1. Introduction

Driven by the desire to improve air travel and shorten flight time, aircraft engines have evolved from simple reciprocating internal combustion engines to advance axil flow jet engines. Jet engines fall into several categories. These include air-breathing, turbine powered, turbojet, turbofan, ramjet compression and scramjet compression engines. Ramjet and scramjet compression engines are unique in that they represent the latest development on the evolutionary path of jet engines. The ramjet, unlike conventional jet engines which uses turbine driven compressors to compress the incoming air, uses shockwaves to achieve this goal. The compressed air is burnt in the combustor under sub-sonic conditions. The scramjet is basically an air-breathing jet engine designed to fly at hypersonic speeds between Mach 4 and 12 or speeds in the range of 1207–2995 m/s (2700–6700 mph). A scramjet engine captures its airflow from the atmosphere and also compresses it across shockwaves before the air enters the combustor. Fuel is injected into the combustor where combustion occurs under supersonic conditions. The hot, high-pressure gas leaving the combustor is then accelerated to high velocities in the nozzle to produce thrust as it exits the engine.

Generally speaking, the concepts associated with scramjet engines appear at first glance to be very simple. This however is very misleading as attempts develop a working scramjet engine that has proven to be quite an engineering challenge. Several aspects of scramjet engine development are at various stages of development. These include supersonic fuel-air mixing, aero-thermodynamic heat dissipation from both skin friction and internal combustion, and other thermal management problems associated with operating an engine at exceedingly high temperatures for extended periods of time. Combustion chamber components could experience temperatures on the order of over 3033 K (5000°F). At these temperatures most metals melt and fluids (air and fuel) ionize, making the physics of their associated behavior unpredictable.

This chapter focuses on the design concepts for the forebody, inlet, and isolator sections of an innovative scramjet engine geometry and some of its flow physics.
