Optical Investigation of Auto-Ignition Process in a Small DI Diesel Engine

A optical investigation of injection, and combustion process has been performed in order to understand auto-ignition phenomena into a small 4 cylinder DI Diesel optical engine. Measurements were obtained a representatives partial load condition, corresponding to a motored TDC temperature and density of 800 K and 20 kg/m3. A better comprehension of cyclic fluctuation of auto-ignition sites was provided by a double optical diagnostics set up. Laser induced fluorescence was applied on Diesel fuel liquid phase along with synchronous natural flame imaging.

The auto-ignition process has been investigated by a new experimental set up. A spectrally resolved imaging of the first chemical reaction was performed and revealed errors induced by a pressure transducer analysis. A photomultiplier tube, sensible to the OH* radical emission's band was employed to approach the real auto-ignition delay. The primary step of auto-ignition phenomena is point out to correspond to a weak chemiluminescence emission signal which is not correlated to a significant pressure variation.