Showing papers on "Burn rate (chemistry) published in 2020"

Towards understanding the catalytic properties of lead-based ballistic modifiers in double base propellants.

Abstract: Lead-based ballistic modifiers are additives in double base propellants (DBPs) which render the burn rate insensitive to changes in pressure within a defined pressure range, thus imparting greater control of combustion conditions. In-coming European legislation will soon ban the use of lead in propellant formulations, however, and few suitable candidate replacement materials are currently available. In an effort to understand better the unique properties offered by lead-based modifiers, we present a first-principles computational study on Pb, PbO, PbO2, SnO2 and Bi2O3, all of which have been investigated experimentally as ballistic modifier materials. Our study demonstrates that various quantifiable properties exist for the lead-based materials. Overall, they have narrower electronic band gaps, lower surface energies and lower surface work functions than the lead-free systems, indicating a greater propensity to form stable chemical surfaces with higher catalytic activity. We also show that of the set, only Pb and α-PbO can support the formation of a weakly bound layer of amorphous carbon, a key experimental observable in the burning of DBPs.

Comparison of Propellant Processing by Cast‐Cure and Resonant Acoustic Mixing

Abstract: In this comparative study, a solid composite, AN/HTPB-based propellant was prepared by conventional processing in a mechanical mixer and by applying an advanced processing technique relying on resonant acoustic mixing (RAM). After curing of the propellants, cross-sections were prepared and characterized by scanning electron microscopy. Also the density of the propellants was measured and finally the ballistic properties were measured using chimney burner tests. The experimental results clearly showed that the oxidizer particles, the homogeneity of the propellants, the density and the burn rate properties are hardly affected by the processing method. For the propellant studied in this research, resonant acoustic mixing is a very promising, advanced processing technique that can be applied as an alternative to the conventional mechanical mixing of this high solid load propellant composition. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Study on Friction Sensitivity of Passive and Active Binder based Composite Solid Propellants and Correlation with Burning Rate

Abstract: Friction sensitivity of composite propellants and their ingredients is of significant interest to mitigate the risk associated with the accidental initiation while processing, handling, and transportation. In this work, attempts were made to examine the friction sensitivity of passive binder: Hydroxy Terminated Polybutadiene/Aluminium/Ammonium Perchlorate and active binder: (Polymer + Nitrate Esters)/Ammonium Perchlorate/Aluminium/Nitramine based composite propellants by using BAM Friction Apparatus. As per the recommendation of NATO standard STANAG–4487, the friction sensitivity was assessed by two methods: Limiting Frictional load and Frictional load for 50% probability of initiation (F50). The test results showed that the active binder based formulations were more vulnerable to frictional load as compared to the formulations with passive binders. Examination of a comprehensive set of propellant compositions revealed that the particle size distribution of Ammonium Perchlorate and burn rate catalysts were the most influential factors in dictating the friction sensitivity for HTPB/Al/AP composite propellants. For active binder/AP/Al/Nitramine composite propellants, the formulation with RDX was found more friction sensitive with a sensitivity value of 44 N as compared to its HMX analog (61 N). The correlation studies of friction sensitivity, burning rate, and thermal decomposition characteristics of HTPB/Al/AP composite propellants is described.

Effect of Heat Loss on Propagation Limits of Combustion Fronts in Heterogeneous Mixtures

Abstract: The effect of heat loss on the propagation limits of combustion front is studied by considering one-dimensional chain of discrete point sources using two systems, namely (i) periodic and (i...

Combustion of Ammonium Perchlorate: New Findings

Abstract: The combustion characteristics of ammonium perchlorate (AP) monopropellant have been discussed. Both experimental and computational tools were utilized to explore AP combustion. Three different methods were used to determine the low-pressure deflagration limit (LPDL) of AP monopropellant. Method I and Method II are found to introduce the ignition dynamics and affect the LPDL. Method III (slow depressurization) is independent of ignition and pressure dynamics. The LPDL of AP is found to be 14 bar using method III. Silica grease is found to act as an insulator. The use of silica grease on the sides of pellet reduces the convective heat loss and both the burning rate and the temperature sensitivity of AP are found to increase. The burning rate and temperature sensitivity of AP at 70 bar are 10.66 mm/s and 0.0038 K−1, respectively. LPDL of AP with 1% of iron oxide (IO) and copper chromite (CC) is significantly lower due to reduced convective heat loss and the prominence of the catalytic effect, which was overlooked in literature. A two-dimensional, unsteady combustion model is used to simulate AP. The combustion parameters of the model are suitably updated and a good match is obtained with the experimentally observed burn rate, pressure index, and temperature sensitivity.

System and method for estimating cylinder pressure

Abstract: A method for estimating a peak cylinder pressure associated with operation of an internal combustion engine may include receiving, in a cylinder combustion model, a fuel signal and an air signal. The cylinder combustion model may be configured to estimate at a first crankshaft angle, a first mass fuel burn rate and a first burned fuel-air ratio associated with combustion. The cylinder combustion model may also be configured to estimate at a second crankshaft angle, a combustion ignition delay associated with the combustion, and estimate at the second crankshaft angle, a start of combustion associated with the combustion of the fuel and the air supplied to the cylinder. The cylinder combustion model may be further configured to estimate, based at least in part on the start of combustion, a peak cylinder pressure associated with the combustion of the fuel and the air supplied to the cylinder.