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Relationships between radiant emissions, as measured by an in-cylinder optical sensor, and spark-ignition engine combustion parameters are presented for possible use in engine combustion diagnostics and future engine control strategies. A monochromatic gas radiation model, developed in a previous study, was used to derive a series of relationships between the measured radiant emission characteristics and several spark-ignition engine combustion parameters, such as the amplitude and phasing of the peak heat-release rate, combustion duration, IMEP, NOx emission, pressure, trapped mass and exhaust-gas temperature. In addition, many engine parameters of interest can be estimated indirectly from the radiation signal using empirical models. Correlations of air-fuel ratio and exhaust emissions are presented which contain a combination of radiant emission parameters and known base-engine operating parameters, such as intake manifold pressure, etc.

The influence of flame temperature on NOx, particulate and hydrocarbon emissions from a single-cylinder light-duty direct-injection diesel engine was examined by varying the composition of the intake air with the engine operating at different speeds and loads. At a fixed engine speed, load, and start-of-combustion timing, the effects of intake-gas composition on emissions were found to correlate with variations in the characteristic diffusion flame temperature. Furthermore, this flame temperature dependence was not significantly affected by the engine operating conditions. These results indicate that the flame temperature correlations originally developed for divided-chamber diesel engines can be applied to direct-injection diesel engines.