Air-standard Cycle Research Articles

Performance analysis and multi-objective optimization of an irreversible isothermal heating modified air standard Brayton cycle

In this paper, a new five-branch Brayton cycle, i.e., isothermal heating modified air standard Brayton cycle, is proposed based on the isothermal heating modified steady flow Brayton cycle models established in previous literatures. The finite time thermodynamics theory is used to build the irreversible isothermal heating modified air standard Brayton cycle model. The impacts of the cycle maximum temperature ratio (τ), pre-expansion ratio (ρ) and various losses on the properties of power (P) versus compression ratio (γ), efficiency (η) versus γ, power density (Pd) versus γ, ecological function (E) versus γ, P versus η, Pd versus η and E versus η are examined. The multi-objective genetic algorithm is used to optimize different objective (η, E, P and Pd) combinations when γ is taken as the optimization variables. The deviation indexes (Ds) of the Shannon Entropy, TOPSIS and LINMAP are calculated to determine the optimal solution set. The findings demonstrate that raising ρ and τ, and lowering various losses can clearly improve cycle performance. For the optimization of P−E, the decision-making schemes of TOPSIS is better and corresponding D is 0.1342. The performance of the modified BC is better than that of the classical BC.

SPECIFIC NET WORK AND MEAN EFFECTIVE PRESSURE BASED THERMODYNAMIC ANALYSIS AND OPTIMIZATION OF IDEAL ATKINSON CYCLE

In this study, the criteria for maximum values of specific net work and mean effective pressure in the air standard Atkinson cycle, which is the ideal thermodynamic cycle of internal combustion engines used in hybrid electric vehicles, were examined. For this, it was assumed that the cycle operates in a certain temperature range. Thus, while the maximum temperature of the cycle is constant, the compression ratio was optimized for maximum specific net work and maximum mean effective pressure. A case study was conducted for this study. For the case study, assuming the geometric expansion ratio of 12, the maximum temperature value of the cycle was determined as 1961.923 K. Based on this maximum temperature value, the maximum values of the specific net work and the ambient effective pressure were determined as 580.139 kJ/kg and 373.857 kPa, respectively. In addition, the geometric compression ratios for the maximum values of the specific net work and the ambient effective pressure were determined as 15.462 and 31.063, respectively. Looking at the geometric compression ratio values of today's engines, it was seen that these values were closer to the compression ratio at which the maximum specific net work was achieved. It was observed that the thermal efficiency increased when the compression ratio was optimized for the conditions where the maximum average effective pressure was achieved. The results obtained from this study are particularly attractive to engine designers.

Design And Analysis Of Modified Four Stroke Four Revolution Engine

In today’s world, one of the important tasks is to handle the energy available and to minimize the heat losses. In automotive sector, engine is the primary energy source and there are many losses associated with an engine out of which engine cooling and exhaust losses takes major share. In four-stroke SI/CI engines, four strokes of reciprocating cylinder involve two rotations of the crankshaft. These strokes are suction, compression, power and exhaust respectively. A large amount of fuel energy is wasted when fuel is not compressed completely and also at the exhaust of internal combustion engines. This paper focusses on minimizing losses of internal combustion engine by secondary expansion of exhaust gases through 180 ° of crank revolution. For this purpose, four stroke four revolution mechanism is proposed and this is achieved by modifying current slider crank mechanism with double connecting rod arrangement. This modified engine shows an increase in the air standard cycle efficiency by 4.10% where as fuel air cycle efficiency rise is observed to be 5.25%. There is also significant rise observed in the modified engine over conventional engine in terms of gross indicated thermal efficiency and brake thermal efficiency as well.

Thermodynamic analysis of cogeneration system with diesel engines for offshore oil production facilities under variable loads

ABSTRACT Diesel engines are common power generation equipments used in offshore oil production facilities, and their waste heat can be recycled. But the working conditions of diesel engines usually vary with the fluctuated electricity loads due to the unstable crude oil production. In this paper, the off-design conditions were identified under the variable loads. Then, with the ideal air standard Brayton cycle for diesel engines, thermodynamic models of the system with/without heat recovery were developed to study the effects of the pressure ratio and temperature ratio on the thermal efficiency and exergy efficiency of diesel engines. The results show that for the irreversible Brayton system without heat recovery, the thermal efficiency and exergy efficiency increase with the increase of pressure ratio until reaching the peak value, then decrease with the increase of the pressure ratio under the constant temperature ratio. Under the condition of β = 0.25, 0.50, 0.75, 1.0, and 1.10, the highest value of ε efficiency is 0.2517, 0.3302, 0.3913, 0.4168, and 0.4391, respectively (when there is no residual heat recovery); And the highest value of ε efficiency is 0.4645, 0.5448, 0.6053, 0.6297, and 0.6507, respectively (when there is residual heat recovery). Our research can optimize the performance of the compressor pressure ratio and temperature ratio parameters of the thermal power plant under the condition of variable load of diesel engine, which has a high reference value for the transformation of waste heat recovery.

Thermodynamic analysis of the turbocharged marine two-stroke engine cycle with different scavenging air control technologies

Scavenging air control has been recognized as a practical approach to optimizing the marine two-stroke engine performance under off-design conditions. This paper aims at providing a comprehensive comparison of different tuning technologies from thermodynamic perspectives. A new theoretical model for the marine two-stroke diesel engine is first built with all assumptions of an air-standard cycle relaxed. Thermodynamic characteristics of the two-stroke engine cycle integrating the turbocharged scavenging process are then studied, followed by parametric studies of different scavenging air control methods. The results show that there exists an optimal exhaust valve closing timing to minimize the so-called “Miller loss” with the high-pressure tuning. Despite similar fuel saving potential of 2.5 g/kWh is observed at low to medium loads, the high-pressure tuning is superior to the exhaust gas bypass tuning because of a lower engine thermal load. The power turbine bypass appears to be the best solution when the engine frequently operates at loads higher than 60%, while the sequential turbocharging system shows better performance at engine loads lower than 50%. Thus, factors including the engine thermal and mechanical limitations, ship’s operational profile, cost and package should be considered for selecting the optimal scavenging tuning method in a practical case.

Evaluation of a Combustion-Based Mesoscale Thermal Actuator in Open and Closed Operating Cycles

A combustion-based mesoscale thermal actuator is proposed and its performance is studied in both open and closed cycle operations using a physics-based lumped-parameter model. The actuator design is unique as it implements a free-piston complaint architecture where the piston is free to move in a linear direction. Our objective is to study the actuator behavior in both the cycles to help identify the benefits and highlight the differences between the two cycles. The actuator is modeled as a spring-mass-damper system by taking an air standard cycle approach. Three observations are reported: (1) for nominal heat inputs (140 J/cycle), the actuator can produce large displacement strokes (16 cm) that is suitable for driving mesoscale robots; (2) the efficiency of the actuator depends on the heat input; and (3) for a specific heat input, both the open and closed cycles operate differently—with different stroke lengths, peak pressures, and thermal efficiencies. Our study reveals that the performance metrics of the actuator make it an ideal candidate for high speed, large force, and large displacement stroke related applications.

Internal combustion engines

Review of basic principles air-standard cycles and their analysis fuel-air cycles and their analysis actual cycles and their analysis fuels carburetion injection ignition combustion and combustion chambers engine friction and lubrication heat rejection and cooling measurements and testing performance parameters and characteristics two-stroke engines.

Effective temperature and performance characteristics of heat engines

For a heat engine working between two heat reservoirs, a hot reservoir at high temperature TH and a cold reservoir at low temperature TL, an effective temperature and an effective efficiency are introduced. The effective temperature is defined as the square root of the ratio between the net work output of the heat engine wnet and the SOT function (a new function introduced in this article). The SOT function is defined as the negative of the cyclic integral of the heat transfer change divided by the square of the temperature. The effective efficiency of the heat engine is defined (a novel definition) as one minus the ratio between the low temperature and the effective temperature. The effective temperature and the effective efficiency are worked out in details for the Carnot heat engine and the air standard cycles (Otto, Brayton, Stirling, and Ericsson). It was found for the considered cycles that the effective temperature is given by the expression () and the effective efficiency is given by the expression () for all the considered cycles. The importance of these two proposed measures is twofold: educational and they could be used as a quick tool by the designer.

Effective temperature and performance characteristics of heat engines

For a heat engine working between two heat reservoirs, a hot reservoir at high temperature T H and a cold reservoir at low temperature T L , an effective temperature and an effective efficiency are introduced. The effective temperature is defined as the square root of the ratio between the net work output of the heat engine w net and the SOT function (a new function introduced in this article). The SOT function is defined as the negative of the cyclic integral of the heat transfer change divided by the square of the temperature. The effective efficiency of the heat engine is defined (a novel definition) as one minus the ratio between the low temperature and the effective temperature. The effective temperature and the effective efficiency are worked out in details for the Carnot heat engine and the air standard cycles (Otto, Brayton, Stirling, and Ericsson). It was found for the considered cycles that the effective temperature is given by the expression () and the effective efficiency is given by the expression () for all the considered cycles. The importance of these two proposed measures is twofold: educational and they could be used as a quick tool by the designer.

Effect of Heat Transfer on the First and Second Law Efficiency Analysis and Optimization of an Air-standard Atkinson Cycle

In this paper, the first and second-law analysis for the thermodynamic air-standard Atkinson cycle with an account for heat transfer is performed using finite-time thermodynamics. In order to have more accurate evaluations, the effects of thermodynamic and design key parameters on the performance characteristics of Atkinson cycle are shown. Further, artificial neural network and imperialist competition algorithm are employed to predict and optimize the net work output value versus the minimum cycle temperature and also the compression ratio. The results obtained show that the heat loss is an effective factor of the performance of the cycle and it should be considered in the analysis and comparison of practical internal combustion engines.

Thermodynamic performance of Dual-Miller cycle (DMC) with polytropic processes based on power output, thermal efficiency and ecological function

This study reports a new model of an air standard Dual-Miller cycle (DMC) with two polytropic processes and heat transfer loss. The two reversible adiabatic processes which could not be realized in practice are replaced with two polytropic processes in order to more accurately reflect the practical working performance. The heat transfer loss is taken into account. The expressions of power output, thermal efficiency, entropy generation rate (EGR) and ecological function are addressed using finite-time thermodynamic theory. Through numerical calculations, the influences of compression ratio, cut-off ratio and polytropic exponent on the performance are thermodynamically analyzed. The model can be simplified to other cycle models under specific conditions, which means the results have an certain universality and may be helpful in the design of practical heat engines. It is shown that the entropy generation minimization does not always lead to the best system performance.

Thermodynamic Analysis and Comparison of Performances of Air Standard Atkinson, Otto, and Diesel Cycles with Heat Transfer Considerations

AbstractThis paper focuses on the overall performances of Otto, Atkinson, and Diesel air standard cycles. This study compares performance of these cycles with regard to parameters such as variable specific heat ratio, heat transfer loss, frictional loss, and internal irreversibility based on finite‐time thermodynamics. The relationship between thermal efficiency and compression ratio, and between power output and compression ratio of these cycles are obtained by numerical examples. In this study, it is assumed that during the combustion process, the heat transfer occurs only through the cylinder wall. The heat transfer is affected by the average temperature of both the cylinder wall and the working fluid. The results show that for each cycle, with the increase of the compression ratio in the specific mean piston speed, power output and thermal efficiency first increase and after reaching their maximum value, start to decrease. The results also indicate that maximum power output and maximum thermal efficiency of an Atkinson cycle could be higher than the values of these parameters in Diesel cycle and Otto cycle in the same operating conditions. The maximum power output and the maximum thermal efficiency of the Otto cycle have the lowest value among studied cycles. By increasing the mean piston speed, power output and thermal efficiency of Atkinson, Diesel, and Otto cycles start to decrease. The results of this study provide guidance for the performance analysis and show the improvement areas of practical Otto, Atkinson, and Diesel engines.

Thermal performance analysis of Brayton cycle with waste heat recovery boiler for diesel engines of offshore oil production facilities

This paper presents the theoretical analysis and on-site testing on the thermal performance of the waste heat recovery system for offshore oil production facilities, including the components of diesel engines, thermal boilers and waste heat boilers. We use the ideal air standard Brayton cycle to analyse the thermal performance. In comparison with the traditional design, the fans at the engine outlet of the waste heat recovery boiler is removed due to the limited space of the offshore platform. The cases with fan and without fan are compared in terms of thermal dynamics performance, energy efficiency and thermo-economic index of the system. The results show that the application of the WHRB increases the energy efficiency of the whole system, but increases the flow resistance in the duct. It is proved that as the waste heat recovery boiler takes the place of the thermal boiler, the energy efficiency of whole system without fan is slightly reduced but heat recovery efficiency is improved. This research provides an important guidance to improve the waste heat recovery for offshore oil production facilities.

Comparative analysis and evaluation of turbocharged Dual and Miller cycles under different operating conditions

In this paper, an accurate turbocharged Dual cycle model integrating the pumping process is proposed with all the assumptions of an air-standard cycle are relaxed. Effects of the turbine cross section, turbocharger efficiency, excess air coefficient, load and wastegate on the turbocharged Dual cycle are investigated based on a calibrated diesel engine model in Matlab software. The Miller cycle under different turbocharger matching conditions is compared with the original turbocharged Dual cycle. The results show that there exists an optimum excess air coefficient for the indicated efficiency of the turbocharged Dual cycle when considering the pumping process, and the optimum value increases with the increase of the turbocharger efficiency and the decrease of the engine load. With the wastegate, the amount of intake air can be restricted, and variations of the indicated efficiency depend on the turbocharger matching. The exclusive adoption of the Miller cycle can only increase the engine performance when the original matched turbine has a small cross section. The Miller cycle always needs a high efficiency turbocharger with a small size turbine and a more efficient charge air cooler to realize the low temperature cycle and guarantee the fuel economy at the same time.

First and Second-Law Efficiency Analysis and ANN Prediction of a Diesel Cycle with Internal Irreversibility, Variable Specific Heats, Heat Loss, and Friction Considerations

The variability of specific heats, internal irreversibility, heat and frictional losses are neglected in air-standard analysis for different internal combustion engine cycles. In this paper, the performance of an air-standard Diesel cycle with considerations of internal irreversibility described by using the compression and expansion efficiencies, variable specific heats, and losses due to heat transfer and friction is investigated by using finite-time thermodynamics. Artificial neural network (ANN) is proposed for predicting the thermal efficiency and power output values versus the minimum and the maximum temperatures of the cycle and also the compression ratio. Results show that the first-law efficiency and the output power reach their maximum at a critical compression ratio for specific fixed parameters. The first-law efficiency increases as the heat leakage decreases; however the heat leakage has no direct effect on the output power. The results also show that irreversibilities have depressing effects on the performance of the cycle. Finally, a comparison between the results of the thermodynamic analysis and the ANN prediction shows a maximum difference of 0.181% and 0.194% in estimating the thermal efficiency and the output power. The obtained results in this paper can be useful for evaluating and improving the performance of practical Diesel engines.

The Application of Entransy Dissipation Theory on the Performance Analysis of an Irreversible Atkinson Cycle

Several techniques on the Second Law of Thermodynamics have been used in the past for the analysis of Air standard Cycles. The terms used for these techniques include irreversibility analysis, entropy generation minimization, exergy analysis and thermodynamic efficiency. Entransy is a recently developed concept reflecting the heat transfer potential, rather than the ability to convert heat to work. This paper extends this concept to optimize thermodynamic processes of an irreversible Atkinson cycle. The entransy balance equation of thermodynamic processes is introduced, with which the concept of entransy dissipation is developed. For the irreversible Atkinson cycle where the working fluid is heated by the streams with prescribed inlet temperatures and specific capacity flow rates, it is found that the maximum entransy dissipation leads to the maximum output work, which is the maximum principle of entransy dissipation in thermodynamic processes. At the same time, it is found that minimum entropy generation alone could not describe change of the output work for the Atkinson cycle. The operation parameters are optimized for evaluating the maximum output work of Atkinson cycle by incorporating maximum entransy dissipation and minimum entropy generation when both, entransy dissipation and entropy generation, are induced by dumping the used streams into the environment is considered.

Power and Efficiency Analysis of Diesel Cycle Under Alternative Criteria

Model studies of the internal combustion engine cycles are useful for illustrating some important parameters affecting engine performance. The Diesel cycle is considered as a special case of an internal combustion engine. In the diesel cycle, combustion is controlled in order to obtain constant pressure at the beginning of the expansion stroke. It is important to choose the proper optimization criterion for the optimum design of the internal combustion engines. The choice of optimization criterion can be changed depending on the purpose of engine design and working conditions of the internal combustion engine. In this study, a comparative performance analysis is carried out for a reversible air standard Diesel cycle based on three alternative performance criteria, namely, maximum power (mp), maximum power density (mpd) and maximum efficient power (mep). The effects of the design parameters such as volume ratio and extreme temperature ratio of the cycle have been investigated under mp, mpd, mep and maximum efficiency conditions. The results show that the design parameters at mep conditions lead to more efficient engines than that at the mp conditions and that the mep criterion may have a significant power advantage compared to mpd criterion.

Performance Analysis and Comparison of Air Standard Diesel and Diesel-Atkinson Cycles

This study is concerned with the performance analysis and comparison of air standard Diesel and Diesel-Atkinson cycles with heat-transfer loss, friction like term loss and variable specific-heat ratio of the working fluid based on finite-time thermodynamics. Also numerical examples are detailed to show the relations between the output power and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the output power and the thermal efficiency of both cycles. Furthermore, the effects of variable specific-heat ratio of the working fluid, heat transfer and the friction-like term loss on the performance of both irreversible cycles are analyzed. Comparison of the performance of cycles shows that the heat efficiency and the output power of an air standard Diesel-Atkinson are higher than the Diesel ones and the points of maximum output power and thermal efficiency of Diesel-Atkinson cycle occur at the lower compression ratio. Reduction of Noxis another advantage of Diesel-Atkinson cycle. The results obtained in this paper provide guidance for the design of Diesel and Diesel-Atkinson engines.

Entransy analysis of open thermodynamic systems

The concept of entransy developed in recent years can describe the heat transport ability. This paper extends this concept to the open thermodynamic system and defines the concept of enthalpy entransy. The entransy balance equation of steady open thermodynamic systems, as well as the concept of entransy loss, is developed. The entransy balance equation is applied to analyzing and discussing the air standard cycle. It is found that the entransy loss rate can describe the change in net power output from the cycle but the entropy generation rate cannot when the heat absorbed by the working medium is from the combustion reaction of the gas fuel. When the working medium is heated by a high temperature stream, both the maximum entransy loss rate and the minimum entropy generation rate correspond to the maximum net power output from the cycle. Hence, the concept of entransy loss is an appropriate figure of merit that describes the cycle performance.

Theoretical and experimental investigation of Alfa type bio mass Stirling engine with effect of regenerator effectiveness, heat transfer, and properties of working fluid

A bio mass Stirling cycle engine system with all necessary components is designed for 1 kW power output. The designed engine is simulated for air standard cycle analysis for thermodynamic performance evaluation. The relationship of cycle efficiency and power output with temperature ratio, initial pressure, and regenerator effectiveness is established. The effect of engine heat transfer, regenerator effectiveness, and properties of the working fluid on cycle performance is studied with the help of cycle simulation, and the optimum values of the temperature ratio and regeneration effectiveness are obtained. The designed and simulated engine is constructed with all necessary components and tested for validation of simulation results. The engine cycle efficiencies attained in this simulation is from 54% to 38% for corresponding regeneration effectiveness from 1 to 0.6. The temperature ratio 0.25 has shown best engine thermal performance. The results of experimentation show close association with simulation results. The results obtained by the simulation will be useful in selection of temperature range and proper working fluid for Stirling engine and will provide helpful guideline to design Stirling engine components.