Research Summary
Professor 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, pre-chamber turbulent jet
ignition for lean-burn natural gas and gasoline engines, supercritical
behaviors in high-pressure propulsion systems, MEMS power devices, and novel
laser and x-ray diagnostic method.
1. High-performance
Fuels for High-speed Propulsion
Nanofluid
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. 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. Advanced
Ignition System for Lean-burn Engines (Spark Ignition, Plasma-assisted
Ignition, Pre-chamber Jet Ignition)
Ultra-lean combustion
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.
|
Instability at the lean
flammability limit for gas engines
|
3. Transcritical
and Supercritical Behaviors in High-pressure Propulsion Systems
Practical engines 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.
|
Liquid N2
jet into gaseous He (Meyer&Smith,
2004)
|
Subcritical-dominated and
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 Smaller Scales for MEMS and Portable Power
Generation
Combustion-based
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
chip
|
SEM image of the
microelectrodes and the platinum sensor
|
a) b) c)
a) Graphene
nano-pellets (GNP) doped fuel layer. b) Graphite sheet (GS) with fuel
deposited on the top. c) Graphene form (GF) sheet after the fuel
deposition.
Ignition
and flame front propagation along a typical sample.
|
|
|
|
|
|
|
|