: ARL has recently made discoveries in the area of interior ballistic propellant combustion product interactions with a gun tube bore. These discoveries were based on two hypotheses. The first was that the products could and are dynamically nitriding the bore of the gun, thus creating a nitride coating which inhibits the dissociation of CO and subsequently reducing the amount of carbon uptake. The second was that the combustion products richer in nitrogen have a lower temperature upon expansion in our experimental fixture as well as in a gun barrel. This is due to Joule and or Joule-Thomson cooling effects. Both of these hypotheses were proven and validated through numerical and experimental methods. Higher nitrogen containing combustion products have definitively been shown to have relatively lower erosivity with respect to those having lower nitrogen content. These results have revolutionized the gun propellant development community in that for the first time there is guidance for erosivity control through propellant chemical constituent formulation.

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The Role of Nitrogen in Gun Tube Wear and Erosion

HAN is one of the high energy materials and chemical formula is NH 3 (OH)NO a , hydroxylammonium nitrate. HAN is easily soluble in the water and it is the stable material and the combustion performances of HAN propellents are relatively high. So it has been used the oxidizer of liquid gun propellants. HAN has been studied as the liquid gun propellants""61, however not studied as an oxidizer of solid propellants. In this study theoretical combustion performances and decomposition characteristics of HAN propellants were obtained. In theoretical study HTPB(hydroxyl terminated polybutadiene) was used and the concentration of it was 14 percents and the concentration of HAN and aluminum (Al) were 86 percents. The calculating conditions were that the pressure in the chamber was 5 MPa and the nozzle expansion ratio was the optimum at sea level. The specific impulse (Isp) of HAN/HTPB/A1 propellant reached

Thermal decomposition characteristics of HAN composite propellant

: Future systems performance requirements have led to a heightened awareness of the erosion issue and to the development of erosion investigations in the U.S. Army and Navy. These investigations involve experimental and modeling efforts to understand the thermal, chemical, and mechanical contributions to erosion/wear. A description of the mechanistic erosion representation follows in this report. The calculation procedure is illustrated, including details of the mass transport scheme, gas surface interface, surface melt wipe model with dynamic gridding, and the equilibrium kinetics model, which utilizes the NASA Lewis thermochemical library. The following cartridges are investigated: the M829A2 APFSDS in the M256 12O-mm tank cannon and the M79l-APDS-T and 616W-APFS (the "original" M919), both in the 25-mm Bushmaster cannon. The resulting mass lost per round for these systems compares well qualitatively with the experimental data, providing some support to the assumptions in the code. The primary conclusion is that carburization leading to iron carbide formation is an important contributing factor for much of the material lost from the steel barrel once it is exposed through cracks or chips in the surface coating.

An Investigation of the Erosion Physics/Mechanisms of Current Army Systems (Point Studies)

: This patent application describes a liquid propellant gun loading process wherein a predetermined small amount of air or other gas is included in the charge.

Liquid Propellant Guns.

For solving timely ignition of travelling charge and regular energy releasing, a new mode of travelling charge has been proposed. Propellant is substrate propellant, adopt existing energetic binder, use the energetic binder with lower burning rate and energy by compaction technology to shrink and wrap the propellant with higher burning rate and energy, press it into travelling charge cylindrical grain with high density and high strength, and achieve the purpose of controlling energy releasing control of travelling charge. Clad the end of the cylindrical grain with newly developed slow-burning material, combine cylindrical grain's compactness, and achieve the timely ignition of travelling charge. And research it through closed-vessel experiments, the results show that combine the cylindrical grain's compactness, travelling charge timely ignition can achieve by slow-burning layer; the whole combustion performance of travelling charge is stable, repeatability is good, it has good macro properties of progressive combustion and energy release rule.

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The Research on Energy Releasing Control of Travelling Charge

: The erosivity of a series of LOVA propellants was evaluated with the BRL 37-mm blowout gun and with heat input measured in a 105-mm M68 tank cannon. The results in the 37-mm blowout gun suggested that three of the eight propellants were as erosive as M30. Subsequent review of the closed bomb data used to calculate charge weights indicated that it is likely the extraordinary erosivity of these three propellants was caused by overestimating the propellant needed to match peak pressure of M30.

Erosivity of LOVA Propellants

: Some findings from the phenomenological studies during the earlier bulk-loaded liquid propellant gun programs are reviewed for possible relevance to the electrothermal chemical (ETC) propulsion program. The review includes studies on the basic combustion mechanism, conditions that resulted in relatively flat pressure-time profiles, and conditions that may have contributed to catastrophic failures. The studies on the basic combustion mechanisms concluded that the hydrodynamic instabilities occurring during the interior ballistic cycle are sufficient to break-up the charge and result in complete combustion during the interior ballistic cycle. The dominant instabilities include the penetration of a gas cavity into the liquid propellant, called a Taylor cavity; and the rapid liquid break-up due to mixing at the gas liquid interface, referred to as Helmholtz mixing. The initial conditions are also summarized for tests which resulted in relatively flat pressure-time traces. For relevance to the electrothermal chemical program, it is concluded that proper control of the initial conditions will likely be critical for establishing a reasonable level of repeatability.... Thermochemical propulsion, Liquid propellants, Interior ballistics.

A Review of the Bulk-Loaded Liquid Propellant Gun Program for Possible Relevance to the Electrothermal Chemical Propulsion Program

: A Technoproducts drop weight tester was used to evaluate impact sensitivity of four liquid monopropellants; OTTO II, NOS 365, LP 1845 and LP 1846. The monopropellants were evaluated for impact sensitivity at ambient temperatures and at temperatures in excess of 50 C. The propellants were all relatively insensitive to impact compared to the calibration liquid n-propyl nitrate at ambient temperatures. The impact sensitivity increased slightly for the HAN-based monopropellants at temperatures up to 50 degrees. The impact sensitivity of OTTO II increased dramatically as a function of increased temperature.

Impact Sensitivity of Han-Based Liquid Propellants at Elevated Temperatures

: Gun barrel wear tests have uncovered the need for a small scale device to test barrel treatments like 'thick' chromium. Small caliber barrels have traditionally served this role, but results with high-firing rates used to produce measurable wear are ambiguous. An ideal erosion test device would be a small caliber gun with standard projectiles, cartridge cases and propellants which would produce wear comparable to wear in large-caliber guns. Interior ballistic tests were done with M2 or M9 propellant in place of the standard ball powder in the M55A2TP-T round to determine charge masses which would not exceed the peak chamber pressure of the reference M55A2TP-T round. The wear produced with the high-flame temperature propellants was estimated with the Frankle-Kruse empirical formula. The results showed an M9 propellant could be loaded to the same charge mass as the reference WC870 ball powder with a lower peak chamber pressure but 100 m/s higher velocity. The wear estimated for such a round is 5 micrometer/shot, comparable to wear -limited Army guns, but less than the desired 25 micrometer/shot (1 mil/shot) for an erosion test device. Hence the 20-mm gun with M9 propellant could be useful for evaluating chromium-plating for existing guns, but it has too little wear for conveniently assessing future platings and coatings.

Irvin C. Stobie

Papers

Erosivity of LOVA Propellants

A Review of the Bulk-Loaded Liquid Propellant Gun Program for Possible Relevance to the Electrothermal Chemical Propulsion Program

Impact Sensitivity of Han-Based Liquid Propellants at Elevated Temperatures

Interior Ballistic Evaluation of High-Flame Temperature Propellants in 20mm Ammunition and Assessment as an Erosion Test Device

Technical Note: Effect of Surface Oxide on Gun Barrel Wear