Aberdeen Proving Ground, Maryland: Ballistic Research Laboratory. June 1982.The subject program is part of a continuing effort to identify distinct mechanisms that contribute to gun barrel wear and erosion. The thermo¬chemical effects of altering the CO/CO2 ratio of a propellant gas in a gun tube was the main topic for investigation in this program. Experiments were conducted in the Shock Tube Gun (STG), a ballistic compressor, designed and developed by Calspan Corporation. This facility can compress mixtures of pure gases to simulate propellant gas flow conditions and cycle times experienced in large caliber guns.
Tests were conducted with mixture ratios of carbon monoxide and carbon dioxide that characterize the normal range of CO/CO2 ratios found in propellant gas, i.e., 2.0 to 8.1. Progressive substitution of carbon monoxide for nitrogen in the mix quantified erosion as a function of increasing CO concentration or CO/CO2 ratio. Subsequent tests were conducted with gas mixtures containing double the amount of carbon monoxide and carbon dioxide but with the same effective CO/CO2 ratio, to measure erosion as a function of absolute reactant concentration for the two gas species.
The basic chemical effect was observed to be a shift in the erosion threshold to less severe convective heating conditions in response to increasing the C0/C02 ratio above a value of 5.6. The magnitude of the shift appeared to be directly proportional to the absolute concentrations of the two reactant gases. Variation of both CO/CO2 ratio and absolute amounts of the two gases resulted in distinct changes in specimen surface characteristics, both at near threshold and above threshold flow conditions.
