Atkinson Cycle Research Articles

Variable valve timing complementing Hybrid-EGR at diesel engines

To understand the benefits of the Atkinson cycle added to a two-stage boosting system including Hybrid-EGR, engine simulations were carried out by BorgWarner. The possible valve curves were determined by a real variable valve timing device consisting of two concentric camshafts with an integrated cam phaser. The results promise a higher degree of freedom in tradeoffs between fuel economy, NOx emission and Particulate Matters (PM).

The Quest for Thermodynamic Efficiency: Atkinson Cycle Machines Versus Otto Cycle Machines

Abstract The vigorous way in which Nicholas Otto defended his four-stroke cycle patents of 1876/77 in the courts of England, France and Germany acted as a stimulus for the development of ingenious designs to both circumvent, and improve upon, the Otto Cycle. This paper describes various engines built to operate on the Atkinson Cycle, a sound theoretical idea, first put forward in the 1880s, which offers an improved thermal efficiency over that of the Otto cycle. In this paper, the term 'Atkinson Cycle' relates to an engine, operating on an Ideal Constant Volume Thermodynamic Cycle, which has been modified to have an expansion ratio that exceeds the compression ratio.

Where Is the Early Market for PHEVs?

The relative fuel consumption reduction strengths of multiple passenger car powertrains are investigated. These include [A] conventional compression ignition (CI) direct injection (DI) turbocharged (TC) diesel (D) [CI-DI-TC-D]; [B] Atkinson cycle charge sustaining (CS) “split-hybrid” electric vehicles (HEV) fueled by gasoline/petrol (G) [HEVG]; plug-in (P) hybrid gasoline/petrol [PHEVG)]; and indirect fuel injected (IDI) spark-ignited (SI) internal combustion engines (ICE) fueled by gasoline/petrol [SI-IDI-NA-G]. When we use simulation to evaluate the behavior of PHEVG powertrains, the size is a four-to-five passenger car platform that would be regarded as “compact” in the U.S. and standard in Europe. A careful distinction between probable driving patterns for PHEVGs when in charge-depletion (CD) mode vs. charge sustaining (CS) operation is made. Effects of variation in the amount of kWh storage and the CD strategy, between PHEVs with varying km of electric-equivalent range are also investigated. The effect of electric drive (battery and motor) power (kW) on ability of a vehicle to operate all-electrically, relative to its ability to reduce oil use, is examined. Four degrees of hybridization are briefly examined, including stop-start (SS), integrated starter-generator (ISG), mild parallel (MP), and full parallel (FP). Each of the parallel PHEVs examined is an FP. Powertrain model simulations and limited dynamometer test results for such PHEVGs are compared to the other vehicle types for certification and “on-road” driving cycles from Europe and the U.S. It is illustrated that the conventional wisdom that HEVG has significant superiority over CG primarily in urban stop and go driving should not automatically be extended to PHEVGs. The driving cycle information is related to systematically varying consumer patterns of dwelling choice and vehicle use in cities, suburbs, and rural areas, as well as across nations. Effects of fuel taxation choices by nation — for gasoline, diesel and electric fuel — are investigated. The effects that residential location and type, driving cycle, and fuel cost have on the relative marketability of the studied powertrains, when initially entering the market, are summarized. The sequence of events leading to early emergence of original equipment automaker production and marketing of PHEVGs is discussed.

흡.배기를 고려한 고팽창 저속 디젤 기관의 이론 해석과 기관 성능에 대한 연구

One of the methods to increase the efficiency of an engine is to expand pressures obtained from combustions equal to the pressure of atmosphere as much as possible and then convert thermal energy into mechanical energy also as much as possible. In this research, the Diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting Diesel engines to the Atkinson cycle, and general cycle features were analyzed after comparing these two cycles. In the case of fuel air the Diesel-Atkinson cycle considering intake and exhaust similar to real cycles, the value of thermal efficiency and average effective pressure increased, though their values were smaller than those of standard air amount cycle, when expansion compression ratio increased. When normal Diesel engines of which compression stroke and expansion stroke are all the same, was converted to the Atkinson cycle by changing the time of intake value close, combustion pressure reduced due to reduced expansion compression ratio and intake air amount due to decreased effective cycle volume.

Potential of Atkinson cycle combined with EGR for pollutant control in a HD diesel engine

An experimental investigation has been performed on the potential of the Atkinson cycle and reducing intake oxygen concentration for pollutant control in a heavy-duty diesel engine. In this study the Atkinson cycle has been reproduced advancing the intake valve closing angle towards the intake stroke. In addition, the intake oxygen concentration has been reduced introducing exhaust gas recirculation. This research has been carried out at low engine load (25%), where the Atkinson cycle is known to improve the efficiency of the spark-ignition engines. The main interest of this investigation has been the comparison between the Atkinson cycle and the conventional diesel cycle at the same oxygen concentration in the intake gas. This analysis has been focused on in-cylinder gas thermodynamic conditions, combustion process, exhaust emissions and engine efficiency. In compression ignition engines, the Atkinson cycle basically promotes the premixed combustion, but in the range of these tests, a complete premixed combustion was not attained. Regarding exhaust emissions, the Atkinson cycle reduces notably the nitrous oxides but increases soot emissions. Finally, better global results have been found reducing intake oxygen concentration by the recirculation of exhaust gas than by the operation of an Atkinson cycle.

The Hybrid Automobile and the Atkinson Cycle

The hybrid automobile is a strikingly new automobile technology with a number of new technological features that dramatically improve energy efficiency. This paper will briefly describe how hybrid automobiles work; what are these new technological features; why the Toyota Prius hybrid internal combustion engine operates on the Atkinson cycle instead of the Otto cycle; and what are the advantages and disadvantages of the hybrid automobile. This is a follow-up to my two previous papers on the physics of automobile engines.1,2

Unified thermodynamic description and optimization for a class of irreversible reciprocating heat engine cycles

A unified description of a class of generalized irreversible reciprocating heat engine cycles is given in this paper. The model cycle consisting of two heating branches, two cooling branches, and two adiabatic branches with heat transfer, friction, and variable specific heats of working fluid is established. The thermodynamic performance of the universal cycle is analysed and optimized 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 the working fluid and cycle process on cycle performance are analysed and the major differences of cycle performance are compared when the specific heats of the working fluid are constant and variable respectively. The results obtained herein include the performance characteristics of endoreversible and irreversible reciprocating Diesel, Otto, Atkinson, Brayton, Braysson, Carnot, dual, and Miller cycles with constant and variable specific heats of the working fluid. They can provide some new guidelines for the design practice of real internal combustion engines.

A search for maximum efficiency and NOx reduction through spark-ignition engine design optimization at λ=1

In this study a multizone model of spark-ignition engine combustion is validated and used to predict the thermal efficiency and NO x emissions of the engine. The model is validated against an engine map obtained from an extensive series of experiments. An optimizing algorithm based on particle swarm concepts is applied to the model to find a trade-off between efficiency and NO x emissions using a predefined cost function. Optimization is performed for three cases, each of which progressively includes more variables for optimization. A further constrained optimization case is performed with constant values of several of the variables set at the average values found in the three prior cases. These variables are the ones that change over a small domain. The results show the potential improvement in efficiency while achieving remarkably low NO x emissions. They emphasize the importance of exhaust gas recirculation (EGR) at high compression ratio and high loads when the maximum in-cylinder pressures are very high. They also suggest some strategies for valve timings that use internal EGR (residual gas) and move towards different compression and expansion ratios (Atkinson cycle).

Influence of heat loss on the performance of an air-standard Atkinson cycle

This study is aimed at investigating the effects of heat loss, as characterized by a percentage of fuel’s energy, friction and variable specific heats of the working fluid, on the performance of an air-standard Atkinson cycle under the restriction of the maximum cycle-temperature. A more realistic and precise relationship between the fuel’s chemical-energy and the heat leakage is derived through the resulting temperature. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the cycle are presented. The results show that the power output as well as the efficiency, for which the maximum power-output occurs, will rise with the increase of maximum cycle-temperature. The temperature-dependent specific heats of the working fluid have a significant influence on the performance. The power output and the working range of the cycle increase while the efficiency decreases with the rise of specific heats of working fluid. The friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the Atkinson cycle decrease with increasing friction loss. It is noteworthy that the results obtained in the present study are of significance for providing guidance with respect to the performance evaluation and improvement of practical Atkinson-cycle engines.

Performance of endoreversible Atkinson cycle

AbstractThe performance of an air standard Atkinson 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 and between the thermal efficiency and the compression ratio, as well as the optimal relationship between the work output and the efficiency of the cycle, are derived from 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 these effects are obvious and they should be considered in practice cycle analysis. The results obtained in the present paper may provide guidance for the design of practical internal combustion engines.

Comparison of performances of air standard Atkinson and Otto cycles with heat transfer considerations

In this paper, the effects of heat transfer on the net output work and the indicated thermal efficiency of an air standard Atkinson cycle are analyzed. Comparisons of the performances of air standard Atkinson and Otto cycles with heat transfer considerations are also discussed. We assume that the compression and power processes are adiabatic and reversible and that any convective, conductive or radiative heat transfer to the cylinder wall during the heat rejection process may be ignored. The heat loss through the cylinder wall is assumed to occur only during combustion and is further assumed to be proportional to the average temperature of both the working fluid and cylinder wall. It is found that the net output work versus efficiency characteristics, the maximum net work output and the corresponding efficiency bound are significantly influenced by the magnitude of the heat transfer. An increase in heat transfer to the combustion chamber walls decreases the peak temperature and pressure and, consequently, reduces the work per cycle and efficiency. The effects of other parameters, in conjunction with heat transfer, including combustion constants, compression ratio and intake air temperature are also reported. An Atkinson cycle has a greater work output and a higher thermal efficiency than the Otto cycle at the same operating condition. The compression ratios that maximize the work of the Otto cycle are always found to be higher than those for the Atkinson cycle at the same operating conditions. The results are of importance to provide good guidance for performance evaluation and improvement of practical Atkinson engines.

Power, efficiency, entropy-generation rate and ecological optimization for a class of generalized irreversible universal heat-engine cycles

The optimal performance for a class of generalized irreversible universal steady-flow heat-engine cycle models, consisting of two heating branches, two cooling branches and two adiabatic branches, and with losses due to heat-resistance, heat leaks and internal irreversibility was analyzed using finite-time thermodynamics. The analytical formulae for power, efficiency, entropy-generation rate and an ecological criterion of the irreversible heat-engine cycle are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of the cycle process on the performance of the cycles. The results obtained include the performance characteristics of Diesel, Otto, Brayton, Atkinson, Dual and Miller cycles with the losses of heat-resistance, heat leak and internal irreversibility.

Performance of an Atkinson cycle with heat transfer, friction and variable specific-heats of the working fluid

The performance of an air standard Atkinson cycle with heat-transfer loss, friction-like term loss and variable specific-heats of the working fluid is analyzed 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 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 analyzed. The results show that the effects of variable specific-heats of working fluid and friction-like term loss on the irreversible cycle performance should be considered in cycle analysis. The results obtained in this paper provide guidance for the design of Atkinson engines.

Maximum profit performance for a class of universal endoreversible steady flow heat engine cycles

SYNOPSIS The operation of a universal steady flow endoreversible heat engine cycle mode consisting of a constant thermal-capacity heating branch, a constant thermal-capacity cooling branch and two adiabatic branches is viewed as a production process with exergy as its output. The finite time exergoeconomic performance optimisation of the engine is investigated by taking profit optimisation criterion as the objective. The relationships between profit rate and temperature ratio of the working fluid, between thermal efficiency and temperature ratio of the working fluid, as well as the optimal relationship between profit rate and efficiency of the cycle are derived. The focus of this paper is to investigate the compromised optimisation between economics (profit) and the utilisation factor (efficiency) for endoreversible cycles. Moreover, analysis and optimisation of the model are carried out in order to investigate the effect of cycle process on the performance of the cycles, using numerical examples. The results obtained herein include the performance characteristics of Diesel, Otto, Atkinson, and Brayton cycles.

Universal ecological performance for endo-reversible heat engine cycles

SYNOPSIS The optimal ecological performance of a universal endoreversible steady flow heat engine cycle consisting of a constant thermal-capacity heating branch, a constant thermal-capacity cooling branch and two adiabatic branches with heat transfer loss is derived by taking an ecological optimisation criterion as the objective, which consists of maximising a function representing the best compromise between the power output and exergy loss rate of the heat engine. Some special examples are discussed. A numerical example is given to show the effects of heat reservoir temperature ratio on the ecological criterion versus the efficiency characteristic of the cycle. The results include the performance characteristics of endoreversible steady flow Diesel, Otto, Atkinson and Brayton cycles. The results can provide some theoretical guidance for the design of practical engines.

05/02523 Performance analysis and comparison of an atkinson cycle coupled to variable temperature heat reservoirs under maximum power and maximum power density conditions

05/02523 Performance analysis and comparison of an atkinson cycle coupled to variable temperature heat reservoirs under maximum power and maximum power density conditions

Comparison of basic gas cycles under the restriction of constant heat addition

Theoretical thermal efficiencies and theoretical effectivenesses of six kinds of basic gas cycles, including the Carnot, Otto, Diesel, Takemura, Atkinson and Joule cycles, were compared with one another under the restriction of constant heat-addition. Relations between the available work content of heat added and the exergy change in several thermodynamic processes were also examined. It is concluded that the Atkinson cycle has the highest thermal efficiency and the second best effectiveness among the gas cycles examined. The exergy changes in an isochoric heating-process in closed systems and in an isobaric heating-process in open systems agree with the available work contents of heat added in these processes. Thus, the exergy increment in a heating process should not be generally adopted as the denominator for the theoretical effectiveness.

Influence of quantum degeneracy and regeneration on the performance of Bose-Stirling refrigeration-cycles operated in different temperature regions

The Stirling refrigeration cycle using an ideal Bose-gas as the working substance is called the Bose-Stirling refrigeration cycle, which is different from other thermodynamic cycles such as the Carnot cycle, Ericsson cycle, Brayton cycle, Otto cycle, Diesel cycle and Atkinson cycle working with an ideal Bose gas and may be operated across the critical temperature of Bose–Einstein condensation of the Bose system. The performance of the cycle is investigated, based on the equation of state of an ideal Bose gas. The inherent regenerative losses of the cycle are considered and the coefficient of performance and the amount of refrigeration of the cycle are calculated. The results obtained here are compared with those derived from the classical Stirling refrigeration cycle, using an ideal gas as the working substance. The influence of quantum degeneracy and inherent regenerative losses on the performance of the Bose Stirling refrigeration cycle operated in different temperature regions is discussed in detail, and consequently, general performance characteristics of the cycle are revealed.

Performance analysis and comparison of an Atkinson cycle coupled to variable temperature heat reservoirs under maximum power and maximum power density conditions

In this paper, performance analysis and comparison based on the maximum power and maximum power density conditions have been conducted for an Atkinson cycle coupled to variable temperature heat reservoirs. The Atkinson cycle is internally reversible but externally irreversible, since there is external irreversibility of heat transfer during the processes of constant volume heat addition and constant pressure heat rejection. This study is based purely on classical thermodynamic analysis methodology. It should be especially emphasized that all the results and conclusions are based on classical thermodynamics. The power density, defined as the ratio of power output to maximum specific volume in the cycle, is taken as the optimization objective because it considers the effects of engine size as related to investment cost. The results show that an engine design based on maximum power density with constant effectiveness of the hot and cold side heat exchangers or constant inlet temperature ratio of the heat reservoirs will have smaller size but higher efficiency, compression ratio, expansion ratio and maximum temperature than one based on maximum power. From the view points of engine size and thermal efficiency, an engine design based on maximum power density is better than one based on maximum power conditions. However, due to the higher compression ratio and maximum temperature in the cycle, an engine design based on maximum power density conditions requires tougher materials for engine construction than one based on maximum power conditions.

Reciprocating heat-engine cycles

The performance of a generalized irreversible reciprocating heat-engine cycle model consisting of two heating branches, two cooling branches and two adiabatic branches with heat-transfer loss and friction-like term loss was analyzed 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 the power output and the efficiency of the cycle are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of the cycle process on the performances of the cycles using numerical examples. The results obtained herein include the performance characteristics of irreversible reciprocating Diesel, Otto, Atkinson, Brayton, Dual and Miller cycles.