A simple propulsion engine utilizing unheated
atmospheric air as the
propellant, and driven by a
single cycle (unicycle) engine with internal
combustion cylinder and free
piston is disclosed. A plain
piston is slidably displaceable in an elongated cylinder containing cylinder heads on opposite ends. The
piston receives a combustive impulse at each end of its
stroke. The cylinder also has exhaust / inlet ports and propulsive nozzles at each end with relevant valves and actuators to effect the requisite timing of the
combustion, air induction, and propulsion functions. During the piston's
traverse of the elongated cylinder's midsection, air is induced into the expanding volume of the moving piston / cylinder chamber while air is compressed and expelled through the
nozzle of the decreasing volume chamber, producing
usable thrust. The large amounts of
atmospheric air induced provides inherent internal cooling and exhaust
scavenging of the propulsion engine. The preferred embodiment combines a free piston with an annularly arranged thrust piston to divide a dual-
diameter cylinder into two
combustion chambers and two thrust chambers. Scavenge feeder lines connected the thrust chambers to the combustion chambers via check valves provide exhaust
scavenging, additional thrust output through exhaust nozzles, and feeding of
fresh air into the combustion chambers. Also, pressure-actuated fuel injectors utilize pressure changes in respective combustion chambers to inject fuel at the appropriate time. The fuel
injector includes an
intensifier piston and pintle to raise the fuel pressure.