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Previously we reported (SAE Paper 2005-01-0475) that emissions of toxicologically relevant compounds from an engine operating at low NOx conditions using Fischer-Tropsch fuel (FT100) were lower than those emissions from the engine using an ultra-low sulfur (15 PPM sulfur) diesel fuel (BP15). Those tests were performed at two operating modes: Mode 6 (4.2 bar BMEP, 2300 RPM) and Mode 11 (2.62 bar BMEP, 1500 RPM). We wanted to evaluate the effect on emissions of operating the engine at low power (near idle) in conjunction with the low NOx strategy. Specifically, we report on emissions of total hydrocarbon (HC), carbon monoxide (CO), NOx, particulates (PM), formaldehyde, acetaldehyde, benzene, 1,3-butadiene, gas phase polyaromatic hydrocarbons (PAH's) and particle phase PAH's from a DaimlerChrysler OM611 CIDI engine using a low NOx engine operating strategy at Mode 22 (1.0 bar BMEP and 1500 RPM).

The dioiefin content of unstable gasolines has been implicated in the restriction of multi-port fuel injectors by deposits. Vehicle tests of the effect of adding a diolefin mixture to a stable (olefinic) gasoline indicated that a deposit-producing gasoline resulted. Laboratory oxidation tests showed that addition of a “dienophile” to an unstable gasoline significantly reduced deposit formation, increased oxidation stability, and reduced gum formation. Additional vehicle tests with a dienophile-treated fuel showed that some injector deposits were reduced, but new deposits occurred in other areas of the fuel system. Apparently, diolefins can be a factor in producing plugged fuel injectors, but other fuel factors are also likely to play important roles whether diolefins are present or not.