Methanol Ejector Ramjet
The Ejector Ramjet is the simplest of all Rocket-Based combined Cycle (RBCC) propulsion systems. In the past the two main propellants of interest for such systems have been hydrogen and kerosene. For many applications, the ease of handling of kerosene makes it a more desirable fuel than hydrogen, despite the latter's' much higher energy-to-mass ratio. However, at flight speeds beyond Mach 4 to 4.5, kerosene fails because the high temperatures generated in the engine causes it to break down and coke up the system. Methanol's energy/mass ratio is even lower than kerosene, causing it to not be considered in the past for Ejector Ramjet propulsion. However, because methanol, CH3OH, contains one oxygen atom for every carbon atom, high temperatures will cause it to decompose not into carbon and hydrogen, but carbon monoxide and hydrogen. Thus, when used as an engine coolant, methanol should not cause coking. Because the maximum flight velocity of a hydrocarbon fueled Ejector Ramjet is limited not by fuel energy, but by cooling capacity, methanol may be a better option for fueling such systems than kerosene. We therefore chose to examine the potential performance of a methanol fueled ejector ramjet system.
In the course of the Methanol Ejector Ramjet (MER) program, 18 methanol, burning rocket engines were built, and tested inside of five different ramjet engines in static tests. Over 1000 seconds of hot engine firings were achieved. A flight vehicle was built, and is currently available for testing.