Flame Speed Measurement of a Racing Engine by IR Method and Chemiluminescence Method

Abstract In this study, the optical diagnostics techniques of infrared (IR) absorption and chemiluminescence were applied to a racing engine. A small M5 IR sensor and Cassegrain optics sensors were developed to measure in-cylinder fuel concentrations and local chemiluminescence intensities. The small IR sensor was able to withstand racing engine operating conditions up to 16,000 rpm and exhibited little vibration noise. The IR sensor was mounted in the engine in place of a pressure transducer. It had an optical path length of 11.34 mm, which proved to be adequate for practical applications. The results contained little vibration noise and provided an adequate signal for analyzing the flame propagation speed. In separate tests, two micro Cassegrain (MC) sensors were installed in the cylinder head near the wall to evaluate the cylinder-to-cylinder fluctuations and the flame propagation characteristics. The local air excess ratio (λ) was estimated from the ratios of the emission intensities using the chemiluminescence and the micro Cassegrain system (MCS) after deriving a calibration function. The averaged values of λ in cylinders 2 and 3 were similar, but cylinder 2 had higher cyclic variations. The cyclic fluctuation of the flame propagation speed in cylinder 2 was also larger, indicating that combustion was more stable in cylinder 3. The measured flame propagation speed increased with the engine speed, but the propagation speeds normalized by the piston speed remained at a constant level. The flame propagation speed increased with and was strongly influenced by the engine speed. Under the high engine-speed conditions found in a racing engine, the flame propagation speed was influenced by the fluid dynamics of the in-cylinder flow. The IR and MC sensors were successfully used to analyze the flame propagation characteristics in a racing engine at high engine speeds and high loads. The MC system detected the radical signals without any problems, despite transient engine operating conditions, and could be used to measure the flame characteristics.