نشریه سوخت و احتراق
سال ششم شماره 2 (پیاپی 12، پاییز و زمستان 1392)

The temperature sensitivity of solid propellant burning rate directly affects the accuracy and performance of the rocket motor. In this study، the effect of additives such as iron oxide (IO) on burning rate temperature sensitivity of solid composite propellants based on HTPB was investigated by burning rate، DTA، density and auto ignition temperature experiments. Also the effect of various coarse to fine ratios of oxidizer ammonium per chlorate on temperature sensitivity was studied. The experimental results showed that the burning rates of these propellants were increased by addition of iron oxide or decreasing coarse to fine ratios of ammonium per chlorate particles. DTA results indicated that decomposition temperatures of AP were decreased by addition of iron oxide. Also the auto ignition temperatures of AP with iron oxide were decreased according to the results of auto ignition temperature test. The results also showed that the burning rate temperature sensitivity of AP/HTPB based propellants was reduced by addition of IO or decreasing coarse to fine ratios of ammonium per chlorate particles. The enhancement of burning surface temperature of AP/HTPB/IO and AP/HTPB with low coarse to fine ratios is responsible for the reduced temperature sensitivity. Very small values of the temperature sensitivity are seen when fine AP particles and IO are mixed together.

The effects of kinetics of drying and pyrolysis processes of organic particles such as lycopodium on analytical models of combustion ofthis type of particlesare studied in this paper.DTG curves are investigatedusing experimental TGA curvesand an analytical model for the kinetics of drying and pyrolysis processes of particlesin combustion phenomena is presented. The results show excellent agreement between this analytical model and experimental results. It is possible toconfidentlyuse the results of thisanalytical model for future analytical models of lycopodium particles.

One of the main challenges in HCCI engines is lack of suitable control system as exists in conventional internal combustion engines. Therefore، controlling HCCI combustion can improve the commercial application of these types of engine. In this study a control oriented model (COM) that can predict SOC، BD، and CA50hasbeen developed. The validity of the model has been verified by comparing the predicted pressure traces with the corresponding experimental data، resulted from analysis of in cylinder pressure data، in a wide range of operating conditions. Then، various amounts of intake temperature، intake pressure، and equivalence ratio in HCCI engine in the developed model have been implemented. These data are used to optimize coefficients in Modified Knock Integral Model (MKIM) correlation، and other correlations for predicting combustion parameters. One of the advantages of this COM is easy access to inlet parameters.

This paper presents the influence of heat-loss on the structure of flame during propagation through two-phase mixture including micro-organic particles and air in the framework of thermal-diffusive model with non-unity Lewis number and Damköhler number (ratio of chemical reaction rate to vaporization rate). Then، burning velocity as a combustion parametere is analytically characterized with heat-loss impact. The model predictions are validated with both published experimental data and previous theoretical models، and reasonable agreement is achieved. The obtained results demonstrate that heat-loss plays a significant role in the reduction of the burning velocity.

In the present study, a large eddy simulation (LES) of the flame acceleration and the transition from turbulent flame jet to detonation in a tube with a single obstacle containing premixed stoichiometric hydrogen-air was conducted. The subgrid-scale combustion was represented by the artificially thickened flame (ATF) approach. For detailed modeling of chemical reactions effects on the present phenomenon, a 21-step kinetic scheme was used. In situ adaptive tabulation (ISAT) method was also exploited to reduce the computational cost of using detailed chemistry. The present results show that the proposed LES/ATF/ISAT approach well reproduces the physical phenomenon that occurs during the flame propagation and the transition from turbulent flame jet to detonation. It is observed that the flame behavior and the detonation initiation are influenced by tube walls. Indeed, detonation initiation occurs close to the wall and behind a Mach stem which is formed due to reflection of the leading shock from the wall. Morever, the detonation initiates following a series of local explosions that occurs behind the leading shock.

In this research experimental measurements of adiabatic burning velocities in methane-air and propane-air flames were carried out over a wide range of equivalence ratios at atmospheric pressure. Heat flux method was used for measurement of burning velocities. Experiments were done for methane-air and propane-air mixtures at various equivance ratios.The maximum burning velocity for methanr-air and propane-airwas obtained at equivalence ratio of 1.1 as 37.33 and 42.1cm/s respectively.The results were in satisfactory agreement with published data in the literature. Simulations were performed using Premix code of ChemkinII with GRI Mech3.0 and Princeton university reaction mechanisms for the combustion of methane and propane respectively. The simulation and experimental results also showed good agreement