Coalescence features of planar collision between particulate matters of same diameter from diesel engine

It is usually assumed that collision means simultaneous coalescence for particulate matters of diesel engine combustion process. However, the limitation of this assumption is that the recovery phenomenon in collision period cannot be taken into consideration, while compression and recovery are two inevitable periods for collision of incomplete elastic particulate matters, in which Van de Waals force and elastic deformation force influence the coalescence features. In present research, the planar collision between particulate matters of same diameter in post-combustion period of diesel engine was studied and coalescence features of it was investigated further according to compression and recovery phenomena. In addition, the force analyses of particulate matters was utilized to reveal force effect and incomplete elastic collision function based on Van de Waals force and elastic deformation force was solved. In this case, coalescence feature parameters, namely, diameter, collision rate, incidence angle, compression distance and coalescence efficiency, as well as the relation between each other were investigated in terms of recovery phenomenon. The mathematic analyses showed that, Van de Waals force and elastic deformation force both gradually increased for particulate matters under any diameters when particulate matters compressed; furthermore, elastic deformation force was always larger than Van de Waals force with a trend of greater difference considering invariant diameters; and the larger the diameter was, the weaker the elastic deformation force became under the same compression distance, but Van de Waals force followed the opposite pattern of elastic deformation force. On the other hand, collision frequency of 50 nm between 45 and 40 nm was the lowest because higher diameter dispersivity caused greater collision frequency, for instance, it was 1.2×10 16 and 6.2×10 15 m - 3 s - 1 for particulate matters of 15 and 45 nm respectively. Besides this, the compression distance increased with raising incidence angle under the same initial relative velocity, which indicated that central collision had the widest compression distance; increasing initial relative velocity resulted in wider compression distance under the same incidence angle. Recovery factor was an essential element both for critical velocity and coalescence efficiency considering the central collision of 50 nm particulate matter; to be specific, both of critical velocity and coalescence efficiency reduced with raising recovery factor; the coalescence efficiency was approximately 50.05% when recovery factor was about 0.026 suggesting highly efficient collision and rapid coalescence; however, the coalescence efficiency was almost close to zero as long as the recovery factor was larger than 0.063, suggesting immediate separation after collision and barely no coalescence; in summary, a little variation of recovery factor could lead to the huge change of coalescence efficiency.