Search Results

To investigate the ignition process in a diesel spray, the ignition in a transient fuel spray is analyzed numerically by a discrete droplet spray model (DDM) coupled with the Shell kinetics model at various operating conditions. Predicted results show that the fuel mixture injected at the start of injection, which travels along midway between the spray axis and the spray periphery, contributes heavily to the first ignition in a spray. The equivalence ratio and temperature of the first ignited mixture are kept nearly constant until the start of hot ignition. The temperature of the first ignited mixture is kept at a constant value of higher temperature than the thermodynamic equilibrium temperature of the mixture before the hot ignition starts. The equivalence ratio of the first ignited mixture is around 1.6 at initial gas temperatures between 750 K and 850 K.

The time of, and location where ignition first occurs in a diesel fuel spray were investigated in a rapid compression machine (RCM) using the two–dimensional techniques of silicone oil particle scattering imaging (SSI), and the planar laser induced fluorescence (LIF) of formaldehyde. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the LIF images of the formaldehyde formed in a diesel fuel spray during ignition process have been successfully obtained for the first time by exciting formaldehyde with the 3rd harmonic of the Nd:YAG laser. SSI images of the vaporizing spray, and the LIF images of formaldehyde were obtained together with the corresponding time record of combustion chamber pressures at initial ambient temperatures ranging from 580 K to 790 K.