Development and application of high speed optical diagnostic techniques for conducting scalar measurements in internal combustion engines

Modern combustion devices, such as direct-injected spark-ignition engines, place strict requirements on the state of the fuel mixture near the time of ignition. Even slight variances from ideal conditions can lead to combustion instability and in the worst case, misfire events. For widespread application of such devices, the causes of these instabilities must be determined so that preventative measures can be taken. Diagnosing the causes of misfire in internal combustion engines requires techniques that can provide spatial detail in the sub-millimeter range and temporal resolution in the tens of microsecond range, and do so for several consecutive cycles. Optical diagnostics were previously found to be capable of meeting the spatial detail requirements, however failed at producing data with sufficient temporal resolution. These methods relied on averaging over several engine cycles which gives information on bulk behavior, but did little to address cyclic variations and ultimately misfire.;This work addresses these shortcomings by providing two optical diagnostic techniques based on laser-induced fluorescence. For the first time, methods capable of recording fuel distribution images at a rate of 12 kHz for several hundred consecutive engine cycles are presented. The first technique utilizes two relatively low speed KrF excimer lasers to excite toluene in iso-octane to obtain two qualitative LIF fuel distribution measurements per engine cycle. In addition, the subsequent ignition and flame development process is tracked using the natural luminosity from the hydroxyl radical. From this technique, key relationships between the spray, spark and flame are observed. The second technique provides a means for tracking fuel distribution throughout the entire injection and ignition process through use of a high-speed Nd:YAG laser and biacetyl as a fuel tracer. As with the first technique, ignition and flame development is simultaneously recorded and this is done for several hundred consecutive engine cycles. Using this diagnostic technique, several quantitative observations are made regarding the fuel distribution within the engine under different combinations of fuel injector and spark plug orientations. Finally, the applicability of both techniques to determining the cause of misfire is demonstrated through observing several misfiring cycles and noting a number of potential causes.