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

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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.