Otto Cycle Research Articles

Optimization of the power, efficiency and ecological function for an air-standard irreversible Dual-Miller cycle

This paper establishes an irreversible Dual-Miller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Miller cycle ratio (rM) on the power output (P), thermal efficiency (η) and ecological function (E), obtain the optimal ρopt and optimal rMopt, and compare the performance characteristics of DMC with its simplified cycles and with different optimization objective functions, the P, η and E of irreversible DMC are analyzed and optimized by applying the finite time thermodynamic (FTT) theory. Expressions of P, η and E are derived. The relationships among P, η, E and compression ratio (e) are obtained by numerical examples. The effects of ρ and rM on P, η, E, maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) are analyzed. Performance differences among the DMC, the Otto cycle (OC), the Dual cycle (DDC), and the Otto-Miller cycle (OMC) are compared for fixed design parameters. Performance characteristics of irreversible DMC with the choice of P, η and E as optimization objective functions are analyzed and compared. The results show that the irreversible DMC engine can reach a twice-maximum power, a twice-maximum efficiency, and a twice-maximum ecological function, respectively. Moreover, when choosing E as the optimization objective, there is a 5.2%of improvement in η while there is a drop of only 2.7% in P compared to choosing P as the optimization objective. However, there is a 5.6% of improvement in P while there is a drop of only 1.3% in η compared to choosing as the optimization objective.

Single-Atom Heat Machines Enabled by Energy Quantization

Quantization of energy is a quintessential characteristic of quantum systems. Here we analyze its effects on the operation of Otto cycle heat machines and show that energy quantization alone may alter and increase machine performance in terms of output work, efficiency, and even operation mode. We show that this difference in performance occurs in machines with inhomogeneous energy level scaling, while quantum machines with homogeneous level scaling behave like classical machines. Our results demonstrate that quantum thermodynamics enables the realization of classically inconceivable Otto machines, such as those with an incompressible working substance. We propose to measure these effects experimentally using a laser-cooled trapped ion as a microscopic heat machine.

Realization of variable Otto-Atkinson cycle using variable timing hydraulic actuated valve train for performance and efficiency improvements in unthrottled gasoline engines

Variety of technologies along with the mechanisms for their implementations have been developed in order to pursue possible improvements in the performance and efficiency of gasoline engines. However, most of the commonly used techniques, such as the cam-based variable valve timings (VVT) and variable compression ratio (VCR), are realized by different kinds of complicated mechanisms, providing an extended but still relatively limited adjustability for attaining improved valve timings and different engine cycles according to the varying working conditions of the engine. In this research, by using the flexibility offered by the hydraulic actuated valve train (HAVT), a set of new valve motion strategies is developed for realizing a newly introduced engine cycle, the variable Otto-Atkinson cycle (VOAC), to achieve an unthrottled engine load control. The demonstrative VOAC test engine in this research is a converted baseline single-cylinder engine that is able to carry out a variable Otto cycle (VOC) at full load operations for achieving higher power performance while realizing a variable Atkinson cycle (VAC) at partial load operations for gaining better fuel economy without having any further modifications or attaching additional components to the engine. The baseline single-cylinder engine is modeled in GT-Suite and carefully calibrated by a series of experiments. Benefited from the HAVT features, the tunings of the VOAC engine can be realized easily to fulfill any requirements towards different desired engine characteristics. By adopting the proposed VOAC with optimized parameters, a 13.5% average improvement in the engine's output can be achieved under full load operations across the entire speed range. On top of that, it also shows that the resulted BSFC could be lowered by 16.1 g/kW·h on average over the sampled speed-load map of the engine running at partial load operations.

Performance improvement of a direct carbon solid oxide fuel cell through integrating an Otto heat engine

A novel system consisting of an external heat source, a direct carbon solid oxide fuel cell (DC-SOFC), a regenerator and an air standard Otto cycle engine is proposed to improve the performance of the DC-SOFC. Considering the electrochemical/chemical reactions, ionic/electronic charge transport, mass/momentum transport and heat transfer, a 2D tubular DC-SOFC model shows that the overall heat released in the cell can be smaller than, equal to or larger than the heat required by the internal Boudouard reaction. Three different operating modes of the proposed system are identified, and accordingly, analytical expressions for the equivalent power output and efficiency of the proposed system are derived under different operating conditions. The modeling results show that the Otto heat engine can effectively recover the waste heat from the DC-SOFC for additional power production especially at large operating current density. Comprehensive parametric studies are conducted to investigate the effects of the different operating conditions of DC-SOFC on its performance and heat generation. The effects of compression ratio, internal irreversibility factor and power dissipation of the Otto heat engine on the system performance improvement are also studied.

THERMODYNAMICAL EFFICIENCY OF A DETONATION ENGINE

An attempt has been made to analyze qualitatively and quantitatively the thermodynamic cycle of detonative combustion and to compare it with the Otto and Brayton cycles in order to establish the degree of its thermodynamic perfection. A comparison of the thermodynamic cycles of Otto, Brayton, and detonation was carried out for equivalent Carnot cycles, which has the same degree of thermodynamic perfection as the investigated cycles. To determine the parameters of the detonation cycle, the classical detonation theory based on the laws of thermodynamics and gasdynamics was used. It is shown that the detonation cycle in comparison with the cycles of Brayton and Otto has larger entropy at the end of the heat supply and smaller one at the end of the heat removal. That means it has a higher mean-integral temperature of heat input and a lower mean-integral temperature of heat removal. Thus, in the range of characteristic values of the adiabatic index k, the temperature at the end of the heat input process in the detonation cycle exceeds the Otto cycle temperature by about 7–15 %. Consequently, the detonation cycle is thermally more efficient, since the thermal efficiency of the cycle increases with the expansion of the temperature boundaries of the equivalent Carnot cycle.

Technical feasibility study of scroll-type rotary gasoline engine: A compact and efficient small-scale Humphrey cycle engine

This paper reports the study of a conceptual gasoline Internal Combustion Engine (ICE) using scroll type rotary device rather than conventional piston as the main engine component. The proposed innovation engine adopts Humphrey Cycle to maximise the power performance of ICE. A performance comparison of the Humphrey Cycle, Otto cycle and Brayton cycle has been conducted and studied. The effects of using different designed compression ratio under variable expansion ratio have been investigated, which identify the optimal operational conditions under different compression/expansion ratio of the engine. Optimal performance can be achieved under the compression/expansion ratio at 2:1/4.8:1, 4:1/7.4:1, 6:1/9.9:1, 8:1/11.8:1 and 10:1/14.1:1, when the energy efficiency of the system can be respectively achieved at 42.22%, 49.13%, 52.82%, 55.08% and 56.96%. A case study has been conducted to study the performance of small-scale scroll-type rotary ICE. Results pointed out under designed compression ratio from 2:1 to 10:1 the effective power from the system ranges from 3.343 to 19.01 kW. The analysis of fuel efficiency pointed out the Brake Specific Fuel Efficiency (BSFC) of the scroll-type rotary engine burning gasoline ranges from 130.5 to 148.5 g/kWh, which improve the fuel efficiency by 28.02% and 65.89% compared to that of the conventional gasoline engine.

Thermodynamics and London office property cycles

PurposeThe purpose of this paper is to extend the studies of commercial property cycles by providing a cross-field approach to property markets modelling.Design/methodology/approachThe approach allows for the incorporation of market shocks into the property cycle model as fundamental building blocks; assessment of overall market absorption generated through cyclic activity; and timing estimation of major market events. An ideal model is first constructed, which relies on an observation that a property cycle consists of four distinctive phases. These are described formally through appropriate formulae. Subsequently, it is observed that an analogous cyclic behaviour is described in physics as the Otto cycle. The formulae derived in physics for the Otto cycle are now redefined so to be applicable to the property market.FindingsThe model has been applied to the London office market, both to the historic and the current data sets. This allowed for the comparison of model predicted absorption and vacancies with the historic records, providing for assessment of the model accuracy. The model predicted that absorption was also compared with historic space supply allowing for estimation of oversupply and resultant vacancies. London office submarkets were analysed and compared to each other, allowing for estimation of their relative attractiveness as perceived by tenants and developers.Practical implicationsThe model may be used to estimate cycle generated absorption; therefore, over and under supply of space due to developers’ activity may be assessed. It is also possible to use the model to assess the timing of future market peaks and troughs.Originality/valueThis is the first research directly applying the methodology developed in physics to commercial property cycles.

A quantum Otto engine with finite heat baths: energy, correlations, and degradation

We study a driven harmonic oscillator operating an Otto cycle by strongly interacting with two thermal baths of finite size. Using the tools of Gaussian quantum mechanics, we directly simulate the dynamics of the engine as a whole, without the need to make any approximations. This allows us to understand the non-equilibrium thermodynamics of the engine not only from the perspective of the working medium, but also as it is seen from the thermal baths’ standpoint. For sufficiently large baths, our engine is capable of running a number of perfect cycles, delivering finite power while operating very close to maximal efficiency. Thereafter, having traversed the baths, the perturbations created by the interaction abruptly deteriorate the engine’s performance. We additionally study the correlations generated in the system, and, in particular, we find a direct connection between the build up of bath–bath correlations and the degradation of the engine’s performance over the course of many cycles.

Thermodynamic optimization for an air-standard irreversible Dual-Miller cycle with linearly variable specific heat ratio of working fluid

This paper establishes an air-standard irreversible Dual-Miller cycle (DMC) model with the specific heat ratio (SHR) of working fluid (WF) linearly varying with its temperature. Because the specific heat (SH) of WF varies with combustion reaction in actual internal combustion engine (ICE), the SHR of WF should be a function of temperature but not a constant. In order to accurately reflect the practical characteristics of DMC engine, performance of DMC with linearly variable SHR, and with heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses (IILs) is analyzed and optimized by applying finite-time thermodynamics. Analytical formulae of the power output (P), efficiency (η), entropy generation rate (EGR) and ecological function (E) are derived. Relationships among P, η, E and compression ratio are obtained via numerical calculations. Effects of the design parameters, cycle temperatures and linearly variable SHR of WF on P, η and E are investigated. Performance differences among the DMC and its simplified cycles, including Otto cycle (OC), Dual cycle (DDC) and Miller cycle (OMC) are compared. Performance characteristics of the DMC with different optimization objective functions (OOFs) are analyzed. The results indicate that the maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) of the DMC are superior to those of OC, DDC and OMC, and optimizing E is the best compromise between optimizing P and optimizing η. The presented results may be helpful to optimize the performance of practical DMC engines.

Thermodynamic Optimization for an Endoreversible Dual-Miller Cycle (DMC) with Finite Speed of Piston.

Power output (), thermal efficiency () and ecological function () characteristics of an endoreversible Dual-Miller cycle (DMC) with finite speed of the piston and finite rate of heat transfer are investigated by applying finite time thermodynamic (FTT) theory. The parameter expressions of the non-dimensional power output (), and non-dimensional ecological function () are derived. The relationships between and cut-off ratio (), between and , as well as between and are demonstrated. The influences of and piston speeds in different processes on , and are investigated. The results show that and first increase and then start to decrease with increasing . The optimal cut-off ratio will increase if piston speeds increase in heat addition processes and heat rejection processes. As piston speeds in different processes increase, the maximum values of and increase. The results include the performance characteristics of various simplified cycles of DMC, such as Otto cycle, Diesel cycle, Dual cycle, Otto-Atkinson cycle, Diesel-Atkinson cycle, Dual-Atkinson cycle, Otto-Miller cycle and Diesel-Miller cycle. Comparing performance characteristics of the DMC with different optimization objectives, when choosing as optimization objective, improves 26.4% compared to choosing as optimization objective, while improves 74.3% compared to choosing as optimization objective. Thus, optimizing is the best compromise between optimizing and optimizing . The results obtained can provide theoretical guidance to design practical DMC engines.

Carbon dioxide emissions by tetrafuel technology vehicles (gasoline-ethanol-NGV) with air conditioning on and off

This research aims to estimate and compare CO2 emissions from fuel consumption by motor vehicles operating with different types of fuel, such as gasoline (E00), gasoline blended with 25% anhydrous ethyl alcohol fuel (E25), hydrous ethanol, and natural gas vehicles (NGV), as well as showing the impacts of the air conditioning of the vehicle on CO2 emissions. The CO2 emissions from the fuel consumption of a vehicle with tetrafuel technology in roller dynamometer that simulates an urban path and road are estimated. The tests were carried out on a climate chamber under controlled conditions, and the results were corrected for a default condition, 101,325 kPa and 20 °C. The study demonstrates that CO2 emissions, by the very burning of liquid and gaseous fuels in an Otto cycle engine, essentially depends on the mechanical characteristics of the propellant, on the specific weight of the fuel, and the conditions of operation of the vehicle and not only of the calorific value of fuel. The results showed that the NGV fuel, to deliver the same torque and power of ethanol to the motor of the vehicle, would be producing 13.5% more of CO2 in urban areas and at least 9.5% on the road with the air conditioning system turned off. With the air conditioning system turned on, the four kinds of fuels in urban route conditions showed similar values of CO2 as in the road; the NGV that presented CO2 emissions is in about 12% more than other fuels, which had equivalent values. For a vehicle to achieve its best performances in combustion and reduce its CO2 emissions, it is necessary to have an individualized propellant, prepared specifically for the type of fuel it might be using.

Effect of specific heat variations on irreversible Otto cycle performance

Considering internal irreversibility loss, friction loss and heat transfer loss, an irreversible Otto cycle model is built up by using finite-time thermodynamics with air standard assumption. Using the various irreversible losses in the cycle to compute the entropy generation rate, the optimal ecological function performance of the cycle is studied when the specific heats of working fluid are nonlinear relation with its temperature. Some important expressions, including ecological function, entropy generation rate, efficiency and power output, are obtained. The cycle ecological function performances with constant specific heats, specific heats changed with linear and nonlinear relations of its temperature are compared. Moreover, the impacts of internal irreversibility loss, friction loss and heat transfer loss on ecological function performance are analyzed. The results show that optimization of the exergy-based ecological function not only represents a compromise between the power output and the rate of entropy generation but also represents a compromise between the power output and the thermal efficiency, the specific heat models have no qualitative effect and only have quantitative effect on the performance characteristics of ecological function versus power output and ecological function versus efficiency, and the ecological function, power output and efficiency decrease with the increase of heat transfer, friction and internal irreversibility losses.

The Unruh quantum Otto engine

We introduce a quantum heat engine performing an Otto cycle by using the thermal properties of the quantum vacuum. Since Hawking and Unruh, it has been established that the vacuum space, either near a black hole or for an accelerated observer, behaves as a bath of thermal radiation. In this work, we present a fully quantum Otto cycle, which relies on the Unruh effect for a single quantum bit (qubit) in contact with quantum vacuum fluctuations. By using the notions of quantum thermodynamics and perturbation theory we obtain that the quantum vacuum can exchange heat and produce work on the qubit. Moreover, we obtain the efficiency and derive the conditions to have both a thermodynamic and a kinematic cycle in terms of the initial populations of the excited state, which define a range of allowed accelerations for the Unruh engine.

Finite-Time Thermodynamic Modeling and a Comparative Performance Analysis for Irreversible Otto, Miller and Atkinson Cycles.

Finite-time thermodynamic models for an Otto cycle, an Atkinson cycle, an over-expansion Miller cycle (M1), an LIVC Miller cycle through late intake valve closure (M2) and an LIVC Miller cycle with constant compression ratio (M3) have been established. The models for the two LIVC Miller cycles are first developed; and the heat-transfer and friction losses are considered with the effects of real engine parameters. A comparative analysis for the energy losses and performances has been conducted. The optimum compression-ratio ranges for the efficiency and effective power are different. The comparative results of cycle performances are influenced together by the ratios of the energy losses and the cycle types. The Atkinson cycle has the maximum peak power and efficiency, but the minimum power density; and the M1 cycle can achieve the optimum comprehensive performances. The less net fuel amount and the high peak cylinder pressure (M3 cycle) have a significantly adverse effect on the loss ratios of the heat-transfer and friction of the M2 and M3 cycles; and the effective power and energy efficiency are always lower than the M1 and Atkinson cycles. When greatly reducing the weights of the heat-transfer and friction, the M3 cycle has significant advantage in the energy efficiency. The results obtained can provide guidance for selecting the cycle type and optimizing the performances of a real engine.

The Influences of Air Intake Temperature on the Gasoline Engine’s Otto Cycle

This thesis is about the calculations and researches of the improved coolant system of turbocharged gasoline engine, it introduces the basic concept of gasoline engine’s turbo technology, and shows the detailed information and parameters of 486 turbocharged gasoline engine, established the formulas of the Otto cycle and its relevant parameters, emphasized to analyze the influences of the intake air temperature on the engine’s Otto cycle. The effects of the turbo gasoline intake temperature mainly contains 2 points: the outlet temperature of the turbo and the temperature decline effect of the coolant system; This thesis compares the effects of gasoline’s Otto Cycle which configures or not with a middle cooler, utilized a thermal dynamics calculation method to research, calculate and analysis the parameters of the turbocharged engine’s Otto cycle, the results are corresponding with the experiment(the thermal balance experiment), the property indices are included circulate thermal efficiency, exergy efficiency and average valid pressure. Through the contrasts and analysis, it obviously shows that, with the middle coolant, it has an advantage in the average valid pressure, intake temperature, and exergy efficiency. Absolutely it is necessary and efficient configured with middle coolant on the turbocharged gasoline engine.

Optimization of an irreversible Otto and Diesel cycles based on ecological function

In this paper the solutions some practical problems of cointegration analysis are discussed. We mainly focus on the following phases of the Johansen procedure: the baseline model specification, t determination of the number of cointegrating vectors, the inclusion of the determines components and design of partial mode This is the most commonly used approach analyzing nonstationary macroeconomic time series, due to its complexity and simple modeling based on the computer packages. However, as the application of statistic packages may be useless when methodology is partly known, its full understanding makes computer software a reliable source. The purpose of this paper is to popularize (correct) application of cointegration methods. .

Control Unit for a Coreless Stator for use with SI Engine Stepping Valve

Engine efficiency could be increased if valve timing could change with engine revolutions per minute. Poppet valves are fitted with strong springs which return them to their rest positions after being pushed down by cam lobes. Overcoming the spring loaded camshaft drive train requires a lot of engine power. Valve lift, lift duration and phase cannot be adapted with cam lobes on the camshaft but electromagnetic actuators or hydraulic/pneumatic phasing mechanisms could achieve change of lift duration and phase change. Stepping valves with flexible valve event software control, move perpendicular to the piston, thus avoiding piston valve collision problem. Engine cranking requiring fuel, spark and valve event can be done electronically without engine turning. The design of a control unit for an axial coreless stator to control the motion of the stepping valve through the Otto cycle positions intake, exhaust and power / compression is presented with successful simulation of the control algorithm. A 3phase, 12V coil prototype stator with 4 coils per phase, connected in series and consuming 3A from a 12V car battery has been prototypically realized. The project aims at essential processes to run the engine as fuel, air, spark all being software controlled, leading to a more efficient, environmentally friendly, reliable and powerful engine.

Energy Management Strategy for Atkinson Cycle Engine Based Parallel Hybrid Electric Vehicle

Energy management strategies are widely used for the fuel efficiency of hybrid electric vehicle (HEV). Most of the on road hybrid cars use Atkinson cycle engine instead of Otto cycle engine, on account of better efficiency. The authors have already proposed a control oriented extended mean value engine model (EMVEM) of the Atkinson cycle engine and also developed and evaluated its control framework. The prior research was limited to evaluate the fuel efficiency of the engine only, while HEV employs both the engine and the motor. The presented work is an attempt to devise and demonstrate energy management strategy (EMS) by giving full consideration to the powertrain using Atkinson cycle engine. A novel energy management strategy based on the vehicle speed for Atkinson cycle engine for HEV is proposed. A parallel hybrid electric vehicle is modeled in Matlab/Simulink through a forward facing simulator. The proposed EMS with Atkinson cycle engine control framework exhibits the significant improvement in the fuel economy around 12.30% for standard Manhattan driving cycle and 7.22% for the modified federal urban driving schedule (FUDS) driving cycle in comparison with the Otto cycle engine.

Design, Development, and Evaluation of a Control Framework for an Atkinson Cycle Engine

The efficiency of the spark ignition (SI) engine degrades while working at part loads. It can be optimally dealt with a slightly different thermodynamic cycle termed as an Atkinson cycle. It can be implemented in the conventional SI engines by incorporating advanced mechanisms as variable valve timing (VVT) and variable compression ratio (VCR). In this research, a control framework for the Atkinson cycle engine with flexible intake valve load control strategy is designed and developed. The control framework based on the extended mean value engine model (EMVEM) of the Atkinson cycle engine is evaluated in the view of fuel economy at the medium and higher load operating conditions for the standard new European driving cycle (NEDC), federal urban driving schedule (FUDS), and federal highway driving schedule (FHDS) cycles. In this context, the authors have already proposed a control-oriented EMVEM model of the Atkinson cycle engine with variable intake valve actuation. To demonstrate the potential benefits of the VCR Atkinson cycle VVT engine, for the various driving cycles, in the presence of auxiliary loads and uncertain road loads, its EMVEM model is simulated by using a controller having similar specifications as that of the conventional gasoline engine. The simulation results point toward the significant reduction in engine part load losses and improvement in the thermal efficiency. Consequently, considerable enhancement in the fuel economy of the VCR Atkinson cycle VVT engine is achieved over conventional Otto cycle engine during the NEDC, FUDS, and FHDS cycles.

Road vehicle emission inventory of a Brazilian metropolitan area and insights for other emerging economies

The vehicle fleet in the Ceará state has grown 180% over the last ten years. The growth of the resulting emissions is unknown in view of the expansion of this fleet in the greater Fortaleza Metropolitan Area (FMA). The largest fleet in the FMA is in the Fortaleza city itself, where flex fuel vehicles predominate (∼30%). Flex fuel motorcycles increased significantly (greater than 800%) between 2010 and 2015. This paper aims to estimate the road vehicle emissions of carbon monoxide (CO), non-methane hydrocarbons (NMHC), aldehydes (RCHO), nitrogen oxides (NOx), and particulate matter (PM) from the main road vehicle fleets of Fortaleza and its metropolitan area using a macrosimulation, bottom-up method, between 2010 and 2015. The results showed that road vehicle emissions of CO, NMHC and RCHO increased mainly by Otto cycle vehicles increase due to the introduction of flex fuel vehicles; however, the NOx and PM emissions noticeable reduction is also a result of emission policies that seed the introduction of new technologies. In 2015, more than 70,000 tons of CO (21.2 ton/1000person), 8000 tons of NMHC (2.5 ton/1000person), 290 tons of RCHO (0.09 ton/1000person), 15,000 tons of NOx (4.4 ton/1000person) and 600 tons of PM (0.2 ton/1000person) were emitted in the region under study. Comparing with other Brazilian regions, FMA emit higher levels of pollutants per inhabitant than the state of São Paulo and the state of Rio de Janeiro but lower levels than Porto Alegre city.