Adiabatic Core Research Articles

A Fundamental Model for Predicting Fuel Consumption, NOxand HC Emissions of the Conventional Spark-Ignited Engine

Abstract A model of the four-stroke S.I. engine cycle has been developed which predicts fuel consumption, NOx and HC emissions as a function of engine design and operating conditions. The model is primarily thermodynamic in nature containing no formal spatial dependence. The major new features of the model are: first, a treatment of heat transfer which confines heat losses to a boundary layer region surrounding a central adiabatic core; second, an integral boundary-layer analysis of in-cylinder burnup of quenched hydrocarbons; and third, a calculation of exhaust port HC oxidation which considers the temperature history of each element of gas leaving the cylinder. The main adjustable parameters of the model relate to the rate of heat transfer and the ratio of the two-plate quench to the single-wall thickness. An extensive comparison of model predictions with experimental CFR engine data is presented. The results show excellent agreement between predicted and experimental fuel consumption and NOx emissions....

Gravitational collapse to neutron stars and black holes - Computer generation of spherical spacetimes

A new, general relativistic, hydrodynamical computer code for spherical, stellar colapse to neutron stars and black holes is presented. The code is employed to construct spacetimes for the geometrodynamical evolution of spherical masses which are initially at rest and obey an adiabatic GAMMA-law equation of state. Collapse to a black hole can be followed accurately; the evolution outside the event horizon can be determined far into the future without having the integration terminate because of spacetime singularities inside.We use the code to address several fundamental points of principle regarding spherical, gravitational collapse and requiring a reliable, fully relativistic, numerical computation. We sample a variety of possible collapse and requiring a reliable, fully relativistic, numerical computation. We sample a variety of possible collapse scenarios, characterized by different masses, mass distributions, and equations of state, to examine stellar core collapse and its end fate. We distinguish three possible outcomes for adiabatic core collapse: homologous core, bounce, nonhomologous core bounce, and catastrophic collapse to a black hole. Even a very massive stellar core may undergo a nonhomologous bounce and only later collapse to a black hole on a secular time scale rather than a dynamical one. Accretion-driven neutron star collapse is also treatedmore » numerically. The implications of our findings for realistic core collapse believed to occur in nature are considered.« less

On the opaque core appearing in the early phase of star formation

The spherical collapse of a protostar with one solar mass is calculated from a gravitationally unstable initial stage, by solving the equations of hydrodynamics and pherical radiative transfer. The temperature dependence of the dust opacity is taken into account in contrast to the earlier calculations with temperature independent opacities. It is shown that the opaque core is equivalent to the adiabatic core in the purely adiabatic case. The blanketing effect of dust grains strengthens the shock of the opaque core and may result in raising the central entropy of protostars.

Observations of Moist Adiabatic Ascent in Northeast Colorado Cumulus Congestus Clouds

The characteristics of entrainment in and below 12 developing cumulus congestus clouds in the north-eastern Colorado area were investigated using measurements obtained with the NCAR/NOAA sailplane, supporting aircraft and rawinsondes. A region of moist adiabatic ascent was found in eight of the most vigorous clouds sampled. A gradual increase was noted in the equivalent potential temperature and the ratio of the liquid water content to the adiabatic value from the edge of the updraft region inward to the moist adiabatic core. Previous measurements and conceptual and theoretical models of entrainment are discussed in the context of the present set of measurements. The moist adiabatic core was positioned off-center with respect to the boundaries of the updraft region. The measurements supported previous conceptual cloud models in which the updraft acts as an obstacle to the horizontal wind thereby causing the environmental air to flow around the upshear portion of the cell, protecting that region from entrainment. A turbulent wake would be expected to occur in the down-shear portion of the cell, producing increased turbulence and mixing in that region.

Physical properties of the Earth's core

Calculations of the compression and temperature gradient of the core are facilitated by the use of the thermodynamic Gruneisen ratio, γ=3αKs/ρ{variant}CP. A pressure-dependent factor in γ is found to have the same numerical value for the core as for laboratory iron, justifying the use of a constant value for γ (1.6) in core calculations. The density of the outer core is satisfied by the assumption that it contains about 15% of light elements, particularly sulphur, whereas the inner core is probably ironnickel with very little lighter component. The presence of sulphur in the outer core reduces its liquidus at least 600° below pure iron, so that the adiabatic gradient does not intersect the liquidus, as Higgins and Kennedy have shown would occur in a pure iron core. The inner core is probably close to its melting point, 4700 K, and the adiabatic temperature gradient of the outer is calculated with this as a fixed point, giving 3380 K at the core-mantle boundary. The estimated electrical resistivity of the outer core, 3×10-6 Σm, corresponds to a thermal conductivity of 28 W·m-1·deg-1, which, with the adiabatic core gradient gives a minimum of 3.9×1012 W of heat conduction to the mantle. The only plausible source of this much heat is the radioactive decay of potassium in the core. As pointed out by Goles, Lewis, and Hall and Murthy, the presence of potassium becomes geochemically probable once sulphur is admitted as a core constituent. Thus it appears that the recognition of sulphur in the core resolves the two major difficulties which we have faced in attempting to understand the core.