Efficiency of harmonic quantum Otto engines at maximal power

Recent experimental breakthroughs produced the first nano heat engines that have the potential to harness quantum resources. An instrumental question is how their performance measures up against the efficiency of classical engines. For single ion engines undergoing quantum Otto cycles it has been found that the efficiency at maximal power is given by the Curzon-Ahlborn efficiency. This is rather remarkable as the Curzon-Alhbron efficiency was originally derived for endoreversible Carnot cycles. Here, we analyze two examples of endoreversible Otto engines within the same conceptual framework as Curzon and Ahlborn's original treatment. We find that for endoreversible Otto cycles in classical harmonic oscillators the efficiency at maximal power is, indeed, given by the Curzon-Ahlborn efficiency. However, we also find that the efficiency of Otto engines made of quantum harmonic oscillators is significantly larger.Comment: 6 pages, 2 figure

Irreversible thermodynamic analysis and application for molecular heat engines

The aim of this paper is to determine lost works in a molecular engine and compare results with macro (classical) heat engines. Firstly, irreversible thermodynamics are reviewed for macro and molecular cycles. Secondly, irreversible thermodynamics approaches are applied for a quantum heat engine with -1/2 spin system. Finally, lost works are determined for considered system and results show that macro and molecular heat engines obey same limitations. Moreover, a quantum thermodynamic approach is suggested in order to explain the results previously obtained from an atomic viewpoint.Comment: 32 pages, 2 Tables, 1Figur

Finite-Time Thermodynamics

The theory around the concept of finite time describes how processes of any nature can be optimized in situations when their rate is required to be non-negligible, i.e., they must come to completion in a finite time. What the theory makes explicit is “the cost of haste”. Intuitively, it is quite obvious that you drive your car differently if you want to reach your destination as quickly as possible as opposed to the case when you are running out of gas. Finite-time thermodynamics quantifies such opposing requirements and may provide the optimal control to achieve the best compromise. The theory was initially developed for heat engines (steam, Otto, Stirling, a.o.) and for refrigerators, but it has by now evolved into essentially all areas of dynamic systems from the most abstract ones to the most practical ones. The present collection shows some fascinating current examples

Fluctuation Relations and Nonequilibrium Thermodynamics in Classical and Quantum Systems

This Special Issue contains novel results in the area of out-of-equilibrium classical and quantum thermodynamics. Contributions are from different areas of physics, including statistical mechanics, quantum information and many-body systems

An Empirical Study for Achieving Economies of Scale by Utilization of (HHO) Hydrogen Hydroxy Gas as Additional Fuel

The scarcity of fossil fuel and Compressed Natural Gas (CNG) has made every 2nd fuel user to think on some alternative resources, or at least devise some sort of technique to overcome the shortage of fuel during CNG holidays. Thus this study covers an overview of HHO gas production, principles behind the reactions and statistical examples, observations of many engineers and observers who determined to make a use of HHO as additional fuel source. Up to now studies reveals that it is possible to produce burnable vapors of HHO gas in result of hydrolysis of distilled water with combination of some electrolyte sodium or potassium hydro oxides. That Mixture is   generally called Hydrogen-Hydro oxide mixture (H-OH) can give 25%-28% efficiency to fuel combustion if used with fossil fuel. With thermodynamics advantages, by hydrolysis of steam and using different materials as electrode, using 1.3volt to 1.7volt at 0.4 A/cm² the total efficiency can be increased to 40-50% to enhance its utilization for industry use. But need to refine the misconceptions HHO gas is a standalone replacement of fossil fuel for a practical use in cars, scoters and other means of transport. This study suggest policy makers and entrepreneurs to take some supportive actions to promote HHO gas generators/ kits production because this is a low cost solution to cover the shortage of fossil fuel. Keywords: HHO, Hydrogen, Hydroxy, Brown gas, Fuel efficiency.

Utilization of Ammonia Hydroxide /Diesel Fuel Blends in Partially Premixed Charge Compression Ignition (PPCCI) Engine: A Technical Review

Almost 50% of new car registrations in Europe at the turn of the century were diesel. However, reports of harmful NOx emissions have been corroborated by diesel emissions scandals, which have sent the diesel engine market into a tailspin and raised concerns about the diesel engine\u27s long-term viability. Developing of diesel cars with low NOx emissions has been announced by major automakers. Modern posttreatment systems can be installed, and they will result in decreased NOx emissions for heavy-duty, marine, or power production applications. Despite attempts to lower NOx emissions, the automobile, marine, and power generation industries must decarbonize if we are to reach greenhouse gas emission objectives and prevent global warming. Using fuels with low carbon, like ammonia, can help decarbonize a diesel engine. Using ammonia as a fuel for diesel engines is discussed at length in this work. To drastically lower carbon emissions, Ammonia could be burned when mixed with diesel or another low-temperature fuel in a dual-fuel system. Creating advanced injection technologies can improve overall emissions while also improving performance. However, due to the coupling of nitrogen to the fuel, dual fuel combustion of ammonia currently has relatively large emissions of ammonia and nitrogen oxides. As a result, post-processing mechanisms need to be put in place. With the introduction of modern combustion systems like HCCI, PCCI, and RCCI systems, ammonia is currently only a practical alternative in specific applications including maritime, power generating, and maybe heavy duty

Reaction Kinetics of Hydroxyl Radical with Polycyclic Aromatic Hydrocarbon Precursors

The incomplete combustion of fuels inside of an internal combustion engines generates unwanted byproducts such as soot. Because of health and environmental concerns, soot formation has been a very active area of research in combustion chemistry. However, the mechanism of formation of soot is still not well understood. It has been proposed that the soot formation is initiated by the reaction of small free radicals with abundant hydrocarbon fuel molecules producing aromatic ring structures at high temperatures. These aromatic ring structures further react to form polycyclic aromatic hydrocarbons (PAHs) that are stable at the high temperatures of combustion environments. These PAHs collide and stick with each other forming dimers, trimers, tetramers, etc. Eventually such stable PAHs-stabilomers condense and transform into solid particles (soot). To minimize pollutants and increase the efficiency of engines, it is very important to understand the chemistry of the elementary reactions at the molecular level.;The reactions of hydroxyl free radicals with polycyclic aromatic hydrocarbon precursor molecules are studied experimentally in a quasi-static gas cell using laser pump-probe spectroscopy. Hydroxyl free radicals are generated by pulsed laser photolysis (PLP) using the third (355 nm) or fourth (266 nm) harmonic of Nd:YAG laser and their concentration is monitored as a function of laser delay-time using a frequency-doubled tunable dye laser perpendicular to the photolysis laser. The off-resonance fluorescence from the hydroxyl free radicals at 310 nm is collected by a photomultiplier tube (PMT) placing it orthogonal to the photolysis and probe laser beams. The reactions of hydroxyl radicals (OH) with phenylacetylene and fulvenallene have been investigated from 298 K to 450 K. The concentrations of the hydrocarbon reactants are measured using FTIR spectroscopy and UV absorption. The room temperature reaction rate of the OH + phenylacetylene reaction is measured to be 8.75(+/-0.73)x10-11 cm3s-1. The reaction rate coefficient is pressure and temperature independent over the 1-7.5 Torr and 298-423 K pressure and temperature ranges. The rate coefficient is larger than that expected based solely on association with the aromatic ring, which suggests reaction with the triple bond. For the OH + fulvenallene reaction, the room temperature rate coefficient is found to be 8.8(+/-1.7)x10-12 cm3s-1 with the negative temperature dependence. The comparison of the experimental rate coefficients with the calculated abstraction rate coefficients suggests that over the experimental range, association of hydroxyl radical (OH) to fulvenallene plays the significant role toward the formation of PAH precursors