In the second part of the present study, experimental results on the round and plane hydrogen microjets diffusion combustion at various nozzle diameter depending on microjet velocity are shown. Of special interest is the contribution to the combustion process of the so-called << bottleneck flame >> region which is observed at diffusion combustion of hydrogen both in the round and plane microjets. The << bottleneck flame >> appears as a spherical closed volume of laminar combustion at mixing of the hydrogen microjet with ambient air. This spherical volume is surrounded by a narrow layer of density gradient overcoming which the laminar microjet and its flame become turbulent. A diminution of the bottleneck flame with growth of the microjet velocity is revealed. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.