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In-cylinder cycle-resolved LDV measurements have been made in a diesel engine having a high-squish re-entrant combustion chamber with compression ratio of 21:1. The engine has been motored in the range of 1000 to 3000 rpm thanks to the use of self-lubricating seeding particles. Conventional ensemble-averaging and filtering techniques have been used for analyzing instantaneous velocity data obtained at two points along a diameter located in a horizontal plane at 5 mm below the engine head. The dependence of the mean motion and turbulence on engine speed has been evaluated. The effect of cut-off frequency selection on turbulence values has been also analyzed. Moreover, the Kolmogorov's -5/3 power domain has been investigated in detail by spectral analysis on the instantaneous velocity data.

A high swirl divided-chamber Diesel engine system with longitudinal and lateral optical access was developed to study the air-fuel mixing and combustion processes using both conventional and optical techniques. In particular, the spatial and temporal spray evolution, the mixture formation and the combustion phenomena were visualized by a high speed camera. The spatial distribution of soot temperature and soot volume fraction were estimated by spectral flame emissivity measurements using a polychromator with an intensified CCD camera. A modified version of the KIVA-3 numerical code was used to compute the flow field and spray combustion. The code was coupled with a pre-processor to generate the grid of the divided-chamber system and included models of droplet deformation breakup (DDB), single step ignition delay and turbulent mixing-controlled combustion.

The present paper aims at developing a general method to estimate integral and microtime scales of turbulent in-cylinder flow field in reciprocating engines. The ensemble average technique was used to compute the integral time scale from the single point time autocorrelation function, whereas the microtime scale, representative of the most rapid changes that occur in the fluctuation, was computed as the intercept of the parabola that matches the autocorrelation function at the origin. Further, the microtime scale was also estimated by spectral analysis through the energy spectral density function of the ensemble turbulent fluctuation and the results obtained by the two methods were compared. The procedures were applied to the tangential component of the instantaneous velocity data collected, at different engine speeds (1,000, 1,500, 2,000 rpm), within a motored d.i. diesel engine equipped with a re-entrant combustion chamber, using the Laser Doppler Anemometry (LDA) technique.