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The liquid phase penetration of diesel sprays under reacting conditions is measured in an optical heavy-duty Direct Injection (DI) diesel engine. Hot gas reservoirs along the diffusion flames have previously been shown to affect the liftoff length on multi hole nozzles. The aim of this study is to see if they also affect the liquid length. The inter-jet spacing is varied together with the Top Dead Center density and the inlet temperature. To avoid unwanted interferences from the natural flame luminosity the illumination wavelength is blue shifted from the black body radiation spectrum and set to 448 nm. Filtered Mie scattered light from the fuel droplets is recorded with a high speed camera. The liquid fuel penetration is evaluated from the start of injection to the quasi steady phase of the jets. Knowledge of jet-jet interaction effects is of interest for transferring fundamental understanding from combustion vessels to practical engine applications.

Soot emissions from diesel internal combustion engines are strictly regulated nowadays. Laser extinction measurement (LEM) and natural luminosity (NL) of sooty flames are commonly applied to study soot. LEM measures soot along the laser beam path and it can probe soot regardless of temperature. NL integrates the whole field of view and relies on soot temperature. In this work, a comparison of simultaneously recorded LEM and NL data has been performed in a heavy-duty optical engine. A 685 nm laser beam is used for LEM. The laser was modulated at 63 kHz, which facilitated subtraction of the background NL signal from the raw LEM data. By Beer-Lambert’s law, KL factor can be calculated and used as a metric to describe soot measurements. A compensation of transmitted laser intensity fluctuation and soot deposits on optical windows has been performed in this work.

Emissions and in-cylinder pressure traces are used to compare the relative importance of soot formation and soot oxidation in a heavy-duty diesel engine. The equivalence ratio at the lift-off length is estimated with an empirical correlation and an idealized model of diesel spray. No correlation is found between the equivalence ratio at lift-off and the soot emissions. This confirms that trends in soot emissions cannot be directly understood by the soot formation process. The coupling between soot emission levels and late heat release after end of injection is also studied. A regression model describing soot emissions as function of global engine parameters influencing soot oxidation is proposed. Overall, the results of this analysis indicate that soot emissions can be understood in terms of the efficiency of the oxidation process.