Investigation of Preflame Reactions and Flame Propagation in Direct- Injection Diesel Enginees

摘要

It was to investigate (invisible) preflame reactions taking place in a direct-injection compression ignition (DI-CI) engine during the ignition delay period and their effects on subsequent (visible) combustion reactions. The investigation was focused on the subject for an engine equipped with a high- pressure injection (HPI) unit in order to support the development of high-power- output Diesel engines. The use of HP was found to facilitate more air utilization in a DI-CI engine even operated with intake air at unusually high temperatures (e.g., encountered in uncooled engines). In order to achieve these goals, several new research methods were developed-advanced for the study, including Rutgers or Super Imaging System (SIS), spectrometric methods, and Rutgers Animation Program. The tools were employed on an optical single-cylinder Cummins 903 engine. Among the significant results in system development is that the basic methods for high-speed imaging achievable at consecutive cycles, which shed some new insight into complex in-cylinder phenomena. The new research methods developed under the present ARO study permits observation of timed global pictures of preflame propagation under various engine-fuel conditions. New findings of the study include that the fuel injected into the cylinder immediately commences to chemically react, unlike the previous thought that there is a physical delay proceeding actual chemical reactions. The reactions involved during the preflame reactions appear to be low-temperature kinetics controlled processes to affect the onset of visible-ray flame formation and combustion reactions. The preflame reaction species were found rapidly consumed as soon as the heat-releasing flame propagation took place.