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This paper describes a preliminary characterization of in-cylinder spray and combustion behavior from a high-pressure common rail injection system. The engine used in the tests was a single-cylinder optical research diesel engine, adequately developed in a full-fired version, equipped with a common rail injection system. An elongated piston allows for the optical access to the combustion chamber for diagnostic applications. Characteristic of the optical engine is the availability to investigate different combustion system designs due to an interchangeable head-cylinder group. The system configuration tested in the present work corresponds to a four-cylinder engine of 1930 cc of displacement that is representative in the class of light duty d.i. diesel engine. Spray and combustion evolutions were visualized through a high-speed CCD camera synchronized with a copper vapor laser acting as light source.

The present paper aims at investigating the flow field behavior within a reciprocating engine under motoring conditions. Simultaneous two velocity components of the air velocity were acquired at different engine speeds within the cylinder at different radii from the cylinder axis. Mean motion, integral time scales and Reynolds shear stresses, for the radial and tangential components, were estimated from the instantaneous velocity data by applying an ensemble averaging technique. The integral time scale was obtained from the single point time autocorrelation function whereas, the Reynolds shear stresses were computed through the estimate of the degree of the fluctuations correlation. Tests, carried out at 1,000, 1,500, and 2,000 rpm, showed that the tangential mean motion scales approximately with engine speed whereas a radial inward motion can be observed during the last part of compression.