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Two competing in-cylinder processes, soot formation and soot oxidation, govern soot emissions from diesel engines. Previous studies have shown a lack of correlation between the soot formation rate and soot emissions. The current experiment focuses on the correlation between soot oxidation rates and soot emissions. Laser extinction is measured using a red (690nm) laser beam, which is sent vertically through the cylinder. This wavelength is long enough to minimize absorption interference from poly-aromatic hydrocarbons, while still in the visible regime. It is modulated at 72 kHz in order to produce 10 pulses per crank angle degree at an engine speed of 1200 rpm. The intake oxygen concentration is varied between 9% and 21%. The time resolved extinction measurements are used to estimate soot oxidation rates during expansion.

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.

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 engines are the net result of two competing processes: soot formation and soot oxidation. Previous studies have shown poor correlation between soot formation rates and the soot emissions. This article presents a systematic study of a number of parameters affecting soot oxidation rate and how it correlates with the soot emissions. An optical heavy-duty engine is used in conjunction with a laser extinction setup in order to collect time resolved data of the soot concentration in the cylinder during the expansion stroke. Laser extinction is measured using a red (685 nm) laser beam, which is sent vertically through the cylinder and modulated to produce 10 pulses per crank angle degree. Information is obtained about the amount of soot formed and the soot oxidation rate. The parameters studied are the motored density at top dead center (TDC), motored temperature at TDC, injection pressure, engine speed, swirl level and injector orifice diameter.