Cycle resolved measurements of Diesel particulate by optical techniques

The capabilities of the spectral extinction and scattering technique to follow the time history of the particulate concentration in the exhaust of a Diesel engine were evaluated. Simultaneous measurements of extinction and scattering coefficients from UV to visible were performed at 1.5 m downstream the exhaust valve. The measurements were triggered with the exhaust valve lift. The exhaust stroke was divided in three time windows of 1 ms in which the optical signals of 100 consecutive cycles were detected. The mean diameter, the concentration and the properties of soot particles were evaluated. The cyclic variation of measurements was also estimated. The present paper focuses the attention on the evaluation of transient capabilities and the dispersion of the measured data. Real-time measurements of scattering and extinction in the wavelength range 200 to 600 nm, synchronized with exhaust valve opening, are reported. Ensemble averaging procedure on 1ms time interval and on consecutive 100 cycles has been used to compute the scattering and extinction mean values. An estimation of data dispersion has been made at different air-fuel ratios and fixed engine speeds.