Abstract
Combustion processes with fully premixed cylinder load combined with self-ignition, e.g. HCCI, provide high combustion efficiency and low emissions of Nitrogen Oxides (NO_x) and particulate matter at the same time. However, a high effort in the control of combustion start has to be made and afterwards no further control of the ongoing combustion is possible since it is only reaction controlled. In addition to that these combustion systems are always limited in load. Partially premixed systems offer the possibility to control both start and progress of combustion because of the presence of slower diffusion processes. Nevertheless a significant reduction of the raw emissions is possible due to an increase of the share of premixed combustion. Since the number of diesel operated passenger cars is still rising it is certainly of economical interest wether such a combustion process can be realized with an ordinary DI-Diesel engine which is operated with conventional diesel or diesel-like fuels. Here, a fuel variation is of great interest, because the fuel properties can be seen as one of the key-factors for a successful realization. In this study, the influence of several fuels (different chemical composition and cetane numbers) and injection strategies on the functioning chain of combustion is analyzed in a transparent single-cylinder CR diesel engine by means of optical measurement techniques. These optical diagnostics (laser-based and non-laser-based) are used simultaneously to study the fuel distribution, ignition and combustion inside the test engine. The investigation shall demonstrate to what extent a partially premixed mixture can be reached with different fuels and how this affects the spatial distribution of the ignition locations as well as the combustion progress.
