Engine diagnostics and computational fluid dynamics

Successful engine design tailors the cylinder aerodynamics to achieve the desired burn rate. In recent times, this has been aided by laser diagnostics and computational fluid dynamics. In-cylinder diagnostic techniques for production engines include the use of rapid response pressure transducers, ion gauges as markers of flame progress, laser doppler velocimetry and emission spectroscopy. These have been reviewed historically by Witze [103]. The two zone analysis of Chun and Heywood [104] enables the net heat release rate to be derived from the pressure-volume relationship [105]. 

By subtracting the heat release rate in a non-knocking cycle from that in a knocking cycle it is possible to estimate the heat released by autoignition as a function of crank angle [106]. The variations in heat release rates for three different knock intensities are shown in Fig. 7.13. The onset of knock is indicated by an asterisk and occurs at the maximum heat release rate, which is appreciable at the highest knock intensity. The unburned mass fraction is shown by the axis at the left and it shows that 

Pressure-time records, for a knocking and non-knocking cycle are shown in Fig. 7.14, together with the digitally filtered pressure signal for the former, filtered between 5 and 25 kHz [92]. The minimum pressure for the autoignition to lead to knock, or knock threshold pressure, also was measured. Knock was defined, arbitrarily, as a knock intensity greater than 0.2 bar, and the knock onset pressure as the pressure at which the filtered pressure first reached 0.1 bar. 

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