Acknowledgement

Design of Optical Diagnostic System for Wave Rotor

Constant Volume Combustor Students: Fatin Baharuddin, Zhen Wei Yong,

Kok Hwang Chow

Mentors: Dr. Mani Rajagopal, Dr. Razi Nalim, Mr. Kyong-Yup Paik Indiana University-Purdue University Indianapolis

Abstract Wave Rotor Constant Volume Combustors (WRCVC) are a

growing interest in gas turbine propulsion and power generation

applications. Experiments and numerical studies have been

conducted to study the ignition and flame propagation process for

different hydrocarbon fuels (methane, ethylene and propane).

Currently, hydrogen cannot be used for experiments because it

does not produce soot; consequently, the flame propagation

process cannot be visualized using high speed camera images.

Therefore, the objective of the present research is to design an

optical system to visualize the flame propagation process in a

WRC for many fuels including hydrogen. Among various optical

techniques available for flow visualization, Schlieren photography

is commonly utilized for flows with sharp density gradients. Based

on the configuration, there are different types of Schlieren

imaging system such as Z-type, parallel beam and single mirror

system. It was identified that Z-type Schlieren system meets all

our requirements; suitable for present study, low cost, easy to set-

up. Experiments will be conducted using different fuels to

visualize the flame propagation process inside the wave rotor

combustor.

Methods

Introduction

It is identified from the present research that Z-type Schlieren

system is suitable for the wave rotor ignition rig experiments.

Z-type Schlieren system (Fig. 3) consist of two concave

mirrors, light source, mirror holder and knife edge.

The light source is carefully adjusted no more than 10 degree

respect to the horizontal line to avoid the image distortion.

Light source is directed at mirror 1 and is located one focal

length from the mirror.

The first mirror collimates the light, which produces parallel

rays of light in the test region. A second mirror then focuses

the collimated light towards the camera and filter.

Knife edge is placed at a focal point to block half of the light.

Adjusting height of the knife edge will increase the contrast of

the image.

The recent energy price hike brings the urge to produce more

efficient power generation engines, which could result in lower

fuel consumption, higher efficiency, and less pollutants. Such

an approach is being developed at IUPUI with the participation

of global engine maker Rolls Royce, utilizing a alternate

thermodynamic cycle (Humphrey cycle) and a novel pulsed

combustor for gas turbine engines, called WRCVC. The

performance of a WRCVC is presented in Temperature-entropy

diagram in Fig. 1.

References 1. Amrita, M. (2013, June 18th). PRINCIPLES AND TECHNIQUES OF SCHLIEREN IMAGING SYSTEMS. Columbia University New York, NY

2. Denise, G. (2008, October 27th). The Mysterious Cough, Caught on Film. the New York Times. Retrieved from

http://www.nytimes.com/2008/10/28/science/28cough.html?_r=1&

3. Sean Michael, R. (2009, July 26). How-To: Take Schlieren photographs at home. Makezine. Retrieved from

http://makezine.com/2009/07/26/how-to-take-schlieren-photographs-a/

4. P. Akbari , M. R. N. (2009, February). Recent Developments in Wave Rotor Combustion Technology and Future Perspectives: A Progress

Review. Indiana University-Purdue University Indianapolis (IUPUI).

5. Prasanna , C., Abdullah , K., Manikanda , R., & Razi, N. (2013, May). Experimental Study of Transversing Hot-Jet Ignition of Lean

Hydrocarbon-Air Mixtures in a Constant-Volume Combustor. Indiana University-Purdue University Indianapolis (IUPUI).

6. Ozasa, T., Kozuka, K., and Fujikawa, T., "Schlieren Observations of In-Cylinder Phenomena Concerning a Direct-Injection Gasoline

Engine," SAE Technical Paper 982696, 1998, doi:10.4271/982696.

7. Salazar, V. and Kaiser, S., "Influence of the Flow Field on Flame Propagation in a Hydrogen-Fueled Internal Combustion Engine," SAE Int.

J. Engines 4(2):2376-2394, 2011, doi:10.4271/2011-24-0098..

Fig. 2 Experimental set-up of Wave Rotor Ignition Rig at IUPUI

Fig. 5 Schlieren images captured for candle flame

The wave rotor ignition rig (Fig. 2) established at IUPUI consists

of two combustion chambers (a rotating pre-chamber, and a

stationary main chamber), electrical and ignition systems, high

speed camera and data acquisition system. Experiments and

computer simulations of combustion in the rig have been

performed to understand the jet penetration and mixing, vortex

structures, ignition kernels, propagating turbulent flames,

pressure waves, and flame-wave interactions. However, much of

the modern knowledge about conventional combustion processes

have come from relatively recent optical and laser diagnostics,

such as laser-induced fluorescence and Raman spectroscopy. It

is expected that optical diagnostics will illuminate the design of

improved combustion systems to meet the challenges of

tomorrow’s energy conversion systems. The present study is

aimed to design an optical diagnostic system to visualize the

combustion process inside the wave rotor ignition rig. The high

speed camera is employed for the visualization of ignition and

flame propagation, but it does not capture the mixing and

turbulence processes. Moreover, the optical system technique will

be useful to visualize to ignition process for hydrogen fuel which

does not produce soot.

Current Status of Research

From the present research, we have identified that Z-type

Schlieren system meets all our requirements; suitable for this

study, low cost, easy to set-up. However, such imaging in a

closed channel is challenging, and will require special mirrors

and optical techniques. All the components required to design Z-

type Schlieren system have been finalized, ordered and all the

components have been received. The optical diagnostic system

has been built (Fig. 4). Initially, Schlieren system has been tested

using a simple combustion light source such as candle flame.

The images captured using candle flame is shown in Fig. 5.

Further, experiments will be conducted to capture & visualize the

flame and ignition process in the wave rotor ignition rig.

Tturbine

Entropy

Te

mp

era

ture 2

3 b

4 b

1

4

3

1-2-3-4: Humphrey Cycle

(Constant-Volume Combustion)

with Pressure Gain

1-2-3b-4b: Brayton Cycle

Combustor

Compressor Turbine

1

2 3

4

Fig. 1 Performance of the Humphrey cycle over Brayton cycle

Fig. 3 Schematic of the proposed Z-type Schlieren System [1]

Fig. 4 Set-up of the Schlieren system designed at IUPUI

Mirror 1 Light Source

Knife Edge

Mirror 2

Candle

Camera

We would like to acknowledge Multi-disciplinary Research Institute (MURI) for

sponsoring this research and also, Mr. Joe Huerkamp (MET Lab Technician) for his

support in designing the mirror holders.