The reduction of total hydrocarbon (THC) emissions during cold start conditions is very important in order to achieve a tight control over exhaust emissions.The key factors to reduce these emissions include the spray characteristicsr mixture formation, ignition, and iniection control. In order to understand cold start combustion in a cylinder, the air-to-fuel ratio (AfF) near the spark plug was measured using a micro Cassegrain system (MCS). The local AIF and flame propagation speed were detected under the cold start conditions. This optical system consisted ofa micro Cassegrain sensor (MC sensor), a spectroscopic unit with optical filters, photo-multipliers, and associated software. The AIF was determined from the intensity ratio of the radicals measured using their flame chemilumineseence.A practical engine and an MI4 spark plug MC sensor were used for the measurements.
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