EXPERIMENTAL INVESTIGATION OF NO_x FORMATION IN A DUAL FUEL ENGINE

摘要

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 US 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 NO_x formation for high substitution DF engines. Experimental results have demonstrated that NO_x emission trends (as a function of lambda) for DF engines differ from both traditional diesel engines and lean burn natural gas engines. For high energy substitution (>70%) conditions, NO_x emissions are a function of the premixed gas lambda (λ_(ng)) and contain a local minimum, with NO_x increasing as lambda is either leaned or richened beyond the local minimum which occurs from approximately λ_(ng) = 1.7-1.85. It is hypothesized that at richer conditions (λ_(ng)< 1.7), NO_x formed in the burning of gaseous fuel results in increased total NO_x emissions. At leaner conditions (λ_(ng) > 1.85) the NO_x formed in the diesel post flame regions, as a result of increased oxygen availability, results in increased total NO_x emissions. Between these two regions there are competing effects which result in relatively constant NO_x.