A. A. Belyaev

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).

Convective burning of pressed aluminum-ammonium perchlorate charges

The convective burning of pressed aluminum-ammonium perchlorate (AP) charges with a porosity of 7 to 18% was studied. The experiments were performed at pressures of up to 300 MPa in a constant volume bomb provided with means for recording pressure-time diagrams, and in a nozzle setup equipped with a streak photocamera and piezoelectric pressure gauges. In contrast to loose-packed-density charges, which are highly explosive, the burning of pressed aluminum-AP charges propagates without marked acceleration, with a moderate velocity and a relatively slow rise in pressure in the bomb. The basic regularities were studied, and the key factors that determine the characteristics of convective burning, such as the aluminum particle shape (when a finely dispersed spherical-particle powder was replaced by a flaky aluminum powder with the same speciic surface area, the convective burning velocity decreased by more than an order of magnitude), ratio of mixture components, and charge porosity, were identified. The effects of the ammonium perchlorate particle size, an organic additive, and the ignitor mass were also studied. The experimental data were analyzed by invoking numerical modeling. The calculations were performed using a program developed earlier based on a model of the convective burning of aluminum-AP mixtures. The calculation results, which were in qualitative agreement with the available experimental data, made it possible to explain the main experimentally observed regularities. The compositions tested and the results obtained are of considerable interest for designing convective-burning charges for multipurpose pulse engines and thermo-and gas generators with operation durations from a few milliseconds to several tens of milliseconds.

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.

Erosive burning of a propellant in the field of a traveling acoustic wave

The response of the propellant burning rate to periodically varied pressure and the tangential mass flow of the combustion products is examined within the framework of the phenomenological theory of unsteady combustion. The effect of an elementary acoustic disturbance, a plane monochromatic traveling acoustic wave, is examined. The analytical and numerical results are obtained for the simplest propellant model with a minimum number of parameters. The roles of the steady and unsteady components of erosion at low and high values of the erosion ratio are established.