Dairene Uy

Friction, Wear, and Surface Film Formation Characteristics of Diamond-Like Carbon Thin Coating in Valvetrain Application

The friction and wear characteristics of thin diamond-like carbon (DLC) coatings have been investigated extensively in recent years mostly in laboratory bench tests. These coatings are known to provide significant friction reduction in the absence of lubricants. In the presence of lubricants, the friction benefits of these coatings are not clearly demonstrated. The current investigation is focused on exploring the friction reduction potential of a DLC coating obtained from a supplier in laboratory bench tests and in a motored valve train test. The DLC coating was deposited on the bucket tappet. In laboratory bench tests, results showed significant friction reduction in the absence of any lubricant but not in the presence of engine oil. In motored valve train tests a significant reduction in friction torque was observed when compared against a slightly rougher uncoated bucket, but no reduction was observed when compared against uncoated bucket tappet with comparable surface finish. Under boundary lubrication conditions, no lubricant-derived surface films were present on the DLC-coated surface. However, under mixed lubrication conditions, evidence of patchy antiwear surface films could be observed on DLC-coated buckets. The antiwear film appears to be primarily composed of calcium phosphate.

Sub-Doppler resolution limited Lamb-dip spectroscopy of NO with a quantum cascade distributed feedback laser

A quantum cascade distributed feedback laser operating at 5.2 microm is used to obtain sub-Doppler resolution limited saturation features in a Lamb-dip experiment on the R(13.5)1/2 and R(13.5)3/2 transitions of NO. The dips appear as transmission spikes with full widths of ~ 4.3 MHz. At this resolution the 73 MHz _-doubling of the R(13.5)3/2 line, which is normally obscured by the 130 MHz Doppler broadening, is easily resolved.

Observation of Strained PdO in an Aged Pd/Ceria-Zirconia Catalyst

A model automotive-exhaust catalyst, Pd on Zr-rich ceria–zirconia, was characterized by X-ray diffraction, optical and electron microscopies, and micro-Raman spectroscopy following high-temperature aging. A broad bimodal distribution of Pd, introduced amongst the 10-μ m spherical particles of support material during catalyst preparation, was found to persist upon aging, and strained PdO was detected predominantly in those particles containing the higher concentration of Pd. The strain, approximately -1% by volume, was determined from the shift of the strong PdO Raman line at 650 cm-1 and the Grüneisen parameter, which was measured in a separate experiment in a diamond-anvil cell. The origin of the compressive stress that gives rise to this strain is believed to be the same as in the previously known phenomenon of Pd–metal encapsulation, but the Pd particles involved here are apparently not highly constrained within the sintered ceria–zirconia matrix prior to their oxidation.

UV Raman spectroscopy of adsorbed SOx on γ-alumina and Pt/γ-alumina catalysts

Raman spectra of SOx adsorbed on γ-alumina and Pt/γ-alumina model catalysts have been obtained with a 244 nm Raman spectrometer. Strong peaks in the 980–1380 cm-1 region characteristic of adsorbed sulfates are clearly portrayed in the spectra, which contrast with fluorescence-dominated scans obtained using visible excitation. Broad bands are also observed in the 3500–3700 cm-1 O–H stretch region on the γ-alumina, which belong to weakly-bound physisorbed water and more strongly-bound surface hydroxyls. These features are monitored as the samples are heated up to 600°C in the presence of nitrogen. The sulfate peaks vary in position depending on whether or not the γ-alumina is loaded with platinum, hydrated, or dehydrated. Platinum appears to inhibit the physisorption of water and the formation of hydroxyls on the γ-alumina surface, as evidenced by the absence of O–H stretch vibrations on the Pt-loaded sample. Our spectral data demonstrate that UV Raman spectroscopy is a useful technique for analytical studies of adsorbed SOx on γ-alumina, and holds promise for future in situ investigations of other adsorbed species on catalytic substrates of automotive interest.

Comparison of the Effects of Biodiesel and Mineral Diesel Fuel Dilution on Aged Engine Oil Properties

Dilution of engine oil occurs when fuel is injected late in the combustion cycle to regenerate the diesel particulate filter used for trapping particulate emissions. Fuel dilution reduces oil viscosity and the concentration of engine oil additives, potentially compromising lubricant performance. Biodiesel usage may compound these issues due to its oxidative instability, and its higher boiling point compared to mineral diesel potentially causes it to concentrate more in the oil sump. In this work, different amounts of mineral diesel and biodiesel (soy methyl ester, SME) were combined with 15W-40 CJ-4 diesel engine oil in laboratory oil aging experiments. Fuel was added and oil samples were withdrawn at periodic intervals. The oils were analyzed using typical oil analysis procedures to determine their condition, and wear evaluations under boundary lubricating conditions were determined using a high-frequency reciprocating rig (HFRR). Results showed that fuel dilution accelerated engine oil degradation, with biodiesel having a larger effect. However, friction remained unchanged with dilution, and wear actually decreased for fuel-diluted oils after 48 h of aging compared to aging without fuel dilution. Examination of the tribofilms by ultraviolet (UV) and visible Raman spectroscopy as well as Auger electron spectroscopy showed that additional carbon-containing components were present on tribofilms formed from fuel-diluted oils. These fuel-derived components may be responsible for the decreased wear observed.

Mechanical characterization of diesel soot nanoparticles: in situ compression in the transmission electron microscope and simulations

Incomplete fuel burning inside an internal combustion engine results in the creation of soot in the form of nanoparticles. Some of these soot nanoparticles (SNP) become adsorbed into the lubricating oil film present on the cylinder walls, which adversely affects the tribological performance of the lubricant. In order to better understand the mechanisms underlying the wear caused by SNPs, it is important to understand the behavior of SNPs and to characterize potential changes in their mechanical properties (e.g. hardness) caused by (or during) mechanical stress. In this study, the behavior of individual SNPs originating from diesel engines was studied under compression. The experiments were performed in a transmission electron microscope using a nanoindentation device. The nanoparticles exhibited elasto-plastic behavior in response to consecutive compression cycles. From the experimental data, the Youngs modulus and hardness of the SNPs were calculated. The Youngs modulus and hardness of the nanoparticles increased with the number of compression cycles. Using an electron energy loss spectroscopy technique, it was shown that the sp2/sp3 ratio within the compressed nanoparticle decreases, which is suggested to be the cause of the increase in elasticity and hardness. In order to corroborate the experimental findings, molecular dynamics simulations of a model SNP were performed. The SNP model was constructed using carbon and hydrogen atoms with morphology and composition comparable to those observed in the experiment. The model SNP was subjected to repeated compressions between two virtual rigid walls. During the simulation, the nanoparticle exhibited elasto-plastic behavior like that in the experiments. The results of the simulations confirm that the increase in the elastic modulus and hardness is associated with a decrease in the sp2/sp3 ratio.

Recent advances in Raman scattering studies of exhaust-gas catalysts

Raman scattering is a powerful technique for studying catalysts used in the treatment of automotive exhaust gas. It has the sensitivity and chemical specificity needed to identify the oxide phases of many of the precious metals (Pt, Pd, Rh) used in these catalysts, even when they are highly dispersed on high-surface-area supports such as (gamma) -Al2O3. Moreover, this technique can be employed in situ under temperature (300 - 600 degree(s)C) and pressure (1 atm) conditions typically encountered in normal operation. Bulk Pd oxide (PdO) is readily detected with visible excitation, because of a strong resonance Raman enhancement, and its formation and decomposition on Pd/(gamma) -Al2O3 and Pd/ZrO2 catalysts can be followed in real time. Pt does not oxidize as easily as Pd, but a layer of atomic O will form on Pt, and it produces a Raman signature that can be detected with UV excitation at 244 nm. Similarly, UV excitation enhances spectra from adsorbed NOx and SOx and hydroxyls on model Pt/(gamma) -Al2O3 catalysts. In situ UV Raman spectra of Ba-containing catalysts, being considered for use as NOx traps, show adsorbed NOx and SOx and, thus, can be used to characterize the NOx trapping, S poisoning, and regeneration of the trap. UV excitation has several advantages in addition to the eletronic resonance enhancment: the signal is increased because of the dependence of the Raman cross section on the fourth power of the frequency, the fluorescence is often Stokes shifted well beyond the range of the Raman lines, and the thermal background from a heated sample is negligible.