Qiao’s research focuses on the development of new technologies and the
understanding of basic science in the areas of fuels, combustion and
sustainable energy. Research
interests include nanoscale energetic materials, alternative fuels and fuel synthesis
by coal and biomass gasification, ultra-lean natural gas combustion
technologies, supercritical behaviors in high-pressure propulsion systems,
MEMS power devices, and novel x-ray diagnostic method.
1. High-performance Fuels for Advanced Propulsion
fuels, an exciting new class of nanotechnology-based fuels, are liquid
fuels with a stable suspension of nanometer-sized particles. Depending on
the physical and chemical properties of the added nanomaterials, nanofluid
fuels can achieve better performance, e.g., increased energy density,
easier and faster ignition, enhanced catalytic effects, improved combustion
efficiency, and reduced emissions. The social benefits of this research lie
in the areas of fuel economy, pollution control, and aerospace and space
applications. In aerospace engineering, interest is increasing in
developing a new generation of hypersonic flights, which largely depend on
the ability to use liquid fuels that offer high- energy density, short
ignition delays, and high reaction rates. Nanofluid-type fuels with the
addition of nanoenergetics or nanocatalysts could potentially be used for
hypersonic vehicles. Nanofluid fuels can also be used for power/thrust
generation under special circumstances such as unmanned aerial vehicles
(UAVs) or power microelectromechanical systems (MEMS). However, knowledge
about nanofluid fuels remains very limited. This research starts down the
path of developing a fundamental understanding of these types of fuels. It
explains the fundamental mechanisms of how the addition of nanoscale
materials to liquid fuels can enhance combustion performance.
2. Turbulent Hot Jet Ignition for Ultra-lean Natural Gas Gas
technologies have been regarded as a potential solution for the engine and
power industries to meet the ever-stringent emission regulations.
Ultra-lean combustion however has serious challenges. Ignition is difficult
when the mixture is very lean. Misfire can lead to reduction in efficiency,
increase in unburned hydrocarbon emissions, and rough operation. An
approach that can potentially solve these problems is to use a hot
turbulent jet to ignite the lean mixture, rather than using a conventional
electric spark. The hot jet can be generated by burning a small quantity of
fuel/air mixture in a prechamber. The high pressure in the prechamber
resulting from heat release will force the products of combustion at high
velocities into the main chamber generating a turbulent jet which then
ignites the mixture in the main chamber. By introducing turbulence and
possibly active species, better and multiple-location ignition as well as
fast flame propagation can be achieved. Thus hot jet ignition has the potential
to enable combustion systems to operate near the fuel’s lean
flammability limit, leading to ultra-low emissions. However, knowledge
about turbulent jet ignition remains very limited. This research aims to
develop a fundamental understanding of the underlying physics of hot jet
ignition using high-speed imaging/diagnostic techniques. The fundamental
understanding developed in this project will be transferable to better
design of prechamber igniters for extra-lean gas engines.
Time sequences of
simultaneous Schieren and OH* chemiluminescence images showing the ignition
process by a hot turbulent jet issued from prechamber combustion.
Simultaneous planar time-dependent
radiation intensity measurements of hot jet with H2O
(2.58 ± 0.03 μm) band pass filter and high-speed Schlieren
imaging reveal the shock structure of supersonic jets.
the lean flammability limit for gas engines
3. Supercritical Behaviors in High-pressure Propulsion Systems
such as liquid rockets and diesel engines operate at high pressures. As a
result, the injected fuel may be at transcritical or supercritical state
during the injection, mixing and vaporization processes. Previous studies
have provided important insights on supercritical behaviors, as well as
limitations of current theoretical modeling and numerical simulations of
such behaviors. The
introduction of thermodynamic nonidealities and transport anomalies near
the critical point is one of the main challenges to model these phenomena.
Very limited experimental data are available for either quantitative
understanding of the physics or for assessment of various models. Although
we have good knowledge of the classical two-phase atomization regime and
the supercritical one-phase mixing regime, the transition from the former
to the latter is less understood.
This research intends to understand the physics of fuel injection,
mixing and vaporization at high pressures by applying novel diagnostic
methods and molecular dynamics simulations.
jet into gaseous He
supercritical-dominated regimes on the P-T diagram, which are separated by
a dimensionless transition time of 0.35 for three different n-alkanes.
4. Combustion at Nano- and Micro-scales for NEMS and MEMS
small-scale energy devices have applications in many fields, e.g., portable
power devices, sensors, actuators, unmanned aerial microvehicles,
microthrusters, and micro-heating devices. In particular, micro-propulsion
systems are designed to provide small amounts of thrust ranging from
micro-newtons to a few milli-newtons that are used for precise altitude and
orbit corrections, drag compensations, and small impulse maneuvers. A
variety of micro-propulsion systems have been proposed including
field-emission electric propulsion thruster and solid-propellant thruster.
In addition to their use in micro-thrusters, microcombustion systems have
also been proposed to achieve highly efficient thermal-electric energy
conversion. Thermoelectric (TE) systems exploit the unique electrical,
semiconducting, and thermal properties of TE materials in order to both
achieve and facilitate the processes of heating, cooling, power generation,
and waste heat recovery. Such systems directly convert thermal energy into
electrical energy by manipulating the flow of charge carriers through
electrically conducting materials. This research explores the new physics
of combustion at smaller scales with the assistance of nanoscale materials
for various applications.
The cross-section of the
combustion electrode device
Packaging of the combustion
SEM image of the
microelectrodes and the platinum sensor
a) b) c)
nano-pellets (GNP) doped fuel layer. b) Graphite sheet (GS) with fuel
deposited on the top. c) Graphene form (GF) sheet after the fuel
and flame front propagation along a typical sample.
Sponsors: Federal Aviation Agency (FAA), National Science
Foundation (NSF), Army Research Office (ARO), Air Force Office of Scientific
Research (AFOSR), American Chemical Society Petroleum Research Funds
(ACS/PRF), Caterpillar Inc.,
Argonne National Lab, Purdue Energy Fund, and Purdue Research Foundation.