Fall Technical Meeting
of the Western States Section of the Combustion Institute
Hosted by the University of California, Irvine, CA
October 26-27, 2009
Computational and Experimental Investigation
of a Turbine-less Jet Engine Concept
C. C. Wu1, L. Ly2 and N. Doan2
Department of Mechanical Engineering, California State University, Los Angeles
Los Angeles, California 90032, USA
Conceptual design of a small subsonic jet engine that does not require a turbine has been
developed, and its feasibility is being investigated. This turbine-less jet engine design is
simply composed of a ducted-fan, a combustion chamber and a nozzle. The ducted-fan
plays the same role as the compressor in a typical gas turbine jet engine. It is driven by
electrical power from solar panels or fuel cells, which may use the same fuel (such as
hydrogen) for the combustion chamber. The nozzle further accelerates the flow from the
combustion chamber to produce more thrust. Both computational fluid dynamics (CFD)
simulations and wind tunnel experiments are being conducted to study the performance
of the jet engine, and promising preliminary results have been obtained.
1. Introduction
It is well known that the simplest engine for jet-propulsion powered by combustion of fuels is the
ramjet, which is simply composed of an inlet, a combustor and a nozzle, and has no mechanical
moving parts. However, it is not self-starting and must be launched from another moving
vehicle or from a ground launcher. Most jet aircraft nowadays are propelled by turbo-jet or
turbo-fan engines, in which there is a gas turbine to drive the compressor to draw in a steady
flow of air. The turbine is the most complex moving part in an engine driven at high rotation
speed by high temperature - high pressure gas from the combustion chamber, and is always
subject to the highest mechanical and thermal stresses. Eliminating the need of turbine in a jet
engine will greatly reduce the complexity and hence the cost of the engine. The objective of this
research is to develop a small turbine-less jet-engine, conduct both computational simulations
and wind tunnel testing to investigate the performance of such an engine, and study the
feasibility for possible applications on subsonic unmanned aerial vehicles (UAV).
_______________________________
1
Professor of Mechanical Engineering
2
Graduate Research Assistants
1
2.
Ducted-Fan Turbine-less Jet Engine
2.1. Conceptual Design
A turbine-less engine concept (Figure 1) has been developed at the Multidisciplinary Flight
Dynamics and Control (MFDC) Laboratory at California State University, Los Angeles.
Basically, it is composed of a ducted-fan, a combustion chamber and a nozzle. In other words, it
is a compromise between a ramjet and a turbo-jet. The ducted-fan plays the role of the
compressor to draw air into the engine. It is driven by electrical power from solar panels
installed on the wing of the aircraft or from fuel cells onboard, instead of a turbine. The fuel
cells may also use the same fuel (such as hydrogen) for the combustion chamber. The propulsive
nozzle downstream of the combustion chamber further accelerates the flow to produce thrust.
The absence of the turbine also simplifies the design of the transition between the combustor and
the nozzle. This concept has been inspired by previous experience of the principal author in the
development of solar-powered vehicles and fuel-cell powered UAV. This innovative jet engine
concept may be most applicable to future high performance UAV.
Fig. 1: Ducted-Fan Turbine-less Jet Engine Concept
2.2.
Preliminary Test Model
A model for preliminary wind tunnel testing has been fabricated (Figure 2). The DF-70 ductedfan developed by Jetpro Technology, Inc. has been selected. The internal diameter of the ducted
fan is 70 mm and the total length of the engine model is 46 cm. A streamlined transition unit
which houses the brushless motor (Hacker B20-26L) for driving the fan and the necessary
channels for fuel injection and ignition systems has also been fabricated (Figure 3).
2
Fig. 2: Test Model
Fig. 3: Motor Mount and Fuel Injection Unit
This first version of the engine model is meant for preliminary wind tunnel testing without
combustion, and is made of plastic and plexi-glass to allow for flow visualization in the chamber.
A metallic version is also being developed for future tests involving combustion.
3. Wind Tunnel Tests
Preliminary tests have been performed in the subsonic wind tunnel at the MFDC Lab. The
model is mounted on a fixture in the wind tunnel, with a load cell to measure the thrust (Fig. 4).
A pitot-static tube is installed inside the combustion chamber to measure the static and dynamic
pressures downstream of the ducted-fan, which is driven by a DC brushless motor (Hacker B2026L) powered by a power supply. A strobe tachometer is used to sense the rotation speed of the
rotor blades of the ducted-fan and digital multi-meters are used to measure the power input to the
motor. Test data are collected via a data-acquisition system running LabView. Typical results
are summarized in Figures 5 – 9.
3
Fig. 4: Wind Tunnel Test Model with DF-70 Ducted-Fan
4
Fig. 5: CFD Results and Measured Data
Fig. 6: Measured Velocity in Chamber
Fig. 7: Measured Thrust Performance
Fig. 8: Measured Electrical Power Input
5
4. CFD Simulation
A CFD model has been developed in Cosmos/Flowork, and some preliminary flow simulations
have been conducted. Figures 9 and 10 show the computed result of pressure variation of a
typical case. These results match very well with the wind tunnel data, as shown in Figure 9. A
more advanced CFD model for combustion simulation in the chamber is also being developed
with FLUENT.
Fig. 9: CFD Simulation - Pressure Distribution
Fig. 10: CFD Simulation – Velocity Field
6
5. Conclusion
Feasible design of a turbine-less jet engine making use of an electric ducted-fan has been
developed. Preliminary wind tunnel tests display a consistent performance trend, and CFD
simulations also match very well with the experimental data. Further investigation on the
performance of the jet engine with combustion involved will be conducted, and the potential
applications of this type of engines for small UAV is certainly a possibility.
Acknowledgment
The research project was conducted at Center for Structure, Propulsion Aerospace and Control
Engineering supported by the NASA University Research Center Grant #NNX08BA44A.
7