UDC 634.222.2 + 662.7

DEFLAGRATION TO DETONATION TRANSITION IN GASES IN TUBES WITH CAVITIES

N. N. Smirnov, V. F. Nikitin, and Yu. G. Phylippov

The existence of supersonic second combustion mode - 
detonation - discovered by Mallard and Le Chatelier and by Bertelot 
and Vieille in 1881 posed the question of mechanisms for transition 
from one mode to the other. In the period 1959-1969 experiments 
by Salamandra, Soloukhin, Openheim, and their co-workers provided 
insights into this complicated phenomenon. Since then, among all the 
phenomena relative to combustion processes deflagration to detonation 
transition is, undoubtedly, the most intriguing one. Deflagration 
to detonation transition (DDT) in gases is relative to gas and vapor 
explosion safety issues. Knowing mechanisms of detonation onset control 
is of major importance for creating effective mitigation measures 
addressing the two major goals: to prevent the DDT in case of mixture 
ignition, or to arrest the detonation wave in case it was initiated. 
The new impetus to the increase of interest in deflagration to detonation 
transition (DDT) processes was given by the recent development of 
pulse detonation devices.  The probable application of these principles 
to creating the new generation of engines put the problem of pulse 
detonating devices effectiveness on top of current research needs. 
The effectiveness of the pulse detonation cycle turned to be the key 
factor characterizing the Pulse Detonation Engine (PDE), which operation 
modes were shown to be closely related to periodical onset and degeneration 
of a detonation wave. Those unsteady-state regimes should be self-sustained 
to guarantee a reliable operation of devices using the detonation 
mode of burning fuels as a constitutive part of their working cycle. 
Thus deflagration to detonation transition processes are of major 
importance for the issue. Minimizing the predetonation length and 
ensuring stability of the onset of detonation enable to increase effectiveness 
of PDE. The DDT turned to be the key factor characterizing the PDE 
operating cycle. Thus, the problem of DDT control in gaseous fuel-air 
mixtures became very acute.

The paper contains the results of theoretical and experimental 
investigations of DDT processes in combustible gaseous mixtures. In 
particular, the paper investigates the effect of cavities incorporated 
in detonation tubes on the onset of detonation in gases. Extensive 
numerical modeling and simulations allowed studying peculiarities 
of deflagration to detonation transition in gases in tubes incorporating 
cavities of a wider cross-section. The presence of cavities essentially 
affects the combustion modes being established in the device and its 
dependence on the governing parameters of the problem. The influence 
of geometrical characteristics of the confinement and flow turbulization 
on the onset of detonation and the influence of temperature and fuel 
concentration in the unburned mixture are discussed. It was demonstrated 
both experimentally and theoretically that the presence of cavities 
of a wider cross-section in the ignition part of the tube promotes 
DDT and shortens the predetonation length. At the same time cavities 
incorporated along the whole length or in the far end section inhibit 
detonation and bring to the onset of low velocity galloping detonation 
or galloping combustion modes. The presence of cavities in the ignition 
section turns the increase of initial mixture temperature into the 
DDT promoting factor instead of the DDT inhibiting factor.

Keywords: deflagration, detonation, shock waves, combustion, 
flame, transition, onset.
 
Faculty of Mechanics and Mathematics, Moscow M. V. Lomonosov State 
University, Moscow, 119992, Russia; e-mail: ebifsun1@mech.math.msu.su. 
Original article submitted May 19, 2010.