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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.

Optical engines of Bowditch design may suffer from distortion of the in-cylinder volume trace due to mechanical deformation from inertial, pressure and thermal forces. Errors in heat release calculation associated with such deformation were investigated in detail. The deformations were quantified by measuring the squish height during operation using high speed video. Deformations of all-metal engines were also estimated for comparison. The volume change caused by deformations did not change the calculated load significantly but caused errors in the heat release calculations both for optical and all metal engines. The errors at a given operating condition are smaller for all-metal engines but the importance is not necessarily smaller, since these engines normally are operated at higher loads. The errors can be eliminated by a corrected in-cylinder volume equation and a subtraction of heat release from a motored case.