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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.

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.

Previously measured particulate mass concentrations from a single-cylinder indirect-injection diesel, obtained under conditions of both varying dilution ratio and varying filter temperature, are examined in detail. Considering the mechanisms of condensation, adsorption, and diffusion, the observed variations in total particulate mass are attributed primarily to the adsorption and desorption of exhaust hydrocarbons on the solid particulate matter. A simple Langmuir adsorption model is used to explain qualitatively the observed effects of dilution ratio and sample temperature. Only under conditions of relatively high hydrocarbon emission is the condensation mechanism also shown to be important. The simple adsorption analysis also predicts the trends observed in CVS (Constant Volume Sampling) dilution tunnels in which filter temperature and dilution ratio change simultaneously.

A dilution mini-tunnel is described that allows collection of diesel exhaust particulate samples with independent control of the dilution ratio and the sample filter temperature. This tunnel was used to determine the individual effects of these two tunnel operating variables on the samples collected from a single-cylinder indirect-injection test engine run at constant speed and load. Either increasing the filter temperature at fixed dilution ratio or increasing the dilution ratio at fixed filter temperature resulted in a decrease in total particulate mass. These changes in total mass were attributed to changes in the soluble fraction of the particulate sample.

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.