Otto Cycle Research Articles

Dynamic simulation of fuel tank aging for LNG‐fueled ship apparatus in an X‐DF Otto cycle engine

AbstractThe increased density in a liquefied natural gas (LNG) tank caused by boil‐off gas (BOG) is a key factor to consider for LNG‐fueled ships with Otto cycle engines. This study conducted dynamic simulation using Aspen HYSYS to solve LNG aging in the fuel gas supply system (FGSS) of an extra‐long stroke dual fuel (X‐DF) engine. The aging phenomenon is severe in the Otto cycle internal combustion engine because heavy hydrocarbon (HHC) components must be removed during the process to satisfy the methane number (MN) requirement. HHC components such as ethane, propane, butane are separated in the HHC removal process so that HHC can be returned to the LNG storage or fuel tank without increased risk of equipment failure relative to steady‐state design conditions. Dynamic process simulations for four cases were conducted to verify the behavior of LNG aging for two fuel compositions and two fuel tank capacities. The results indicate that the different composition of LNG affects the pump duty, the duty of heat exchanger and BOG compressor in steady‐state simulation. Additionally, based on the analysis results, solutions to the problem caused by LNG aging for the FGSS in an X‐DF engine were provided.

MATHEMATICAL MODEL OF PETROL ENGINE WORKING ON ATKINSON CYCLE

The article discusses ways to improve the fuel efficiency of internal combustion engines. The main approaches to improving the fuel efficiency of automotive engines are considered. Improving the fuel economy of cars by regulating the degree of compression on the partial modes of the engine and controlling the load by changing the valve timing. Gasoline internal combustion engines operate in a narrow range of changes in the composition of the working mixture, therefore at partial loads it is necessary to reduce the mass of the working body to maintain the required composition of the mixture. This is ensured by throttling the air entering the cylinders, which leads to a significant deterioration in the indicator indicators of the internal combustion engine due to an increase in pumping losses. The solution to the problem is a transition from throttling the air to mass regulation of the charge by delaying the moment of closing the intake valve, that is, adjusting the engine load according to Atkinson's method. For the internal combustion engine with load control according to the Atkinson method, the task is to select a design scheme for the gas distribution mechanism and parameters of the working process. This is possible by developing certain calculation methods. The article proposes a general methodology and mathematical models of the elements and subsystems of the workflow of the internal combustion engine with Atkinson method load control, which allow making the choice of rational parameters of the engine design and workflow at the stages of its development, development and research. Empirical dependencies of engine operation parameters are obtained. The obtained empirical dependencies allow you to track the changes in the main parameters of the engine operating cycle. The mathematical model takes into account the kinematics of the engine, as well as options for controlling the load of the engine and the degree of compression according to the Atkinson method. According to the results of theoretical studies using the mathematical model of the engine workflow, the load characteristics of the engine with load regulation according to the Atkinson method and the engine operating in the Otto cycle are constructed. It is noted that the regulation of the load by the Atkinson method is advisable to use at low speed, and with increasing speed go to the use of other auxiliary elements of the engine design. For example, a mechanical supercharger.

Thermodynamic Uncertainty Relations from Exchange Fluctuation Theorems.

Thermodynamic uncertainty relations (TURs) place strict bounds on the fluctuations of thermodynamic quantities in terms of the associated entropy production. In this Letter, we identify the tightest (and saturable) matrix-valued TUR that can be derived from the exchange fluctuation theorems describing the statistics of heat and particle flow between multiple systems of arbitrary dimensions. Our result holds for both quantum and classical systems, undergoing general finite-time nonstationary processes. Moreover, it provides bounds not only for the variances, but also for the correlations between thermodynamic quantities. To demonstrate the relevance of TURs to the design of nanoscale machines, we consider the operation of a 2-qubit swap engine undergoing an Otto cycle and show how our results can be used to place strict bounds on the correlations between heat and work.

An assessment of fuel consumption and emissions from a diesel power generator converted to operate with ethanol

This work presents an analysis of a diesel power generator converted to operate in Otto cycle using ethanol as fuel. This conversion was done without changing the compression ratio of 17:1, with the build-up of adequate control for intake air mass flow rate, fuel injection, and ignition timing when operating with ethanol. The new conversion approach allows for simplicity of reversion to the original configuration. In Diesel cycle, the engine was fuelled with diesel oil containing 7% biodiesel injected directly into the combustion chamber. The in-cylinder pressure, emissions of carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOX), unburned hydrocarbons (THC), as well as fuel conversion efficiency, when operating with pure hydrous ethanol, were evaluated. The results showed no significant changes on THC emissions in Otto cycle configuration, in comparison with engine operation in Diesel cycle configuration. The emissions of CO2, CO, and NOX were increased when operating in Otto cycle with ethanol.

Optical simulation of a quantum thermal machine

We introduce both a theoretical and an experimental scheme for simulating a quantum thermal engine through an all-optical approach, with the behavior of the working substance and the thermal reservoirs implemented via internal degrees of freedom of a single photon. By using the polarization and propagation path, we encode two quantum bits and then implement the thermodynamical steps of an Otto cycle. To illustrate the feasibility of our proposal, we experimentally realize such simulation through an intense laser beam, evaluating heat and work at each individual step of the thermodynamical cycle. In addition, from the analysis of the entropy production during the entire cycle, we can study the amount of quantum friction produced in the Otto cycle as a function of the difference of temperature between hot and cold reservoirs. Our paper constitutes, therefore, an all-optical-based thermal machine simulation and opens perspectives for other optical simulations in quantum thermodynamics.

Quantum heat machines enabled by the electronic effective mass

In this letter, we analyze a conceptual design for the operation of an Otto cycle heat machine driven by adiabatic modifications on the electronic effective mass. Such tailoring of it can be implemented, for instance, via the application of external electron fields in some materials, as in Gallium Nitride (GaN). We show that due both the energy quantization on this structure and the adiabatic transformation of the effective mass, the machine performance can be improved. The realization of classically inconceivable Otto machines, with an incompressible working substance, can be realized as well. Our finds hold in cases where the electronic effective mass, in the low temperature regime, remains constant during the isochoric strokes.

Giant elastocaloric effect with wide temperature window in an Al-doped nanocrystalline Ti–Ni–Cu shape memory alloy

Ti–Ni based shape memory alloys are promising elastocaloric materials for solid-state refrigeration. In this paper, we made a comprehensive study on elastocaloric effect of a nanocrystalline Ti–44Ni–5Cu–1Al (at%) alloy exhibiting successive B2–B19–B19′ transformation. The maximum adiabatic temperature decrease by stress removal from 600 MPa is ΔTadi∼25 K with a small temperature distribution of ∼0.5 K. The value of ΔTadi is consistent with that calculated from strain-temperature relation. The effective working temperature window is ∼55 K, resulting in a high refrigeration capacity of RC = 4.2 kJ/kg. Material coefficient of performance reaches COP ∼9.6 when an Otto cycle is considered. The middle eigenvalue of the transformation matrix is λ2 ∼ 0.99, implying high lattice compatibility between the parent and martensite phases. These properties are related to the diffuse nature of successive B2–B19–B19’ martensitic transformation of this alloy.

Improving the constant‐volume degree of combustion considering generatable range at low speed in a free‐piston engine linear generator system

Series hybrid vehicles using free‐piston engine coupled with linear generator are expected for high‐efficiency energy conversion systems. Such engines do not have a crank mechanism, which greatly reduces the friction loss. In addition, the piston action can be controlled freely by the generation braking thrust by using an inverter control. In a conventional crank engine, past research has shown that delaying the piston motion after the combustion increases the maximum combustion pressure, and this delay brings a constant‐volume degree close to the Otto cycle. In the free‐piston system, a high braking thrust is needed at a low piston speed immediately after combustion. However, the highest braking thrust was limited in the low‐speed range because the back electromotive force of a permanent magnet synchronous generator was too small. This article shows the range that can be theoretically attained for a low‐speed generator. The delaying piston movement with only the braking thrust improved the effective work by 25% near the top dead center. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Finite-power performance of quantum heat engines in linear response.

We investigate the finite-power performance of quantum heat engines working in the linear response regime where the temperature gradient is small. The engine cycles with working substances of ideal harmonic systems consist of two heat transfer and two adiabatic processes, such as the Carnot cycle, Otto cycle, and Brayton cycle. By analyzing the optimal protocol under maximum power we derive the explicitly analytic expression for the irreversible entropy production, which becomes the low dissipation form in the long duration limit. Assuming the engine to be endoreversible, we derive the universal expression for the efficiency at maximum power, which agrees well with that obtained from the phenomenological heat transfer laws holding in the classical thermodynamics. Through appropriate identification of the thermodynamic fluxes and forces that a linear relation connects, we find that the quantum engines under consideration are tightly coupled, and the universality of efficiency at maximum power is confirmed at the linear order in the temperature gradient.

Coupled quantum Otto heat engine and refrigerator with inner friction

We investigate two coupled spins 1/2 in a magnetic field as the working substance of the quantum Otto cycle. In the quantum adiabatic strokes, finite-time parametric transformations are employed either in the coupling strength or in the magnetic field. The operation regimes, where the mode of the cycle is a refrigerator or a heat engine, are explored. The role of the total allocated time to the quantum adiabatic stages on the performance of the quantum Otto refrigerator and the heat engine is investigated in detail. The finite-time adiabatic transformations are found to increase the Shannon entropy which is quantum in origin. The effect known as the inner friction is found to negatively effect the performances of the quantum heat engine and the refrigerator. The strong frictional losses are also found to induce inactive operation regimes where the mode of the cycle is neither a refrigerator nor a heat engine.

Quantized refrigerator for an atomic cloud

We propose to implement a quantized thermal machine based on a mixture of two atomic species. One atomic species implements the working medium and the other implements two (cold and hot) baths. We show that such a setup can be employed for the refrigeration of a large bosonic cloud starting above and ending below the condensation threshold. We analyze its operation in a regime conforming to the quantized Otto cycle and discuss the prospects for continuous-cycle operation, addressing the experimental as well as theoretical limitations. Beyond its applicative significance, this setup has a potential for the study of fundamental questions of quantum thermodynamics.

Inverse Problem of Selection of the Theoretical Cycle for the Real Cycle of Internal Combustion Engine

Abstract The effectiveness of work of an internal combustion engine can be assessed by means of the energy efficiency: theoretical, internal and effective... In the problem regarding the efficiency of obtaining a work from the tested SI engine, the theoretical Seiliger-Sabathe cycle was adopted as a reference model for the real engine cycle. For comparison, the OTTO cycle was also analysed. The engine indicating allows direct determination only of internal work. However, determining the work of the theoretical cycle first requires solving the problem of selecting the parameters of the theoretical cycle, according to the real cycle of the engine (inverse problem). In order uniquely to determine the course of the theoretical Seiliger-Sabathe cycle, it is necessary to determine the parameters of the starting point and the heat distribution number. The selection of the theoretical cycle for the real cycle, within the scope of determining the number of heat distribution, is to some extent of a contractual nature. Therefore, the problem of determining the number of heat distribution was solved by two own original methods. A comparison of the real cycle with the theoretical cycle determined for it is presented.

6-Stroke Engine: Thermodynamic Modelling and Design for Testing

Abstract In the study AVL BOOST™ is used to perform a thermodynamic simulation of a six-stroke engine, being built by a research team based in Saudi Arabia. The six-stroke cycle consists of a standard four-stroke Otto Cycle followed by a heat recovering steam expansion cycle. Water is injected into the hot combustion chamber towards the end of the Otto expansion stroke producing steam, which is used to perform work on a piston. This process produces power using waste heat and therefore increases the overall efficiency of the engine. The Robin EY28D engine, which is a single cylinder, four-stroke, gasoline engine was used for this simulation study. The engine was modelled and converted into six-stroke engine in AVL BOOST. The results show that six-stroke engine is more efficient than four-stroke engine. In six-stroke engine, the engine power is increased by 33.1% and brake specific fuel consumption (BSFC) is decreased by approximately 16%. Where emissions are concerned, Nitrogen Oxide (NOx) emission from six-stroke engine is reduced by 80%, while the Hydrocarbon (HC) emission increases by 85% compared with the original 4-stroke. Moreover, the most efficient camshaft was found and designed according to the most efficient valve profile for this engine, which is combination of 60CA° of valve duration and 10 mm of valve lifting.

Thermodynamic analysis of endoreversible six-stroke Otto cycle with respect to equivalence ratio, residual gas fraction and mean piston speed

The analysis of the six-stroke Otto cycle was performed using the finite-time thermodynamics dependence on mean piston speed, equivalence ratio and residual gas fraction. In the analysis, friction loss, internal irreversibilities, heat transfer losses were taken into account by empirical correlations. Relations between power output, thermal efficiency, and compression ratio were obtained by detailed numerical examples. The results were presented as comparative for four- and six-stroke Otto cycle. It was assumed that the cycles operate with the same mixture flow per second so that both performances of cycles can be compared. The study showed that more fuel flow can be supplied to the six-stroke Otto cycle for the same mixture flow. However, there was a slight increase in the maximum cycle temperature. For this reason, the results are crucial in providing a good guideline for evaluating and improving the performance of real six-stroke Otto engines.

Magnetic Otto Engine for an Electron in a Quantum Dot: Classical and Quantum Approach.

We studied the performance of classical and quantum magnetic Otto cycle with a working substance composed of a single quantum dot using the Fock–Darwin model with the inclusion of the Zeeman interaction. Modulating an external/perpendicular magnetic field, in the classical approach, we found an oscillating behavior in the total work extracted that was not present in the quantum formulation.We found that, in the classical approach, the engine yielded a greater performance in terms of total work extracted and efficiency than when compared with the quantum approach. This is because, in the classical case, the working substance can be in thermal equilibrium at each point of the cycle, which maximizes the energy extracted in the adiabatic strokes.

Non-Markov enhancement of maximum power for quantum thermal machines

In this work we study how the non-Markovian character of the dynamics can affect the thermodynamic performance of a quantum thermal engine, by analysing the maximum power output of Carnot and Otto cycles departing from the quasi-static and infinite-time-thermalization regime respectively, introducing techniques for their control optimization in general dynamical models. In our model, non-Markovianity is introduced by allowing some degrees of freedom of the reservoirs to be taken into account explicitly and share correlations with the engine by Hamiltonian coupling. It is found that the non-Markovian effects can fasten the control and improve the power output.

Effects of water injection to the fuel and air mixture on equilibrium gas composition in combustion products and selected parameters of the theoretical Otto cycle

Moisturizing the intake air by spraying water in the liquid phase significantly lowers the intake air temperature, mainly due to the high value of latent heat of evaporation. The paper presents a methodology for calculating the parameters of the air-fuel mixture after water injection and during subsequent processes of the Otto cycle: compression, combustion and expansion of exhaust gases. For octane as a fuel, exemplary calculations have been carried out to investigate the effect of water injection on the composition of combustion products and selected parameters of the theoretical Otto cycle (temperature, pressure, output power and thermal efficiency).

The efficiency of quantum engines using the Pöschl – Teller like oscillator model

In this work, the quantum-mechanical properties of the strongly non-linear quantum oscillator described by the Pöschl-Teller [PT] model is examined. This model has a relation with two well-known models, the free particle [FP] in a box and the harmonic oscillator [HO], as described in our previous works [1–3]. Using the [PT] model, a quantum-mechanical analogue of the Joule-Brayton [JB] cycle and Otto cycle have been constructed through changes of both, the width of the well and its the quantum state. The efficiency of quantum engines based on the Pöschl-Teller-like potential is derived, which is analogous to classical thermodynamic engines.

Spin quantum heat engines with shortcuts to adiabaticity.

We consider a finite-time quantum Otto cycle with single- and two spin-1/2 systems as its working medium. To mimic adiabatic dynamics at a finite time, we employ a shortcut-to-adiabaticity technique and evaluate the performance of the engine including the cost of the shortcut. We compare our results with the true adiabatic and nonadiabatic performances of the same cycle. Our findings indicate that the use of the shortcut-to-adiabaticity scheme significantly enhances the performance of the quantum Otto engine as compared to its adiabatic and nonadiabatic counterparts for different figures of merit.

Cooperative efficiency boost for quantum heat engines

The power and efficiency of many-body heat engines can be boosted by performing cooperative non-adiabatic operations in contrast to the commonly used adiabatic implementations. Here, the key property relies on the fact that non-adiabaticity is required in order to allow for cooperative effects, that can use the thermodynamic resources only present in the collective non-passive state of a many-body system. In particular, we consider the efficiency of an Otto cycle, which increases with the number of copies used and reaches a many-body bound, which we discuss analytically.