Chemical species tomographic imaging of the vapour fuel distribution in a compression-ignition engine

This article reports the first application of chemical species tomography to visualise the in-cylinder fuel vapour concentration distribution during the mixing process in a compression-ignition engine. The engine was operated in motored conditions using nitrogen aspiration and fired conditions using a gasoline-like blend of 50% iso-dodecane and 50% n-dodecane. The tomography system comprises 31 laser beams arranged in a co-planar grid located below the injector. A novel, robust data referencing scheme was employed to condition the acquired data for image reconstruction using the iterative Landweber algorithm. Tomographic images were acquired during the compression stroke at a rate of 13 frames per crank angle degree within the same engine cycle at 1200 r min−1. The temperature-dependent fuel evaporation rate and mixing evolution were observed at different injection timings and intake pressure and temperature conditions. An initial cross-validation of the tomographic images was performed with planar laser-induced fluorescence images, showing good agreement in feature localisation and identification. This is the first time chemical species tomography using near-infrared spectroscopic absorption has been validated under engine conditions, and the first application of chemical species tomography to a compression-ignition engine.