Fluctuation analysis of diesel combustion process by means of the optical fiber thermometer (comparison of combustion fluctuation between conventional injection and pilot injection)

In order to clarify the characteristics of combustion fluctuation in diesel engines quantitatively, the fluctuations of pressure and flame temperature were measured, and the root mean square value, the autocorrelation coefficient and the power spectrum density of the measured fluctuations were analyzed by comparing the cases with and without pilot injection. The following concluding remarks are obtained. (1) The frequency power spectrum of the in-cylinder pressure history is reduced markedly by pilot injection in two frequency ranges from 0.2 to 2.0 kHz and from 2 to 5 kHz. ( 2 ) The fluctuation of combustion pressure is dependent on the maximum rate of pressure rise, which is dependent on the ignition delay. ( 3 ) The maximum rms of the flame temperature fluctuation during diffusion combustion has a clear correlation with that of the pressure fluctuation in the initial combustion. (4 ) The fluctuation of the flame temperature during diffusion combustion has the characteristics of isotropic turbulence.