Erscheinungsdatum: 07/2010, Medium: Taschenbuch, Einband: Kartoniert / Broschiert, Titel: CFD Simulation of Internal Combustion Engines, Titelzusatz: Study of mixture formation process in GDI engines, Autor: Vaidya, Abhijeet, Verlag: LAP Lambert Acad. Publ., Sprache: Englisch, Rubrik: Technik // Sonstiges, Seiten: 276, Informationen: Paperback, Gewicht: 421 gr, Verkäufer: averdo
Stringent emission regulations aim to restrict soot emissions by particle mass and particle number in the transport sector. Whilst the concept of direct-injection gasoline (GDI) engines is very promising with respect to efficiency, complying with the legislative soot emission limits is challenging for GDI-engines. A sufficient reduction of soot emissions in GDI engines requires a detailed understanding and accurate modeling of soot formation processes of gasoline fuels in engines. This study provides fundamental investigations of the soot formation process of common gasoline surrogate components.Soot volume fraction profiles in laminar counterflow flames burning ethylene, n-heptane, iso-octane, and toluene were determined experimentally for a wide range of flame conditions. Simulations of these flames reveal that applied models are capable of predicting the soot volume fraction with remarkable accuracy for ethylene. For the gasoline surrogate components, however, the overall soot volume fractions are overpredicted. Reaction pathway analysis suggests that, in these flames, more soot precursors are formed via the reaction pathways involving fuel pyrolysis products.Furthermore, flame structure, local gas temperature, local soot volume fraction, and primary soot particle diameter were simultaneously detected by means of optical diagnostics in turbulent toluene flames. Joint statistics of flame and soot properties indicate that, due to differential diffusion of soot, high soot concentrations are present at conditions of low temperatures and low OH concentrations. In the soot oxidation region, the presence of large particles suggest that the oxidation is not sufficiently fast to burn soot completely.
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.
The Direct-Injection (DI) combined with downsizing, variable valve timing and turbocharging promises a strong reduction of fuel consumption for Spark-Ignition (SI) engines. The advantages of DI have been widely demonstrated in terms of fuel economy, transient response, air-to-fuel ratio (AFR) control and reduced emissions. The control of fuel spray and air-fuel mixture formation is fundamental for fully taking advantages of DI in SI engines. This work investigates the influence of injection parameters on air/fuel mixture and combustion processes in a DISI engine. In the first part the main fuel spray parameters were investigated: Particle Image Velocimetry allowed to characterize the spray velocity field while Phase Doppler Anemometry was applied for droplets size and velocity measurements. An innovative X-ray tomography technique allowed to investigate the inner structure of the fuel spray in the region immediately downstream of the nozzle. Finally, the effect of the injection duration and phasing on the combustion process and pollutant emissions formation was studied in a GDI optically accessible engine, through UV-visible imaging and spectroscopy.