Essentially pure, ∼1.5 μm thick, polycrystalline diamond films DC–PACVD deposited on polycrystalline α-SiC flats were friction and wear tested against similarly coated α-SiC pins. The oscillatory sliding tests were performed with a Knudsen cell-type, wide temperature range tribometer built into a scanning electron microscope. Experiments were completed in 1.33 × 10−3 Pa (1 × 10−5 Torr) and 13.3 Pa (1 × 10−1 Torr) Pair, at test flat temperatures cycled to 850°C and back to room temperature. The results are compared with similar tests previously completed with diamond versus bare α–SiC and diamond versus Si(100) sliding combinations. In the absence of in situ surface analytical capability in the SEM tribometer, the findings are interpreted based on relevant information collected from the literature. The data indicate that the friction of the respective, tangentially sheared interfaces depends on the generation and annihilation of dangling bonds. Desorption of hydrogen during heating and sliding under the electron beam, in vacuum, create unoccupied orbitals on the rubbing surfaces. These dangling bonds spin-pair with others donated from the counterface, leading to high friction. Resorption of adsorbates such as hydrogen (e.g., by cooling the tribosystem) lowers the interfacial adhesion and friction. At high temperatures, in vacuum, the interaction energy may also be reduced by surface reconstruction and graphitization. At high temperatures, in Pair, the coefficient of friction of diamond versus itself is substantially lower than that in vacuum. This reduction is most probably caused by the generation of oxidation products combined with the temperature-shear-oxygen-induced phase transformation of diamond to graphite. The wide temperature wear rates of pure, polycrystalline diamond, characteristic of our test procedure, varied from ∼4 × 1016 m3/N · m in 1.33 × 10−3 Pa vacuum to ∼1 × 10−15 m3/N · m in 13.3 Pair.

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Diesel particulate matter (PM) reduction efficiencies for backup generators (BUGs) (> 300 kW) equipped with a diesel oxidation catalyst (DOC), DOC+fuel-borne catalyst additive combination (DOC+FBC), passive diesel particulate filter (DPF), and an active DPF were measured. Overall, the DOC and DOC+FBC technologies were found to be effective in reducing mainly organic carbon (OC) emissions (56-77%) while both DPFs showed excellent performance in reducing both elemental carbon (EC) and OC emissions (> 90%). These findings demonstrate the potential for applying DOCs to older engines where PM is dominated by the OC fraction. In most modern engine applications, where the PM consists of mainly EC, the DOC will be largely ineffective. Alternatively, passive and active DPFs are expected to be efficient for most engine technologies. Measurements of particle size distributions provided evidence of the high temperature formation of sulfate nanoparticles across the control technologies despite the use of ultralow sulfur diesel. Changes in the particle size distribution and the organic fraction of PM indicate that the OC component of PM is primarily found in the smaller sized particles.

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