Advanced combustion concepts are required to meet the increasing global energy demand and stringent emission regulations imposed by the governments on automobile manufacturers. Improvement in efficiency and reduction in emissions can be achieved by downsizing the Spark Ignition (SI) engines. The operating range of SI engine is limited by occurrence of knock, pre-ignition and the following super-knock due to boosting of intake pressure, to account for the reduction of power, as a result of downsizing the engine. Super-knock, which represents high momentary pressure accompanied with pressure oscillations, is known to permanently damage the moving component of the engines. Therefore fundamental comprehensive understanding of the mechanism involved in pre-ignition and super-knock are required to design highly efficient spark ignition engines with lower emissions that can meet the increasing government regulations. \nThe thesis focuses on auto-ignition characteristics of endgas and the bulk mixture properties that favor transition of pre-ignition to super-knock. Direct numerical studies indicate that super-knock occurs to due to initiation of premature flame front that transition into detonation. In literature, many sources are reported to trigger pre-ignition. Due to the uncertainty of the information on the sources that trigger pre-ignition, it is extremely difficult to predict and control pre-ignition event in SI engines. Since the information on the source of pre-ignition is not available, the main focus of this work is to understand the physical and chemical mechanisms involved in super-knock, factors that influence super-knock and methods to predict super-knock. \n
Pre-ignition was initiated at known locations and crank angle using a hotspot of known size and strength. Different parametric cases were studied and the location and timing of pre-ignition initiation is found to be extremely important in determining the transition of pre-ignition event to super-knock. Pre-ignition increases the temperature of the endgas and the overall bulk mixture, that transitions the pre-ignition flame front to a detonation. The transition of the flame propagation mode from deflagration to detonation was investigated with different type of analysis methods and all results confirmed the transition of pre-ignition flame front to detonation that results in super- knock.

This study investigates the impact of employing the Miller cycle on a high specific power downsized gasoline engine by means of Early Intake Valve Closing (EIVC) and Late Intake Valve Closing (LIVC). This investigation assesses the potential for the Miller cycle to improve fuel economy at part load points, as well as high load points with significantly elevated boost pressures (Deep Miller) of up to 4 bar abs. The impact of geometric Compression Ratio (CR) and Exhaust Back Pressure (EBP) has also been investigated. The knock mitigating qualities of Deep Miller have been assessed, and its ability to increase maximum engine load explored. Low Speed Pre-ignition (LSPI) and autoignition tendencies with reduced coolant flow rates and with aged and new fuels have also been studied. This study comprises both experimental and analytical studies. A Ricardo Hydra single cylinder thermodynamic engine was developed and used for the experimental component of the study. This engine features a high specific power output (120kW/l) cylinder head from the Mahle 1.2l 3 cylinder aggressively downsized engine. The analytical component was carried out using a 1-dimensional GT-Power model based on the Ricardo Hydra experimental engine. A Design of Experiments (DoE) based test plan was adopted for this analytical study. The experimental study found that EIVC was the optimal strategy for improving fuel economy at both part-load and high-load conditions. LIVC yielded a fuel economy penalty at part-load operations and a fuel economy improvement at high-loads. The unexpected part-load LIVC result was attributed to the engine breathing dynamics of the experimental engine. The analytical study found moderate LIVC to be the optimal strategy at lower speeds, unless compensation for the increased degree of scavenging experienced with EIVC was compensated for, in which case EIVC was optimum. At higher speeds EIVC was found to be optimum regardless of whether or not compensation for scavenging was employed. It was generally found that less sensitivity to EBP was exhibited the more extreme the EIVC and LIVC. It was also found that a higher geometric CR could be tolerated with extreme EIVC and LIVC, and a fuel economy benefit could be obtained through the elevation of Geometric CR.

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.

There is a growing interest in alternative transport fuels. There are two underlying reasons for this interest; the desire to decrease the environmental impact of transports and the need to compensate for the declining availability of petroleum. In the light of both these factors the Diesel Dual Fuel, DDF, engine is an attractive concept. The primary fuel of the DDF engine is methane, which can be derived both from renewables and from fossil sources. Methane from organic waste; commonly referred to as biomethane, can provide a reduction in greenhouse gases unmatched by any other fuel. The DDF engine is from a combustion point of view a hybrid between the diesel and the otto engine and it shares characteristics with both. This work identifies the main challenges of DDF operation and suggests methods to overcome them. Injector tip temperature and pre-ignitions have been found to limit performance in addition to the restrictions known from literature such as knock and emissions of NOx and HC. HC emissions are especially challenging at light load where throttling is required to promote flame propagation. For this reason it is desired to increase the lean limit in the light load range in order to reduce pumping losses and increase efficiency. It is shown that the best results in this area are achieved by using early diesel injection to achieve HCCI/RCCI combustion where combustion phasing is controlled by the ratio between diesel and methane. However, even without committing to HCCI/RCCI combustion and the difficult control issues associated with it, substantial gains are accomplished by splitting the diesel injection into two and allocating most of the diesel fuel to the early injection. HCCI/RCCI and PPCI combustion can be used with great effect to reduce the emissions of unburned hydrocarbons at light load. At high load, the challenges that need to be overcome are mostly related to heat. Injector tip temperatures need to be observed since the cooling effect of diesel flow through the nozzle is largely removed. Through investigation and modeling it is shown that the cooling effect of the diesel fuel occurs as the fuel resides injector between injections and not during the actual injection event. For this reason; fuel residing close to the tip absorbs more heat and as a result the dependence of tip temperature on diesel substitution rate is highly non-linear. The problem can be reduced greatly by improved cooling around the diesel injector. Knock and preignitions are limiting the performance of the engine and the behavior of each and how they are affected by gas quality needs to be determined. Based on experiences from this project where pure methane has been used as fuel; preignitions impose a stricter limit on engine operation than knock. / QC 20120626 / Diesel Dual Fuel

This paper deals with the problem of two-stroke engine pre-ignition controller with the use of microcontroller for single-cylinder engine and double-cylinder engine. The mechanical design is drawn for motorcycles JAWA and ČZ and for engines of the same mechanical type. The establishment uses non-contact status analysis of engine with non-electric sensor. The very important thing for the design is the simplicity of the establishment. The other important thing is the minimisation of mechanical arrangement of engine and the vehicle as a whole. The importance of this establishment is non-contact switching and the possibility of changing pre-ignition maps depending on the number of rotations per minute, the temperature and the load of the engine.

L'augmentation continue des charges de fonctionnement des moteurs à allumage commandé a conduit à l'apparition d'une nouvelle forme de combustion anormale à bas régime sous la forme d'un pré allumage. Dans des conditions de pression et de température extrêmes, une auto-inflammation incontrôlée du mélange carburé peut en effet se produire avant l'allumage normal à la bougie et conduire à une seconde auto-inflammation de type cliquetis donnant naissance à des oscillations de pression inacceptables même pour les moteurs les plus robustes. Cette anomalie constitue donc une véritable limite au downsizing des moteurs et à l'augmentation de leurs performances spécifiques. Cette dernière forme de combustion anormale est bien plus critique que le cliquetis car son apparition est aléatoire, le plus souvent sporadique et généralement très violente. Ces caractéristiques fondamentales expliquent que de nouveaux outils et de nouvelles méthodologies d'analyse aient dû être développés pour mieux caractériser le processus d'auto-inflammation dans ces conditions extrêmes. Des méthodes statistiques avancées ont notamment été mises au point pour quantifier de manière fiable la fréquence d'apparition du pré allumage malgré son caractère aléatoire. En parallèle, un travail expérimental important a été réalisé pour mettre au point une méthodologie de réalisation de visualisations endoscopiques permettant de mieux analyser le processus de combustion, et d'identifier de manière plus précise les zones préférentielles d'apparition du pré allumage dans la chambre de combustion. Les impacts des paramètres fondamentaux régissant l'auto-inflammation (aérodynamique interne, thermique et chimie du mélange) ont d'abord été analysés sur un monocylindre de recherche. Le processus de combustion a ainsi été détaillé et l'hypothèse d'une auto-inflammation spontanée en phase gazeuse a également pu être abordée en parallèle de l'analyse expérimentale par une approche numérique RANS. Une étude plus approfondie a ensuite montré qu'il était possible qu'un pré allumage conduise à une auto-inflammation de type détonation, ce qui explique qu'un nombre réduit d'occurrences suffise à détériorer irrémédiablement le moteur. La versatilité du monocylindre a également permis de mettre en évidence la diversité des phénomènes qui pouvaient conduire au pré allumage et d'autres hypothèses que celle d'une auto-inflammation spontanée en phase gazeuse ont ainsi pu être formulées. Celles-ci ont finalement été testées sur un multicylindre en appliquant des méthodologies d'essais et d'analyse éprouvées sur monocylindre. Les investigations tournées vers l'impact des réglages moteur ont alors notamment confirmé que les impacts du carburant sur les parois de la chambre de combustion conduisaient à la formation de films liquides dont les caractéristiques locales pouvaient être favorables à une auto-inflammation. / The continuous increase of engine loads on SI engines has provoked the apparition of a new form of abnormal combustion at low engine speed in the guise of a pre-ignition. Under extreme conditions of pressure and temperature, an uncontrolled auto-ignition of the fresh mixture can happen well before the normal ignition at the spark and lead to a knocking-like second auto-ignition and to unacceptable pressure oscillations even for modern and robust engines. This anomaly constitutes thus a strong limit to the downsizing of gasoline engines and to the increase of their specific performance. This latter abnormal combustion is far more critical than knocking combustion since its apparition is random, most often sporadic and usually very violent. These fundamental characteristics explain that new tools and methodologies had to be developed to achieve a better characterization of the auto-ignition process under such extreme conditions. Advanced statistical methods have notably been defined to obtain a reliable quantification of the pre-ignition frequency despite its randomness. A significant work has simultaneously been realized to develop an experimental methodology dedicated to endoscopic visualizations allowing a better analysis of the combustion process and a more precise identification of the preferential areas of auto-ignition inside the combustion chamber. The impacts of fundamental parameters governing auto-ignition (the mixture's charge motion, thermal and chemical evolutions) have first been analyzed thanks to a research single cylinder engine. That way, the combustion process has been detailed and the hypothesis of a spontaneous auto-ignition of the gaseous mixture has also been tackled at the same time with the help of a numerical RANS approach. Then, a deeper analysis has showed that pre-ignition could lead to a developing detonation mode during the second auto-ignition, explaining so that a reduced number of events could cause irremediable damages. Thanks to the flexibility of the single cylinder engine, it has also been shown that a wide variety of phenomena could lead to pre-ignition and it has made possible the formulation of other hypotheses than a spontaneous auto-ignition of the gaseous mixture. These ones have finally been tested on a serial multi-cylinder engine with test and analysis methodologies validated on the single cylinder engine. The investigations focused on the impacts of settings have then confirmed that the fuel impacts on the liner and on the piston lead to the formation of liquid films whose local characteristics could be favorable to auto-ignition.