October 2000 Newsletter - Naval Postgraduate School

FEATURED PROJECT
JP-10/AEROSOL FOR PULSE DETONATION APPLICATIONS, continued from page 6
successfully detonated a JP-10/air aerosol in a PDE combustor.
Previous research at the laboratory resulted in the first
two-phase detonation of a JP10/oxygen mixture and recent
efforts resulted in the first documented two-phase detonation
of JP-10 and air. The results demonstrate the practicality of
liquid-fuel detonations for PDE applications.
Due to the nature of the combustion process, the mode of
operation for a typical PDE is cyclical. The fuel/
air mixture is loaded into a combustor, rapidly
detonated, and then the products are exhausted.
The resulting pressure behind the detonation wave
presses on the head-end, or thrust wall, of the
combustor to generate thrust. After the combustion
event is complete, the exhaust is expelled
from the combustor and a new fuel/air mixture is
loaded and the procedure repeats. This repeated
fill/detonate/exhaust process typically must occur
at frequencies of 40 Hz or greater to generate a
reasonable thrust level for most systems.
Gaseous systems possess an inherent simplicity
since all of the fuel is already in a vapor state and
is therefore more likely to react rapidly with the
oxidizer, which is required in a detonation wave.
Generally, the energy release must occur within
1cm of the detonation leading shock. If the heat
release occurs too late, the combustion zone
decouples from the shock and the detonation will
likely fail. In a two-phase condition, such as a JP-
10/air aerosol, the fuel must be significantly
vaporized before a substantial reaction can occur.
Calculations indicated that a spray possessing
droplets below 6 microns in diameter would be
required to support a two-phase detonation wave.
The experimental facility used for this work,
shown in Figures 1 and 2, was operated at air flow
rates of up to 1.3 kg/s (3 lbm/s) and provided the
engine with air inlet temperatures of up to 500 K.
The air was heated by a hydrogen vitiator with
make-up oxygen and a maximum outlet temperature
of 725 K. The vitiator outlet was connected
to the engine inlet through a 6.35 cm (2.5 inch)
diameter flex hose. The engine geometry is shown
in Figure 3 with exploded views of selected areas.
The engine inlet choke isolated the vitiator from
pressure oscillations in the main combustor and
allowed for redundant metering of the vitiated air flow. Fuel
was injected just after the inlet choke and was allowed to mix
completely before being discharged into a plenum region and
then injected into the main combustor through a perforated
cone segment in order to provide increased turbulence,
mixing, and partial acoustic isolation.
--continued on page 41
From top to bottom:
Figure 1. Experimental
Layout
Figure 2. Test Cell
View of Experimental
Setup
Figure 3. Pulse
Detonation Engine
Geometry
NPS Research page 7
October 2000