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# Extending Lean Operating Limit and Reducing Emissions of Methane Spark-Ignited Engines Using a Microwave-Assisted Spark Plug

Journal of Combustion

Hindawi Limited

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### Abstract

A microwave-assisted spark plug was used to extend the lean operating limit (lean limit) and reduce emissions of an engine burning methane-air. In-cylinder pressure data were collected at normalized air-fuel ratios of $λ = 1.46$, $λ = 1.51$, $λ = 1.57$, $λ = 1.68$, and $λ = 1.75$. For each $λ$, microwave energy (power supplied to the magnetron per engine cycle) was varied from 0 mJ (spark discharge alone) to 1600 mJ. At lean conditions, the results showed adding microwave energy to a standard spark plug discharge increased the number of complete combustion cycles, improving engine stability as compared to spark-only operation. Addition of microwave energy also increased the indicated thermal efficiency by 4% at $λ = 1.68$. At $λ = 1.75$, the spark discharge alone was unable to consistently ignite the air-fuel mixture, resulting in frequent misfires. Although microwave energy produced more consistent ignition than spark discharge alone at $λ = 1.75$, 59% of the cycles only partially burned. Overall, the microwave-assisted spark plug increased engine performance under lean operating conditions $( λ = 1.68 )$but did not affect operation at conditions closer to stoichiometric.

### Most cited references13

• Record: found

### Plasma assisted ignition and combustion

(2006)
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• Record: found

### Application of high energy ignition systems to engines

(1997)
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• Record: found

### Spark ignition natural gas engines—A review

(2007)
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### Author and article information

###### Journal
Journal of Combustion
Journal of Combustion
Hindawi Limited
2090-1968
2090-1976
2012
2012
: 2012
:
: 1-8
###### Article
10.1155/2012/927081