Home  Research  People  Publications 



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, 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

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. 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 Engines

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.    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)

three alkanes regimes

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 Nano- and Micro-scales for NEMS and MEMS applications

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.




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.