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The paper presents results of spectroscopic research of the air excess ratio in a combustion chamber of a spark- ignited engine fuelled with gasoline and LPG. For the evaluation of air excess ratio a correlation with relative concentration of HC and C2 radicals existing in combustion flame was used. Concentration of radicals was measured on the basis of chemiluminescence forming as a result of transition from electron-excited states. Light emission from the combustion chamber was recorded using measurement system composed of optical combustion sensor, transmission optical waveguides, optical filters, monochromators and electronic devices for signal conversion. A strong correlation of relative optical emission with air excess ratio in combustion chamber was confirmed. However, for different engine loads and rotational speeds, some scattering of measurement points was noticed. Therefore it was necessary to use artificial neural networks to analyze courses of optical signal.

The paper describes investigations on the nature of the misfire phenomenon in a SI engine. Authors performed a series of experiments on a single-point gasoline injection engine in a wide range of loads and rotational speeds, including different air-fuel ratios. The data was gathered using optical combustion sensor integrated with a spark plug. The main aim of the experiments was to develop fast and reliable misfire detection algorithm basing on the optical signal, which would be simple and easy to use within the engine control system. Misfire identification algorithm proved to be reliable, with neglectable detection error. Analysis of the results included not only quantitative measurements, but also those regarding distribution and probability of occurrence. Results made it possible to establish conditions in which the investigated engine is more likely to misfire. The influence of misfire occurrence on the further engine performance was also analyzed.