Ofodike A. Ezekoye













Janet L. Ellzey













Laxminarayan L. Raja
Investigation of a Railplug Ignition System for
Lean-Burn Large-Bore Natural Gas Engines



by

Hongxun Gao, B.E.; M.E.




Dissertation
Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of
Doctor of Philosophy






The University of Texas at Austin
December 2005

To my family v
Acknowledgements

First I want to thank Dr. Matthews, Dr. Ezekoye and Dr. Hall from the
bottom of my heart for their support and numerous discussions that helped me
accomplished this work.

Thanks to Marcus who gave me some valuable suggestions about the
engine set-up. Kims helps was also appreciated with all the problems
encountered with the DSP. I need to mention the others who made this work
more pleasurable: Hari, Ozgur, Alok, Alex, Dr. Joo and other combustion group
members. Thanks to Curtis Jonhson, Danny Jares, and Don Artieschoufsky in the
machine shop who gave me a lot of assistance for the engine set-up and railplug
fabrication.

Special thanks to Dongmei Zhou, Huijie Xu, and Daijiao Wang for their
care and friendship. It is never easy for a student to both pursues a degree and
raise a family, especially for a foreigner, so many nice people have helped me out
and made Austin such an unforgettable city in my life.

Finally, I want to thank my wife, Jong Fang, who accepted to spend all
this time with me and help me so much during the hard time. My lovely daughter,
Erin Yiran Gao, and son, Jerry Gao, have given me so much pleasures. My family
in China, they never stop encouraging me and praying for me. I want to dedicate
this dissertation to my family.



vi

Investigation of a Railplug Ignition System for
Lean-Burn Large-Bore Natural Gas Engines

Publication No.



Hongxun Gao, Ph.D.
The University of Texas at Austin, 2005



Supervisor: Matthew J. Hall

The characteristics of three ignition systems, such as inductive ignition,
capacitor discharge ignition, and railplug ignition system, are investigated. Based
on the characteristics, the railplug is a very promising ignition system for lean
burn natural gas engines with its high-energy deposition and high velocity plasma
arc. Parallel railplugs are designed, fabricated and tested on an operating natural
gas fueled engine. The engine tests shows that the lean-stability-limit (LSL) can
be extended from a fuel/air equivalence ratio of
= 0.62 for spark plugs down to
= 0.535 using a railplug. Thus, engine-out NO
x
emission is also reduced using
railplugs. A heat transfer model is proposed to aid the railplug design. A
parameter study is performed both in a constant volume bomb and in an operating
natural gas engine to improve and optimize the railplug designs.

vii
Table of contents
List of Figures ix
List of Tablesxiii

Chapter 1.0 Introduction and Background ........................................................1
1.1 Background of ignition...................................................................................8
1.1.1 Estimates of the minimum ignition energy ............................................8
1.1.2 Effects of experimental factors on ignition ..........................................10
1.2 New emerging ignition systems ....................................................................12
1.3 Railplug ignition systems .............................................................................16
1.4 Overview.......................................................................................................22
Chapter 2.0 Characteristics of Three Ignition Systems...................................24
2.1 Ignition discharge measurement techniques ................................................24
2.2 Inductive ignition system..............................................................................26
2.2.1 Phases of spark discharge.....................................................................27
2.2.2 Arc to glow transition...........................................................................33
2.2.3 Discharge energy..................................................................................38
2.2.4 Effects of spark plug resistance on discharge ......................................41
2.2.5 Effects of spark gap on discharge ........................................................43
2.3 Capacitor discharge ignition systems ..........................................................46
2.4 The Railplug ignition system ........................................................................48
2.5 Chapter summary .........................................................................................53
Chapter 3.0 Railplug Design ..............................................................................55
viii
3.1 Railplug geometric design............................................................................57
3.2 Railplug design to prevent sparkover of insulating surfaces .......................63
3.3 Parameter study to improve arc movement..................................................66
Chapter 4.0 Engine Experimental Set-up .........................................................73
4.1 Engine modification to run natural gas .......................................................74
4.2 Ignition timing control .................................................................................77
4.3 The dynamometer and its controller ............................................................79
4.4 In-cylinder pressure measurement and data acquisition .............................80
4.5 Ignition noise suppression............................................................................82
Chapter 5.0 Engine Tests and Results...............................................................85
5.1 Comparison of the three ignition systems ....................................................89
5.2 Effects of spark duration on igniter performance ........................................96
5.3 Geometry design to improve railplug performance .....................................98
5.4 Parameter study to optimize railplug designs............................................103
5.5 Engine-out emission measurements ...........................................................107
5.6 Chapter summary .......................................................................................111
Chapter 6.0 Railplug Temperature Measurements and Heat Transfer
Analysis ..............................................................................................................114
6.1 Railplug and spark plug temperature measurements.................................115
6.2 Railplug and spark plug heat transfer analysis .........................................120 ix
Chapter 7.0 Summary, Conclusions and Recommendations for Future
Research .............................................................................................................128
7.1 Summary and conclusions..........................................................................128
7.1.1 The characteristics of the three ignition systems ...............................128
7.1.2 Railplug development ........................................................................130
7.1.3 Plug temperature measurements and heat transfer analysis ...............131
7.2 Recommendations for future work .............................................................132
References ..........................................................................................................134
VITA...................................................................................................................145
x
List of Figures
Figure 1.1. Sources of primary energy in US in 2001.............................................2
Figure 1.2. Specific heat ratio for different chemical components of engine
combustion. .............................................................................................................4
Figure 1.3. Schematic of the railplug electronics circuit.......................................17
Figure 1.4. Schematic of a railplug. ......................................................................17
Figure 1.5. Images of arc moving down the rails of a parallel railplug............19
Figure 2.1. Characteristics of an inductive ignition spark discharge. ...................27
Figure 2.2. Details of a breakdown phase. ............................................................29
Figure 2.3. Comparison of breakdown current measured by different methods...30
Figure 2.4. The effects of air/fuel ratio (as volume percent methane) for a
methane/air mixture on breakdown voltage at 2 bar, the error bars show one
standard deviation. ................................................................................................31
Figure 2.5. The effects of surrounding gas (Helium) on breakdown voltage at 1
bar and 298 K. .......................................................................................................32
Figure 2.6. Shot-to-shot variation in arc-to-glow transition..................................35
Figure 2.7. The effects of electrode material on discharge. ..................................36
Figure 2.8. The effects of flow field on discharge, flow velocity of 9.8 m/s, room
temperature.............................................