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In our previous work, diesel late combustion heat release is suspected to originate from rich fuel mixture cloud stagnating at the spray tip. Injection rate shaping is gaining attention as an attractive strategy to control diesel spray combustion characteristics where it could be an effective approach in reducing the late combustion. Progressive ramp-down injection rate as in “inversed-delta” shape is achieved by using a novel rate shaping injector called TAIZAC (TAndem Injectors Zapping Activation); rate shaping can be realized by controlling the actuation timing of two directly-connected commercially available injectors. To investigate the potential of inversed-delta rate shaping for reduction of diesel late combustion, simultaneous high-speed UV laser diffuse back illumination (DBI), UV emissions and soot luminosity imaging of inversed-delta and conventional rectangle-injected spray flames conducted in a constant volume combustion chamber are compared.

In order to better understand in-flame diesel soot oxidation processes, soot particles at the oxidation-dominant periphery of diesel spray flame were sampled by a newly developed “suck” type soot sampler employing a high-speed solenoid valve and their morphology and nanostructure were observed via high-resolution transmission electron microscopy (HR-TEM). A single-shot diesel spray flame for the soot sampling experiment was achieved in a constant-volume vessel under a diesel-like condition. The sampler instantaneously sucks out a small portion of soot laden gases from the flame. A TEM grid holds inside the flow passage close to its entrance is immediately exposed to the gas flow induced by the suction at the upstream of the solenoid valve, so that the quick thermophoretic soot deposition onto the grid surface can effectively freeze morphology variation of soot particles during the sampling processes.