Emissions compliance is a driving factor for internal combustion engine research pertaining to both new and old technologies. New standards and compliance requirements for off-road spark ignited engines are currently under review and include greenhouse gases. To continue operation of legacy natural gas engines, research is required to increase or maintain engine efficiency, while reducing emissions of carbon monoxide, oxides of nitrogen, and volatile organic compounds such as formaldehyde. A variety of technologies can be found on legacy, large-bore natural gas engines that allow them to meet current emissions standards — these include exhaust after-treatment, advanced ignition technologies, and fuel delivery methods. The natural gas industry uses a variety of spark plugs and tuning methods to improve engine performance or decrease emissions of existing engines. The focus of this study was to examine the effects of various spark plug configurations along with spark timing to examine any potential benefits. Spark plugs with varied electrode diameter, number of ground electrodes, and heat ranges were evaluated against efficiency and exhaust emissions. Combustion analyses were also conducted to examine peak firing pressure, location of peak firing pressure, and indicated mean effective pressure. The test platform was an AJAX-E42 engine. The engine has a bore and stroke of 0.216 × 0.254 meters (m), respectively. The engine displacement was 9.29 liters (L) with a compression ratio of 6:1. The engine was modified to include electronic spark plug timing capabilities along with a mass flow controller to ensure accurate fuel delivery. Each spark plug configuration was examined at ignition timings of 17, 14, 11, 8, and 5 crank angle degrees before top dead center. The various configurations were examined to identify optimal conditions for each plug comparing trade-offs among brake specific fuel consumption, oxides of nitrogen, methane, formaldehyde, and combustion stability.

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