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PDE is a new concept of propulsion that can be used in air breathing and/or in rocket propulsion. The advantages claimed of PDE over conventional propulsion system are based on estimate of its performances. Due to nonsteady dynamics, analysis of such engine is more complex than that of steady ones and therefore the first estimations of performance given by computational and theoretical studies (/1/, /2/), vary widely. Recently, an extensive experimental and numerical efforts were undertaken in order to quantify the propulsion potential of this device. Ideal PDE configurations, in particular the single cycle tube experiment, are currently under study in different laboratories. Pulse functioning PDEs are also working but their global performances are not really known because unpublished. This paper reports the main significative past and recent results, available in the literature on PDE performance, and on parameters it depends. In this respect, up to now, many keys issues have not still been addressed.Advantage of detonation regime over classical combustion lies in high rate energy release. It is about two order of magnitude faster than deflagration propagation (in internal combustion engine for instance). Moreover, detonation in propulsion systems does not need any pre-compression system (used to increase efficiency). PDE belongs to the class of unsteady alternative combustion engines. In this respect, a simple comparison of propulsion performance can be done between exhaust of combustion products into the atmosphere resulting from i) the adiabatic isochoric combustion, ii) the detonation of the same mixture (initiated at the closed end or at the open end of the detonation chamber of the same size as isochoric combustion chamber). The detonation regime gives a few percent gain over isochoric combustion (Fig.1). Our 2D computations provide respectively 183s and 176s for the mixture-based specific impulse for C 2 H 4 +3O 2 mixture at standard conditions. In addition, as it is well known, thermal losses are important in the case of realistic isochoric combustion (long characteristic time) and remain limited in detonation regime (short characteristic time).

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The subject of hydrocarbon sensitization by nitrates under conditions of a heterogeneous spray has been of interest due to its applicability in promoting ignition. To gain insight into the mechanisms of the nitrate sensitization effect, the present work was limited to vapour phase studies at elevated temperatures in order to avoid the influence of heterogeneous factors. The experiments performed included studies of flammability, flame propagation, shock ignition and detonation. The mixtures used were composed of air, hexane, and isopropyl nitrate (IPN) with IPN concentrations ranging from 0 to 100 mole % in hydrocarbon-IPN. In addition, methane and propane were also included in the flame experiments. For the shock ignition and detonation experiments, the measured ignition delay and detonation cell size had minimum values for IPN-air and maximum values for hexane-air. With increases in the IPN concentration, the ignition delay and detonation cell size fell monotonically between the values for hexane and IPN. This monotonic behaviour was explained to be the result of mixing the hydrocarbon with the more sensitive nitrate whose energetics are larger than or comparable to the hydrocarbon when mixed with air. For the slow combustion mode, the results also confirmed the monotonic behavior and showed that the lean flammability limit and the flame velocity fell between those of the hydrocarbon and IPN.

In this paper, we report the results of our investigation into the transmission of a detonation from a gas-filled section of pipe into a water-filled portion. Experimental studies were performed using a detonation in a H2-N2O mixture within a 2-inch, Schedule 40 pipe. The detonation wave impinges on a vertical column of water just downstream of a 90-degree bend. A shock wave is transmitted into the water-filled section and propagates slower than the sound speed in the water due to the coupling of flexural waves in the pipe with pressure waves in the liquid. Incident, transmitted, and reflected pressures in the gas are monitored, along with hoop and longitudinal strain throughout the pipe length. Results are presented for a both prompt initiation of an ideal (Chapman-Jouguet) detonation and deflagration-to-detonation transition (DDT) occurring just upstream of the gas-liquid interface. The results of the experiments are analyzed using computational modeling and simulation with an Eulerian hydrodynamic code as well as classical wave interaction methods. For a Chapman-Jouguet (CJ) detonation, the reflected and transmitted pressures agree with the classical one-dimensional theory of wave interaction. The values of the peak reflected pressure are close to those that would be obtained considering the water as a perfectly reflecting boundary. The transmitted wave propagates at a speed consistent with the Korteweg speed of classical water hammer theory and little to no attenuation in amplitude over ∼ 1.5 m of travel. In one DDT event, peak pressures up to 11 times the CJ pressure were observed at the end of the water-filled section.