Search Results

A nonintrusive diagnostic technique has been developed by which dynamic axial piston-position and tilt-angle measurements have been made in a single-cylinder research engine. A laser beam, introduced into the combustion chamber through an optical port in the cylinder head, was reflected by a polished surface on the piston crown. Motion of the reflected beam, carrying with it information on piston position and piston tilt, was monitored by a set of receiving optics. Piston motion was studied as a function of both engine speed and cylinder pressure (i.e., piston loading.) Measured axial piston-position was found to deviate from the theoretical position calculated from the measured crank-shaft position owing to the effects of tilt and piston loading. Furthermore, evidence of piston veer (tilt of the piston in a plane parallel to the axis of the wrist pin) was observed, which had an effect on the accuracy of the axial piston-position measurement.

Evaluation of the combustion process in a wall-wetting direct-injection diesel was accomplished by calculation of the apparent rate of heat release from the measured pressure history for several engine speeds, loads, and start-of-combustion timings. At most of the conditions tested, the combustion process seemed to be characterized by transitions from premixed burning to airborne-diffusion burning, and finally to wall-type diffusion burning. Advancing the timing increased the amounts of premixed and airborne-diffusion burning relative to wall burning. The premixed portion of the burn also increased as the engine speed was increased. The results of this study suggest that the diffusion burn in this engine progresses from being mostly airborne at the lightest load to being mostly from the wall at the heaviest load.

Because combustion in direct injection engines is strongly influenced by the details of the fuel spray in these engines, we have begun a broad research effort of jet breakup experiments and modelling of these high pressure sprays. The main objective of this effort is to better understand fuel injection from the study of the spray-jet breakup process and the associated fuel-oxidant mixing. The focus of this paper is the development of specific models for atomization of the spray-jet. These models are then compared to each other and to preliminary data from the spray-jet breakup experiments. Initial results indicate that KIVA with this proposed spray model shows good agreement with low pressure data (69 MPa) but underestimates spray penetration for higher pressures (104 MPa).