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Ignition of extremely lean mixtures is a very challenging problem, especially for the low speed, high load conditions of large-bore natural gas engines. This paper presents initial results from testing a high energy ignition system, the railplug, which can assure ignition of very lean mixtures by means of its high energy deposition and high velocity jet of the plasma. Comparisons of natural gas engine tests using both a spark plug and a railplug are presented and discussed in this paper. The preliminary engine test show that the lean stability limit (LSL) can be extended from an equivalence ratio, φ, of ∼0.63 using a spark plug down to 0.56 using a railplug. The tests show that the railplug is very promising ignition system for lean burn natural gas engines and potentially for other engines that operate with very dilute mixtures. The ignition characteristics of different railplug geometric and circuit designs are also discussed.

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This Final Technical Report discusses the progress that was made on the experimental and numerical tasks over the duration of this project. The primary objectives of the project were to 1) develop an improved understanding of the spark ignition process, and 2) develop the railplug as an improved ignitor for large bore stationary natural gas engines.We performed fundamental experiments on the physical processes occurring during spark ignition and used the results from these experiments to aid our development of the most complete model of the spark ignition process ever devised. The elements in this model include 1) the dynamic response of the ignition circuit, 2) a chemical kinetics mechanism that is suitable for the reactions that occur in the plasma, 3) conventional flame propagation kinetics, and 4) a multi-dimensional formulation so that bulk flow through the spark gap can be incorporated. This model (i.e., a Fortran code that can be used as a subroutine within an engine modeling code such as KIVA) can be obtained from Prof. Ron Matthews at rdmatt@mail.utexas.edu or Prof. DK Ezekoye at dezekoye@mail.utexas.edu.Fundamental experiments, engine experiments, and modeling tasks were used to help develop the railplug as a new ignitor for large bore natural gas engines. As the result of these studies, we developed a railplug that could extend the Lean Stability Limit (LSL) of an engine operating at full load on natural gas from φ = 0.59 for operation on spark plugs down to φ = 0.53 using railplugs with the same delivered energy (0.7 J). However, this delivered energy would rapidly wear out the spark plug. For a conventional delivered energy (<0.05 J), the LSL is φ = 0.63 for a spark plug. Further, using a permanent magnet to aid the plasma movement, the LSL was extended to φ = 0.54 for a railplug with a delivered energy of only 0.15 J/shot, a typical discharge energy for commercial capacitive discharge ignition systems. Here, it should be noted that railplugs and the associated ignition circuit should not cost much more than a conventional spark ignition system. Additionally, it is believed that the railplug performance can be further improved via continued research and development.iii TABLE OF CONTENTS Abstract iii EXECUTIVE SUMMARYThis Final Technical Report discusses the progress that was made on the experimental and numerical tasks over the duration of this project. The primary objectives of the project were to 1) develop an improved understanding of the spark ignition process, and 2) develop the railplug as an improved ignitor for large bore stationary natural gas engines.Due to these two objectives, the experimental subtasks involved 1) detailed measurements regarding the physical processes occurring during spark ignition, and 2) measurements of the factors that affect railplug performance. Similarly, the modeling subtasks involved developing an improved model for the conventional spark ignition process and developing a model for railplug performance and ignition.The four phases of spark ignition are ...

It is a very challenging problem to reliably ignite extremely lean mixtures, especially for the low speed, high load conditions of stationary large-bore natural gas engines. If these engines are to be used for the distributed power generation market, it will require operation with higher boost pressures and even leaner mixtures. Both place greater demands on the ignition system. The railplug is a very promising ignition system for lean burn natural gas engines with its high-energy deposition and high velocity plasma jet. High-speed photography was used to study the discharge process. A heat transfer model is proposed to aid the railplug design. A parameter study was performed both in a constant volume bomb and in an operating natural gas engine to improve and optimize the railplug designs. The engine test results show that the newly designed railplugs can ensure the ignition of very lean natural gas mixtures and extend the lean stability limit significantly. The new railplug designs also improve durability.