The North American oil and gas industry has experienced a market pull for dual fuel (DF) engines that can run on any ratio of fuels ranging from 100% diesel to a high proportion of field gas relative to diesel, while also meeting the U.S. Tier 4 Nonroad emissions standards. A DF engine must meet complex and at times competing requirements in terms of performance, fuel tolerance, and emissions. The challenges faced in designing a DF engine to meet all of the performance and emissions requirements require a detailed understanding of the trade-offs for each pollutant. This paper will focus on the details of NOx formation for high substitution DF engines. Experimental results have demonstrated that NOx emission trends (as a function of lambda) for DF engines differ from both traditional diesel engines and lean burn natural gas (NG) engines. For high energy substitution (>70%) conditions, NOx emissions are a function of the premixed gas lambda (λng) and contain a local minimum, with NOx increasing as lambda is either leaned or richened beyond the local minimum which occurs from approximately λng = 1.7 – 1.85. It is hypothesized that at richer conditions (λng < 1.7), NOx formed in the burning of gaseous fuel results in increased total NOx emissions. At leaner conditions (λng > 1.85), the NOx formed in the diesel post flame regions, as a result of increased oxygen availability, results in increased total NOx emissions. Between these two regions there are competing effects which result in relatively constant NOx.
Experimental Investigation of NOx Formation in a Dual Fuel Engine
Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received April 9, 2018; final manuscript received April 13, 2018; published online August 9, 2018. Editor: David Wisler.
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Hagen, L., Breaux, B., Flory, M., Hiltner, J., and Fiveland, S. (August 9, 2018). "Experimental Investigation of NOx Formation in a Dual Fuel Engine." ASME. J. Eng. Gas Turbines Power. December 2018; 140(12): 122802. https://doi.org/10.1115/1.4040179
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