S. M. Frolov

Detonation initiation by shock wave interaction with the prechamber jet ignition zone

255 Detonation initiation in a stoichiometric propane–air mixture by controlled shock wave (SW) interaction with the cloud of hot combustible gas forming upon the discharge of a combustion product jet from the prechamber has been experimentally observed for the first time. It has been shown that detonation initiation requires the careful synchronization of the SW arrival at the cloud with the moment of spontaneous ignition in it.

Deflagration-to-detonation transition in a kerosene-air mixture

The low detonability of jet kerosene–air mixtures is the major obstacle to the development of an air-breathing pulse detonation engine (PDE) [1]. Currently, work is underway to considerably decrease the detonation initiation energy of hydrocarbon fuels, as well as to reduce the predetonation distance and time [2]. On the one hand, to achieve this aim, it is suggested to use active chemical additives to fuels, fuel blends, emulsified fuels, barbotage of fuel with an active gas, preliminary thermal and radiation treatment of fuel, fuel prevaporization, and premixing of fuel with oxygen or air. Notwithstanding the fact that some of these solutions are believed to be promising, their use in PDEs for flying vehicles is limited by severe safety requirements for their operation, weight restrictions, etc. On the other hand, physical methods aimed at reducing the DDT distance and time are currently being studied. It is suggested to use prechamber jet [3] and plasma jet [4] ignition, traveling igniters [5], regular obstacles [6, 7], tubes of near-limiting diameter [7], regular shaped reflectors of shock waves [8], or tube U bends [9] or tube coils [7, 10], as well as different combinations thereof [7, 10, 11].

Detonation Initiation in a Natural Gas-Air Mixture in a Tube with a Focusing Nozzle

It was shown experimentally for the first time that, when an axisymmetric nozzle of special shape is placed in a tube, the shocktodetonation transition in a stoichiometric natural gas-air mixture occurs under normal conditions at a shock wave (SW) velocity at the nozzle inlet exceeding 1150 ± 30 m/s, which corre� sponds approximately to a Mach number of 3.3. This finding is important for the development of newgen� eration burners using pulsed detonative (PD) combus� tion of natural gas, as well as for a better understanding of the dynamics of accidental gas explosions in mine

Simulation of auto-ignition of iso-octane and n-heptane in an internal combustion engine

A detailed kinetic mechanism is proposed for the oxidation of iso-octane, n-heptane, and mixtures of them in air (number of particles 43, number of reactions 284), which satisfactorily describes the distinctive features of low-temperature and high-temperature oxidation at an initial temperature of 1200 K, pressure of 15–40 absolute atmospheres or higher, and a fuel excess ratio of 0.5–2. The abbreviated mechanisms obtained to describe the auto-ignition of fuel with an octane number of 90 involve 27 particles (38 reactions) and 18 particles (22 reactions).

Pulse-Detonation Hydrojet

Geometrical configuration and operational parameters of a valveless pulse-detonation hydrojet have been determined based on extensive numerical simulations using 2D two-phase flow equations. The theoretical propulsive performance of such a hydrojet in terms of the specific impulse was shown to be on the level of modern liquid propellant rocket engines and amount 350–400 s. Based on the results of numerical simulation a valveless pulse-detonation hydrojet operating on liquid hydrocarbon fuel (regular gasoline) and gaseous oxygen has been designed and fabricated. For firing the hydrojet, a special test rig with flowing water was designed and assembled. Experiments showed that the measured values of the specific impulse varied within the range from 255 to 370 s which overlaps the theoretical range, thus demonstrating the predictive capabilities of the numerical approach.

EFFECT OF THERMAL RADIATION ON DROPLET COMBUSTION

The effect of thermal radiation on self-ignition and combustion of n-heptane droplets is considered. As shown by the experiments with hydrocarbon fuel performed at the International Space Station in microgravity conditions (the Russian–American space experiment CFI (“Zarevo”)), after ignition of a single large droplet 2–5 mm in diameter, the arising flame quenches and the droplet undergoes subsequent low-temperature oxidation and combustion. Calculations show that this phenomenon is due to the thermal emission of soot formed during the burning of the droplet. Unlike large droplets, the combustion of small droplets of submillimeter diameter occurs without the determining influence of thermal radiation: the droplet has time to burn nearly completely before the effects of thermal radiation manifest themselves.

Wind Tunnel Testing of a Detonation Ramjet Model at Approach Air Stream Mach Number 5.7 and a Stagnation Temperature of 1500 K

The mode of continuous detonation combustion of hydrogen in the annular combustor of a model of a detonation air-breathing ramjet at the approach air stream Mach number 5.7 and a stagnation temperature of 1500 K was experimentally detected for the first time in a pulsed wind tunnel. The thrust and fuelbased specific impulse of the ramjet model were 1550 N and 3300 s, respectively.

Continuous Detonation Combustion of Hydrogen: Results of Wind Tunnel Experiments

Combustion tests of a ramjet model 1.05 m long and 0.31 m in diameter with an expanding annular combustor operating in the regime of detonation combustion of hydrogen are described. The tests are performed in a short-duration wind tunnel at free-stream Mach numbers of the incoming air flow from 5 to 8 and stagnation temperature of 290 K. Continuous detonation and longitudinally pulsating regimes of hydrogen combustion with characteristic frequencies of 1250 and 900 Hz, respectively, are observed. The maximum measured values of the fuel-based specific impulse and the thrust generated by the engine are 3600 s and 2200 N, respectively.