Sensitivity analysis on the effect of background temperatures and densities on the diesel spray characteristics

In this paper, a direct imaging and schlieren technique of high-speed photography is applied to optimize the background temperature and density at the time of diesel spray inside an engine cylinder and consequently improve the spray characteristic and increase power. Accordingly, an in-house image processing program is used to process the data. The concept of sensitivity is then introduced. Furthermore, a sensitivity analysis is performed on the effect of the background temperatures and densities on the diesel spray characteristics. The background temperature sensitivity against the volume percentage of the gas phase is far more than the density sensitivity (i.e., approximately 10 times that of the density at 770 K and 26 kg/m³) when the density and the temperature varied from 13 to 26 kg/m³ and 304 to 770 K, respectively. Moreover, the density sensitivity against the average air-fuel ratio of the spray is slightly higher than the temperature sensitivity (i.e., approximately 1.18 times that of the temperature at 770 K and 26 kg/m³) under the same condition. The power can be increased by 2.8% by applying the sensitivity law to an engine-simulating calculation at some behaviors when the background temperature and the density at the initial diesel spray moment are slightly adjusted, with a variation scope within 3.5%.