Performance Of Heat Engine Research Articles

Catalytic enhancement in the performance of the microscopic two-stroke heat engine.

We consider a model of heat engine operating in the microscopic regime: the two-stroke engine. It produces work and exchanges heat in two discrete strokes that are separated in time. The working body of the engine consists of two d-level systems initialized in thermal states at two distinct temperatures. Additionally, an auxiliary nonequilibrium system called catalyst may be incorporated with the working body of the engine, provided the state of the catalyst remains unchanged after the completion of a thermodynamic cycle. This ensures that the work produced by the engine arises solely from the temperature difference. Upon establishing the rigorous thermodynamic framework, we characterize twofold improvement stemming from the inclusion of a catalyst. Firstly, we prove that in the noncatalytic scenario, the optimal efficiency of the two-stroke heat engine with a working body composed of two-level systems is given by the Otto efficiency, which can be surpassed by incorporating a catalyst with the working body. Secondly, we show that incorporating a catalyst allows the engine to operate in frequency and temperature regimes that are not accessible for noncatalytic two-stroke engines. We conclude with a general conjecture about the advantage brought by a catalyst: including the catalyst with the working body always allows to improve efficiency over the noncatalytic scenario for any microscopic two-stroke heat engines. We prove this conjecture for two-stroke engines where the working body is composed of two d-level systems initialized in thermal states at two distinct temperatures, as long as the final joint state leading to optimal efficiency in the noncatalytic scenario is not a product state, or at least one of the d-level system is not thermal.

Dissipation-induced collective advantage of a quantum thermal machine

Do quantum correlations lead to better performance with respect to several different systems working independently? For quantum thermal machines, the question is whether a working medium (WM) made of N constituents exhibits better performance than N independent engines working in parallel. Here, by inspecting a microscopic model with the WM composed by two non-interacting quantum harmonic oscillators, we show that the presence of a common environment can mediate non-trivial correlations in the WM leading to better quantum heat engine performance—maximum power and efficiency—with respect to an independent configuration. Furthermore, this advantage is striking for strong dissipation, a regime in which two independent engines cannot deliver any useful power. Our results show that dissipation can be exploited as a useful resource for quantum thermal engines and are then corroborated by optimization techniques here extended to non-Markovian quantum heat engines.

Heating and cooling are fundamentally asymmetric and evolve along distinct pathways

According to conventional wisdom, a system placed in an environment with a different temperature tends to relax to the temperature of the latter, mediated by the flows of heat or matter that are set solely by the temperature difference. It is becoming clear, however, that thermal relaxation is much more intricate when temperature changes push the system far from thermodynamic equilibrium. Here, by using an optically trapped colloidal particle, we show that microscale systems under such conditions heat up faster than they cool down. We find that between any pair of temperatures, heating is not only faster than cooling but the respective processes, in fact, evolve along fundamentally distinct pathways, which we explain with a new theoretical framework that we call thermal kinematics. Our results change the view of thermalization at the microscale and will have a strong impact on energy-conversion applications and thermal management of microscopic devices, particularly in the operation of Brownian heat engines.

Особливості застосування альтернативних палив у теплових двигунах

The subject of the study is the use of alternative fuels and hydrogen in heat engines in different concentrations at different operating modes. The purpose of this study is to decarbonize various types of transport, especially aviation, to increase the energy efficiency and environmental performance of heat engines. Task: to investigate the use of such alternative fuels as biofuels, synthetic fuels, hydrogen and hydrogen mixtures. The use of aviation fuels shows that they must satisfy the relevant requirements, so the choice of alternative fuels must satisfy these requirements with the improvement of their characteristics, first in terms of energy efficiency and environmental indicators. To do this, starting with the ground test of a modern aircraft engine, Rolls-Royce conducted tests on an early conceptual demonstrator using green hydrogen. Green hydrogen was created by wind and tidal energy to prove that hydrogen could be the zero carbon aviation fuel of the future with zero carbon emissions. After analyzing the early ground test concept, the developers are planning a series of further bench tests leading to a full-scale ground test of a green hydrogen jet engine with the goal of achieving zero net carbon emissions from the engine Research Methods. According to the recommendations of the IPCC on the use of scarce fuel, the coefficients of harmful emissions (EI) are calculated for some types of aircraft for the Landing Take Off (LTO) cycle (landing / takeoff). Harmful emissions are calculated using the same method when alternative fuels are used in engines Since jet fuel emissions play an important role in the greenhouse effect, new technologies are being introduced to reduce emissions, among which one of the most effective and environmentally friendly is the use of biofuels, as biofuels are produced using modern biological processes. In this study, an experimental study of the influence of hydrogen addition on a traditional internal combustion diesel engine was conducted. The results. It was determined that the supply of small additions of gaseous hydrogen to the diesel manifold increases the efficiency of the engine at nominal and, largely, at partial modes of operation. The environmental parameters of the diesel engine are improved: the concentration of nitrogen oxides in the exhaust gases decreases, the soot content decreases by 30-40% and by 35%. A calculation method for the quantitative assessment of harmful emissions when using alternative fuels in aircraft engines is defined. Conclusions. The practical significance of the obtained results is that the obtained dependencies can be used when choosing the type of fuel for heat engines and determining the optimal concentration of an alternative fuel such as hydrogen to increase energy efficiency and improve the environmental performance of heat engines.

Quantum Stirling heat engine operating in finite time

Quantum Stirling heat engine operating in finite time

Multi compression–expansion process for chemical energy conversion: Transformation of methane to unsaturated hydrocarbons and hydrogen

With the global energy system moving towards renewable energies, there is an increasing demand for flexible conversion processes which can cope with the temporally and locally fluctuating nature of energy supply and energy demand. Promising candidate processes are based on coupled chemical/energy conversion. In this work, the pyrolytic conversion of methane to valuable high-energy content substances like hydrogen and unsaturated hydrocarbons by the compression/expansion process of a piston engine is investigated. In particular, the potential of running this conversion in a multi-compression–expansion (MCE) mode where a gas sample is subject to multiple compression–expansion strokes, is assessed. The methane conversion and target species yields of this multi-compression mode relative to a single compression–expansion mode are assessed. Experimental studies with a rapid compression–expansion machine are used for this. The experiments are complemented by numerical simulations, which help to interpret the experimental findings. We found that both conversion and target species yields can be increased significantly by the multi-compression–expansion processes relative to a single compression–expansion. For instance, at typical engine operation conditions, ten compression–expansion cycles increase the methane conversion by a factor of three to four (from approx. 15 % to 68 %), the hydrogen yield by a factor of five, and the unsaturated hydrocarbon yields by a factor of three, compared to a single compression–expansion process. The results encourage considering a new role for piston-engines as work-to-chemical energy converters, in addition to their conventional heat-engine (chemical energy to work) operation.

Enhancement of Quantum Heat Engine by Encircling a Liouvillian Exceptional Point.

Quantum heat engines are expected to outperform the classical counterparts due to quantum coherences involved. Here we experimentally execute a single-ion quantum heat engine and demonstrate, for the first time, the dynamics and the enhanced performance of the heat engine originating from the Liouvillian exceptional points (LEPs). In addition to the topological effects related to LEPs, we focus on thermodynamic effects, which can be understood by the Landau-Zener-Stückelberg process under decoherence. We witness a positive net work from the quantum heat engine if the heat engine cycle dynamically encircles a LEP. Further investigation reveals that a larger net work is done when the system is operated closer to the LEP. We attribute the enhanced performance of the quantum heat engine to the Landau-Zener-Stückelberg process, enabled by the eigenenergy landscape in the vicinity of the LEP, and the exceptional point-induced topological transition. Therefore, our results open new possibilities toward LEP-enabled control of quantum heat engines and of thermodynamic processes in open quantum systems.

Collective effects on the performance and stability of quantum heat engines.

Recent predictions for quantum-mechanical enhancements in the operation of small heat engines have raised renewed interest in their study both from a fundamental perspective and in view of applications. One essential question is whether collective effects may help to carry enhancements over larger scales, when increasing the number of systems composing the working substance of the engine. Such enhancements may consider not only power and efficiency, that is, its performance, but, additionally, its constancy, that is, the stability of the engine with respect to unavoidable environmental fluctuations. We explore this issue by introducing a many-body quantum heat engine model composed by spin pairs working in continuous operation. We study how power, efficiency, and constancy scale with the number of spins composing the engine and introduce a well-defined macroscopic limit where analytical expressions are obtained. Our results predict power enhancements, in both finite-size and macroscopic cases, for a broad range of system parameters and temperatures, without compromising the engine efficiency, accompanied by coherence-enhanced constancy for finite sizes. We discuss these quantities in connection to thermodynamic uncertainty relations.

Non-Markovian thermal operations boosting the performance of quantum heat engines.

It is investigated whether non-Markovianity, i.e., the memory effects resulting from the coupling of the system to its environment, can be beneficial for the performance of quantum heat engines. Specifically, two physical models are considered. The first one is a well-known single-qubit Otto engine; the non-Markovian behavior is there implemented by replacing standard thermalization strokes with so-called extremal thermal operations which cannot be realized without the memory effects. The second one is a three-stroke engine in which the cycle consists of two extremal thermal operations and a single qubit rotation. It is shown that the non-Markovian Otto engine can generate more work-per-cycle for a given efficiency than its Markovian counterpart, whereas performance of both setups is superior to the three-stroke engine. Furthermore, both the non-Markovian Otto engine and the three-stroke engine can reduce the work fluctuations in comparison with the Markovian Otto engine, with their relative advantage depending on the performance target. This demonstrates the beneficial influence of non-Markovianity on both the average performance and the stability of operation of quantum heat engines.

Realization of a coupled-mode heat engine with cavity-mediated nanoresonators.

We report an experimental demonstration of a coupled-mode heat engine in a two-membrane-in-the-middle cavity optomechanical system. The normal mode of the cavity-mediated strongly coupled nanoresonators is used as the working medium, and an Otto cycle is realized by extracting work between two phononic thermal reservoirs. The heat engine performance is characterized in both normal mode and bare mode pictures, which reveals that the correlation of two membranes plays a substantial role during the thermodynamic cycle. Moreover, a straight-twin nanomechanical engine is implemented by engineering the normal modes and operating two cylinders out of phase. Our results demonstrate an essential class of heat engine in cavity optomechanical systems and provide an ideal platform platform for investigating heat engines of interacting subsystems in small scales with controllability and scalability.

Review on the Effect of the Phenomenon of Cavitation in Combustion Efficiency and the Role of Biofuels as a Solution against Cavitation

Concerning the problem of wanting the performance of heat engines used in the automotive, aeronautics, and aerospace industries, researchers and engineers are working on various possibilities for improving combustion efficiency, including the reduction of gases such as CO, NOx, and SOx. Such improvements would also help reduce greenhouse gases. For this, research and development has focused on one factor that has a significant impact on the performance of these engines: the phenomenon of cavitation. In fact, most high-performance heat engines are fitted with a high-speed fuel supply system. These high speeds lead to the formation of the phenomenon of cavitation generating instabilities in the flow and subsequently causing disturbances in the combustion process and in the efficiency of the engine. In this review article, it is a question of making a state-of-the-art review on the various studies which have dealt with the characterization of the phenomenon of cavitation and addressing the possible means that can be put in place to reduce its effects. The bibliographic study was carried out based on five editors who are very involved in this theme. From the census carried out, it has been shown that there are many works which deal with the means of optimization that must be implemented in order to fight against the phenomenon of cavitation. Among these solutions, there is the optimization of the geometry of the injector in which the fuel flows and there is the type of fuel used. Indeed, it is shown that the use of a biofuel, which, by its higher viscosity, decreases the effects of cavitation. Most of these jobs are performed under cold fluidic conditions; however, there is little or no work that directly addresses the effect of cavitation on the combustion process. Consequently, this review article highlights the importance of carrying out research work, with the objective of characterizing the effect of cavitation on the combustion process and the need to use a biofuel as an inhibitor solution on the cavitation phenomenon and as a means of energy transition.

RESEARCH OF THE PHYSICAL PROPERTIES OF DIESEL FUEL-HYDROGEN MIXTURES

The change in the viscosity of diesel fuel with dissolved hydrogen, the rate of dissolution of hydrogen in the diesel fuel, and the hydrogen diffusion coefficient in diesel fuel were experimentally determined. Dissolving hydrogen in liquid fuel changes its physical-chemical properties. It has been found that the viscosity and density of diesel fuel change little when it is saturated with hydrogen. The flashpoint in a closed crucible is reduced by 3–4 °C. The rate of dissolution of hydrogen in diesel fuel has been investigated. It has been found that the diffusion coefficient of hydrogen in diesel fuel depends significantly on the initial concentration of H2 in the fuel. The liquid fuel is advisable to supply with saturated hydrogen for the safety of the heat engine operation. The design of the hydrogen fuel saturation system with a special hydrogen sensor based on the MQ-8 sensor was proposed. The system of protection of the research stand from unauthorized emissions of hydrogen into the environment has been worked out. The protection ensures the shutdown of the stand equipment when the hydrogen concentration in the zone of its generation and supply to the fuel is at the level of 1%.

Thermodynamics of a continuous quantum heat engine: Interplay between population and coherence

We present a detailed thermodynamic analysis of a three-level quantum heat engine coupled continuously to hot and cold reservoirs. The system is driven by an oscillating external field and is described by the Markovian quantum master equation. We use the general form of the dissipator which is consistent with thermodynamics. We calculate the heat, power, and efficiency of the system for the heat-engine operating regime and also examine the thermodynamic uncertainty relation. The efficiency of the system is strongly dependent on the structure of the dissipator, and the correlations between different levels can be an obstacle for ideal operation. In quantum systems, the heat flux is decomposed into the population and coherent parts. The coherent part is specific to quantum systems, and in contrast to the population part, it cannot be expressed by a simple series expansion in the linear-response regime. We discuss how the interplay between the population and coherent parts affects the performance of the heat engine.

Broadband frequency filters with quantum dot chains

Two-terminal electronic transport systems with a rectangular transmission can violate standard thermodynamic uncertainty relations. This is possible beyond the linear response regime and for parameters that are not accessible with rate equations obeying detailed-balance. Looser bounds originating from fluctuation theorem symmetries alone remain respected. We demonstrate that optimal finite-sized quantum dot chains can implement rectangular transmission functions with high accuracy and discuss the resulting violations of standard thermodynamic uncertainty relations as well as heat engine performance.

Parametric study for optimal performance of Coulomb-coupled quantum dots

We study the optimal output power and efficiency of the three-terminal quantum heat engine with Coulomb-coupled quantum-dots (CCQD). It has been well known that in the weak coupling regime, two kinds of dominant transport mechanisms are sequential tunneling and cotunneling processes in CCQD. What process becomes dominant, which can be controlled by several parameters such as temperature difference, bias voltage, Coulomb interaction and tunneling parameters, is one of the key problems to determine the performance of the heat engine. We show the parametric dependence of the output power and coefficient and find the optimal performance of this CCQD heat engine through genetic algorithm.

Grid-Scale Ternary-Pumped Thermal Electricity Storage for Flexible Operation of Nuclear Power Generation under High Penetration of Renewable Energy Sources

In this work, the integration of a grid-scale ternary-Pumped Thermal Electricity Storage (t-PTES) with a nuclear power generation to enhance operation flexibility is assessed using physics-based models and digital real time simulation. A part of the electricity from the nuclear power generation is delivered to the grid, and the balance is used to power a heat pump that can be augmented by an auxiliary resistive load element to increase the charging rate of the thermal storage. This increases the thermal potential between hot and cold thermal stores (usually solid materials or molten salts inside large storage tanks). The thermal energy is transformed back into electricity by reversing the heat pump cycle. Different transient scenarios including startup, shutdown, and power change for grid-connected operation are simulated to determine the behavior of the hybrid nuclear-t-PTES system operating under variable loads that constitute a departure from conventional, baseload nuclear plant operation schemes. Ternary refers to the three modes operation: (i) heat pump (including heating coil), (ii) heat engine, and (iii) simultaneous operation of heat pump (including heating coil) and heat engine during changeover from pumping to generation or vice-versa. The controllability of t-PTES in the short timescales as a dynamic load is used to demonstrate operational flexibility of hybrid nuclear plants for flexible operation through advanced load management. The integration of t-PTES into nuclear power systems enhances the system flexibility and is an enabler for high penetration of renewable energy resources.

Two-level quantum Otto heat engine operating with unit efficiency far from the quasi-static regime under a squeezed reservoir

Recent theoretical and experimental studies in quantum heat engines show that, in the quasi-static regime, it is possible to have higher efficiency than the limit imposed by Carnot, provided that engineered reservoirs are used. The quasi-static regime, however, is a strong limitation to the operation of heat engines, since an infinitely long time is required to complete a cycle. In this paper we propose a two-level model as the working substance to perform a quantum Otto heat engine surrounded by a cold thermal reservoir and a squeezed hot thermal reservoir. Taking advantage of this model we show a striking achievement, that is to attain unity efficiency even at non-null power.

Revisiting the nature of dark sunspots: the sun as a heat engine

This work is a continuation of the author's studies,1,2,3 related to the elucidation of the physical nature of dark sunspots. They showed that the appearance of cold sunspots, the temperature of which is below the temperature of the photosphere, is incompatible with the second law of thermodynamics. Sunspots in the Sun's photosphere can only be hot. This article provides a thermodynamic analysis of the work of the Sun as a heat engine. It is shown that sunspots are dissipative structures that spontaneously appear in the photosphere of the Sun and ensure its viability as a source of optical radiation. Sunspots play the role of a cooler for the sun's global heat engine, and without them its radiant glow would be impossible, just like the operation of any heat engine without a cold heat sink. In addition, it is shown that all the phenomena of solar activity are caused by the operation of the photospheric heat engine of the Sun, in which sunspots are the source of heat.

Attaining Carnot efficiency with quantum and nanoscale heat engines

A heat engine operating in the one-shot finite-size regime, where systems composed of a small number of quantum particles interact with hot and cold baths and are restricted to one-shot measurements, delivers fluctuating work. Further, engines with lesser fluctuation produce a lesser amount of deterministic work. Hence, the heat-to-work conversion efficiency stays well below the Carnot efficiency. Here we overcome this limitation and attain Carnot efficiency in the one-shot finite-size regime, where the engines allow the working systems to simultaneously interact with two baths via the semi-local thermal operations and reversibly operate in a one-step cycle. These engines are superior to the ones considered earlier in work extraction efficiency, and, even, are capable of converting heat into work by exclusively utilizing inter-system correlations. We formulate a resource theory for quantum heat engines to prove the results.

Optimization of heat engines using different heat transfer laws by means of the method of saving functions

In 2000 Velasco et al [1] introduced a new optimization criterion for the CA-engine model in terms of a profitable type process in the operation of a power plant model. This approach is based on using the so-called saving function as a measure of possible reduction of undesired side effects in heat engine operation. Velasco et al [1] defined two saving functions; one associated with fuel consumption and another associated with thermal pollution, where each saving function takes into account three weight coefficients that measure the participation degree of the corresponding process in the optimization criterion. We made use of this criterion to analyse the Novikov’s power engine model [2] but by using different heat transfer laws: Newtonian and Dulong-Petit (DP) heat transfer laws [3]. We compare our results with those reported by Velasco et al [1]. Our results show a saving in fuel consumption of approximately 44% and a reduction in thermal pollution of 42% with respect to the operating regime of maximum power, a value that is in agreement with some reported in the literature.