Initial Two-Dimensional Laser Induced Fluorescence Measurements of OH Radicals in an Internal Combustion Engine

The imaging of two–dimensional laser–induced fluorescence is used for simultaneous, multiple point visualization of OH radical concentration in the combustion chamber of a single cylinder internal combustion engine. Sheet illumination from the frequency doubled output of a Nd:YAG pumped dye laser is used to excite the fluorescence which is detected using an image–intensified Reticon diode array camera. The camera is interfaced to an IBM–PC AT microcomputer for data acquisition and processing. The laser and camera are synchronized with the crankshaft of the engine so that 2–D images of the OH fluorescence can be obtained at different times through the engine cycle. The OH fluorescence was measured over a 3 cm × 3 cm field of view with 0.3 mm spatial resolution and temporal resolution of < 10 ns. The measurements were made with propane/air mixtures at equivalence ratios of 0.8, 0.9, 1.0 and 1.1 at an engine speed of 600 rpm and at a chamber pressure of 1.34 ± .03 MPa. The OH fluorescence rises sharply through the flame front to a peak value and then decreases gradually in the post–flame gases.