Theory of Flame Propagation in Open Obstructed Channels

Obstructed pipes constitute one of the most relevant configurations for extremely fast premixed flame acceleration and deflagration-to-detonation transition. While the flame propagation through obstacles is often associated with turbulence and/or shocks, a conceptually-laminar and shockless mechanism of extremely fast flame acceleration in semi-open tooth-brush -like obstructed pipes has been developed by Bychkov et al [ Phys. Rev. Lett. 101 (2008) 164501]. Namely, a flame front is ignited at the closed end of a pipe, with the flame propagating towards the open pipe end. This acceleration scenario is devoted to a powerful jet-flow, which is produced by delayed combustion in the spaces between the obstacles. This mechanism is scale-invariant (Reynolds-independent), with turbulence playing only a supplementary role in the flame evolution. In the present work, the Bychkov formulation is extended from semi-open channels and tubes to open or vented ones, for the sake of the industrial needs fulfillment, and in order to describe the recent experiments at Karlsruhe Institute of Technology (KIT), Germany [http://arxiv.org/abs/1208.6453]. Both two-dimensional channels and cylindrical tubes are studied. It is demonstrated that flames accelerate extremely fast in open/vented obstructed pipes, with tubes providing stronger acceleration as compared to channels of the same width. The acceleration mechanism is qualitatively the same as that for the semi-open pipes with the ignition at the closed end: namely, it is conceptually-laminar, shockless, and Reynolds-independent, being associated with the delayed burning in pockets between the obstacles. Although the acceleration rate is large enough in open obstructed pipes, it is nevertheless lower than that in the semi-open ones, because the flame-generated flow spreads both upwards and downwards of the flamefront when both pipe ends are open. Starting with obstructed pipes within the inviscid approximation, the analysis subsequently incorporates the viscous forces (hydraulic resistance), comparing their roles with that of the jet-flow driving the acceleration. It is shown that, on the contrary to the common belief, hydraulic resistance is not required to drive the flame acceleration. In contrast, this is a supplementary effect, which actually moderates the acceleration. Besides, hydraulic resistance can be responsible for the initial delay, before the flame acceleration onset, observed in the experiment

On the application of gas detonation-driven water jet for material surface treatment process

The recent advances in pulsed waterjet technology create new opportunities for developing green manufacturing process. New methods of generating pulsed water jets in a simple, controlled fashion are sought after to improve the efficiency of current techniques. This paper examines an unconventional concept for producing high-speed liquid jets, created by detonation phenomenon. The technique relies on harnessing the pressure gain from a detonative combustion to drive a piston that in turn propels a liquid jet at high speed. The proof-of-concept, together with recent pulsed detonation engine development, holds promising potential for detonation-driven pulsed water jet generation applied to manufacturing process

Controlled release using gas detonation in needle-free liquid jet injections for drug delivery

The advent of new drug therapies has resulted in a need for drug delivery that can deal with increased drug concentration and viscosities. Needle-free liquid jet injection has shown great potential as a platform for administering some of these revolutionary therapies. This investigation explores the detonative combustion phenomenon in gases as a simple and efficient means of powering needle-free liquid jet injection systems. A preliminary, large-scale prototype injector was designed and developed. In contrast with the widely used air-powered and electrical driven needle-free injectors, the proposed detonation-driven mechanism provides equivalent liquid jet evolution and performance but can efficiently provide a controllable power source an order magnitude higher in strength by varying combustible mixtures and initial conditions. The simplicity and power output associated with this concept aid in improving current needle-free liquid injector design, especially for delivery of high volume, high viscosity drugs, including monoclonal antibodies, which target precise locations in skin tissue

Development of a Needle-Free Liquid Jet Injection Technology by Pressure-Gain Combustion

In this work, the aim is to develop a practical method of controlled release for drug delivery using the concept of needle-free injection as a replacement for traditional hypodermic needles. The basic idea behind the needle-free injection technology is to generate a high-speed liquid jet to effectively deliver medication to the different layers of skin. The power source and the release mechanism remain the key factors influencing the exit velocity and jet diameter for such technology, which in turn are critical in determining how deep the injection will penetrate the skin and how much medication can be effectively delivered. The idea for this work is to implement a pressure gain combustion process as the power source into the needle-free injection system design. Two types of combustion-driven injector devices are proposed and developed, namely a system driven by detonative combustion for high power injection applications and a small-scale, handheld device powered by a deflagration combustion mode. Experiments and modeling are proposed to understand the basic relationship between different injection parameters using the proposed mechanism of controlled release in order to design more efficient injectors and resolve many of the current shortcomings of needle-free injection technology. The proposed injectors are assessed by measurement of the output jet's stagnation pressure and the associated penetration depth

Tailored Functional Monolayers Made from Mesoionic Carbenes

Significant progress has been made over the last decades in surface functionalization of coinage metals using thiols and more recently N-heterocyclic carbenes. As shown in this work, mesoionic carbenes (MICs) provide straightforward access to a novel class of surface ligands and thus materials. Importantly, MICs are easily accessed from triazolium salts (TS) onto which functional groups may be attached with little synthetic effort. Here, we present a library of TS that were further converted into MICs, in situ, and grafted to gold surfaces. The modified surfaces were thoroughly characterized by advanced spectroscopic methods and electrochemistry for MICs bearing electroactive moieties. We also prepared mixed MIC/thiol self-assembled monolayers, which opens the route to multifunctional surfaces