Abstract
A Pulse Detonation Engine (PDE) is a new invented propulsion device that takes advantage of the pressure rise inherent to the efficient burning of fuel-air mixtures via detonations. Detonation initiation is a critical process that occurs in the cycle of a PDE. A practical method of detonation initiation is Deflagration-to-Detonation Transition (DDT), which describes the acceleration of a subsonic deflagration created using low initiation energies to a supersonic detonation. The DDT process is not well understood due to a wide range of time and length scales involving complex chemistry, turbulence and unsteady pressure waves. This paper discuss about the effects of blocking ratio in the augmentation of detonation pressure and velocity inside a cylindrical tube of diameter 0.0254m and a length of 1 m. The blockages are rectangular in shape placed at 2/3rd distances of the length of the tube and the heights of the blockages are varied in terms of the diameter of the tube as 1/4th, 1/3rd, ½, 2/3rd and 3/4th the diameter of the tube. The setup is then analyzed in MATLAB using the physics of Friedlander’s equation, which formulate the decay time duration of pressure across the tube length, with and without the blockage. Further, a 2D CFD analysis through ANSYS Workbench is conducted which gave the effective blocking ratio in a rectangular type of blockage placed at the 2/3rd position of the length of the tube and the results are compared. For variable pressures ranging from 1 MPa to 100 MPa input, the effective pulse length is around 0.25 seconds after which the decay of pressure and temperature attain the critical limit. Also it is found that the maximum feasible velocity occurs for an inlet pressure of 10 MPa and 2/3rd height of the blockage where the corresponding outlet velocity is 4692m/s and outlet total pressure being 10.542 MPa.
Highlights
The new era of detonation of air-breathing propulsion has conceived from the studies on fuel energy transformation in stabilized oblique detonation waves
While it may be argued that a very powerful igniter, or array of igniters, may be capable of near-direct initiation of detonation, studies of detonation initiation by turbulent flames emerging from obstacleladen tubes and suggest that turbulent flame velocities in the 700-1000 m/s range are necessary for detonation initiation, with turbulent fluctuating velocities on the order of the sonic speed
Based on the 2D CFD analysis and MatLab coding done for the tube of length 1m and diameter 0.0254m with blockages setup at the 2/3rd distance of the length of tube and by varying the height of the blockages, the following conclusions have been drawn: 1. It has been observed that for a maximum pressure of 100 MPa and 1/3rd height of the blockage the velocity at the exit is maximum at 15244 m/s, which may not be feasible for the actual working process
Summary
The new era of detonation of air-breathing propulsion has conceived from the studies on fuel energy transformation in stabilized oblique detonation waves. From cited research inactivation the PDE advantages mentioned above, a number of challenging fundamental and engineering problems has yet to be solved in order to use propagating detonations for propulsion and realize. These problems deal basically with low cost achievement and control of successive detonations in a propulsion device. For variable pressures ranging from 1 MPa to 100 MPa input, the effective pulse length is around 0.25 seconds after which the decay of pressure and temperature attain the critical limit This result gives a predictive analysis of detonation wherein the frequency of spark for inducing controlled combustion inside the tube can be studied
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