Yanlin Ge

Progress in Finite Time Thermodynamic Studies for Internal Combustion Engine Cycles

On the basis of introducing the origin and development of finite time thermodynamics (FTT), this paper reviews the progress in FTT optimization for internal combustion engine (ICE) cycles from the following four aspects: the studies on the optimum performances of air standard endoreversible (with only the irreversibility of heat resistance) and irreversible ICE cycles, including Otto, Diesel, Atkinson, Brayton, Dual, Miller, Porous Medium and Universal cycles with constant specific heats, variable specific heats, and variable specific ratio of the conventional and quantum working fluids (WFs); the studies on the optimum piston motion (OPM) trajectories of ICE cycles, including Otto and Diesel cycles with Newtonian and other heat transfer laws; the studies on the performance limits of ICE cycles with non-uniform WF with Newtonian and other heat transfer laws; as well as the studies on the performance simulation of ICE cycles. In the studies, the optimization objectives include work, power, power density, efficiency, entropy generation rate, ecological function, and so on. The further direction for the studies is explored.

Finite-time thermodynamic modeling and analysis for an irreversible Dual cycle

The performance of an air standard Dual cycle is analyzed by using finite-time thermodynamics. An irreversible Dual cycle model which is more close to practice is established. In the model, the nonlinear relation between the specific heats of working fluid and its temperature, the frictional loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies, and heat transfer loss are considered. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, and the optimal relation between power output and the efficiency of the Dual cycle are derived by detailed numerical examples. Moreover, the effects of internal irreversibility, heat transfer loss, frictional loss and pressure ratio on the cycle performance are analyzed. The power output versus compression ratio and efficiency versus compression ratio curves of the Diesel and Otto cycles are the maximum and minimum envelope lines of the performance of the Dual cycle, respectively. The results obtained herein may provide guidelines for the design of practical internal combustion engines.

The effects of variable specific heats of working fluid on the performance of an irreversible Otto cycle

The performance of an air-standard Otto cycle with variable specific heats of working fluid and heat resistance and friction irreversible losses is analysed by using finite-time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of variable specific heats of working fluid on the irreversible cycle performance are analysed. The results show that the effects of variable specific heats of working fluid on the cycle performance are obvious, and it should be considered in practice cycle analysis. The results obtained in this paper may provide guidance for the design of practice internal combustion engines.

Effects of heat transfer and variable specific heats of working fluid on performance of a Miller cycle

SYNOPSIS The performance of an air-standard Miller cycle with heat transfer loss and variable specific heats of working fluid is analysed by using finite-time thermodynamics. The relationships between the work output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relationship between work output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of heat transfer loss and variable specific heats of working fluid on the cycle performance are analysed. The results show that the effects of heat transfer loss and variable specific heats of working fluid on the cycle performance are obvious, and they should be considered in practice for cycle analysis. The results obtained herein may provide guidance for the design of practical internal combustion engines.

Finite-time thermodynamic modelling and analysis for an irreversible Miller cycle

The performance of an air-standard Miller cycle is analysed using finite-time thermodynamics. An irreversible Miller cycle model which is more close to practice is founded. In the model, the non-linear relation between the specific heats of working fluid and its temperature, the friction loss computed according to the mean velocity of the piston, the internal irreversibility described using the compression and expansion efficiencies, and heat transfer loss are considered. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, and the optimal relation between power output and the efficiency of the Miller cycle are derived by detailed numerical examples. Moreover, the effects of internal irreversibility, heat transfer loss, friction loss and pressure ratio on the cycle performance are analysed. The power output versus compression ratio and the efficiency versus compression ratio curves of Atkinson and Otto cycles will be maximum and minimum envelope lines of the Miller cycle, respectively. The results obtained herein may provide guidelines for the design of practical internal combustion engines.

Ecological performance analysis of an endoreversible modified Brayton cycle

An endoreversible closed modified simple Brayton cycle model with isothermal heat addition coupled to variable-temperature heat reservoirs is established using finite-time thermodynamics. Analytical expressions of dimensionless power output, thermal efficiency, dimensionless entropy generation rate and dimensionless ecological function are derived. Influences of cycle thermodynamic parameters on ecological performance and optimal compressor pressure ratio, optimal power output, optimal cycle thermal efficiency and optimal entropy generation rate corresponding to maximum ecological function are obtained and compared with those corresponding to maximum power output. The results show that cycle thermal efficiency improvement and entropy generation rate reduction are obtained at the expense of higher compressor pressure ratio and a little sacrifice of power output at maximum ecological function. The compromises between power output and entropy generation rate and between power output and cycle thermal efficiency, respectively, are achieved.

Exergy performance analyses of an irreversible two-stage intercooled regenerative reheated closed Brayton CHP plant

A combined heat and power (CHP) plant model composed of an irreversible constant- temperature heat reservoirs two-stage intercooled regenerative reheated closed Brayton cycle and a heat recovery device is proposed using finite time thermodynamics. By taking dimensionless exergy output rate and exergy efficiency as the objectives, the performance of the plant is investigated. The two cases with fixed and variable total pressure ratio are discussed. By means of detailed numerical calculations, the two intercooling pressure ratios, the two reheating pressure ratios and the total pressure ratio are optimised respectively, and the corresponding power to heat ratios are obtained. The effects of design parameters (such as compressors and turbines efficiencies, pressure drop losses, regeneration, intercooling and reheating degrees, etc.) on the exergy performances of the CHP plant are analysed. It is found that both dimensionless exergy output rate and exergy efficiency have double-maxima with respect to consumer-side temperature.

Performance of reciprocating Brayton cycle with heat transfer, friction and variable specific heats of working fluid

SYNOPSIS The performance of an irreversible air-standard reciprocating simple Brayton cycle with heat transfer loss, friction-like term loss and variable specific heats of working fluid is analysed by using finite-time thermodynamics. The relationships between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relationship between the power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of variable specific heats of the working fluid and the friction-like term loss on the irreversible cycle performance are analysed. The results show that the effects of variable specific heats of the working fluid and friction-like term loss on the irreversible cycle performance are obvious, and they should be considered in practical cycle analysis. The results obtained in this paper may provide guidelines for the design of practical reciprocating Brayton engines.

Performance of an endoreversible Diesel cycle with variable specific heats working fluid

SYNOPSIS The performance of an air-standard Diesel cycle with heat transfer loss and variable specific heats of working fluid is analysed by using finite-time thermodynamics. The relationships between work output and compression ratio, between thermal efficiency and compression ratio, as well as the optimal relationship between work output and efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of heat transfer loss and variable specific heats of working fluid on the cycle performance are analysed. The results show that the effects of heat transfer loss and variable specific heats of working fluid on the cycle performance are obvious and should be considered in practical cycle analysis. The results obtained in this paper may provide guidance for the design of practical internal combustion engines.

Fundamental optimal relation of a generalised irreversible quantum Carnot heat pump with harmonic oscillators

An irreversible quantum Carnot heat pump model working with many non-interacting harmonic oscillator systems is established in this paper. The quantum heat pump cycle is composed of two isothermal processes and two irreversible adiabatic processes. The irreversibilities of heat resistance, internal friction and bypass heat leakage are considered in the model. Based on the quantum master equation, semi-group approach and finite time thermodynamics (FTT), the cycle period, heating load and coefficient of performance (COP) of the quantum Carnot heat pump are derived, and detailed numerical examples are provided. At high temperature limit, the fundamental optimal relations between the heating load and COP of the quantum heat pump are deduced and analysed by using numerical examples. The effects of internal friction and bypass heat leakage on the optimal performance of the quantum heat pump are discussed in detail. The endoreversible, frictionless and without bypass heat leakage cases are discussed. The obtained results are general to the performance optimisation of quantum Carnot heat pumps and can provide some guidelines for optimal design of real quantum heat pumps.