Ideal Thermodynamic Cycle Research Articles

Analysis of thermally coupled chemical looping combustion-based power plants with carbon capture

A number of CO2 capture-enabled power generation technologies have been proposed to address the negative environmental impact of CO2 emission. One important barrier to adopting these technologies is the associated energy penalty. Chemical-looping Combustion (CLC) is an oxy-combustion technology that can significantly lower this penalty. It utilizes an oxygen carrier to transfer oxygen from air/oxidizing stream in an oxidation reactor to the fuel in a reduction reactor. Conventional CLC reactor designs employ two separate reactors, with metal/metal oxide particles circulating pneumatically in-between. One of the key limitations of these designs is the entropy generation due to reactor temperature difference, which lowers the cycle efficiency. Zhao et al. (Zhao et al., 2014; Zhao and Ghoniem, 2014) proposed a new CLC rotary reactor design, which overcomes this limitation. This reactor consists of a single rotating wheel with micro-channels designed to maintain thermal equilibrium between the fuel and air sides. This study uses three thermodynamic models of increasing fidelity to demonstrate that the internal thermal coupling in the rotary CLC reactor creates the potential for improved cycle efficiency. A theoretical availability model and an ideal thermodynamic cycle model are used to define the efficiency limits of CLC systems, illustrate the impact of reactor thermal coupling and discuss relevant criteria. An Aspen Plus® model of a regenerative CLC cycle is then used to show that this thermal coupling raises the cycle efficiency by up to 2% points. A parametric study shows that efficiency varies inversely with pressure, with a maximum of 51% at 3bar, 1000C and 60% at 4bar, 1400C. The efficiency increases with CO2 fraction at high pressure ratios but exhibits a slight inverse dependence at low pressure ratios. The parametric study shows that for low purge steam demand, steam generation improves exhaust heat recovery and increases efficiency when an appropriate steam production strategy is adopted.

Viability of fuel switching of a gas-fired power plant operating in chemical looping combustion mode

CLC (chemical looping combustion) promises to be a more efficient way of CO2 capture than conventional oxy-fuel combustion or post-combustion absorption. While much work has been done on CLC in the past two decades, the issue of multi-fuel compatibility has not been addressed sufficiently, especially with regard to plant layout and reactor design. In the present work, it is shown that this is non-trivial in the case of a CLC-based power plant. The underlying factors have been examined in depth and design criteria for fuel compatibility have been formulated. Based on these, a layout has been developed for a power plant which can run with either natural gas or syngas without requiring equipment changes either on the steam side or on the furnace side. The layout accounts for the higher CO2 compression costs associated with the use of syngas in place of natural gas. The ideal thermodynamic cycle efficiency, after accounting for the energy penalty of CO2 compression, is 43.11% and 41.08%, when a supercritical steam cycle is used with natural gas and syngas, respectively. It is shown that fuel switching can be enabled by incorporating the compatibility conditions at the design stage itself.

Ideal thermodynamic cycle analysis of free piston engine based on expansion ratio

Ideal thermodynamic cycle analysis of free piston engine based on expansion ratio

Required time response of a variable valve actuator equiping a hybrid pneumatic–combustion engine

This work is a part of a research program that aims to modify a conventional internal combustion engine and turn it into a hybrid pneumatic–combustion engine. The hybrid pneumatic–combustion engine should be able to convert mechanical energy into compressed air and convert compressed air back into mechanical energy. The potential application for the concept is any use of the internal combustion engine where the load oscillates between a negative and a positive value, such as automobiles and hybrid wind diesel systems for remote area power generation. In the first application, during vehicle decelerations, an excess of power occurs, and a negative load could be applied to the engine, whereas during vehicle accelerations, a positive load is applied. In the second application, if the generated wind power is higher than consumption demand, then the load applied to the engine could be negative, and if the generated wind power is lower than consumption demand, then the load is positive. In previous work, we exposed an optimization followed by a fuel-saving evaluation of a new hybrid pneumatic–combustion engine concept that uses a variable valve actuator system. The optimization of the valve actuation was based on ideal thermodynamic cycle modeling, assuming therefore an instant response of the variable valve actuator system. In the present work, a more realistic analysis of the system is provided by taking into consideration the dynamic response of the variable valve actuator system. Variable valve actuators have been widely studied for optimizing performance and fuel consumption of the internal combustion engine, especially in spark-ignition engines. For these engines, it is possible to reduce the pumping losses and to optimize the engine filling by controlling the intake and exhaust valve opening and closing angles, as well as their lifts. However, the variation of valve actuation crank angles required in a conventional internal combustion engine is significantly smaller than the one required in the hybrid pneumatic–combustion engine. This paper describes, through simulation, how the valve time response affects the performance of the hybrid pneumatic–combustion engine and recommends a required valve time response.

Fuel consumption evaluation of an optimized new hybrid pneumatic–combustion vehicle engine on several driving cycles

In this paper, we describe an optimization followed by a fuel-saving evaluation of a new concept of a hybrid pneumatic–combustion engine that can be obtained by modifying a conventional internal combustion engine without developing a new cylinder head. Until now, most studies on the pneumatic hybridization of internal combustion engines have dealt with a two-stroke pure pneumatic mode. The few concept studies that have dealt with a hybrid pneumatic–combustion four-stroke mode required a supplementary valve to be added to charge compressed air in the combustion chamber. This heavy modification cannot be carried out by simply adjusting an existing internal combustion engine because a new cylinder head should be developed. It is therefore not logical to suggest this concept as an option in vehicle powertrains to reduce fuel consumption. Moreover, those studies focus on spark-ignition engines; there are reasons to think that their concepts might not work adequately for diesel engines. Our concept is capable of making a diesel engine operate under two-stroke pneumatic motor modes, two-stroke pneumatic pump modes and four-stroke hybrid modes, without requiring an additional valve in the combustion chamber. This fact constitutes our study’s strength and innovation. The evaluation of our concept is based on ideal thermodynamic cycle modeling. The optimized valve actuation timings for all modes lead to generic maps that are independent of the engine size. The fuel economy is calculated based on the new European driving cycle and on the assessment and reliability of transport emission models and inventory system urban and rural cycles.

A new hybrid pneumatic combustion engine to improve fuel consumption of wind–Diesel power system for non-interconnected areas

This paper presents an evaluation of an optimized Hybrid Pneumatic-Combustion Engine (HPCE) concept that permits reducing fuel consumption for electricity production in non-interconnected remote areas, originally equipped with hybrid Wind–Diesel System (WDS). Up to now, most of the studies on the pneumatic hybridization of Internal Combustion Engines (ICE) have dealt with two-stroke pure pneumatic mode. The few studies that have dealt with hybrid pneumatic-combustion four-stroke mode require adding a supplementary valve to charge compressed air in the combustion chamber. This modification means that a new cylinder head should be fabricated. Moreover, those studies focus on spark ignition engines and are not yet validated for Diesel engines. Present HPCE is capable of making a Diesel engine operate under two-stroke pneumatic motor mode, two-stroke pneumatic pump mode and four-stroke hybrid mode, without needing an additional valve in the combustion chamber. This fact constitutes this study’s strength and innovation. The evaluation of the concept is based on ideal thermodynamic cycle modeling. The optimized valve actuation timings for all modes lead to generic maps that are independent of the engine size. The fuel economy is calculated for a known site during a whole year, function of the air storage volume and the wind power penetration rate.

Giant electro-mechanical energy conversion in [011] cut ferroelectric single crystals

Giant electro-mechanical energy conversion is demonstrated under a ferroelectric/ferroelectric phase transformation in [011] cut and poled lead titanate-based relaxor perovskite morphotropic single crystals. It is found that under mechanical pre-stress, a relatively small oscillatory stress drives the material reversibly between rhombohedral and orthorhombic phases with a remarkably high polarization and strain jump induced at zero bias electric field and room temperature. The measured electrical output per cycle is more than an order of magnitude larger than that reported for linear piezoelectric materials. Ideal thermodynamic cycles are presented for this electro-mechanical energy conversion followed by a presentation and discussion of the experimental data.

AirСar CAES-Compressed Air Energy Source-Compendium

This paper is a re evaluation of CAES Compressed Air Energy Source. CAES is not new, experimental air car compressed air propulsion vehicles appeared in early 1900’s, and are currently exemplified by the India Tata Motors AirCar MiniCat based on the French MDI Motor Development International AirCar. (see Ulf Bossel, European Fuel Cell Forum) This study focuses on compressed air potential pressure specific energy density and specific power, ideal Global thermodynamic cycle efficiency, US EPA 23 cycle urban driving test schedule overall drive train ideal efficiency and vehicle ideal range. CAES analysis is unique because compression and expansion cycles are remotely linked solely by ambient atmosphere e.g., compression occurs in a stationary device while expansion takes place in a mobile vehicle. Therefore, ideal thermodynamic compression and/or expansion cycles can be treated independently and linked as isothermal entities e.g., both cycles are in fact separate ideal complete compression and/or complete expansion cycles without (TDC) top dead center piston clearance with isothermal ambient temperature compressed air storage. Further, CAES potential pressure energy density and power density are comparable to electro-chemical energy sources on a Ragone chart, e.g., CAES specific energy density and specific power based solely on stored pressure energy potential are similar to the Pb-Acid battery. However, modern forms of multi stage expansion air motors with heat exchangers between stages extract additional thermal energy directly from ambient air to increase vehicle range by a factor of ~ 6 with a four stage expansion motor. To minimize road-load energy consumption air powered vehicles are characterized by low curb (empty) vehicle mass and low speed urban traffic. Based on Tata AirCar design specifications, comparative theoretical driving range tests were simulated with the 23 cycle US EPA Urban (City) driving schedule and a modified low speed 23 cycle Urban schedule suitable for India. We concluded modern multi stage air car propulsion may find applications in temperate zones, particularly highly congested pedestrian trafficked city streets and retirement communities such as Sun City, AZ, India [5a-19a]

Thermodynamic cycle analysis of ramjet engines using magnesium-based fuel

To predict cyclic performance and propulsive performance, and further instructs the integral engine design, an ideal thermodynamic cycle model for a magnesium-based fuel ramjet engine employed in underwater vehicles is established. Especially, the magnesium-based fuel grain consisting of most magnesium, small ammonium perchlorate, and some binder is carried on-board, while water as the main oxidizer and working medium is injected into the chamber through different pipelines. Thus, the ideal thermodynamic cycle model is regarded as a combination of Brayton cycle and quasi-Rankine cycle due to phase-transition characteristics of water. Based on the thermodynamic cycle model and thermodynamic calculation model, thermal efficiency, propulsive efficiency, as well as specific impulse are predicted theoretically in the present study. The results show that thermal efficiency is dominantly influenced by water/fuel ratio and fuel composition distribution when fixing navigational depth of ramjet, instead, the chamber pressure has the slight influence especially under a higher pressure environment. Otherwise, thermal efficiency relies on navigational depth rather than the fuel composition distributions while fixing the water/fuel ratio. As a heat engine and thruster, the rules of propulsive efficiency for this water ramjet also provide qualitative guidance for improving the energy conversion between kinetic energy and propulsive energy. Furthermore, toward rules of specific impulse versus water/fuel ratio under different chamber pressure, the occurrence of peak specific impulse of order 5000 N s kg−1 on each curve is observed.

THERMODYNAMIC EFFICIENCY CLOSED AND BACK (IDEAL) CYCLES OF INTERNAL COMBUSTION ENGINES USING BIOFUELS

Calculated ideal thermodynamic cycles of internal combustion engine when using different types of liquid biofuels. It is shown that a decrease in the heat of combustion of biofuels be proportionally reduced the specific work cycle and the average engine power and increases in proportion to the unit cost of fuel and mean effective pressure.

Ideal Thermodynamic Cycle Analysis for the Meletis-Georgiou Vane Rotary Engine Concept

The Meletis-Georgiou is a patented Vane Rotary Engine concept that incorporates separate compression-expansion chambers and a modified Otto (or Miller) cycle, characterized by (Exhaust) Gas Recirculation at elevated pressures. This is implemented by transferring part of the expansion chamber volume into the compression one through the coordinated action of two vane diaphragms. This results into a very high gas temperature at the end of the compression, something that permits autoignition under all conditions for a Homogeneous Compression Ignition (HCCI) version of the engine. The relevant parametric analysis of the ideal cycle shows that the new cycle gives ideal thermal efficiencies of the order of 60% to 70% under conditions corresponding to homogeneous compression engines but at reduced pressures when compared against the corresponding Miller cycle.

Thermodynamic Cycle of the Atmospheric Upward Heat Convection Process

¶Closed ideal thermodynamic cycles are used to analyze the atmospheric upward heat convection process which is compared to the Brayton gas-turbine cycle. The heat to work conversion efficiency of the atmosphere is shown to be close to the Carnot efficiency calculated using the average temperatures at which heat is received and given up for hot and cold source temperatures, respectively. The efficiency is independent of whether the lifting process is discontinuous or continuous, and nearly independent of whether the heat is transported as sensible or as latent heat.

Fundamental thermodynamics of ideal absorption cycles

Starting from the representation of a real absorption refrigeration cycle on a temperature-entropy diagram, step-by-step idealisations of the binary mixture, together with the thermodynamic transformations are considered, in order to derive the ideal thermodynamic absorption cycle performance and temperature formulae. It is demonstrated that the ideal absorption cycle is the combination of a Carnot driving cycle with a reverse Carnot cooling cycle. The resorption cycle is analysed in the same manner. Information is included on absorption cooling with heat recovery cycles, heat pumps and temperature amplifiers. From the analysis of single-stage cycles, and by superimposing absorption cycles operating at different temperatures and utilising specific residual heat of the higher temperature sub-cycles, the performance and temperature relations of double, triple and multistage cycles are derived. Special attention is given to three types of triple-stage cycle and their ideal equivalence is demonstrated and represted on the pressure-temperature-concentration (PTX) diagram. A simple hybrid absorption-compression cycle is analysed and the results are compared with those of ideal cold generation cycles (combinations of driving and cooling cycles). Consideration is also given to cold generation systems. Finally, the validation of the fundamental thermodynamics of absorption cycles is presented by applying an exergy analysis. This paper presents the thermodynamic principles involved to obtain simple formulae, in a similar way to the Carnot cycle in order to convey the ideal theoretical limitations.

Metal hydride heat pump—New type of heat converter

Selection of materials for metal hydride couples is considered for the development of refrigerating machines and hydride heat pumps (MHHP) in the temperature ranges from −30 to 200 °C. The slope of the plateau and hysteresis of “pressure-composition” isotherms, the influence of the mass of the reactor on the efficiency of cycle, and the choice of operating parameters are taken into account as opposed to the ideal thermodynamic cycle described in literature. Some results, obtained during the development and installation of MHHP for water cooling are presented. MHHP are assembled from modules with heat/cold capacity of 150–200 W. The design of the modules provides hydrogen transfer at approximately equal pressure in the high- and low-temperature sides of reactor when the valves between them are absent.

A Feasibility Study into the Use of Direct Injection of Exhaust Generated Steam for Improving the Efficiency of Reciprocating Internal Combustion Engines

This paper reports on a study into the feasibility of generating steam, using the exhaust gases of a reciprocating internal combustion engine, and expanding it in the cylinders of the engine to produce additional power without increasing the fuel consumption. The study was conducted in three stages; firstly an equivalent ideal thermodynamic cycle was analysed to examine the fundamental principles, secondly a computer simulation was carried out based on a particular engine, and thirdly an attempt was made to modify the engine and run it with steam injection. The results suggest that this proposal is thermodynamically sound and could in practice permit substantial gains in efficiency using relatively straightforward technology.

Transient Response of the Miniature, Reversed Stirling-Cycle, Cryogenic Cooling Machine—An Empirical Approach

By regarding the ideal thermodynamic cycle as being artificially separated from the hardware, and by treating the former as a simple energy flux path, an energy-rate balance is set up for the miniature, reversed-cycle, Stirling cooling machine. Account is taken of thermal energy storage and release rates corresponding to the rates of change of temperature of regenerator and cylinder walls. There results a first-order, linear differential equation. Solutions are obtained numerically using the parameters of a tentative cooler design. The solutions are presented in the form of curves of temperature ratio, τ (=Tc/Te), against time, t, at uniform angular speed. Regenerator inefficiency, Ie, emerges as the parameter that is most critical in the achievement of desired heat-lifting capacity at cryogenic temperatures. For a machine of given thermal mass, both Ie and ηc (cycle efficiency relative to corresponding Carnot efficiency) strongly influence the cool-down rate. The treatment is capable of application to Stirling machines operating as prime movers.