Dissertations / Theses on the topic 'Fuelling spark ignited engines'

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (p. 59).
Experiments were carried out to collect in-cylinder pressure data and microphone signals from a single-cylinder test engine using spark timings before, at, and after knock onset for four different octane-rated toluene reference fuels. This data was then processed and analyzed in various ways to gain insight into the autoignition phenomena that lead to knock. This was done to develop a more fundamentally based prediction methodology that incorporates both a physical and chemical description of knock. The collected data was also used to develop a method of data processing that would detect knock in real time without the need to have an operator listening to the engine. Bandpass filters and smoothing techniques were used to process the data. The processed data was then used to determine knock intensities for each cycle for both the cylinder pressure data and microphone signal. Also, the rate of build-up before reaching peak amplitude in a bandpass filtered pressure trace was found. A trend was found showing that cycles with knock intensities greater than 1 bar with rapid build-up (5-10 oscillations) before reaching the peak are the type the cycles whose autoignition events lead to engine knock.
(cont.) The cylinder pressure knock intensities and microphone knock intensities were plotted and then fit with a linear trendline. The R2 value for these linear trendlines will transition from considerably lower values to values greater than 0.85 at the spark timing of knock onset. It is believed that the higher cylinder pressure knock intensities, in conjunction with the faster build-up of 5-10 oscillations before reaching peak, helps to explain the knock phenomena. It supports conclusions from previous works that the end gas contains one or more hot spots that autoignite in sequence causing pressure gradients that can trigger rapid pressure oscillations. These pressure oscillations can cause block and head vibrations that lead to audible noise outside the engine.
by Bridget M. Revier.
S.M.

As a supplier of sustainable transport solutions, Scania manufactures gas engines. Fueled with biogas, they offer a significant decrease in carbon dioxide emissions compared to standard diesel. The gas engines are fitted with a three-way catalytic converter, which converts hydrocarbons, carbon monoxide and nitrogen oxides from the combustion process to substances with less adverse effects. A misfire is an undesired lack of combustion. They are typically caused by faults in the ignition system, fuel system or by an unsuitable air/fuel ratio. If a misfire occurs, fuel may enter the catalytic converter where it combusts. This increases the temperature in the catalyst to above its design limit, permanently damaging it. The excess fuel also causes increased hydrocarbon emissions. Emission legislation mandates that malfunctions causing excess emissions must be continuously monitored by the vehicle. The misfire detection on engines sold in the North American market must comply with the stringent CARB legislation. It may also be assumed that upcoming European legislation will be stricter. Furthermore, current production engines use dedicated hardware to detect misfires. A misfire detection method that uses signals from sensors already fitted to the engine could result in cost savings. A literature study was performed, after which suitable methods to proceed with were chosen. Data was collected in an engine test cell, and was analyzed offline. Misfire detection methods based on exhaust pressure sensors and knock sensors were evaluated. A detection algorithm developed for Scania’s diesel engines was evaluated. With some modifications, it appears suitable for gas engines. Simplified variants of this method were developed with promising results. A method based on Fourier transform of a low-order frequency showed excellent results, perhaps at the expense of processor load. A knock sensor based method also showed some promise in detecting misfires. However, the position of the knock sensors appears critical, and further investigation is required. Classified parts of this thesis are replaced by the symbol □. Some plot axes are erased for the same reason.
Som en leverantör av hållbara transportlösningar tillverkar Scania gasmotorer. Tankade med biogas minskar dessa utsläppen av koldioxid avsevärt jämfört med standarddiesel. Gasmotorerna är utrustade med en trevägskatalysator som omvandlar kolväten, kolmonoxid och kväveoxider till mindre skadliga ämnen. En misständning innebär utebliven förbränning. Detta beror typiskt sett antingen på fel i tändsystemet, fel i bränslesystemet eller felaktigt luft/bränsleförhållande i cylindern. Om en misständning sker kan oförbränt bränsle ta sig till katalysatorn, där bränslet förbränns. Detta ökar temperaturen i katalysatorn, vilket kan försämra dess prestanda. Det kan även leda till ökade utsläpp av kolväten. Fel som kan påverka utsläpp måste enligt lagstiftning kontinuerligt övervakas av fordonet. Scanias gasmotorer kan komma att säljas på den nordamerikanska marknaden, där kraven på misständningsdetektering är striktare än i övriga världen. Det kan även förväntas att kommande europeisk lagstiftning kommer att vara strängare än tidigare. Tekniken för misständningsdetektering på nuvarande gasmotorer använder dedikerad hårdvara. En misständningsdetekteringsmetod som använder signalen från befintliga givare kan leda till kostnadsbesparingar. Efter en litteraturstudie valdes lämpliga detekteringsmetoder ut för vidare undersökning. Data inhämtades från körningar i provcell och analyserades offline. Metoder baserade på avgasmottryck och på knacksensordata utvärderades. En algoritm utvecklad för misständningsdetektering på Scanias dieselmotorer utvärderades. Med vissa modifieringar verkar den gå att tillämpa på gasmotorer. Förenklade varianter av denna metod utvärderades, även dessa med lovande resultat. En metod baserad på Fouriertransform av lägre ordningens frekvenser i avgastrycksignalen visade utmärkta resultat, eventuellt på bekostnad av processorlast. En knacksensorbaserad metod uppvisade lovande resultat. Dock verkar placeringen av knacksensorerna vara kritisk, och vidare utvärdering krävs. Hemligstämplade delar i denna rapport har ersatts av symbolen □. Axelvärden i vissa figurer har raderats av samma skäl.

Spark-ignited engines are known to produce PM composed of solid, volatile or semi-volatile particles including spheres of carbon soot formed into agglomerates, other forms of carbonaceous particles, metal particles and charred droplets of engine oil. In this thesis, detailed observation has revealed that SI PM is partly composed of fully-formed carbon nanotubes and fullerenes in addition to known particle types previously presented in the literature. The purpose of this work is to ascertain the shape and size of particulate matter being emitted by SI engines. In this thesis, PM thermophoretic sampling and transmission electron microscopy were used to collect and analyze engine soot samples, respectively. Furthermore, the operation of the thermophoretic sampling device used in engine PM sample collection was characterized to identify the sampling efficiency based on particle deposition and sampling biases based on differences in particle thermoconductivity for various forms of carbon such as turbostratic soot, crystalline carbon nanotubes and calcium. In general, the efficiency of the TPS method was roughly estimated to be 30-80% efficient based on experimental results. In this thesis, carbon nanotubes and fullerenes have been identified as being emitted from in-use, spark-ignited natural gas and gasoline burning auto-rickshaw engines tested in New Delhi, India. Emission of fullerenes and CNTs was on the order of 10% +/- 7% of the non-volatile particulate matter. Agglomerates, dense spherical particles believed to be charred engine oil, and unidentified or compound particles were also cataloged. Confirmation that nanotubes are being produced by SI engines was achieved using PM samples collected from the Ricardo Hydra laboratory test engine at the University of British Columbia, Clean Energy Research Centre. Under more controlled conditions than can be achieved sampling in-use vehicles, SI engine PM is found to be a complex collection of dense, dark (possibly charred oil) spheres, small primary particle agglomerates, small particle deposits, volatile droplets, carbon nanotubes and fullerenes and large ‘other’ particles. High resolution TEM confirmed tube-shaped particles to be fully formed multi-walled carbon nanotubes.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 130-134).
Direct Fuel Injection (DI) extends engine knock limits compared to Port Fuel Injection (PFI) by utilizing the in-cylinder charge cooling effect due to fuel evaporation. The use of gasoline/ethanol blends in DI is therefore especially advantageous due to the high heat of vaporization of ethanol. Additionally ethanol blends also display superior chemical resistance to auto-ignition, therefore allowing the further extension of knock limits. An engine with both DI and port fuel injection (PFI) was used to obtain knock onset limits for five gasoline/ethanol blends and different intake air temperatures. Using PFI as a baseline, the amount the intake air needed to be heated in DI to knock at the same conditions as PFI is the effective charge cooling realized and ranges from ~14°C for gasoline to ~49°C for E85. The Livengood-Wu auto-ignition integral in conjunction with the Douad-Eyzat time to auto-ignition correlation was used to predict knock onset. The preexponential factor in the correlation was varied to fit the experimental data. An "Effective Octane Number-ONEFF" is thus obtained for every blend ranging from 97 ONEFF. for gasoline to 115 ONEFF. for E85. ONEFF. captures the chemistry effect on knock and shows that there is little antiknock benefit beyond 30-40% ethanol by volume unless the fuel is used in a DI engine. Using this approach, the anti-knock benefit of charge cooling can also be quantified as an octane number. To achieve that, the ONEFF. calculated for an actual DI operating point including charge cooling effects is compared to the ONEFF. obtained from the auto-ignition integral if the unburned mixture temperature is offset to cancel the charge cooling out. The resulting increase in ONEFF., which can be viewed as an "Evaporative Octane Number" ranges from 5 ONEFF. for gasoline to 18 ONEFF. for E85.
by Emmanuel P. Kasseris.
Ph.D.

Thesis (M.S.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains xi, 79 p. : ill. Includes abstract. Includes bibliographical references (p. 67-70).

Increasing demands for lower carbon dioxide emissions and fuel consumption drive technological developments for car manufacturers. One trend that has shown success for reducing fuel consumption in spark ignited engines is downsizing, where the engine size is reduced to save fuel and a turbocharger is added to maintain the power output. A drawback of this concept is the slower torque response of a turbocharged engine. Recent hardware improvements have facilitated the use of variable geometry turbochargers (VGT) for spark ignited engines, which can improve the transient torque response. This thesis addresses the transient torque response through three papers. Paper 1 presents the optimal control of the valve timing and VGT for a fast torque response. Optimal open-loop control signals are found by maximizing the torque integral for a 1-d simulation model. From the optimization it is found that keeping the ratio between exhaust and intake pressure at a constant level gives a fast torque response. This can be achieved by feedback control using vgt actuation. The optimal valve timing differs very little from a fuel consumption optimal control that uses large overlap. Evaluation on an engine test bench shows improved torque response over the whole low engine speed range. In Paper 2, model based, nonlinear feedback controllers for the exhaust pressure are presented. First, the dynamic relation between requested VGT position and exhaust pressure is modeled. This model contains an estimation of the on-engine turbine flow map. Using this model, a controller based on inverting the input-output relation is designed. Simulations and measurements on the engine show that the controller handles the strong nonlinear characteristic of the system, maintaining both stability and performance over the engine’s operating range. Paper 3 considers the dependence of the valve timing for the cylinder gas exchange process and presents a torque model. A data-based modeling approach is used to find regressors, based on valve timing and pressures, that can describe the volumetric efficiency for several engine speeds. Utilizing both 1-d simulations and measurements, a model describing scavenging is found. These two models combine to give an accurate estimation of the in-cylinder lambda, which is shown to improve the torque estimation. The models are validated on torque transients, showing good agreement with the measurements.

QC 20120928

Thesis (M.S.)--University of Missouri--Rolla, 2007.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 29, 2007) Includes bibliographical references (p. 153-155).

[ES] A pesar de la tendencia actual hacia la electrificación del transporte por carretera, los motores de combustión interna alternativos han sido esenciales en este sector y se espera que sigan siendo una tecnología con notable presencia durante las próximas décadas. Los vehículos de pasajeros actuales basados en motores de combustión interna son más ecológicos que los utilizados hace años, aunque todavía queda trabajo por hacer. Los sistemas de postratamiento están enfocados a minimizar tanto como sea posible el impacto de los motores de combustión interna en términos de emisiones contaminantes. En el caso de los motores de encendido provocado, los catalizadores de tres vías representan la tecnología más extendida en las últimas décadas, debido a su compacidad y buena relación precio-prestaciones. Estos convertidores son capaces de oxidar hidrocarburos y monóxido de carbono al mismo tiempo que reducen los óxidos de nitrógeno. No obstante, para lograr su mejor eficiencia, el dosado debe controlarse con precisión en torno a condiciones estequiométricas. En este sentido, los sistemas electrónicos de gestión del motor son esenciales para aprovechar las características de estos convertidores. En particular, las estrategias de control y diagnóstico desempeñan un papel clave para lograr una reducción efectiva de las emisiones en el amplio rango de condiciones de operación que se dan en condiciones de funcionamiento reales. El desarrollo de estas estrategias es fundamental, especialmente teniendo en cuenta el bajo nivel de emisiones permitido por las normativas de emisiones actuales y la tendencia hacia cero emisiones. El propósito de esta tesis doctoral es analizar el comportamiento del sistema de postratamiento en condiciones específicas pero a la vez muy comunes en conducción real, y desarrollar estrategias que proporcionen una reducción adicional de las emisiones en sistemas basados en catalizador de tres vías. Con la popularización de pequeños motores turboalimentados de encendido provocado, ha aumentado el uso de estrategias de barrido de la cámara de combustión para mitigar los típicos problemas de falta de par a bajo régimen. Esta tesis analiza el impacto de los pulsos de cortocircuito en el catalizador y en las sondas ¿. El proceso de cortocircuito de aire fresco al escape tiene un impacto importante en la dinámica intraciclo de la composición de los gases de escape. En particular, los pulsos de monóxido de carbono e hidrógeno seguidos por los pulsos de aire fresco perturban el normal funcionamiento del sensor de oxígeno. Por lo tanto, se ha propuesto un nuevo método para estimar la tasa de cortocircuito abordo. Este método permite corregir la desviación sufrida por el sensor y, por lo tanto, ayuda a reducir la penalización en emisiones de este tipo de estrategias. Para mejorar la eficiencia del catalizador en condiciones transitorias, no solo se requiere un control preciso del dosado aguas arriba del catalizador, sino que también resulta imprescindible considerar el comportamiento dinámico del convertidor en sí mismo. Por ejemplo, el almacenamiento de oxígeno es un buen indicador del estado del catalizador, pero no se puede medir directamente mediante sensores. Por lo tanto, el desarrollo de modelos es clave en las estrategias de control actuales, para poder estimar abordo diferentes parámetros relacionados con el estado del catalizador. Varios modelos de catalizador se han desarrollado en esta tesis doctoral para lidiar con diferentes cuestiones, desde la predicción de los efectos de la condensación de agua en la evolución de la temperatura del catalizador justo después del arranque en frío, a la cuantificación del nivel de envejecimiento, pasando por el control óptimo de purga del catalizador.
[CAT] Malgrat la tendència actual cap a l'electrificació del transport per carretera, els motors de combustió interna alternatius han sigut essencials en aquest sector i s'espera que continuen sent una tecnologia amb notable presència durant les pròximes dècades. Els vehicles de passatgers actuals basats en motors de combustió interna són més ecològics que els utilitzats fa anys, encara que hi ha treball per fer. Els sistemes de post-tractament estan enfocats a minimitzar tant com siga possible l'impacte dels motors de combustió interna en termes d'emissions contaminants. En el cas dels motors d'encés provocat, els catalitzadors de tres vies representen la tecnologia més estesa en les últimes dècades, pel fet que són compactes i posseeixen bona relació preu-prestacions. Aquests convertidors són capaços d'oxidar hidrocarburs i monòxid de carboni al mateix temps que redueixen els òxids de nitrogen. No obstant això, per a aconseguir la seua millor eficiència, el dosatge ha de controlar-se amb precisió entorn de condicions estequiomètriques. En aquest sentit, els sistemes electrònics de gestió del motor són essencials per a aprofitar les característiques d'aquests convertidors. En particular, les estratègies de control i diagnòstic exerceixen un paper clau per aconseguir una reducció efectiva de les emissions en l'ampli rang de condicions d'operació que es donen en condicions de funcionament reals. El desenvolupament d'aquestes estratègies és fonamental, especialment tenint en compte el baix nivell d'emissions permès per les normatives actuals i la tendència cap a zero emissions. El propòsit d'aquesta tesi doctoral és analitzar el comportament del sistema de post-tractament en condicions específiques però alhora molt comunes en conducció real, i desenvolupar estratègies que proporcionen una reducció addicional de les emissions en sistemes basats en catalitzador de tres vies. Amb la popularització de xicotets motors amb sobrealimentació d'encés provocat, ha augmentat l'ús d'estratègies de curtcircuit per a mitigar els típics problemes de falta de parell a baix règim. Aquesta tesi analitza l'impacte dels polsos de curtcircuit en el catalitzador i en les sondes ¿. El procés de curtcircuit d'aire fresc té un impacte important en la dinàmica intra-cicle de la composició dels gasos. En particular, els polsos de monòxid de carboni i hidrogen seguits pels polsos d'aire fresc pertorben el normal funcionament del sensor d'oxigen. Per tant, s'ha proposat un nou mètode per a estimar la taxa de curtcircuit del motor. Aquest mètode permet corregir la desviació patida pel sensor i, per tant, ajuda a reduir la penalització en emissions d'aquest tipus d'estratègies. Per a millorar l'eficiència del catalitzador en condicions transitòries, no solament es requereix un control precís del dosatge aigües amunt del catalitzador, sinó que també resulta imprescindible considerar el comportament dinàmic del convertidor en si mateix. Per exemple, l'emmagatzematge d'oxigen és un bon indicador de l'estat del catalitzador, però no es pot mesurar directament mitjançant sensors. Per tant, el desenvolupament de models és clau en les estratègies de control actuals, per poder estimar els diferents paràmetres relacionats amb l'estat del catalitzador. Diversos models de catalitzador s'han desenvolupat en aquesta tesi doctoral per a tractar diferents qüestions, des de la predicció dels efectes de la condensació d'aigua en l'evolució de la temperatura del catalitzador just després de l'arrencada en fred, a la quantificació del nivell d'envelliment, passant pel control òptim de porga del catalitzador.
[EN] In spite of the current tendency towards the electrification of the road transport, internal combustion engines have been essential in this sector and it is expected to continue being a technology with a noticeable presence during next decades. Current passenger cars based on internal combustion engines are greener than those used years ago, although it is still a developing process. Aftertreatment systems are aimed to minimize as much a possible the impact of internal combustion engines in terms of pollutant emissions. In case of spark-ignited engines, three-way catalytic converters represent the most widespread technology during last decades, due to their compactness and cost-performance. These converters are capable to oxidise hydrocarbons and carbon monoxide while simultaneously reducing nitrogen oxide. Nonetheless, to achieve their best efficiency, the air-to-fuel ratio must be accurately controlled close to stoichiometric conditions. In this sense, electronic engine management systems are essential to take advantage of the features of these converters. In particular, control and diagnosis strategies play a key role to achieve an effective emissions reduction under the wide range of operating conditions that arise in real driving conditions. The further development of this strategies is fundamental, especially taking into account the low emissions level allowed by current regulatory procedures and the trend towards zero emissions. The purpose of this dissertation is to analyse the behaviour of the aftertreatment system under very specific but at the same time very common conditions, and developing strategies that provide a further emissions reduction for systems based on three-way catalyst. With the popularization of small turbocharged spark-ignited engines, the use of scavenging strategies to solve the typical low-end torque issues has increased. This dissertation analyses the impact of the short-circuit pulses on both three-way catalyst and ¿ sensors. The short-circuit process has an important effect on the in-cycle dynamics of the exhaust gas composition. In particular, the carbon monoxide and hydrogen pulses followed by fresh air pulses cause a sensor bias. Thus a new method to on-line estimate the short-circuit rate has been proposed. This method allows to correct the sensor bias and, therefore, help to reduce the emissions penalty. To improve the TWC efficiency under transient conditions, not only an accurate air-to-fuel ratio control upstream of the converter is required, but also to consider the dynamic behaviour of the converter itself. For example, the oxygen storage is the main responsible for the converter dynamics, and thus, a good indicator of the catalyst state, but it cannot be directly measured. Hence the development of models is key in current control strategies, to on-line track different parameters related with the state of the converter. Several models have been derived in this dissertation in order to fulfil different requirements, from the prediction of water condensation effects on the temperature evolution inside the converter just after cold-start, to the quantification of the ageing level, through the optimal catalyst purge control, or the air-to-fuel ratio disturbances rejection.
Real Minuesa, M. (2020). Modelling, control and diagnosis of aftertreatment systems based on three-way catalyst in spark-ignited engines [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/137040
TESIS

This licentiate thesis concerns one dimensional flow simulation of turbocharged spark ignited engines. The objective has been to contribute to the improvement of turbocharged SI engines’ performance as well as 1 D simulation capabilities.

Turbocharged engines suffer from poor gas exchange due to the high exhaust pressure created by the turbine. This results in power loss as well as high levels of residual gas, which makes the engine more prone to knock.

This thesis presents an alternative gas exchange concept, with the aim of removing the high exhaust pressure during the critical periods. This is done by splitting the two exhaust ports into two separate exhaust manifolds.

The alternative gas exchange study was performed by measurements as well as 1-D simulations. The link between measurements and simulations is very strong, and will be discussed in this thesis.

As mentioned, turbocharged engines are prone to knock. Hence, finding a method to model knock in 1-D engine simulations would improve the simulation capabilities. In this thesis a 0-D knock model, coupled to the 1-D engine model, is presented

This work concerns a systematic study of IC engine operation with 100% biogas as fuel (as opposed to the dual-fuel mode) with particular emphasis on operational issues and the quest for high efficiency strategies. As a first step, a commercially available 1.2 kW genset engine is modified for biogas operation. The conventional premixing of air and biogas is compared with a new manifold injection strategy. The effect of biogas composition on engine performance is also studied. Results from the genset engine study indicate a very low overall efficiency of the system. This is mainly due to the very low compression ratio (4.5) of the engine. To gain further insight into factors that contribute to this low efficiency, thermodynamic engine simulations are conducted. Reasonable agreement with experiments is obtained after incorporating estimated combustion durations. Subsequently, the model is used as a tool to predict effect of different parameters such as compression ratio, spark timing and combustion durations on engine performance and efficiency. Simulations show that significant improvement in performance can be obtained at high compression ratios. As a step towards developing a more efficient system and based on insight obtained from simulations, a high compression ratio (9.2) engine is selected. This engine is coupled to a 3 kW alternator and operated on 100% biogas. Both strategies, i.e., premixing and manifold injection are implemented. The results show very high overall (chemical to electrical) efficiencies with a maximum value of 22% at 1.4 kW with the manifold injection strategy. The new manifold injection strategy proposed here is found to be clearly superior to the conventional premixing method. The main reasons are the higher volumetric efficiency (25% higher than that for the premixing mode of supply) and overall lean operation of the engine across the entire load range. Predictions show excellent agreement with measurements, enabling the model to be used as a tool for further study. Simulations suggest that a higher compression ratio (up to 13) and appropriate spark advance can lead to higher engine power output and efficiency.

Due to the continuous work in the automobile industry to reduce the environmental impact, reduce fuel consumption and increase efficiency, new technologies need to be developed and implemented in vehicles. For spark ignited engines, one technology that has received more attention in recent years is long route Exhaust Gas Recirculation (EGR), which means that exhaust gases after the turbine are transported back to the volume before the compressor in the air intake system of the engine. In this work, the components of the long route EGR system is modeled with mean value engine models in Simulink, and implemented in a existing Simulink engine model. Then different methods for estimating the mass flow over the long route EGR system are compared, and the transport delays for the recirculated exhaust gases in the engines air intake system are modeled. This work is based on measurements done on an engine rig, on which a long route EGR system was installed. Finally, some ideas on how a long route EGR system on a gasoline engine can be controlled are presented based on the results in this thesis work.

Spark ignited engines are still important for conventional as well as for hybrid power trains and are thus objective to optimization. Today a lot of functionalities arise from software solutions, which have to be calibrated. Modern engine technologies provide an extensive variability considering their valve train, fuel injection and load control. Thus, calibration efforts are really high and shall be reduced by introduction of virtual methods. In this work a physical 0D combustion model is set up, which can cope with a new generation of spark ignition engines. Therefore, at first cylinder thermodynamics are modeled and validated in the whole engine map with the help of a real-time capable approach. Afterwards an up to date turbulence model is introduced, which is based on a quasi-dimensional k-epsilon-approach and can cope with turbulence production from large scale shearing. A simplified model for ignition delay is implemented which emphasizes the transfer from laminar to turbulent flame propagation after ignition. The modeling is completed with the calculation of overall heat release rates in a 0D entrainment approach with the help of turbulent flame velocities. After validation of all sub-models, the 0D combustion prediction is used in combination with a 1D gas exchange analysis to virtually calibrate the modern engine torque structure and the ECU function for exhaust gas temperature with extensive simulations
Moderne Ottomotoren spielen heute sowohl in konventionellen als auch hybriden Fahrzeugantrieben eine große Rolle. Aktuelle Konzepte sind hochvariabel bezüglich Ventilsteuerung, Kraftstoffeinspritzung und Laststeuerung und ihre Optimierungspotentiale erwachsen zumeist aus neuen Softwarefunktionen. Deren Applikation ist zeit- und kostenintensiv und soll durch virtuelle Methoden unterstützt werden. In der vorliegenden Arbeit wird ein physikalisches 0D Verbrennungsmodell für Ottomotoren aufgebaut und bis zur praktischen Anwendung geführt. Dafür wurde zuerst die Thermodynamik echtzeitfähig modelliert und im gesamten Motorenkennfeld abgeglichen. Der Aufbau eines neuen Turbulenzmodells auf Basis der quasidimensionalen k-epsilon-Gleichung ermöglicht anschließend, die veränderlichen Einflüsse globaler Ladungsbewegung auf die Turbulenz abzubilden. Für den Brennverzug wurde ein vereinfachtes Modell abgeleitet, welches den Übergang von laminarer zu turbulenter Flammenausbreitung nach der Zündung in den Vordergrund stellt. Der restliche Brennverlauf wird durch die physikalische Ermittlung der turbulenten Brenngeschwindigkeit in einem 0D Entrainment-Ansatz dargestellt. Nach Validierung aller Teilmodelle erfolgt die virtuelle Bedatung der Momentenstruktur und der Abgastemperaturfunktion für das Motorsteuergerät

Turbocharged spark-ignited engines may encounter stochastic events of premature ignition of the fuel-air mixture, termed as pre-ignition. Pre-ignition often leads to extremely high peak pressure and pressure oscillations, causing engine damage. A review of pre-ignition in historic times is done in this dissertation, and the similarities and differences compared to modern pre-ignition issue are brought forth. Experiments conducted with varying injection strategies yielded varying pre-ignition tendency. The pre-ignition tendency correlated with the charge cooling tendency and the mass of liquid fuel impinging on the cylinder liner and diluting the oil film. The diluted oil is trapped in the piston ring area and from time-to-time gets launched into the combustion chamber near top dead center. The fuel-oil mixture droplet may ignite the surrounding charge before the spark timing. Experiments conducted with varying exhaust back pressure showed dependence of pre-ignition tendency on in-cylinder temperature near top dead center, for cases when intake pressure is higher than exhaust pressures. For exhaust pressure higher than intake pressure, fuel wall impingement was critical to pre-ignition. This research also devised ion-current based sensors for pre-ignition detection. Initial experiments were done with DC-power based ion-current sensor, which detected a pre-ignition event when a flame brushed past the sensor. There was a need of faster-response sensor with high signal-to-noise ratio, that would allow pre-ignition detection at its inception stage, thereby giving enough time to trigger an evasive action. In this regard, an AC-powered ion-current sensor was devised and patented. Sudden fuel enrichment at the time of pre-ignition detection was investigated as an evasive method. Various strategies were investigated for their pre-ignition suppression tendency. Split injection, water injection, Octane-on-Demand, injecting different fluids in late compression stroke and dual fuel operation with gasoline and methane were found to be highly effective at suppressing pre-ignition completely. Use of ethanol in blends with different FACE gasolines is investigated to suggest fuel effects on pre-ignition. The strategies were successful at either reducing the mass of liquid fuel impinging the liner, reducing the in-cylinder temperature near top dead center or reducing the potential of residual gas content to trigger pre-ignition in the next cycle.

The current work, through experimental and numerical investigations, analyses the process and cycle level deviations in engine response on fuelling multi-cylinder natural gas engines with producer gas. Producer gas is a low calorific value bio-derived alternative with composition of 19 ± 1% CO and H2, 2 ± 0.5 % CH4, 12 ± 1% CO2 and 46 ± 1% N2 and has thermo-physical properties significantly different from natural gas. Experimental investigations primarily address the energy balance (full cycle analysis) and in-cylinder response (process specific analysis) at various operating conditions covering naturally aspirated and turbocharged mode of operation with natural gas and producer gas. Numerical investigations are based on two thermodynamic scope mathematical models, a zero dimensional model (Wiebe function) and a quasi-dimensional model (propagating flame front heat release). A detailed diagnostic analysis on a six cylinder (E6) indicates, turbocharger mismatch, the first explicit impact of fuel thermo-physical property variation. Turbocharger matching and optimization resulted in a peak load of 72.8 kWe (BMEP 9.47) at a maximum brake torque ignition angles of 22 deg before TDC and compressor pressure ratio of 2.25. Engine energy distribution analysis indicates skewed energy balance with higher cooling load (in excess of 30%) as compared to fossil fuel operation. This is attributed to the presence of nearly 20% H2 which enhances the convective cooling through the higher thermal conductivity. Parametric variation of H2 fraction on a two cylinder engine (E2) with four different syngas compositions (mixture H2 varying from 7.1% to 14.2%) depicts enhanced cooling load from 33.5% to 37.7%. Process level comparison indicates significant deviations in the heat release profile compared to fossil fuels. It has been observed that with an increase in mixture hydrogen fraction (from 7.1% to 14.2%), the fast burn phase combustion duration reduces from 59.6% to 42.6% but the terminal stage duration increases from 25.5% to 48.9%. The enhanced cooling of the mixture (due to the presence of hydrogen), particularly in the vicinity of walls is argued to contribute towards the sluggish terminal phase combustion. Immediate implication of thermo-kinematic response variation is on the magnitude and sensitivity of combustion descriptors and the need for dependent control system calibration for producer gas fuelled operation is established. Descriptor analysis is extended to knocking pressure traces and a new simple methodology is proposed towards identifying the occurrence and regime of knock. Analysing the implications through numerical investigation, the influence of the altered thermo-kinematic response for producer gas fuelled operation impacts 0D simulations. Zero dimensional simulations fail with conventional coefficients requiring fuel specific coefficients. Based on fuel specific coefficients, the suitability of 0D model for the simulation of varying operating conditions ranging from naturally aspirated to turbo charged engines, compression ratios and different engine geometries is established. The analysis is extended to quasi-dimensional through the eddy entrainment and laminar burn up model. The choice of laminar flame speed and turbulent parameters is validated based on the assessment of the flame speed ratio (4.5 ± 0.5 for naturally aspirated operation, turbulent Reynolds number of 2500 ± 250 and 9.0 ± 1.0 for turbocharged operation, turbulent Reynolds number of 5250 ± 250). In the estimation of laminar flame speed, the limitation of GRIMech 3.0 mechanism for H2-CO-CH4 systems is explicitly established and GRIMech 2.11 is used to arrive at experimentally comparable results. In-cylinder engine simulation results covering parametric variation of load, ignition angle and mixture quality, for engine natural gas fuelled naturally aspirated operation and producer gas fuelled naturally aspirated and turbocharged after cooled are compared with experimental results. The quasi dimensional analysis is extended to simulate end gas auto-ignition and is validated by using experimental manifold conditions for turbocharged operation for which knock has been observed. Extending the model to a Waukesha cooperative fuels research engine, motor methane number of 110 is reported for standard composition producer gas. The use of quasi dimensional models with end gas reaction kinetics enabled for knock rating of fuels represents first of its kind initiative.