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.