My name is Li Qiao. I am a professor in
the School of Aeronautics and Astronautics at
Purdue. I also hold a courtesy
appointment in mechanical engineering. I
received my PhD in aerospace engineering
from the University of Michigan in 2007
and then since then I am a faculty
member at Purdue. My research interests
are in the areas of fuels, combustion and
propulsion. It's very exciting that right
now to be doing chemical propulsion
research. There are many new concepts and
new technologies. For example the
reusable rockets concept is being
developed by SpaceX. If that's successful that's going to make
space travel a lot more affordable and
the other example is hypersonics. The
X-51 Wave Rider is designed to ride on
its own waves and then the main
component of that system is a supersonic
combustion scramjet engine burning jp-7
jet fuel. So my lab studies fuels and
propellants in chemical reacting flows
with applications in energy, defense,
space exploration, transportation and
fire safety. Particularly in the past
couple years we have looked into four
areas. The first one is high energy
density fields and propellants for high
speed propulsion systems. And the second
area is ignition, advanced ignition
methods such as plasma assisted ignition
and pre-chamber jet ignition for high
speed flows or for very lean
combustion systems. The third area
was the thermodynamics of non ideal
gases for high pressure flows. The
last area is combustion at small scales for a number of
different applications. One of the areas
that we've been working on is
alternative fuels as you know
alternative fuels is emerging in the
market so it's important for us to
understand the physical property the
chemistry and the combustion
characteristics of these new fuels. So
we have developed a set up over here as
you can see we have a spherical
combustion bomb in house inside the oven. So we have used this facility to test
various alternative fuels and for
example we have measured flame speed of
different fuels of varying temperature
and pressures and these data important
in the sense that they can be used to
validate the chemical kinetics of these
fuels which is a input for our
large-scale computational CFD
simulations of chemical reacting flows
in practical engines. We have also used
this facility to study the fire safety
of alternative fuels. We have worked
with a Federal Aviation agency to look
into several fields that FAA have just
certified in terms their fire safety
characteristics. For example the minimum
ignition energy flammability limits pull
fire spray rates and fire suppression so
the result can help FAA to determine
whether they need to change their
protocols or procedures in terms of
firefighting in aircraft engines and
also in airport. High speed propulsion
systems require high performance fuels.
For example we want high energy density
fast and tunable ignition and fast
burning rate. So we have been studying novel concepts
such as nanofluid fuels and then the
idea was to suspend energetic or
catalyst nanoparticles in liquid fuels
to enhance the energy density and to
promote ignition. So we have looked into
these fuels and found very interesting
physical and chemical and combustion
characteristics of these fuels. Most
recently we also explored a new concept
which is to use a highly conductive
carbon-based nano structures as
additives to enhance the performance of
solid propellants. We have demonstrate
for the first time for example using
graphene foam the burn rate of the
propellant can be enhanced five to six
times and we believe this is because of
the unique structure of graphene foam
the 3d porous highly connected which
promote heat transport. Most recently
we extended that concept one step
further using graphene foam
doped with catalyst for solid
propellants and even more enhancement
was observed which we believe is because
of the combined effect of enhanced
thermal transport and also more site
areas for the dispersion of these
catalysts. Practical propulsion systems
all operate at high pressures. For example
the most powerful liquid rocket the RD-170 families developed by the Soviet Union in
the 60s and 70s the combustion chamber
pressure is around 245 bar. So
that kind of pressure ideal gas law is no
longer valid because the molecules are
very much packed the interaction the
forces between the molecules are long
negligible so you challenging to model
such processes because of the non
equilibrium nature and then departure
from ideal gas law and the lack of
interface between the gas and liquid so
we have been using molecular dynamics
simulations as a tool to study the
thermodynamics of supercritical fuels at
high pressures. The advantage of
molecular simulation is that an accept
of a potential model that described the
forces between particles and there are
no other assumptions. For example we
don't need a equation of state. We don't
need models of thermodynamic transport
properties of the fluids. So with
molecular simulations we have been
studying the thermodynamics and
transport property of hydrocarbon fuels
at high pressures.or example the liquid
gas interface which is up a nanometer
scale as well as the transition from the
classical two phase evaporation to the
one phase the diffusion dominated mixing.
Molecular dynamic is a deterministic technique which studies the temporal evolution of the coordinates and the momentum of a set of
interacting particles via the solution
of Newton's second law of motion. So
basically each time step the forces acting
on the atoms are calculated and combined
with the current position and velocities
to generate new positions and new velocities
at the next time step. So in this way the
MD simulations are able to capture the
dynamics of a system. The thermodynamic averages are obtained from molecular
dynamics as time averages. Understanding and control of the ignition is critical
to the performance of combustion engines
such as reduce emissions improve
efficiency. My group has been studying
the fundamental mechanisms of ignition
for various ignition technologies. For
example spark ignition pre chamber jet
ignition and plasma assisted ignition. Now among these technologies pre chamber
jet ignition is widely used for large
more natural gas engines as well as f1
racing cars. This technology is
currently being considered for gasoline
engines for passenger cars as a
replacement for traditional spark
ignition. Now the idea is to burn a small
amount of fuel air mixture in a small
volume called pre chamber. As a result of
ignition combustion of the mixture in
the pre chamber and multiple jets will
be a suit from the pre chamber these hot
turbulent jets penetrate into the main
chamber cause ignition. Now the
advantage of pre-chamber jet ignition
in comparison to traditional spark
ignition is that the ignition takes
place on the surface of the jet in
multiple places which can
potentially enable us to burn cleaner
mixtures for combustion engines as well
as improve efficiency and reduce engine
cycle variations. I'm standing inside
one of the test cells at Zucrow
Laboratory. We have unique facilities for
energy and propulsion research. What's
worth mentioning is
the natural gas-fired air heater system
which is capable to deliver air at
temperature up to 900 Kelvin a pressure
up to 40 bar and a flow rate up to 0.25
kilogram per second. So we have been
using this heated air system to
study ignition phenomena at engine
relevant conditions without actually
running an engine which could be very
complex and expensive. This is a GM
four-cylinder two-letter gasoline engine.
We have modified it to include optical
axis and instrumentation so with the
heated air and this experiment we have
been examining the ignition mechanisms
of pre chamber. And this will help us
especially our industry collaborators to
design more efficient pre chambers for
gasoline engines. We have also utilized
the high-pressure high-temperature air
facility to study spark ignition for
internal combustion engines. One of the
main issue for spark ignition is erosion
of the electrodes which is due to the
interaction between plasma species and
electro material. So we have used the
high temperature high pressure air in a
very slow rate and running for hours we
have been able to study the in erosion
mechanisms of the different electro
materials
