TABLE OF CONTENTS Bipropellant systems offer the most performance ( I sp as high as 450 s) and the most versatility (pulsing, restart, variable thrust). They also offer the most failure modes and the highest price tags.
The major parts of a pressure-fed engine are the injector, the nozzle and the cooling system, and thrust-chamber valves, as shown in Fig. 4.38. (Launch vehicle systems are pump fed and considerably more complicated.)
The injector introduces the oxidizer and fuel into the combustion chamber in such a way as to promote stable, efficient combustion without overheating the injector face or the chamber walls. The injector design is the single most important contributor to engine performance. It also determines to a large measure whether combustion will be stable. Figure 4.39 shows injector configurations in use.
The most sensitive area in a bipropellant engine is the combustion zone of the thrust chamber just downstream of the injector. Propellants enter this high-pressure zone as room-temperature liquids and leave as supersonic gases at velocities greater than 600 m/s and temperatures as high as 3500 C. Energy release rates may be as great as 200 kW/cc. Mixing, ignition, and combustion occur in milliseconds. Propellants are introduced through the injector plate at high velocity so that the fuel and oxidizer are shattered into droplets small enough to complete combustion upstream of the throat. Continuous and rapid combustion must occur near the...
