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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.

Relative roles of premixed and diffusion burning in diesel combustion have been examined in terms of characteristic times for ignition delay (τig), combustion (τc) and fuel-air mixing (τm). Results indicate that the majority of the diesel combustion process is diffusion controlled, as in gas turbine combustion, since τc << τm over the entire range of operating conditions. During the ignition phase, some premixed burning can occur in the fringe of the fuel spray where τm < τig; however, most of the fuel injected prior to ignition also burns in the diffusion mode, since τm > τig in the majority of the fuel spray. The fraction of premixed burning which occurs during the ignition phase is increased by longer τig, high rates of fuel injection, high air swirl and the use of multi-hole injectors, which increase the surface area of the spray.

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.

Cyclic variation is examined by: (1) conditional grouping and heat-release analysis to reveal different modes of combustion, (2) considering the order in which the burn modes occur to establish prior-cycle effects and (3) comparing the measured variation in IMEP with data generated by simple models. Results show that several burn modes may exist, particularly under fuel-lean conditions. Prior-cycle effects also become more obvious as the air-fuel ratio is increased. Finally, comparisons with data generated by simple models show that the nature of cyclic variation may range from completely stochastic to a superposition of a non-chaotic deterministic process on a stochastic process.

Conditional sampling of cylinder-pressure data is used to investigate cyclic variability in a premixed-charge spark-ignited engine operating under fuel-lean conditions. Unlike straight ensemble averaging of pressure data, conditional sampling applies a set of constraints to the pressure data such that like combustion events can be identified and grouped together. Ensemble averaging of pressure data from an engine that exhibits significant cycle-to-cycle variation is shown to produce a mean pressure history that is not representative of the combustion process. Conditional sampling provides a means of identifying and analyzing the different groups of pressure histories and therefore the different types of combustion processes that occur in an engine that exhibits cyclic variability.