline engines.

The ion current measured from the spark plug in a spark ignited combustion engine is used

as basis for analysis and control of the combustion variability caused by exhaust gas

recirculation. Methods for extraction of in-cylinder pressure information from the ion

current are analyzed in terms of reliability and processing efficiency. A model for the

recognition of combustion variability using this information is selected and tested on both

simulated and car data.

Engine control systems aim to ensure satisfactory output performance whilst adhering to requirements on emissions, drivability and fuel efficiency. Model predictive control (MPC) has shown promising results when applied to multivariable and nonlinear systems with operational constraints, such as diesel engines. This report studies the torque generation from a mean-value heavy duty diesel engine with exhaust gas recirculation and variable-geometry turbocharger using state feedback linearization based MPC (LMPC). This is accomplished by first introducing a fuel optimal reference generator that converts demands on torque and engine speed to references on states and control signals for the MPC controller to follow. Three different MPC controllers are considered: a single linearization point LMPC controller and two different successive LMPC (SLMPC) controllers, where the controllers are implemented using the optimization tool CasADi. The MPC controllers are evaluated with the World Harmonized Transient Cycle and the results show promising torque tracking using a SLMPC controller with linearization about reference values.

This diploma dissertation focuses on the constructional solutions of EGR exchangers in the form of a CAD model, on their CFD simulation, on the drawing of relevant conclusions, and also on the comparison of two developmental types of these exchangers.

The thesis presents investigations of advanced combustion strategies in a modern V6 diesel engine fuelled with mineral diesel and Tallow Methyl Ester (TME)-diesel blends, in order to meet future emissions legislation. One of the main objectives of this research is to improve fuel consumption whilst minimising engine emissions through the combined effects of injection strategy (fuel injection pressure, dwell period, pilot fuel quantity) and cooled Exhaust Gas Recirculation (EGR) on a modern V6 common rail direct injection diesel engine. In the case of using EGR (49–52%) at 1500 rpm and 10% of engine peak torque, by increasing the fuel injection pressure from 300 to 800 bar, engine thermal efficiency increased from 16.5 to 19.1% and 17.1 to 19.7%, BSFC decreased by 13.5% and 13.2%, smoke level decreased by 74.3% and 70.1% and NOx emissions increased by 69.6% and 68.0%, respectively for a short (5 CAD) and a long (40 CAD) dwell period. In addition, the study of a variation of pilot fuel quantities (0.8–3.0 mg/stroke) with a fixed dwell period (5 CAD) at two different fuel injection pressures (250 bar and 800 bar) shows that the smaller pilot quantity with the higher fuel injection pressure can be considered as an enhanced strategy to control engine performance and emissions simultaneously. Therefore, the combination of higher injection pressure, longer dwell, smaller pilot quantity and the use of EGR could potentially improve fuel consumption and minimise engine emissions. The use of TME-diesel blends results in lower engine thermal efficiency and higher fuel consumption and NOx emissions. In the case of 1500 rpm and 25% of engine peak torque, the combustion of TME10 and TME30 reduced the engine thermal efficiency from iii 35.3 to 33.7% and 35.3 to 33.2% and increased the BSFC by 4.9% and 6.5%, respectively. At the same engine condition, the combustion of TME-diesel blends increased NOx emissions by 1.8% and 10.0% and reduced CO by 0.9% and 1.8%, THCs by 18.0% and 23.9 %, smoke by 30% and 51.7% for TME10 and TME30 respectively. However, the engine thermal efficiency, BSFC and NOx emissions could be improved with the application of the combined effect of injection strategy (fuel injection pressure, dwell period, pilot fuel quantity) and EGR as shown in the first phase of this study.

This study was concerned with the performance of biofuels in diesel engines. Generally, the basic combustion and emission characteristics of Rapeseed Oil (RSO) and Soya Oil (SO) result in a lower in-cylinder pressure peak than diesel. This led to the reduction of Nitrogen Oxides (NOx) emissions and to relatively high soot emissions. Further measurements of RSO were done in order to investigate the influence of injection pressure, injection timing and Exhaust Gas Recirculation (EGR) on combustion and emission characteristics. A high soot emission from RSO was reduced by increased injection pressure. Moreover, injection timing also had to be varied in order to reduce the soot emissions from RSO. The retarded injection timing (3 deg bTDC) and increased injection pressure (1200 bar) for the blend of 30% RSO resulted in a reduction of soot emission to the same level as from diesel fuel. Further investigation regarding the soot emissions was done for Rapeseed Methyl Ester (RME) under turbocharged engine operation. The application of the boost pressure resulted in stable engine operation at a late injection timing of 5 deg aTDC. A simultaneous reduction of soot and NOx emissions has been achieved for RME at an injection timing of TDC and high EGR percentage (40 – 50 %). The soot particles size distribution under different engine operating conditions for RME and diesel has also been investigated. Moreover, the characteristic of Electrostatic Mobility Spectrometer (EMS) and the design of primary dilution system have been provided in order to understand the influence of the dilution process and to obtain more real results. Generally, RME showed less particles concentration in the nucleation mode when compared to diesel. Moreover, high EGR caused a shift of the particles from the nucleation mode by agglomeration into the accumulation mode for both fuels. The effect of injection pressure could only be seen in the accumulation mode, where high injection pressure slightly reduced the concentration number. The soot emission was effectively reduced by the usage of the diesel particulate filter (DPF). For this purpose, the soot particles size distributions before and after the DPF have been measured at different engine speeds and loads. At low engine torque, the soot was effectively filtered while the operation under high engine loads resulted in low soot particle concentration especially in the nucleation mode, after the DPF.

With an increased urgency for global action towards climate change mitigation, this research was undertaken with the aim of evaluating post-combustion CO2 capture as an emission abatement strategy for gas-fired power plants. A dynamic rate-based model of a capture plant with MEA solvent was built, with imposed chemical equilibrium, and validated at pilot scale under transient conditions. The model predicted plant behaviour under multiple process inputs and disturbances. The validated model was next used to analyse the process and it was found that CO2 absorption is mass transfer limited. The model was then improved by explicitly adding reactions rate in the model continuity, the first such dynamic model to be reported for the capture process. The model is again validated and is observed to provide better predictions than the previous model. Next, high fidelity models of a gas-fired power plant, a scaled-up capture plant and a compression train were built and integrated for 90% CO2 capture. Steam for solvent regeneration is extracted from the power plant IP/LP crossover pipe. Net efficiency drops from 59% to 49%, with increased cooling water demand. A 40% exhaust gas recirculation resulted in a recovery of 1% efficiency, proving that enhanced mass transfer in the capture plant reduces solvent regeneration energy demands. Economic analysis reveals that overnight cost increases by 58% with CO2 capture, and cost of electricity by 30%. While this discourages deployment of capture technology, natural gas prices remain the largest driver for cost of electricity. Other integration approaches – using a dedicated boiler and steam extraction from the LP steam drum – were explored for operational flexibility, and their net efficiencies were found to be 40 and 45% respectively. Supplementary firing of exhaust gas may be a viable option for retrofit, as it is shown to minimise integrated plant output losses at a net efficiency of 43.5%. Areas identified for further study are solvent substitution, integrated plant part load operation, flexible control and use of rotating packed beds for CO2 capture.

Today, the investigation of fuel economy improvements in internal combustion engines (ICEs) has become the most significant research interest among the automobile manufacturers and researchers. The scarcity of natural resources, progressively increasing oil prices, carbon dioxide taxation and stringent emission regulations all make fuel economy research relevant and compelling. The enhancement of engine performance solely using incylinder techniques is proving increasingly difficult and as a consequence the concept of exhaust energy recovery has emerged as an area of considerable interest. Three main energy recovery systems have been identified that are at various stages of investigation. Vapour power bottoming cycles and turbo-compounding devices have already been applied in commercially available marine engines and automobiles. Although the fuel economy benefits are substantial, system design implications have limited their adaptation due to the additional components and the complexity of the resulting system. In this context, thermo-electric (TE) generation systems, though still in their infancy for vehicle applications have been identified as attractive, promising and solid state candidates of low complexity. The performance of these devices is limited to the relative infancy of materials investigations and module architectures. There is great potential to be explored. The initial modelling work reported in this study shows that with current materials and construction technology, thermo-electric devices could be produced to displace the alternator of the light duty vehicles, providing the fuel economy benefits of 3.9%-4.7% for passenger cars and 7.4% for passenger buses. More efficient thermo-electric materials could increase the fuel economy significantly resulting in a substantially improved business case. The dynamic behaviour of the thermo-electric generator (TEG) applied in both, main exhaust gas stream and exhaust gas recirculation (EGR) path of light duty and heavy duty engines were studied through a series of experimental and modelling programs. The analyses of the thermo-electric generation systems have highlighted the need for advanced heat exchanger design as well as the improved materials to enhance the performance of these systems. These research requirements led to the need for a systems evaluation technique typified by hardware-in-the-loop (HIL) testing method to evaluate heat exchange and materials options. HIL methods have been used during this study to estimate both the output power and the exhaust back pressure created by the device. The work has established the feasibility of a new approach to heat exchange devices for thermo-electric systems. Based on design projections and the predicted performance of new materials, the potential to match the performance of established heat recovery methods has been demonstrated.

[ES] Los objetivos son 2: 1- Determinar el efecto de la dispersión de la recirculación de gases de escape de alta presión (HP EGR) en las emisiones de NOx y humos en motores diésel de automoción en operaciones de funcionamiento constantes. La investigación cuantifica las emisiones de NOx y humos en función del nivel de dispersión de EGR de alta presión entre cilindros. 2- Explorar los límites del modelado 1D para predecir el movimiento del flujo de los gases en la compleja situación en la que estos entran en los cilindros desde el colector de admisión. Los experimentos se realizaron en un banco de pruebas con un motor diésel de 1.6 litros. Para detectar la dispersión de EGR de alta presión se instaló un sistema de válvulas en los conductos de admisión de cada cilindro para medir la concentración de CO2, por tanto la tasa de EGR, en cada conducto. Se instaló también un sistema de válvulas en el escape para medir las emisiones de NOx en cada cilindro. Se instaló un sensor de humos en la línea de escape, aguas abajo de la turbina, para medir el efecto de la dispersión de EGR de alta presión en las emisiones de humos además del sensor para medir el resto de las emisiones contaminantes aguas abajo de la turbina. Se han estudiado 9 puntos de funcionamiento diferentes con distintas velocidades y niveles de carga. El mapa motor se ha estudiado en profundidad, desde 1250 hasta 3000 rpm y entre 3 y 20 bar de presión media efectiva (BMEP). La tasa de EGR varía entre 5 y 42%, dependiendo del punto de funcionamiento. La geometría del modelo reproduce la del motor diésel de automoción de 1.6 litros en el que se realizaron los ensayos experimentales. Incluyendo la línea de EGR de alta presión que fue instalada para controlar los niveles de dispersión durante los ensayos experimentales. La metodología centrada en las herramientas experimentales combina aparatos de medida tradicional con un sistema de válvulas específico que ofrecen una información precisa en cuanto a la concentración de especies tanto en el colector de admisión como en el de escape. El estudio se realizó a emisiones de NOx constantes para observar el efecto de la dispersión de EGR en los valores de opacidad. La metodología está centrada en las herramientas de modelado, las condiciones de contorno y toda la información necesaria para poner en marcha el modelo proviene de los resultados de los ensayos experimentales medidos con los diferentes sensores y aparatos mencionados anteriormente. Muchos de ellos necesarios para ajustar el modelo. La parte más importante para estudiar la capacidad de predicción del modelo es el diseño del colector de admisión. Es necesario poner especial atención en la orientación de los conductos, y en la estructura interna y la superficie para tratar de ser muy fiel a la geometría real, ya que ello determina la predicción de la dispersión. Esta aproximación de modelado cuasi tridimensional (3D) es posible gracias a un programa específico que importa la información necesaria desde un archivo CAD al programa de modelado 1D. Respecto a la parte experimental, el estudio concluye que cuando la dispersión de EGR es baja, los niveles de opacidad se reducen en todos los puntos de funcionamiento. Sin embargo, por encima de ciertos niveles de dispersión de EGR, la opacidad crece seriamente con diferentes pendientes según el punto de operación. El estudio permite cuantificar este límite de dispersión de EGR. La dispersión de EGR incrementa el consumo de combustible por encima del 6.9%. Respecto a la parte de modelado, el estudio concluye que cuando la distribución de EGR entre conductos medida experimentalmente es asimétrica y presenta un alto patrón de concavidad o convexidad, el modelo no predice adecuadamente la distribución del EGR. El estudio concluye que, aunque en los ensayos experimentales la tasa de EGR afecta a la dispersión de EGR, el modelo 1D no es tan sensible como para predecir esta influencia cuando la tasa de EGR está por debajo del 10%.
[CA] L'objectiu de l'estudi és doble. Per una banda, determinar l'efecte de la dispersió de la recirculació de gasos d'escapament d'alta pressió (HP EGR per les seues sigles en anglès) en les emissions d'òxids de nitrogen (NOx) i fums en motors dièsel d'automoció en operacions de funcionament constants. La investigació quantifica les emissions de NOx i fums en funció del nivell de dispersió d'EGR d'alta pressió entre cilindres. Per una altra banda, l'objectiu és explorar els límits del modelatge unidimensional (1D) per predir el moviment del flux dels gasos en la complexa situació en què aquests entren als cilindres des del col·lector d'admissió. Els experiments van ser realitzats en un banc de proves amb un motor dièsel de 1.6 litres. Per detectar la dispersió d'EGR d'alta pressió es va instal·lar un sistema de vàlvules en els conductes d'admissió de cada cilindre per mesurar el percentatge de CO2 i per tant la taxa d'EGR. De la mateixa manera es va instal·lar també un sistema de vàlvules d'escapament, cilindre a cilindre, per mesurar les emissions de NOx. A més també es va instal·lar un sensor de fums en la línia d'escapament, aigües avall de la turbina, per mesurar l'efecte de la dispersió d'EGR d'alta pressió en les emissions de fums, així com el sensor de mesura de la resta d'emissions aigües avall de la turbina. S'han estudiat 9 punts de funcionament diferents amb distintes velocitats i nivells de càrrega, per la qual cosa el mapa motor s'ha estudiat en profunditat, des de 1250 fins a 3000 rpm i entre 3 i 20 bar de pressió mitjana efectiva (BMEP per les seues sigles en anglès). La taxa d'EGR varia entre 5 i 42 %, depenent del punt de funcionament. La geometria del model reprodueix la geometria del motor dièsel d'automoció d'1.6 litres en el qual es van realitzar tots els assajos experimentals. La metodologia centrada en les ferramentes experimentals combina aparells de mesura tradicional amb un sistema de vàlvules específic que ofereixen una informació precisa quant a la concentració d'espècies tant al col·lector d'admissió com al d'escapament. L'estudi es va realitzar a emissions de NOx constants per observar l'efecte de la dispersió d'EGR en els valors d'opacitat. Quant a la metodologia centrada en les ferramentes de modelatge, les condicions de contorn i tota la informació necessària per posar en marxa el model prové dels resultats dels assajos experimentals mesurats amb els diferents sensors i aparells mencionats anteriorment, molts d'ells necessaris per ajustar el model. La part més important per estudiar la capacitat de predicció del model és el disseny del col·lector d'admissió. És necessari posar especial atenció a l'orientació dels conductes, i a l'estructura interna i la superfície per tractar de ser molt fidel a la geometria real, ja que determina la predicció de la dispersió. Esta aproximació del model quasi-tridimensional (3D) és possible gràcies a un programa específic que importa la informació necessària des d'un arxiu de disseny assistit per ordinador (CAD) al programa de modelat 1D. Respecte a la part experimental, l'estudi conclou que quan la dispersió d'EGR és baixa, els nivells d'opacitat es redueixen en tots els punts de funcionament. Tanmateix, per damunt de certs nivells de dispersió d'EGR, l'opacitat creix seriosament amb diferents pendents segons el punt d'operació. L'estudi permet quantificar aquest límit de dispersió d'EGR. A més, la dispersió d'EGR podria contribuir a incrementar el consum de combustible per damunt del 6.9%. Respecte a la part de modelatge, l'estudi conclou que quan la distribució d'EGR entre conductes mesurada experimentalment és asimètrica i presenta un alt patró de concavitat o convexitat, el model no prediu adequadament la distribució d'EGR. A més, l'estudi conclou que, tot i que en els assajos experimentals la taxa d'EGR afecta a la dispersió d'EGR, el model 1D no és tan sensible com per predir aquesta influència quan la taxa d’EGR està per baix del 10%.
[EN] The objective of the study is twofold. On the one hand, it is to determine the effect of the high pressure (HP) exhaust gas recirculation (EGR) dispersion in automotive diesel engines on NOx and smoke emissions in steady engine operation. The investigation quantifies the smoke emissions as a function of the dispersion of the HP EGR among cylinders. On the other hand, it is to explore the limits of the one-dimensional (1D) modeling to predict the movement of the flow in a complex situation as the gases get into the cylinders from the intake manifold. The experiments are performed on a test bench with a 1.6 liter automotive diesel engine. In order to track the HP EGR dispersion in the intake pipes, a valves system to measure CO2, hence EGR rate, pipe to pipe was installed. In the same way, a valves device to measure NOx emissions cylinder to cylinder in the exhaust was installed too. Moreover a smoke meter device was installed in the exhaust line, downstream the turbine, to measure the effect of the HP EGR dispersion on smoke emissions. A probe to measure the other raw emissions was installed downstream the turbine, too. Nine different engine running conditions were studied at different speed and load, thus the engine map was widely studied, from 1250 rpm to 3000 rpm and between 3 and 20 bar of BMEP. The EGR rate variates between 5 and 42 % depending on the working operation point. The geometry of the model reproduces the geometry of a 1.6 liter diesel automotive engine where the tests were performed. It includes an HP-EGR line and the device that was installed to perform the experiments to control the dispersion. The methodology focused on experimental tools combining traditional measuring devices with a specific valves system which offers accurate information about species concentration in both the intake and the exhaust manifolds. The study was performed at constant raw NOx emissions to observe the effect of the EGR dispersion in the opacity values. Regarding the methodology focused on modeling tools, the boundary conditions and all the necessary information to run the model comes from experimental results measured with the different sensors and devices mentioned before. Much of them were needed to adjust the model. The most important part of the modeling to study the capacity of the prediction of the EGR dispersion is the layout of the intake manifold. It is necessary put special attention to the orientation of the pipes, and the internal structure and surface trying to mimic the real geometry because it determinates the prediction of the dispersion. This approximation to quasi-three-dimensional (3D) modeling is possible thanks to a specific software that imports the necessary information from a computer-aided design (CAD) file to the 1D modeling software. Concerning the experimental results, the study leads to conclude that when the EGR dispersion is low, the opacity presents reduced values in all operation points. However, above a certain level of EGR dispersion, the opacity increases dramatically with different slopes depending on the engine running condition. This study allows quantifying this EGR dispersion threshold. In addition, the EGR dispersion could contribute to an increase in the engine fuel consumption up to 6.9%. Regarding to the modeling part, the study concludes that when the experimental EGR distribution among pipes is asymmetric and presents high concavity or convexity spatial pattern, the model does not predict properly the EGR distribution. In addition, the study concludes that, although in the experimental tests the EGR rate affects to the EGR dispersion, the 1D model is not too sensitive to predict this influence when the EGR rate is lower than 10%.
The respondent wishes to acknowledge the financial support received by contract FPI 2015 S2 3101 of Programa de Apoyo a la Investigación y Desarrollo (PAID) from Universitat Politècnica de València (UPV).
Miguel García, J. (2021). Analysis of the high pressure EGR dispersion among cylinders in automotive diesel engines [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/161889
TESIS

This thesis deals with turbulent mixing processes occurring in internal combustion engines, when applying exhaust gas recirculation (EGR). EGR is a very efficient way to reduce emissions of nitrogen oxides (NOx) in internal combustion engines. Exhaust gases are recirculated and mixed with the fresh intake air, reducing the oxygen con- centration of the combustion gas and thus the peak combustion temperatures. This temperature decrease results in a reduction of NOx emissions. When applying EGR, one is often faced with non-uniform distribution of exhaust among and inside the cylinders, deteriorating the emission performance. The mixing of exhaust gases and air is governed by the flow in the engine intake manifold, which is characterized by unsteadiness due to turbulence and engine pulsations. Moreover, the density cannot be assumed to be constant due to the presence of large temperature variations.Different flow cases having these characteristics are computed by compressible Large Eddy Simulations (LES). First, the stationary flows in two T-junction type geometries are investigated. The method is validated by comparison with experimental data and the accuracy of the simulations is confirmed by grid sensitivity studies. The flow structures and the unsteady flow modes are described for a range of mass flow ratios between the main and the branch inlet. A comparison to RANS computations showed qualitatively different flow fields.Thereafter, pulsating inflow conditions are prescribed on the branch inlet in or- der to mimic the large pulsations occurring in the EGR loop. The flow modes are investigated using Dynamical Mode Decomposition (DMD).After having established the simulation tool, the flow in a six-cylinder engine is simulated. The flow is studied by Proper Orthogonal Decomposition (POD) and DMD. The mixing quality is studied in terms of cylinder-to-cylinder non-uniformity and temporal and spatial variances. It was found that cycle-averaging of the concentration may give misleading results. A sensitivity study with respect to changes in the boundary conditions showed that the EGR pulsations, have large influence on the results. This could also be shown by POD of the concentration field showing the significance of the pulses for the maldistribution of exhaust gases.Finally, the flow in an intake manifold of a four-cylinder engine is investigated in terms of EGR distribution. For this geometry, pipe bends upstream of the EGR inlet were found to be responsible for the maldistribution.

QC 20130207

The objectives in this thesis are to present a model of a variable venturi in an exhaust gas recirculation (EGR) system located in a heavy duty diesel engine. A new legislation called EURO~4 will come into force in 2005 which affects truck development and it will require an On-Board Diagnostic system in the truck. If model based diagnostic systems are to be used, one of the advantages is that the system performance will increase if a model of a variable venturi is used.

Three models with different complexity are compared in ten different experiments. The experiments are performed in a steady flow rig at different percentage of EGR gases and venturi areas. The model predicts the mass flow through the venturi. The results show that the first model with fewer simplifications performs better and has fewer errors than the other two models. The simplifications that differ between the models are initial velocity before the venturi and the assumption of incompressible flow.

The model that shows the best result is not proposed by known literature in this area of knowledge and technology. This thesis shows that further studies and work on this model, the model with fewer simplifications, can be advantageous.

This master‘s thesis deals with design adjustment of spark ignition combustion engine, which might offer larger share of recirculated exhaust gases in cylinder for reaching a large number of benefits that exhaust gas recirculation can offer. The introductory theoretical part describes exhaust gas recirculation and its influence on spark ignition combustion engine. In the following part the methods of mixture layering and types of intake ports are described. Further design of spiral intake port is made based on calculations. Capability of mixture layering is valuated by numerical simulation. Flow properties of intake ports are compared to production version by an experiment on flow station.

The object of the diploma thesis is to optimize vacuum function of the ejector using computional fluid dynamics, or CFD. The ejector is inserted to the intake system of the six - cylinder diesel engine to increase the pressure gradient of the exhaust gas recirculation system. The analysis of the current design solution is performed and then the ejector with the new shape affording higher vacuum effect is proposed. The introductory part is devoted to the questions of diesel engines emissions and technology to reduce emissions in the exhaust system focused on the EGR.

The object of this thesis was Proposal and Examination of Supercharging Alternatives of CI-engine with Exhaust Gas Recirculation according required engine power parameters. This goal was meet by use of Turbocharger with Variable Nozzles and Air-Air intercooler.

Petroleum powered vehicles emit volatile organic compounds (VOCs) through combustion that contributes to the pollution of the environment. A technique in the 1970s was developed to decrease these emissions, especially for nitrogen oxides (NOx) and sulphuric oxides (SOx) which is called exhaust gas recirculation (EGR). The technique works by recirculating a portion of the combusted gas back into the engine, this limits the NOx and SOx emissions because of lower temperatures and less available oxygen. The problems that follow these effects is the formation and condensation of acids that corrode the material of the EGR system, which are created by many different reactions. It is of importance to understand how the compounds in the EGR system behaves through analysis of authentic and simulated condensates, which is why a quantitative method for these compounds are of interest. The aim of the project was to develop a simple quantitative analysis method for formic acid, acetic acid, and lactic acid in aqueous solution, which was done at Gränges Sweden AB. The technique used for detection and quantification was gas chromatography (GC) coupled to a flame ionization detector (FID) and a water compatible polyethylene glycol (PEG) column. Fractional factorial design (FFD) was used for determination of adequate operating parameters of the GC method and the sample preparation. Sample preparation only required filtration and pH adjustment prior to direct aqueous injection (DAI) to the chromatographic instrument. Detection of the analytes was very difficult because of non-compatibility with the FID, and quantification of asymmetric peak shapes made this problem worse, omitting lactic acid from further analysis. Limit of detection (LOD) and limit of quantification (LOQ) was 490 and 1640 ppm for formic acid and 120 and 400 ppm for acetic acid, with an injection volume of 0.3 μL and split ratio 10:1. Limits were too high for every EGR sample leaving no peaks detected for the sample preparation used. Further development should be done with complementary techniques and sample reprocessing in order to quantify the compounds.

Controlled Auto Ignition (CAI) combustion is a new combustion principle in internal combustion engines which has in recent years attracted increased attention. In CAI combustion, which combines features of spark ignition (SI) and compression ignition (CI) principles, air/fuel mixture is premixed, as in SI combustion and auto-ignited by piston compression as in CI combustion. Ignition is provided in multiple points, and thus the charge gives a simultaneous energy release. This results in uniform and simultaneous auto-ignition and chemical reaction throughout the whole charge without flame propagation. CAI combustion is controlled by the chemical kinetics of air/fuel mixture with no influence of turbulence. The CAI engine offers benefits in comparison to spark ignited and compression ignited engines in higher efficiency due to elimination of throttling losses at part and idle loads. There is a possibility to use high compression ratios since it is not knock limited, and in significant lower NOx emission (≈90%) and particle matter emission (≈50%), due to much lower combustion temperature and elimination of fuel rich zones. However, there are several disadvantages of the CAI engine that limits its practical application, such as high level of hydrocarbon and carbon monoxide emissions, high peak pressures, high rates of heat release, reduced power per displacement and difficulties in starting and controlling the engine. Controlling the operation over a wide range of loads and speeds is probably the major difficulty facing CAI engines. Controlling is actually two-components as it consists of auto-ignition phasing and controlling the rates of heat release. As CAI combustion is controlled by chemical kinetics of air/fuel mixture, the auto-ignition timing and heat release rate are determined by the charge properties such as temperature, composition and pressure. Therefore, changes in engine operational parameters or in types of fuel, results in changing of the charge properties. Hence, the auto-ignition timing and the rate of heat release. The Thesis investigates a controlled auto-ignition (CAI) combustion in internal combustion engines suitable for transport applications. The CAI engine environment is simulated by using a single-zone, homogeneous reactor model with a time variable volume according to the slider-crank relationship. The model uses detailed chemical kinetics and distributed heat transfer losses according to Woschini's correlation [1]. The fundamentals of chemical kinetics, and their relationship with combustion related problems are presented. The phenomenology and principles of auto-ignition process itself and its characteristics in CAI combustion are explained. The simulation model for representing CAI engine environment is established and calibrated with respect to the experimental data. The influences of fuel composition on the auto-ignition timing and the rate of heat release in a CAI engine are investigated. The effects of engine parameters on CAI combustion in different engine concepts fuelled with various fuels are analysed. The effects of internal gas recirculation (IEGR) in controlling the auto-ignition timing and the heat release rate in a CAI engine fuelled with different fuels are investigated. The effects of variable valve timings strategy on gas exchange process in CAI engine fuelled with commercial gasoline (95RON) are analysed.

This dissertation presents a detailed account of the study undertaken on the subject of fouling of Exhaust Gas Recirculator (EGR) coolers. The fouling process in EGR coolers is identified to be due to two primary reasons â deposition of fine soot particles and condensation of hydrocarbons known as dry soot and wet soot fouling, respectively. Several numerical simulations are performed to study the fouling process. Preliminary analysis of the particle forces for representative conditions reveal that drag, thermophoresis and Brownian forces are the significant transport mechanisms and among them, the deposition process is dominated by thermophoresis. Soot deposition in a representative turbulent plain channel shows a direct relationship of the amount of deposition with the near-wall temperature gradient. Subsequently, periodic and developing flow simulations are performed on a wavy channel geometry, a common EGR design for various Reynolds numbers and thermal boundary conditions. Constant heat flux boundary condition is used in the periodic fully-developed calculations, which assist in establishing various deposition trends. The wavy nature of the walls is noted to affect the fouling process, resulting in specific deposition patterns. For the lower Reynolds number flows, significantly higher deposition is observed due to the higher particle residence times. On the other hand, the developing flow calculations facilitate the use of wall temperature distributions that typically exist in EGR coolers. The linear dependence of the amount of deposition on the near-wall temperature gradient or in other words, the heat flux, is ascertained. It is also observed in all the calculations, that for the sub-micron soot particles considered, the deposition process is almost independent of the particle size. In addition, the nature of the flow and heat transfer characteristics and the transition to turbulence in a developing wavy channel are studied in considerable detail. Finally, a study on the condensation of heavy hydrocarbons is undertaken as a post-processing step, which facilitates the prediction of the spatial distribution and time-growth of the combined fouling layer. From the calculations, the maximum thickness of the dry soot layer is observed to be near the entrance, whereas for the wet soot layer, the peak is found to be towards the exit of the EGR cooler. Further, parametric studies are carried out to investigate the effect of various physical properties and inlet conditions on the process of fouling.
Master of Science

Im Rahmen dieser Arbeit erfolgte eine Analyse des Einflusses von Harnstoff-SCR-Technik auf die Partikelemission. Zudem wurde mit der Partikelkonfektionierung durch motorische Maßnahmen eine Möglichkeit zur Verbesserung der katalytischen Partikeloxidation aufgezeigt und untersucht. Untersuchungen mit einem Nfz-Dieselmotor zeigen, dass im Teillastbetrieb mit einem Harnstoff-SCR-System eine deutliche Partikelminderung möglich ist. Sie basiert im Wesentlichen auf der Oxidation organisch löslicher Bestandteile der Partikel im Katalysator. Reduktionsmitteldosierung drängt die Oxidation leicht zurück, die SCR erweist sich als zur Partikeloxidation konkurrierend. Die Charakteristik der Partikelgrößenverteilung wird durch das SCR-System nicht wesentlich verändert, jedoch kann analog zur emittierten Partikelmasse auch die Partikelanzahl deutlich abgesenkt werden. Eine Analyse hinsichtlich der Partikelbestandteile in unterschiedlichen Partikelgrößenklassen hat gezeigt, dass der Anteil organisch löslicher Substanzen mit zunehmender Partikelgröße absinkt. Durch Veränderung des Einspritzbeginns des Kraftstoffs ist die Konfektionierung der Partikelemission im Sinne besserer katalytischer Oxidation möglich. Dabei wird durch Frühverstellung der Anteil organisch löslicher Komponenten der Partikel deutlich erhöht, gleichzeitig ist eine intensive Nanopartikelbildung zu beobachten. Ein Katalysator auf V2O5/WO3/TiO2-Basis ist sehr gut zur Oxidation sowohl der Nanopartikel als auch des größten Teils der organisch löslichen Komponenten geeignet. Damit wird insgesamt eine deutliche Partikelminderung erzielt. Abgasrückführung behindert die Partikelkonfektionierung zunächst deutlich. Durch die dabei jedoch mögliche noch weitere Verlagerung des Einspritzzeitpunktes nach "früh" kann der negative Einfluss aber weitgehend kompensiert werden, so dass eine ähnlich gute Partikelminderung wie im Betrieb ohne AGR bei gleichzeitiger Minderung der Stickoxidemission möglich ist.

Aujourd’hui, les constructeurs automobiles continuent de chercher les technologies renouvelables face à la pénurie d’énergie et les problèmes d’émission de polluants. Un moyen important pour optimiser l’économie de carburant et réduire les émissions polluantes des moteurs à allumage commandés est le concept ‘downsizing’. Cependant, ce concept est limité par le phénomène de cliquetis dû aux conditions de haute température et haut pression. Dans cette étude, le contrôle de la concentration d’oxygène dans l’air est proposé. Car d’une part, la combustion enrichie en oxygène permet d’améliorer la densité de puissance de moteur avec le même niveau de pression d’admission. Cela permet soit de ‘booster’ la combustion pour augmenter la puissance du moteur ou de l’activer lorsque le moteur fonctionne à faible charge ou dans des conditions de démarrage à froid. D’autre part, une faible concentration en oxygène dans l’air (ou dilution de N2) par un système membranaire peut être considérée comme une alternative à la recirculation des gaz d’échappement. Les expériences ont été effectuées dans un moteur monocylindre ‘downsizing’ avec différents taux d’oxygène et richesse. L’étude de l’impact du contrôle de la concentration d’oxygène sur les caractéristiques de combustion et d’émissions a été effectuée pour plusieurs charges en fonctionnement optimum pour limiter la consommation spécifique de carburant. L’effet de la concentration en oxygène sur les caractéristiques de combustion du moteur a été simulé en utilisant le logiciel commercial AMESim avec le modèle de combustion développé par IFP-EN. En mettant en oeuvre des corrélations de la vitesse de combustion laminaire, déterminées au préalable durant ce travail, et délai d’auto-inflammation, les pressions dans les cylindres sont parfaitement calibrés avec une erreur maximale inférieure à 2% et l’intensité du cliquetis a pu être prédite
Nowadays, car manufacturers continue to lead researches on new technologies facing to the energy shortage and pollutant emission problems. A major way to optimise fuel economy and reduce pollutant emissions for Spark-Ignition (SI) engines is the downsizing concept. However, this concept is unfortunately limited by ‘knock’ phenomena (abnormal combustion) due to high temperature and high pressure in-cylinder conditions. In the present study, control the oxygen concentration in air is proposed. Indeed, on the one hand, oxygen-enriched combustion can improve engine power density with the same intake pressure level. Thus, oxygen-enriched combustion can be used either as a booster to increase engine output or as a combustion enhancer when the engine operates at low loads or in cold start conditions. On the other hand, low oxygen concentration in air (or N2 dilution) can be considered as an alternative to exhaust gas recirculation (EGR). The experiments were carried out in a downsized single-cylinder SI engine with different rates of oxygen and equivalence ratios. The study of the impact of controlling oxygen concentration on the combustion characteristics and emissions was performed at several loads by optimizing the spark advance and the intake pressure to maintain the load and obtain a minimum value of indicated Specific Fuel Consumption (SFC). The effect of oxygen concentration on the engine combustion characteristics was simulated by using the commercial software AMESim, with the combustion model developed by IFP-EN. By implementing correlations for the laminar burning velocity, determined previously during this study, and auto-ignition delay data base, the in-cylinder pressures were perfectly calibrated with a maximum pressure relative error less than 2%, and the knock intensity was predicted

The scope of this dissertation work is a description of modern methods of reducing exhaust emission in diesel engines. The fundamental part is the application of these methods for diesel engines for off-road use that means for engines that are used in tractors and road machines. The mentioned evidence for the practical utility of the results of this dissertation thesis in practice and their verification on the actual engine are given in the conclusion.

A masters thesis deals with the question of deisel engine boosting by rotary turbochargers. The objective of the thesis is to propose suitable turbocharger´s concept for defined diesel combustion engine with power of 430 [kW]. The air boosting pressure is controlled by exhaust gas flow through the turbine and different EGR regimes, which are considered in the basic and corrected calculations. The final turbocharger´s concept is proposed to satisfy the defined technical requirements. Next technical recommendations are briefly summarized in the thesis conclusion for following turbocharger´s concept application.

The aim of pollutant emissions legislation is to bring environmental benefit by helping reduce, for what road transport is responsible, the concentration of pollutants where levels are too high and endanger human health. Europe is considering several changes in “post Euro 6d” regulation from 2025. Several measures have been proposed for Euro 7, most of which introduce new challenges in the development of high-performance turbocharged gasoline engine such as the extension of lambda 1 in the whole engine map. In this Master Thesis, possible technologies to expand the engine operating range with lambda 1 in the entire engine map, without widely reducing the engine performances are analyzed. In particular the focus is on the Pre-Chamber Spark Ignition (PCSI), the Exhaust Gas Recirculation (EGR), the Miller Cylce, the Water Injection and the Ultra High Pressure Injection. Subsequently, the modeling and validation in Simulink/Matlab of thermal models to analyze and monitor the exhaust gas temperature in the entire exhaust system is presented and explained. The aim of the modeling is integrating the modules into the Model-in-the-Loop environment and co-simulating with GT-Power/Simulink for a virtual pre-calibration of exhaust gas temperature control. Finally, homologation cycles are run to obtain a first analysis feedback regarding the pre-calibration and to understand which are the cycle zones where the fuel enrichement will be necessary to reach the desired temperature.

Im Rahmen dieser Arbeit werden die Potenziale zur Steigerung des Gesamtwirkungsgrads von stöchiometrisch homogen betriebenen Ottomotoren in der Teillast untersucht. Im Gegensatz zur konventionellen Laststeuerung über die Drosselklappe bezeichnet die betrachtete, drosselfreie Laststeuerung die Quantitätsregelung einzig über den Hubverlauf der Gaswechselventile. Nach einer Zusammenfassung bisheriger Untersuchungen zur drosselfreien Laststeuerung werden konkurrierende Bilanzierungsverfahren von Ladungswechsel- und Hochdruckteil von 4-Takt Verbrennungsverfahren vorgestellt. Anhand theoretischer Betrachtungen folgt für eine belastbare Bewertung der Prozessgüte allein die Bilanzierung in den Grenzen der Unteren Totpunkte (UT-UT). Im ersten Teil der motorischen Untersuchungen am Vollmotor wird das effektive Potenzial mechanisch variabler Ventiltriebe ermittelt. Dabei bleibt die Verbrauchsverbesserung gegenüber einem gedrosselten Referenzmotor aufgrund sinkender Restgasverträglichkeit als Folge einer nachteiligen Abnahme der Ladungsbewegung hinter den Erwartungen zurück. Im Widerspruch zu mechanisch gekoppelten Systemen wird zur bedarfsgerechten Anpassung der Ladungsbewegung die Forderung nach maximaler Flexibilität der Ventilhubgestaltung abgeleitet. Im zweiten Teil der motorischen Untersuchungen am Einzylinder-Forschungsmotor werden die maximalen Freiheitsgrade eines nockenwellenlosen Ventiltriebs basierend auf dem Prinzip eines elektromotorischen Linearantriebs systematisch eingesetzt. Neben konstruktiven Maßnahmen zur Beeinflussung des Einströmvorgangs in den Brennraum wird die Reduzierung der Drosselverluste durch Hubverlaufsformung sowie gezielte Restgasverdünnung im Vergleich von interner zu externer Rückführung betrachtet. Der Einfluss der Gemischbildung wird über die konkurrierende Darstellung von innerer und äußerer Kraftsteinspritzung aufgezeigt. Neben den maximalen Potenzialen werden ebenso die Grenzen der Entdrosselung dargestellt. Im Gegensatz zu mechanischen Systemen gelingt zwar die Realisierung einer bedarfsgerechten Ladungsbewegung mit Hilfe vollvariabler Ventilhübe, jedoch wird eine fortgesetzte Verbrauchsverbesserung durch die Gewährleistung einer sicheren Entflammung limitiert.

碩士
國立海洋大學
機械與輪機工程學系
89
The popular usage of automobiles has provided convenience to the life of human beings. But the problems left behind like air pollutions, acid rain, and global warming, are getting more and more serious. To resolve the problem of air pollutions, one of the most often used methods is to use alternative fuels, such as LPG or natural gas. The CO and HC exhaust emissions are less for an LPG engine due to the greater extent of combustion. The higher H/C ratio of LPG also causes lower CO2 emissions. However, LPG engines are reported to have higher NOx emissions than gasoline engines. This study aims on the reduction of NOx emissions of an LPG engine by exhaust gas recirculation. The engine used in the study is modified from a diesel engine to be spark-ignited and equipped with a three-way catalytic converter. The effects of exhaust emissions and engine performance are studied by changing parameters like air-ratio, compression ratio, engine speed, load, and the percentage of exhaust gas recirculation. The experimental results show that greater extent of improvement on NOx emissions is obtained at a higher EGR percentage. However, the usage of EGR also caused lower brake torque output due to lower volumetric efficiency, accompanied by slightly increased CO and HC emissions due to poorer combustion characteristics. Although engine brake torque output may be improved by using a higher compression ratio, the HC, CO, and NOx exhaust emissions are also increased accordingly. Better results on exhaust emissions may be obtained by using 20% EGR with air-fuel ratio controlled at 1.1 or 1.2 and with the assistance of three-way catalytic converter.

碩士
國立交通大學
機械工程系所
102
In this research, the property of anode exhaust gas recirculation of a solid oxide fuel cell (SOFC) system equipped with an ethanol steam reforming fuel pre-processing unit is investigated. An integrated steady state system with recycling unit has been built in Matlab/Simulink to examine the effect of recirculation ratio change. In the previous research, the water gas shift reaction and methanation reaction is rarely applied in reforming reaction and electricity generating unit. However, in the system with recycling mechanism, the CO2 density is high. The CO density and methanation reaction configuration inside the whole system are greatly affected by the rising CO2 density. Thus, these two equations are added in both the reformer and full cell stack of this study to construct a more precise simulation. A 5kW system with fuel utilization 70% and water-to-ethanol ratio (Rae) 3 is presented. The chemical equilibrium configuration of reformer and solid oxide fuel cell are calculated by adopting the theory of Van’t Hoff’s equation. The thermal and electricity efficiency are enhanced with the increasing recycling rate. However, the performance of reformer and fuel cell stack is lowered with the increasing Rrec. The gas component has been great diluted with the rising amount of carbon dioxide in recycled gas. Without the anode gas recirculation design, the heat efficiency is 29.83%, the electricity efficiency is 40.75%. With the anode gas recirculation from Rrec 0.2~0.8, the electricity efficiency increases monotonically from 43.07% to 50.01%, the heat efficiency increases from 31.44% to 33.83%. After removing CO2, the efficiencies from Rrec 0.2~0.8 are 26.28% to 29.06% for heat efficiency, and the electricity efficiency from 29.27% to 26.05%, from 46.26% to 53.65%, respectively.

Reducing the emissions of Nitric Oxides from diesel engines is one of the main challenges facing diesel engine designers. Many different methods have been investigated for reducing NO₂ emissions, including exhaust gas recirculation (EGR) and the high pressure direct injection (HPDI) of natural gas. Combining these two techniques offers the potential to reduce NO₂ emissions further than either method can individually. To test the effects of EGR on an HPDI engine, the University of British Columbia's Alternate Fuels Research Group recently received a new Cummins ISX heavy-duty truck engine, modified for single-cylinder operation. The new engine was commissioned on HPDI and a series of tests were run to compare its performance and emissions to a six-cylinder HPDI engine. These results showed good agreement for performance, but some significant differences in emissions between the two engines. Although emissions data are not directly transferable to a six-cylinder engine, the trends and general effects identified through testing on the single cylinder engine should be applicable to all HPDI engines. The new engine has also been used to study the combination of EGR and HPDI. While of a preliminary nature, the results indicate that significant NO₂ reductions can be achieved, with the greatest effects being found at low-speed, moderate-load operating conditions. Reductions in NO₂ emissions of as much as an order of magnitude were detected, but these extreme reductions came at the price of increased hydrocarbon emissions and reduced engine performance. More moderate reductions in NO₂ can be achieved with little penalty in either performance or emissions.

A mini-dilution tunnel was designed and built to measure particulate matter (PM) emissions from a single-cylinder research engine (SCRE) based on the Cummins ISX 400 series. The SCRE relies on the high-pressure direct injection of natural gas, pilot ignited with diesel fuel for combustion. Two methods were used for PM measurements: pre-weighed filters and a tapered element oscillating microbalance (TEOM). A repeatability study was conducted to determine the experimental error associated with PM measurements and to compare results from pre-weighed filters with those taken using a TEOM. The PM emission rate uncertainty was determined to be at maximum 29%, with 10-12% due to measurement uncertainty and the remainder due to poor engine repeatability. PM emission rates from the TEOM showed excellent correlation with measurements using pre-weighed filters by applying a correction factor of 1.43. The second part of this work was to examine the effect of replacement exhaust gas recirculation (EGR) on particulate emissions. EGR is primarily used in engines to reduce the formation of oxides of nitrogen (NOx). The drawback of using high EGR flow rates is a deterioration in combustion and an increase in the amount of unburned species (HC, CO, PM) that are formed. The results show the PM penalty is negligible for EGR rates up to 15% and that increasing the exhaust pressure significantly affects PM and CO emissions. It was also found that increasing the amount of diesel pilot at 800 RPM 75% load with 17% EGR significantly increases PM and CO emissions.

Thesis (M.S.)--University of Wisconsin--Madison, 2001.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 77-78).