10. Combustion and Reacting Flows

The initial stage of flame development has become important with regard to promoting more stable lean/dilute combustion in spark ignition engines. Thus, a means of performing simultaneous, instantaneous measurements of the unburned gas flow and temperature to clarify phenomena related to local extinction is required. Inexpensive two-color inorganic fluorescent particles (f-particles), which the authors previously proposed for velocimetry imaging of the gas flow around solid objects, could be employed for this purpose. Two-color f-particles containing rhodamine B (RhB) and rhodamine 6G (R6G) emit fluorescence derived from each dye. The ratio of the fluorescence intensity at 577 nm to that at 550 nm shows an almost linear relationship with temperature between 333 and 473 K. In the present study, local gas temperature measurements were carried out using this method and the time response was assessed. The fluorescence intensity ratio was also increased so as to obtain improved resolution. This was accomplished by increasing the amount of RhB relative to that of R6G to reduced concentration quenching of the RhB emission. This was possible because the fluorescent intensity derived from R6G was decreased due to the increased absorption by the RhB. Transient temperature changes of at least 1.5 K/ms could be detected based on images acquired during the compression stroke of an optical engine operating at 600 rpm.