There is a gap between shell and inner surface of a mortar used for lifting a fireworks shell because the inner diameter of the mortar is larger than that of the fireworks shell. A combustion gas of lifting charge leaks through the gap and the amount of gas leakages increases with the increase of the gap cross-sectional area. Meanwhile, the amount of gas leakages passing through the gap also changes with a pressure from the combustion gas of lifting charge in the mortar.
Two pressure profiles at bottom and upper location in a mortar respectively were measured and the effects of the combustion gas leakages on the internal ballistics were discussed in this work.
It was found that the amount of gas leakages passing through the gap could be qualitatively explained by the relationship of two pressure profiles at bottom and upper in the mortar. The pressure is not uniform on both the combustion side and the opposite side of a projectile, so that the pressure acting on the surface of the projectile does not equal to that measured at the bottom of the mortar when the amount of the gas leakages is large. If the amount of the gas leakages is small, the calculated internal ballistics by the pressure profile in the mortar agrees well with the experiment results.
煙火の打揚に用いられる筒の内径は，煙火玉の外径よりも大きく，玉は筒と密着せず，隙間がある。隙間が大きいほど，隙間を通る燃焼ガスの流出量が多い。また，同じ隙間でも，揚薬の燃焼ガス圧力によって，隙間を通るガス流出量は異なる。本研究では圧力を打揚筒の底部と上部の2箇所で計測し，得られた2つの圧力プロフィルの関係から，筒内における玉の運動に及ぼす燃焼ガスの流出量の影響を検討した。
筒内の底部と上部における圧力プロフィルにより，燃焼ガスの流出量を定性的に判断することができる。燃焼ガスの流出量が多いと，筒内の圧力は筒軸方向に沿って変化するため，煙火玉に働く圧力は筒内の圧力と等しくならず，測定した圧力を補正しなければ，筒内弾道を正確に解析することはできない。燃焼ガスの流出量が少ない場合，筒内における圧力プロフィルにより，筒内弾道を解析した結果は実験結果とよく一致し，精度は良好であった。
Fireworks, Iinternal ballistics, Mortar, Projectile, Pressure profile