Analysis of temperature and altitude effects on the Global Energy Balance during WLTC

In this work, the Global Energy Balance (GEB) of a 1.6 L compression ignition engine is analyzed during WLTC using a combination of experimental measurements and simulations, by means of a Virtual Engine. The energy split considers all the relevant energy terms at two starting temperatures (20°C and 7°C) and two altitudes (0 and 1000 m). It is shown that reducing ambient temperature from 20°C to −7°C decreases brake efficiency by 1% and increases fuel consumption by 4%, mainly because of the higher friction due to the higher oil viscosity, while the effect of increasing altitude 1000 m decreases brake efficiency by 0.8% and increases fuel consumption by 2.5% in the WLTC mainly due to the change in pumping. In addition, GEB shows that ambient temperature is affecting exhaust enthalpy by 4.5%, heat rejection to coolant by 2%, and heat accumulated in the block by 2.5%, while altitude does not show any remarkable variations other than pumping and break power.

Triaxial stress path tests on artificially prepared analogue alpine permafrost soil

Some degrading rock glaciers have been exhibiting deepening depressions, accelerating strain rates, and, in some rare cases, sudden release of mass movements. Warming permafrost already mobilizes lower strength as temperatures rise; however, unusual stress paths with lateral stresses greater than vertical stresses, instead of vice versa, could exacerbate this condition with lower strength at failure, and hence higher vulnerability. This paper investigates the mechanical behaviour of artificially frozen soil specimens at temperatures between –3.0 and –0.3 °C under various stress paths: axial (A) and lateral (L), compression (C), and extension (E), for total stress paths AC, AE, LE, LC. Acoustic emissions were detected during shearing to expose how the deformation mechanisms develop from a microstructural point of view. Deviatoric stress mobilized in the stress path tests was linearly dependent on the temperature (within the ranges tested): a temperature increase resulted in a decrease in residual deviatoric stress. Comparison between the residual deviatoric stresses obtained from the different stress path tests indicates that (i) values mobilized with radial stress greater than axial stress were lower than vice versa, (ii) more strength was mobilized when changing lateral stress paths than axial, with (iii) the lowest strength mobilized in AE beneath a depression.