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In the last two decades engine research has been mainly focused on reducing pollutant emissions. This fact together with growing awareness about the impacts of climate change are leading to an increase in the importance of thermal efficiency over other criteria in the design of internal combustion engines (ICE). In this framework, the heat transfer to the combustion chamber walls can be considered as one of the main sources of indicated efficiency diminution. In particular, in modern direct-injection diesel engines, the radiation emission from soot particles can constitute a significant component of the efficiency losses. Thus, the main of objective of the current research was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under several representative engine loads and speeds. Moreover, the current research characterized the impact of different engine operating conditions on radiation heat transfer.

A fundamental study to experimentally analyze the effect of cavitation in common-rail diesel nozzles on the soot formation process was carried out. The soot content was characterized by measuring the soot radiation, and an original methodology was developed to suitably characterize the soot formation process from this soot content. After a significant effort to overcome the different difficulties when analyzing the experimental data, the results seem to show a promising conclusion: cavitation reduces the soot formation rate. This reduction is explained, on the one hand, because it leads to a reduction in the effective diameter, thus diminishing the equivalence fuel/air ratio at the lift-off length; and, on the other hand, because it provokes an increase in effective velocity, thus increasing the lift-off length and reducing the corresponding equivalence fuel/air ratio.