Laser-Induced Incandescence Measurements of Tailor-Made Fuels in an Optical Single-Cylinder Diesel Engine

The influence of two oxygenated tailor-made fuels on soot formation and oxidation in an optical single cylinder research diesel engine has been studied. For the investigation a planar laser-induced incandescence (PLII) measurement technique was applied to the engine in order to detect and evaluate the planar soot distribution for the two bio fuels within a laser light sheet. Furthermore the OH* chemiluminescence and broad band soot luminosity was visualized by high speed imaging to compare the ignition and combustion behavior of tested fuels: Two C8 oxygenates, di-n-butylether (DNBE) and 1-octanol. Both fuels have the same molecular formula but differ in their molecular structure. DNBE ignites fast and burns mostly diffusive while 1-octanol has a low cetane number and therefore it has a longer ignition delay but a more homogeneous mixture at time of ignition. The two bio fuels were finally compared to conventional diesel fuel.

The heat release reactions after ignition by means of the OH* chemiluminescence showed the fast igniting behavior of DNBE, with soot formation being delayed. The soot formation for DNBE was very similar to that of conventional diesel fuel. However, the amount of soot formed is lower and starts oxidizing earlier in the cycle according to the PLII signal. The OH* chemiluminescence signal of 1-octanol on the other hand shows a rapid burn out in the combustion chamber. Due to the homogenous mixture, hardly any soot formation takes place.