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Water entry studies traditionally employ homogeneous projectiles of varying impactor shape, entry speed, and surface roughness. Surface heterogeneity is yet another means to manipulate splash dynamics. In this experimental study, we systematically investigate the water entry of smooth, free-falling, hemispherically-coated spheres for Froude numbers in the range of 2.8-6.7. Half-hydrophobic, half-hydrophilic spheres released in various orientations produce deep seal cavities, and provoke orientation dependent super-surface splash features and sphere dynamics.

Splash dynamics associated with impacts of solid projectiles into aqueous pools are traditionally investigated with respect to impactor geometry, velocity, and surface roughness. Fluid surface alteration in some instances, may be more easily accomplished for the tuning of splashes. In this combined experimental and theoretical study, smooth, free-falling, hydrophilic steel spheres impact a quiescent liquid pool for Weber numbers in the range of 430 − 2700 . Spheres strike fabrics resting atop the fluid surface which are either punctured or remain intact. As spheres strike fabrics, flow separation is tripped at low speeds which would otherwise not produce air-entraining cavities. Punctured fabrics suppress splash crowns normally seen for cavity-producing impacts while intact fabrics generate deeper cavities, higher Worthington jets, and pronounced splash crowns. Some fabrics, both punctured and intact reduce drag with respect to clean surface impacts by providing the drag-reducing benefits of flow separation while not offering a high inertial penalty. Such observations augur well for interfacial fluid–structure interactions where splashes warrant control.

All mineral derived base stocks used in lubricants contain waxy hydrocarbons that come out of solution when temperature decreases. They can form a three-dimensional wax crystal network that can totally immobilise the oil. In formulated engine oils some additives have a “waxy” or crystalline structure and further contribute to the formation of a crystal network that impairs oil flow. Waxiness is evidenced at low temperature by higher pour-point, yield stress and viscosity compared to a wax free oil. Inadequate oil flow to critical parts of the equipment may result in costly failures. The function of Pour-Point Depressant (PPD) is given in the name. They depress pour-point by inhibiting the waxy structures that form in mineral oil at low temperature. But for modern engine oils pour-point has little relevance and isn’t included in modern international engine oil standards. Industry experience over the decades has replaced pour-point by other more valid assessments of an engine oil’s suitability at low temperature. In particular low temperature pumpability by Mini Rotary Viscometer (MRV) due to its inclusion in SAE J300 specification is the primary test. In some cases this is now required on used oil, and most recently in Europe on oil oxidised in the presence of biodiesel by CEC-L-105-12. However PPDs exist or have been developed which are effective in these evolved low temperature requirements of engine oils. In this paper we show that PPDs are available which are effective against this latest European CEC L-105 requirement, although extra consideration must be given to their selection. We also show that multiple low temperature requirements tend to narrow the choice of acceptable PPDs, and the choice of PPD can be strongly influenced by the presence of other additives in addition to the mineral oil. These combined with the extra requirement for CEC L-105 has made PPD selection more difficult, but based on our work reported here this new challenge can be met by correct PPD selection.

When subject to low-temperature conditions, the paraffins in a lubricant come out of solution to form structures that can impair oil flow. The size of the paraffinic crystals, and the strength of the three-dimensional network they form, depend on physical parameters, such as temperature, cooling rate and soaking time, as well as on the chemical nature of the wax and of other components in the oil. To evaluate the ability of lubricants to flow under low-temperature conditions, a number of test methods have been developed, from the simple pour-point test (ASTM D-97), to very sophisticated tests such as the MRV TP-1 (ASTM D-4864). In the early 1980s, a new technique, using the scanning Brookfield viscometer (ASTM D-5133), was developed. This method has progressively gained acceptance by industry and is now part of the ILSAC GF-2 specification. The scanning Brookfield technique provides a new approach to continuous measurement of the viscosity of engine lubricants at very low shear rates, with decreasing temperature. It is said to be unique in its ability to identify oils which develop gel structures at low temperature. After presenting background information on the scanning Brookfield viscometer, this paper examines its use with modern engine lubricants, and its ability to evaluate the effect of pour-point depressants on the low-temperature performance of engine lubricants.

The new ILSAC GF-4 specification for Passenger Car Motor Oils includes a measurement of low-temperature viscosity after the Sequence IIIGA engine test. The measurement is conducted according to ASTM D 4684, the well known TP-1 MRV (Mini Rotary Viscometer) procedure. While the limits are the usual values found in SAE J300 which are no measurable yield stress and 60,000 mPas maximum, it is tested five degrees Centigrade warmer than called for by the fresh oils' SAE W grade. The need for this new measurement and specification is based on the finding that some PCMO lubricants' low-temperature/low-shear rate viscosities, but not necessarily their higher temperature rheological properties, were seriously degraded in severe oxidative environments. Because of this new focus on low-temperature rheology after facing a severe oxidative engine test, it became of interest to understand the robustness of the Pour Point Depressant which is the additive usually responsible for controlling wax related cold temperature rheology properties. SAE 5W-30 oils, otherwise fully additized, were formulated with and without Pour Point Depressant (PPD) so that fresh oil, used oil, and used oil with PPD added after use could be compared relative to cold temperature TP-1 MRV behavior. These oils were degraded by 1) laboratory mechanical shearing, 2) field service in extended drain taxi tests, and 3) Sequence IIIGA engine tests.