## 1 Introduction  
A gasdynamic gun is a kind of test facility in which the test models or projectiles are launched at desired velocities and the aerodynamic properties of the flying models are measured during its flight, or shock and damage of the targets are measured upon the projectile impact [1]. With the invention of two-stage light gas gun by [PERSON] in 1946 and [PERSON] in 1950s [2], especially hypervelocity ballistic range, was widely used in the fields of hypervelocity aerothermodynamics and hypervelocity impact effects as the results of development of hypervelocity reentry vehicles, protection of structures/shields against space debris, and kinetic energy weapons [3; 4; 5; 6; 7; 8]. Although there are several other kinds of hypervelocity launchers, such as the electro-magnetic rail gun and coil gun, the two-stage light gas gun remains the most reliable and frequently used device in laboratories. Relative to other launchers, the two-stage light gas gun has advantages in considerable versatility, maturity of technology, low cost, and capability of launching test models of different shapes at hypervelocity. Regardless of the driving method, the energy of the projectile depends on the energy that is stored in the driver section. Therefore, the driving method is of critical significance to the two-stage light gas gun. The simplest method is to utilize the high-pressure gas filled in driver section as the driver gas directly [9]. However, the driving capability of this method is not often sufficient, i.e., the available speed or energy of projectile is often not high enough to meet the experimental requirements within the range of operable pressure. This driving method is therefore mainly limited to situations requiring relatively low speed or energy for the projectile. To improve the driving capability, gunpowder is often used. Owing to the release of chemical energy, the driving capability of gunpowder is much more powerful than that of high-pressure gas. For example, the largest two-stage light gas gun in the world, the Arnold Engineering Development Complex (AEDC) Range-G, is capable of launching a projectile of 10 kg to speeds higher than 4 km/s [10]. Many studies of this driving method have been conducted, and relevant theories and numerical methods have been developed [6; 11; 12; 13]. Although most large-scale two-stage light gas guns are currently driven by gunpowder, this driving method also has disadvantages. First, the transport, storage, and use of gunpowder are highly specialized activities and are restricted to strictly qualified organizations; therefore, the use of gunpowder is often out of reach for many research institutes. Second, it is a cumbersome task to clean the gunpowder residue after each run. Therefore, it is necessary to develop an alternative driving method that not only makes up the deficiency of driving capability of the high-pressure gas but also is more available and convenient compared to methods requiring gunpowder. Gas guns driven by the combustion of flammable and explosive gases have been investigated as an alternative driving method. The combustion light gas gun that uses H\({}_{2}\), O\({}_{2}\), and H\({}_{\text{e}}\) mixture gas as the driving gas was first developed by the UTRON Company [14]. It is capable of launching a projectile of 0.2 kg to speeds higher than 2.8 km/s. The China Aerodynamics Research and Development Center (CARDC) and McGill University also developed combustion two-stage light gas guns capable of a speed of 5.6 km/s [15]. [PERSON] has developed an interior ballistics model of combustion light gas gun and found that the combustion process could be successfully controlled by adding the proper quantity of diluents. Pressure oscillation and average temperature of the chamber were also reduced [16; 17; 18]. However, the combustion light gas gun has difficulty in getting uniform and predictable ignition or muzzle velocities.