Interests in Rocket grade hydrogen peroxide have been renewed in recent years by the research for a non-toxic alternative to rocket propellants currently in use. This renewed interest is because of low toxicity and enhanced versatility.
On the applications of hydrogen peroxide, the performance of catalyst is very important. The utilization of hydrogen peroxide is based on catalytic decomposition. Recently, silver screen catalyst bed has been widely used for hydrogen peroxide decomposition. However silver screen has several shortcomings such as low melting point, non-uniform flow path, high pressure drop, and need of pre-heating.
To overcome the structural failure and need of pre-heating, we designed a concept of hybrid hydrogen peroxide gas generator including hydrogen peroxide vaporizer.
The key point of this research is the hydrogen peroxide vaporizer. The Main purpose of vaporizer is to evaporate hydrogen peroxide and feed it directly to the decomposition catalyst without concentration loss. Therefore vaporizer catalyst should have excellent performance near the room temperature. $K_2MnO_4$ had been experimentally chosen as the vaporizer catalyst of hydrogen peroxide gas generator from the candidates of silver, platinum, LSC, and $K_2MnO_4$. The candidates had reaction with 10g, $10^\circ C$, and 80%wt hydrogen peroxide in a closed chamber. Performance of each catalyst is evaluated by pressure rise of closed chamber inside. $K_2MnO_4$ showed faster pressure rise and shorter ignition delay than any other catalysts. Silver catalyst showed longer ignition delay of 3 seconds compared to $K_2MnO_4$.
From the catalyst performance test, we found $K_2MnO_4$ has adhesion problem. To solve this problem, new synthesis and coating method using modified alumina sol-gel method has been developed to strengthen the adhesion of $K_2MnO_4$ catalyst. This synthesis and coating procedure is based on the pyrolysis of $K_2MnO_4$. Calcination temperature is fixed at 450 ℃ to form γ-alumina.
Using the synthesized catalyst, temperature profile measurement of gas generator is conducted. The purpose of experiment is to figure out the relationship between flow rate of hydrogen peroxide and length of vaporizer. The optimum length of vaporizer is the length of catalyst bed from the spray to the point where the temperature is boiling point of hydrogen peroxide. The design of gas generator was based on NASA CEA code. 80%wt hydrogen peroxide with pressure-fed system has been used. Catalyst bed is diameter of 25mm, length of 80mm, $K_2MnO_4/Al_2O_3$ coated cordierite monolith. From the test, obviously, vaporizer showed satisfactory performance. Because of heat loss, the maximum temperature of catalyst bed is decreased with rise of flow rate. From these results, the length of vaporizer is decided for 40mm. And the chosen vaporizer catalyst is $K_2MnO_4/Al_2O_3$ .
Finally, the performance evaluation of hybrid hydrogen peroxide is conducted. From the test, it showed high $C^*$ efficiency over 90% and the successful cold-start was confirmed.
고농도 과산화수소는 별도의 산화제가 필요치 않은 단일추진제로써 상온에서 액상인 장점이 있어 다양한 장치의 추진제로 이용되고 있다. 현재 가장 널리 이용되고 있는 과산화수소 분해촉매는 은이지만 이는 98%이상의 고농도 과산화수소에의 이용이 어렵다는 단점이 있다. 따라서 본 연구에서는 추진제 등급의 과산화수소 이용을 위해 분해촉매로 $La_{0.8}Sr_{0.2}CoO_3$ (LSC)를 선정하고 고온촉매인 LSC촉매의 저온 시동성능의 보완을 위해 $K_2MnO_4$ 를 저온부 촉매로 선정하였다. 그리고 촉매 선정을 위한 반응성 비교실험에서 발견된 $K_2MnO_4$ 의 접착문제를 해결하고자 알루미나 졸-겔법을 이용한 촉매 합성법과 코팅 방법을 개발하였다. 선정된 저온부 촉매는 촉매의 유실을 막고 최적의 성능을 발휘하기 위해 적정 온도범위에서 운용되는 것이 매우 중요하다. 이를 위해 가스발생기를 이용한 반응실험을 통해 설계유량에 적합한 기화기의 길이를 결정하였고 이를 이용한 이원 촉매 가스발생기의 성능평가를 수행하였다. 성능평가 결과, $10^\circ C$ 이하의 온도에서 냉시동(cold-start)에 성공하였으며 설계유량에 대해 90%이상 높은 분해효율과 충분한 압력 형성을 확인하였다. 이러한 결과를 통해 본 연구에서는 저온부 촉매의 도입을 통한 냉시동이 가능하다는 것을 확인하였고 과산화수소의 기화를 통해 LSC촉매를 이용하여 은을 이용한 종래의 가스발생기보다 훨씬 낮은 압력강하와 동일한 수준의 성능을 갖는 가스발생기의 제작에 성공하였다.
