Abstract
A small flame sensor was developed to measure the local chemiluminescence intensity of OH*, CH* and 2* in a four-stroke spark-ignition engine in order to understand flame front characteristics, flame propagation speed and local air/fuel (A/F) ratios. This sensor was installed where a pressure transducer was located. The dimensions of the sensor were those of the M5 type; the specifications of the developed small Cassegrain optics were the same as those used in previous engine measurements. The measurements were carried out at engine speeds of 600 and 1200 rpm using propane and gasoline fuels with no hardware modification in a 374.7 cc. model engine. Two types of Cassegrain optics were examined to measure local chemiluminescence of the flame in the engine. The small optics developed can provide very stable data for an experiment lasting several hours, which is sufficient to conduct practical combustion diagnostics. The measurements results with propane and gasoline demonstrated that this sensor is little influenced by fuel type, and the flame propagation speed was similar under both conditions. Although the sensor must be calibrated for a particular engine initially, it can measure local A/F and flame parameters in each cycle in practical engines. On-board diagnostics can be performed using this sensor and the flame speed and local equivalence ratio at the flame front can be calculated without modifying the engine hardware. This sensor should prove useful for measuring flame structure and stoichiometry in order to reduce cyclic variation and give the optimum control of each cylinder in practical engines.
