Dissertations / Theses on the topic 'Fuel-air mixture'

The effect of air composition on the formation of a stoichiometric fuel -air mixture for combustion in aircraft engines is showed. A method for increasing the efficiency of burning aviation fuel, based on the actualization of information on the current concentration of oxygen in the atmosphere is proposed.

Диссертация на соискание ученой степени кандидата технических наук по специальности 05.05.03 – двигатели и энергетические установки. Национальный технический университет "Харьковский политехнический институт", Харьков, 2016 г. Диссертация посвящена улучшению эколого-экономических показателей двухтактных ДВС с искровым зажиганием путем применение системы непосредственного впрыска топлива в камеру сгорания. На двигателе ДН-4М проведены экспериментальные исследования с расслоением и обеднением топливновоздушного заряда при непосредственном впрыске топлива. Для обеспечения организации расслоенного топливновоздушного заряда применяется клапанная форсунка с модернизированным распылителем (техническая новизна защищена патентом Украины на изобретение), обеспечивающим кумулятивную топливную струю, направленную на поверхность камеры сгорания возле электродов свечи зажигания. На такте сжатия воздушный поток движется над топливной пленкой, где организуется обогащенная топливновоздушная смесь, которая направляется к электродам свечи зажигания. При этом на режимах холостого хода и на частичных нагрузках на момент подачи искры зажигания на периферии топливновоздушной смеси, возле стенок надпоршневого объема, располагается воздушный заряд с продуктами сгорания. Выявлено, что резервами повышения показателей работы двигателя являются снижение тепловых потерь с отработавшими газами и в систему охлаждения. В двухтактных двигателях с искровым зажиганием при непосредственном впрыскивании топлива и с расслоением топливновоздушного заряда при использовании бензо-этанольных смесей обеспечивается устойчивая работа во всем диапазоне нагрузок без изменений регулировочных параметров с более высокими экономическими и экологическими показателями, чем в аналогичных двигателях с внешним смесеобразованием.
Thesis to obtain scientific degree of Candidate of Engineering sciences on the speciality 05.05.03 – engines and power plants. National Technical University "Kharkiv Polytechnic Institute", Kharkov, 2015. The dissertation is devoted to improving environmental and economic performance two-stroke internal combustion engines with spark ignition by the use of direct fuel injection. Determined that a promising way of internal mixing with direct fuel injection is the organization layered fuel-air charge, providing improved environmental and economic performance. The criterion L, which characterizes the stratification of the fuel-air charge, can qualitatively assess the effect of mixing process on the performance of the engine as a whole. A factor Z, which is deter-mined using indicator efficiency two-stroke engine with external mixture formation, which takes into account only that fuel which is involved in the combustion cylinder engine. The use of direct injection petrol bundle of fuel-air charge modes for loading characteristic at n = 3000 rev/min enabled the reduction in fuel con-sumption of 1.83 times at the effective efficiency rjfmax = 0,31, 7-10 times lower harmful substances (CO, CH) in exhaust gases, the use of gasoline-ethanol blends ensured stable operation of the engine in all load range and a high economic and environmental performance than when using carburetor system power.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.05.03 – двигуни та енергетичні установки. Національний технічний університет "Харківський політехнічний інститут". – Харків, 2016 р. Дисертація присвячена поліпшенню еколого-економічних показників двотактних ДВЗ з іскровим запалюванням шляхом застосування безпосереднього вприскування палива. Визначено, що перспективним способом внутрішнього сумішоутворення при безпосередньому вприскуванні палива є організація розшарованого паливоповітряного заряду, що забезпечує покращення еколого-економічних показників. Запропоновано критерій L, який характеризує рівень розшарування паливоповітряного заряду, дозволяє якісно оцінити вплив процесів сумішоутворення на показники двигуна в цілому. Запропоновано коефіцієнт Z, за допомогою якого визначається індикаторний ККД двотактного двигуна із зовнішнім сумішоутворенням, який враховує тільки те паливо, яке згоряє в циліндрі ДВЗ. Застосування безпосереднього вприскування бензину з розшаруванням паливоповітряного заряду на режимах навантажувальній характеристиці при n = 3000 хв-1 дозволило зменшити в 1,83 рази витрати палива при значенні ефективного ККД ηе max = 0,31, в 7–10 раз знизити вміст шкідливих речовин (СО, СН) у відпрацьованих газах, також використання бензо-етанольних сумішей забезпечило стійку роботу двигуна у всьому діапазоні навантажень та більш високі економічні і екологічні показники, чим при використанні карбюраторної системи живлення.
Thesis to obtain scientific degree of Candidate of Engineering sciences on the speciality 05.05.03 – engines and power plants. National Technical University "Kharkiv Polytechnic Institute", Kharkov, 2015. The dissertation is devoted to improving environmental and economic performance two-stroke internal combustion engines with spark ignition by the use of direct fuel injection. Determined that a promising way of internal mixing with direct fuel injection is the organization layered fuel-air charge, providing improved environmental and economic performance. The criterion L, which characterizes the stratification of the fuel-air charge, can qualitatively assess the effect of mixing process on the performance of the engine as a whole. A factor Z, which is deter-mined using indicator efficiency two-stroke engine with external mixture formation, which takes into account only that fuel which is involved in the combustion cylinder engine. The use of direct injection petrol bundle of fuel-air charge modes for loading characteristic at n = 3000 rev/min enabled the reduction in fuel con-sumption of 1.83 times at the effective efficiency rjfmax = 0,31, 7-10 times lower harmful substances (CO, CH) in exhaust gases, the use of gasoline-ethanol blends ensured stable operation of the engine in all load range and a high economic and environmental performance than when using carburetor system power.

The Partially Stratified Charge (PSC) strategy aims to stabilize the spark ignition of lean-burn natural gas fueled internal combustion engines. This results in an extension of unthrottled load control, as well as a reduction in regulated pollutant and carbon dioxide emissions. While engine experiments demonstrated the feasibility of this technology, its fundamental enabling mechanisms have yet to be identified. An experimental / numerical approach was taken for the current investigation, using an idealized PSC ignition system. The PSC injection took place in a constant volume combustion chamber (CVCC) into an initially quiescent bulk mixture. A customized injection system was also developed. Experimental results indicated that stable combustion could be achieved with PSC at an air-to-fuel ratio of λ = 2.0. Furthermore, the use of double PSC injection facilitated additional consumption of the bulk fuel. The experiments also identified three primary enabling mechanisms under which PSC assists in ultra-lean spark ignited combustion. Additional insights were provided through numerical modeling. The PSC jet was modeled using the standard k−epsilon model and was found to be in excellent agreement with the experimental results in terms of penetration and entrainment. Meanwhile, the Eddy Dissipation Concept (EDC) model was used to simulate the combustion under PSC. While the computational model lacked the ability to properly predict combustion rates in the turbulent-to-laminar flame transition, the ignition and early combustion phases were properly captured. The numerical framework was applied to engine conditions, and the modeled data were validated using existing experimental results. A semi-analytical ignition model was developed using detailed chemical kinetic mechanisms. A turbulent ignition parameter was derived accordingly to characterize the likelihood of an ignition event leading to combustion. The engine simulation results also provided further information in PSC charge formation, as well as flame propagation. The results of this research gave rise to an improved design for future generation PSC injection / ignition devices.

Forskning inom motorutveckling bedrivs för att möta kommande emissionskrav och samtidigt minska bränsleförbrukningen. Kommande förbud mot dieseldrivna fordon planeras i flera städer runt om i världen. Alternativa bränsle som exempelvis naturgas ses som en lovande ersättning även för tunga fordon. Metan som är huvudkomponenten av naturgas har en fördelaktigt förhållande mellan väte och kol vilket gör den attraktiv för CO2-reducering. Hur som helst, bränslets låga cetantal och den höga aktiveringsenergin som krävs för att tända naturgas förutsätter tändstiftsantändning.En fördel av att använda en encylindrig motor inom forskning är möjligheten att studera fenomen utan negativa gasväxlingsinteraktioner från intilliggande cylindrar. Jämfört med en fullmotor möjliggörs även ett snabbare utbyte av motordelar samt lägre bränsleförbrukning.Fokus för detta examensarbete var genomförandet av ett flexibelt bränslesystem för en tändstiftsantänd encylindrig motor. Motorn är en tändstiftsantänd Scania 9 liters som modifieras för encylinder körning. Flexibilitet som t.ex. laddningshomogenitet, selektiv fyllning av inloppsporter och förberedelser för direktinsprutning av flytande bränsle realiserades. För enkel användning är motorn styrd av en eftermarknadsmotorstyrenhet som använder ett användarvänligt grafiskt gränssnitt för ändring av driftsparametrar. Säkerhetshänsyn vid blandning av gasformiga bränsle och luft långt innan inloppsporterna har implementerats.
Most of the fundamental research in internal combustion engines is driven by the ever-increasing stringency of emissions regulations along with the need for increased fuel economy. The proposed ban on diesel vehicles in several cities around the world combined with extensive availability, has made natural gas a promising substitute even for heavy-duty applications. The high hydrogen-to-carbon ratio of methane, the major component of natural gas, makes it attractive from an emissions reduction perspective. CO2 emissions from natural gas combustion are particularly low. However, the low cetane number and high activation energy required to ignite natural gas, requires spark-ignition.In a research setting, it is often advantageous to have a single cylinder engine. The main benefit is the ability to study phenomena without adverse interactions which multi-cylinder operation may cause. This is especially important for gas-exchange studies. Quicker replacement of parts and lower fuel consumption are secondary benefits.The focus of this thesis was the implementation of a flexible fueling system for a single cylinder spark-ignited engine. The engine is a Scania 9-liter spark-ignited engine modified for single cylinder operation. Flexibility in terms of charge homogeneity, selective intake port filling and provisions for liquid fuel direct injection have been provided. For ease of use, the engine is controlled by an aftermarket engine control unit with a graphical user interface for configuration. Safety considerations when mixing gaseous fuels and air well upstream of the intake ports have been implemented.

En la presente tesis se desarrolla un sistema de control de la mezcla de aire y gasolina en un motor alternativo de cuatro tiempos, basado en redes neuronales. Para que el catalizador logre un grado de depuración aceptable con todos los gases contaminantes simultáneamente, debe mantenerse la proporción de aire y combustible, dentro de una banda muy estrecha. En estado estacionario, este objetivo se cumple sin demasiados problemas, pero el funcionamiento habitual de un vehículo es en régimen muy transitorio, donde los sistemas convencionales no logran evitar desviaciones importantes del punto de consigna. Estos se basan además en una gran cantidad de tablas estáticas, que deben calibrarse de forma experimental, lo cual es bastante costoso tanto en tiempo como en dinero.
Para evitar estos problemas se ha diseñado un modelo matemático de un motor, que comprende todo el proceso de formación de la mezcla, sensores, la generación del par motor y la dinámica del vehículo. La realización final se ha realizado en el lenguaje de simulación MatLab/Simulink®. Los datos requeridos son fácilmente obtenibles bien por metrología, bien de forma experimental. Se ha validado con un motor SEAT de 1,6 l y 74 kW.
Como primer paso se ha aplicado una estrategia de control convencional bastante simple, consistente en un controlador feedforward estático, más un controlador feedback de tipo PI ó PID. Esto ha permitido el estudio de las principales características del motor desde el punto de vista de control.
Con los resultados obtenidos se ha diseñado un observador basado en una red neuronal, que elimine los retardos puros del sistema y que pueda ser utilizado para cerrar el lazo de control. Primero se ha usado una red feedforward, pero vistos los malos resultados, se ha desarrollado una red neuronal recurrente a partir de la red de Elman, que se ha modificado convenientemente para adaptarla a las dificultades propias del problema. El algoritmo de entrenamiento utilizado se basa en el de retropropagación clásico, y modifica no sólo los pesos entre capas, sino también los correspondientes a las neuronas de contexto, las cuales permiten memorizar estados internos. La principal mejora consiste en separar las neuronas de contexto en tantos grupos como entradas tiene la red, y entrenarlos por separado, de modo que cada grupo se adapte a la dinámica particular de la entrada a la que va asociado. Se muestra mediante simulación el comportamiento del conjunto motor más observador en lazo cerrado, y se compara con el esquema convencional. Se prueba asimismo la robustez del sistema frente a distintas consignas, ruido en la planta y defectos de sintonía.
In the present thesis a control system for the air-fuel mixture in a reciprocating four-stroke engine is developed, based on neural networks. The air-fuel ratio has to be kept within a very narrow window so that the catalyst achieves an acceptable degree of purification simultaneously with all the polluting gases. In steady state, this goal can be fulfilled without difficulties, but the usual operation of a vehicle is in a very transient state, where the conventional systems are not able to avoid important excursions from the set point. They also rely on a great number of look-up tables, which have to be tuned experimentally, thus with an enormous investment of money and time.
To avoid those problems a mathematical model of an engine has been designed, in such a way that it comprises of the whole mixture formation process, sensors, the torque generation and the vehicle dynamics. Finally it has been implemented in the simulation language MatLab/Simulink®. The required data is easily available both from metrology, and experimental work. It has been validated with a 1,6 litre 74 kW SEAT engine.
As a first step, a quite simple conventional control strategy has been applied, consisting of a static feedforward controller, and a PI or PID feedback controller. This has permitted studying the main features of the engine from the control point of view.
With the obtained results an observer based on a neural network has been designed, which eliminates the delays of the system and that can be used to close the control loop. First a feedforward network has been used, but due to the bad results, a recurrent neural network has been developed starting from the Elman network, which has been properly modified in order to adapt it to the characteristic difficulties of the problem. The training algorithm used is based on that of classical backpropagation, and it modifies not only the weights interconnecting different layers, but also those corresponding to the context neurons, which allow the memorising of internal states. The main improvement consists in separating the context neurons in as many groups as the network has inputs, and to train them separately, so that each group adapts to the particular dynamics of the input with which it is associated. The behaviour of the engine plus the observer in closed loop is shown by means of simulation, and is compared with the conventional scheme. It is proven the robustness of system response to different set points, noise in the plant and tuning defects.

This study investigates peculiarities of the filtration combustion (FC) of the gaseous fuel-air mixtures in a porous inertia media (PIM). Combustion wave velocities and temperatures were measured for hydrogen-air, propane-air and methane-air mixtures in the PIM at different mixture filtration velocities. It is shown that the dependences of the combustion wave velocities on the equivalence ratio are V-shaped, It was further confirmed that the FC in the PIM has more contrasts than similarities with the normal homogeneous combustion. One of the interesting observations in the present study, which is not common in normal homogenous combustion, is the shifting of the fuel-air equivalent ratio at the minimum combustion wave velocity from the stoichiometric condition (¢ = 1). For a hydrogen-air mixture, the fuel-air equivalence ratio at the minimum combustion velocity shifts from the stoichiometric condition to the rich region, while for the propane-air and methane-air mixtures the fuel-air equivalence ratio at the minimum combustion velocity shifts toward fuel-leaner conditions. The measured maximum porous media temperatures in the combustion waves are found to be weakly dependent on the mixture filtration velocities. In general, the effects of the mixture filtration velocities on the measured maximum porous media temperatures are not significant.

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
國立臺灣科技大學
機械工程系
107
The in-cylinder flow characteristics of a single-cylinder, two-stroke motorcycle engine, which would affetct the mixing and combustion performance were studied. A commercial engine with displancement of 115 c.c. was used as the benckmark which was hereafter called the “original engine”. The computational fluid dynamic software CONVERGE was used to calculate fuel distributions, fuel distribution at ignition, concentration variation, air-fuel ratio at ignition, air-fuel ratio near the spark plug at ignition and tumble ratio as main physical parameters by optimizing the injector position and injector angle. Fixed engine injection parameters (total fuel mass, starting injection crack angle and end injection crack angle), and change the position and angle of injector, discuss the changes of the above 7 main physical parameters. The results show that: (I) changing the position and angle of the injector so that it doesn’t affect the overall air-fuel air ratio in the cylinder. (II) Changing the injector to some special position and angle (There are 10 combinations in the case of this study), the air fuel ratio near the spark plug at ignition can be optimized and the air-fuel distribution at other positions in the cylinder is not deteriorated and the tumble ratio is not deteriorated or enhanced. This may contribute to the improvement of the combustion ignition, flame transfer, combustion producets, etc. (III) Except some of the position and angles described in (II), change the injector position and angle make the aforementioned parameters change obviously, so it may affect the combustion ignition, flame transfer, combustion producets, etc. The original engine has been tuned and tested for overall performance, confirming that the injector position and angle are good. Therefore, it can refer to the original engine, and according to above 7 main physical parameters adjust injector position and angle when designing a new engine.

碩士
崑山科技大學
機械工程研究所
96
In motorcycle, the air/fuel mixture ratio is controlled around the stoichiometric value of 14.7 to improve the conversion efficiency of the catalytic converter and reduce the contained exhaust gas. But in such stoichiometric operation the fuel consumption of the motorcycles will be higher. So far the motorcycles in Taiwan are already equipped with the secondary air device to increase the quantity of oxygen in the exhaust gas to raise the efficiency of the catalytic converter (oxidation catalyst). This project proposes the concept of lean air/fuel mixture to reduce the fuel consumption of motorcycles. At the same time, the conversion efficiency of the catalytic converter will not be affected by the lean air/fuel mixture. Under the conditions of low-speed and medium-speed driving, the lean air/fuel mixture can reduce the fuel consumption and maintain the conversion efficiency and life of catalytic converters. Under the high-speed driving, the secondary air device doesn’t work due to the positive pressure in the pipeline, the efficiency of the catalytic converter will be lower. Controlling the lean air/fuel mixture can increase the quantity of oxygen in the exhaust gas can increase the efficiency of the catalytic converter and reduce the contained exhaust gas under high-speed driving condition. The project will do the following steps. First, the ideal air/fuel mixture control technique will be built. By using the feedforward control and feedback control strategies, the air/fuel mixture ratio will be controlled around 14.7. Next, modify the feedforward control and feedback control strategies to get higher air/fuel ratio to reduce fuel consumption. In order to arrive this target of lean air/fuel mixture, correct air/fuel ratio estimator must be developed under the condition of just using Oxygen sensor for feedback signal of air/fuel ratio. After the lean air/fuel mixture control strategies and air/fuel estimator are developed, they will be validated by experiment data on the test rig in the lab of KSU.

碩士
崑山科技大學
機械工程研究所
99
This thesis proposes a research on the neural network estimator applied on the lean air/fuel mixture control for motorcycles. This NN estimator can estimate the air/fuel ratio under different transient load conditions and help the engine control the air/fuel ratio at 16:1. Using NN estimator can result in the reduction of fuel consumption and improve the power output delay due to instantaneous throttle opening and air/fuel ratio too lean (near 18:1). First, using Matlab/Simulink software, the closed-loop fuel injection control system was written and the air/fuel ratio was changed from 14.7:1 to 16:1, in order to carry out lean air/fuel mixture control for motorcycles. Then, the Neural Network air/fuel ratio estimator was developed by using Matlab/Neural Network package to estimate actual air/fuel ratio from the parameters of fuel injection pulse width, manifold absolute pressure, throttle opening, and engine speed signal. At last, the lean air/fuel mixture control strategy and NN air/fuel estimator were validated by the experimental data from the test rig in the lab of KSU. The results show the engine fuel injection control strategy can regulate the air/fuel ratio to 16:1 in the steady state and the NN estimator can estimate the actual air/fuel ratio in the transient state.