Structural characterisation of soot particles for cold-start and hot-start operation of a diesel engine

The current study investigates the morphology and nanostructure of soot particles during cold and hot-start operation of a custom designed drive cycle for a heavy-duty diesel engine. The drive cycle consists of eight repeated sets of 120 seconds each, with abrupt change in the load at 30 second intervals at a constant engine speed (1500 and 2000 rpm). After each segment there is an engine stop period of 60 seconds. Soot samples were collected on TEM grids for the first three consecutive sets (cold-start) and the last three consecutive sets (hot-start). The soot samples were analysed using transmission electron microscope. An in-house automated image processing methodology was used for the quantification of a range of characterisation parameters. The results show that the primary particle size during cold-start is smaller in comparison with hot-start operation. High fractal dimension of soot aggregate for cold-start operation would mean more compact structure of soot particles. Shorter fringes with a higher fringe separation distance for cold-start would mean lower graphitisation of soot particles.