Transient In-Cylinder AFR Management Based on Optical Emission Signals

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. This signal-processing tool allowed for obtaining satisfactory correlation of measured and estimated air excess ratio in combustion chamber.

A verification of elaborated measurement technique was done by realization of time-domain programmed patterns of air excess ratio variations and comparison with estimated value of air excess ratio. This research proved that this method of measurement can be used for analysis of transient air excess ratio variations, especially for the verification of engine injection control algorithms.