Comparison of 1-D Modelling Approaches for Wankel Engine Performance Simulation and Initial Study of the Direct Injection Limitations

Recent interest in the possible use of Wankel engines as range extenders for electric vehicles has prompted renewed investigations into the concept. While not presently used in the automotive industry, the type is well established in the unmanned aerial vehicles industry, and several innovative approaches to sealing and cooling have recently been developed which may result in improved performance for ground vehicle applications.One such UAV engine is the 225CS, a 225 cc/chamber single-rotor engine manufactured by Advanced Innovative Engineering (UK) Ltd. To be able to analyse the parameters, opportunities and limitations of this type of engine a model was created in the new dedicated Wankel modelling environment of AVL BOOST. For comparison a second model was created using the established method of modelling Wankel engines by specifying an ‘equivalent’ 3-cylinder 4-stroke reciprocating engine. The output from both of these models was evaluated using engine test data supplied by Advanced Innovative Engineering (UK) Ltd. The model created in the dedicated Wankel environment was found to fit the experimental data more closely.The model was then used to evaluate the impact on performance and fuel economy of applying direct injection to a Wankel rotary engine. This potential is because the nozzle can be situated in the cold side of the trochoid housing, taking advantage of the longer intake phase of the Wankel in turn permitting lower delivery pressures (the intake ‘stroke’ having 270 degrees of eccentric shaft rotation vs. 180 degrees for the reciprocating engine), plus the fact that the injector can be shielded from combustion pressure and hot burned gases. As it was found to be more accurate, the dedicated Wankel model was used to analyse the interrelationships between injector position, injection pressure and engine speed.Although a number of assumptions were required, and these will affect the accuracy of the model, the results provide a reasonable preliminary assessment of the feasibility of applying direct injection to the 225CS engine. A notable finding was that injection pressures of approximately 4.5 bar should be sufficient to supply fuel at all engine speeds and that the optimum position for the injector (for maximum fuel injection) corresponded to a position defined by the rotor apex tip at 597 degrees of eccentric shaft rotation after top dead centre firing. The advantage of both the injection pressure and injector location suggests a less complex fuel system design (compared to equivalent reciprocating systems) is possible at a reduced cost

Investigating Sustainable Fuel Effects on Mixing and Combustion through Design and Development of a Gasoline Direct Injection Optically Accessible Engine

Due to ever-growing sustainability issues, more demanding exhaust emission regulations are imposed on internal combustion engines. There is growing introduction of full electrification but, as there are practical issues regarding the full electrification, internal combustion engines are proven to be still useful and often coupled with electric motors. It is, therefore, vital to establish detailed understandings of in-cylinder combustion processes so that the release of greenhouse gas and production of pollutant emissions can be reduced and minimised. Therefore, novel fuels, such as second-generation biofuels, are thoroughly studied to explore possible use as future fuels for hybrid gasoline direct injection powertrains which are derived from sustainable feedstock and provide efficient energy release. For this project, a novel optical engine was designed that facilitate easy access to the piston and rapid cleaning of the piston crown window. A state-of-the-art gasoline direct injection engine was selected for hybrid applications. The initial design of the optical engine was modified to resolve the slackness in the extended timing chains. As the optical engine adopted the Bowditch system and only number 1 cylinder operated, various auxiliary components were also designed and developed to accommodate optical systems and oil circulation, and consider the change in the crankshaft balancing and volume of the air intake. Furthermore, an external fuel supply system was designed to enable a use of different fuels, while minimising a risk of damaging or contaminating the conventional fuel supply lines, by allowing easy cleaning processes. To quantitatively compare the difference in both spray and combustion images between various fuels, MATLAB codes were developed to process the captured images from a high-speed camera. Seven fuels were tested namely gasoline, ethanol, acetic acid, anisole, guaiacol, 2-MF and 2-MTHF; one a reference fossil fuel, one a first-generation biofuel and five second-generation biofuels, respectively. Three different injection timings were applied to simulate stratified, quasi-homogeneous and homogeneous states at low and high injection pressures for combustion studies, with only the injection pressure varied for the constant injection timing at the stratified spray studies. In general, injection pressure did not have a significant effect on soot formation, with exception for anisole, with injection timing found to be the dominant factor. Ethanol showed a similar spray development pattern to that of gasoline but displayed narrower sprays around the injector tip and became wider towards the spark plug. Acetic acid showed an indistinctive spray pattern and all six sprays merged together to form a cloud of fuel. Anisole showed wider sprays than gasoline and ethanol, but exhibited a similar penetration rate. Guaiacol exhibited similar spray characteristics to that of acetic acid, in that it formed a fuel cloud rather than maintaining distinct fuel sprays. Both 2-MF and 2-MTHF showed wide sprays

Étude de l'écoulement cavitationnel dans un injecteur diesel simple trou

L’objectif de cette étude est de déterminer les effets des propriétés du diesel ainsi que les conditions d’injection sur l’écoulement interne d’un injecteur diesel simple trou. Pour y parvenir, il a été nécessaire de développer un modèle numérique fiable afin de simuler l’écoulement interne sous des conditions de cavitation. La cavitation a été calculée en utilisant un modèle eulérien avec un fluide homogène qui utilise l’équation de Rayleigh-Plesset pour la croissance des bulles. Le modèle a été validé en calculant plusieurs coefficients, c'est-à-dire les coefficients de débit, de réduction d’aire et de vitesse. Ceux-ci ont été déterminés sous différents nombres de Reynolds et de cavitation afin d’évaluer l’effet de chaque nombre adimensionnel sur l’écoulement. Il a été déterminé que les deux nombres dimensionnels ont un effet sur l’écoulement. L’augmentation du nombre de Reynolds tend à diminuer la cavitation et ainsi augmenter le coefficient de débit. Cependant, l’augmentation du nombre de cavitation augmente la cavitation et donc diminue le coefficient de débit. De plus, il a aussi été déterminé que des simulations à haute pression d’injection peuvent être reproduites avec une pression d’injection plus faible si les nombres de Reynolds et de cavitation sont les mêmes. Ceci revient à dire que les deux seuls nombres adimensionnels qui gouvernent l’écoulement sont le nombre de Reynolds et de cavitation. Ultimement, un modèle numérique a été mis en place pour des études futures

Common Rail System for GDI Engines: Modelling, Identification, and Control

Progressive reductions in vehicle emission requirements have forced the automotive industry to invest in research and development of alternative control strategies. Continual control action exerted by a dedicated electronic control unit ensures that best performance in terms of pollutant emissions and power density is married with driveability and diagnostics. Gasoline direct injection (GDI) engine technology is a way to attain these goals. This brief describes the functioning of a GDI engine equipped with a common rail (CR) system, and the devices necessary to run test-bench experiments in detail. The text should prove instructive to researchers in engine control and students are recommended to this brief as their first approach to this technology. Later chapters of the brief relate an innovative strategy designed to assist with the engine management system; injection pressure regulation for fuel pressure stabilization in the CR fuel line is proposed and validated by experiment. The resulting control scheme is composed of a feedback integral action and a static model-based feed-forward action, the gains of which are scheduled as a function of fundamental plant parameters. The tuning of closed-loop performance is supported by an analysis of the phase-margin and the sensitivity function. Experimental results confirm the effectiveness of the control algorithm in regulating the mean-value rail pressure independently from engine working conditions (engine speed and time of injection) with limited design effort