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An optically-accessible single cylinder small-bore HSDI diesel engine equipped with a Bosch common-rail injection system is used to study the effects of differing injection strategies on combustion and soot. Laser-Induced Incandescence (LII) is used to visualize the evolution and distribution of soot within the combustion chamber from the onset of ignition to late into the expansion stroke. A low-sooting fuel, blended from two single component fuels, is used for experimentation. Because of the low-sooting nature of the fuel blend, the lean operating conditions, and optical distortion of the complex shaped engine, acceptable LII signal levels are difficult to obtain. Therefore a low-sulfur European Diesel fuel is also employed during experimentation. Acceptable LII signal levels are obtained using the Diesel fuel, however, without extreme caution, surface damage to the optical components of the engine are possible.

In this paper, a new-developed forward illumination light extinction (FILE) soot measurement technique is introduced. This technique has the capability to give two-dimensional time-resolved quantitative soot measurements. Applying the light extinction theory, the line-of-sight soot volume fraction is determined by the ratio of reflected light intensities with and without a soot cloud. The advantages of this technique include its non-intrusiveness, ease of application, requirement of only one optically accessible window, and suitability for the study of transient cycle-to-cycle variations. The application of the FILE technique for diesel combustion in a constant volume chamber demonstrates the applicability and advantages of this technique. Three stages of soot formation during diesel combustion were determined using this technique.

Oxygenated diesel fuels were tested inside a constant-volume chamber to explore the potential of soot reduction by adding oxygenate into diesel fuel. DBM and TPME were two oxygenates examined with the newly developed forward illumination light extinction (FILE) soot measurement technique. The quantitative soot measurement capability makes the study of detail soot formation process of oxygenated fuels possible. The two oxygenated fuels and base fuel were studied at baseline ambient environment with 1000K ambient temperature and 21% oxygen. It is found that oxygenated fuels have different soot reduction performance at different periods of combustion and TPME shows more benefits at premixed combustion while DBM at mixing controlled combustion. It is demonstrated that not only the oxygen carried by oxygenates, but also oxygen entrained from ambient benefits soot reduction.

Low Temperature Compression Ignition (LTCI) combustion employing multiple injection strategies in an optically accessible single-cylinder small-bore High-Speed Direct-Injection (HSDI) diesel engine equipped with a Bosch common-rail electronic fuel injection system was investigated in this work. Heat release characteristics were analyzed through the measurement of in-cylinder pressure. The whole cycle combustion process was visualized with a high-speed digital video camera by imaging natural flame luminosity and three-dimensional like combustion structures were obtained by taking flame images from both the bottom of the optical piston and the side window. The transient in-cylinder late cycle soot distribution was obtained by applying a Backward Illumination Light Extinction (BILE) technique through side windows. Based on the flame luminosity and soot spatially integrated signal, new parameters were defined to evaluate the combustion performance and soot formation characteristics.

An optically accessible single cylinder small-bore HSDI diesel engine equipped with a Bosch common-rail injection system was used to study the effects of multiple injection strategies on the in-cylinder combustion processes. The operating conditions were considered typical in the metal engine under moderate load conditions. In-cylinder pressure traces are used to analyze heat release characteristics. The combustion modes transit from the Homogeneous Charge Compression Ignition (HCCI)-like combustion mode to conventional diesel combustion by changing injection parameters. The whole cycle combustion process was visualized through a high-speed digital video camera and the combustion images clearly show the combustion mode transition. Laser-Induced Exciplex Fluorescence (LIEF) technique was used to obtain simultaneous liquid and vapor fuel distributions within the combustion chamber, with tetradecane-TMPD-naphthalene as the base fuel-dopant combination.

In-cylinder soot formation processes of Environmentally Controlled Diesel (ECD), Diesel #2 and Tetradecane were studied with the newly developed forward illumination light extinction (FILE) soot measurement technique. Quantitative soot measurement was achieved in the constant-volume spray chamber with the proper treatment of chamber window reflection and flame radiation when applying the FILE technique. A better understanding of the soot formation process of ECD combustion under the typical engine conditions was obtained based on FILE soot measurement and flame emission measurement. Diesel #2 with higher sulfur content demonstrates a similar combustion process as ECD but more soot is generated within combustion. In contrast, much lower soot amount was found within the flame of Tetradecane. However, during the last soot oxidation period, the differences were small for all fuels.