Research and Development of Two-staged Combustion Strut with Air Intake

保持火焰技术是实现超燃冲压发动机的重要技术之一。以往的研究表明，超声速气流中由支板稳定的火焰通过将燃料氢与注入支板后燃烧区的空气进行预混或预燃而得到加强。特别是预燃有望显著提高火焰保持性能，因为由第一次预燃产生的热量和活性物质被提供给支柱后面的二次燃烧。考虑到实际设计或发动机零件的数量，将空气或氧气与氢气送入支柱应该是麻烦和复杂的。因此，本研究提出将超音速主气流中的空气直接引入支板。针对该支板内带进气口和预燃器的支板，在超声速气流条件下进行了保燃实验，得到了以下结果：(1)在预燃器中点火并不困难，而且在很大程度上，通过从支柱的前缘提供进气口，火焰保持是可能的。(2)在590 ~ 690k的温度范围内，空气总温度对着火的影响较大，而火焰保持的上下限对空气总温度的影响不大。(3)观察到两种类型的阻焰，即低氢流量时燃烧区不附在支板后端，高氢流量时燃烧区附在支板后端。(4)随着氢气流量的增加，预燃器内温度迅速下降，即使在二次燃烧区也无法维持火焰。

Flame holding technology is one of the most important technologies to realize the scramjet engine. Previous studies have shown that the flame stabilized by a strut in supersonic airflow is strengthened by premixing or preburning of fuel hydrogen with air which is injected into combustion zone behind the strut. Especially preburning is expected to improve the flame holding performance significantly because heat and active species produced by the first preburning are supplied to the secondary burning behind the strut. Considering the actual design or the number of engine parts, the feed of air or oxygen with hydrogen into a strut should be troublesome and complicated. Therefore, a direct introduction of air from the main supersonic airflow into the strut is proposed in this study.With respect to this strut with air intake and a preburner inside the strut, flame holding experiments were conducted in supersonic airflow and the following results were obtained. (1) Ignition in the preburner was not difficult and also flame holding was possible in a large extent of hydrogen flow rate by providing an air intake from the leading edge of the strut. (2) Ignition depended on the total temperature of air in the temperature range from 590 to 690 K, but the upper and lower limit of flame holding did not strongly depend on it. (3) Two types of flame holding were observed, namely combustion region did not attach to the rear end of the strut at low hydrogen flow rates and it attached at high hydrogen flow rates. (4) As hydrogen flow rate increased more, temperature in the preburner decreased rapidly, and the flame could not be maintained even in the secondary combustion region.