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An in-cylinder optical sensor has been developed to measure and control the exhaust smoke or soot emission from heavy-duty diesel engines. The sensor directly measures the radiant emission from incandescent soot particles during and after main combustion. Results show a strong correlation between both the measured duration and end of radiant emission, and the amount of soot emitted by the engine. Test results also demonstrated some potential benefits of in-cylinder control using the optical sensor. In one test, the optical signal was used to control high-load soot emission during changes in air intake pressure and temperature. In a second test, the optical signal was used to minimize the variability in exhaust soot levels caused by manufacturing variations in fuel-injector flow characteristics.

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.