Engine Cycle Analysis Research Articles

Energy and exergy analysis of pulse detonation combustor and pulse detonation turbine engine cycle

Energy and exergy analysis of pulse detonation combustor and pulse detonation turbine engine cycle

Axial Compressor Map Generation Leveraging Autonomous Self-Training Artificial Intelligence. Phase 2

Abstract This paper discusses a study performed by SoftInWay as part of a Phase II SBIR project funded by NASA. In contrast with the Phase I project (Burlaka and Moroz, 2023, “Axial Compressor Map Generation Leveraging Autonomous Self-Training Artificial Intelligence,” ASME J. Eng. Gas Turbines Power, 145(1), p. 011001) where three discrete compressors were considered, the Phase II study was focused on addressing the problem of axial compressor long development time and cost with the use of AI models capable of predicting the geometry and performance of various multistage axial compressors with multiple variable vanes. The applicability of the AI models to various compressors enables the opportunity to avoid iterations between engine cycle analysis and compressor design. In this paper, automated compressor design and performance generation workflows are described. The approach for autonomous selection of the architectures and hyperparameters of Machine Learning (ML) models is explained. The uncertainty quantification techniques are considered. The developed ML-powered methods for compressor geometry prediction are discussed. The ML models' accuracy values and representations of typical geometry and performance predictions are given. The utilization of the ML models in engine cycle analysis is discussed.

An Adsorption-Desorption Heat Engine for Power Generation from Waste Heat

According to the United States Department of Energy, waste heat recovery would allow up to a 20% reduction in greenhouse gases (GHG) emission. Most of the waste energy is discharged as a low-grade heat at temperatures less than 250°C. Therefore, the development of new technologies and the enhancement of existing ones to convert low-grade heat into electrical or mechanical energy are of great importance. The working principle of adsorption-desorption heat pumps with cyclic switching between adsorption and desorption is adapted in the proposed heat engine to generate electrical power from low-temperature heat. Thermodynamic analysis of the heat engine cycle is carried out for the pair adsorbant-adsorbent: CO<sub>2</sub>-activated carbon. Its efficiencies are calculated accepting the ideal gas law and an adsorption-desorption equilibrium at the key points of the cycle. The cycle consists of two isochores and two isotherms like the Stirling engine, but at the same temperature range and without heat regeneration, its thermal efficiency (work per heat supplied) can reach 11.3% vs. 5.0% and specific work 50.7 vs. 3.55 in the latter. The proposed unit has thermal efficiency in the range of Organic Rankine Cycle units and can be utilized in small-scale applications up to 40kWe, where manufacturing cost of turbines or expanders for ORCs increases dramatically. Accounting for quality (temperature) of utilized heat, the proposed cycle’s exergy efficiency, <em>ζ<sub>ex</sub></em> = 34.5% approaches that of water-steam Rankine cycles utilizing natural gas or coal combustion.

Thermodynamic analysis of general heat engine cycle with finite heat capacity rates for power maximization

In this study, the ideal cycles with finite heat capacity rates is investigated theoretically to maximize power generation using a sequential Carnot cycle model. Although the Carnot efficiency is important, it is limited to evaluating only in terms of heat source/sink temperatures. For the actual heat engine, maximization of power generation is more important than cycle thermal efficiency when utilizing low-grade heat sources such as a waste heat. In this study, power generation optimization is numerically simulated under the fixed conditions of heat source temperatures, heat source flow rate and heat sink temperature. Effect by two design variables, compressor exit temperature and evaporator size ratio, were evaluated during cycle optimization. The optimization was performed using the pattern search algorithm (PSA) under a given thermal capacitance rate ratios and size of heat exchanger ( UA ) conditions. As a result, designing compressor exit temperature for maximizing the heat received from heat sources does not always maximize the power, but the higher the UA makes the optimum temperature lower, and the power output higher. These idealistic approaches can be useful in designing of cycle where the power maximization is crucial.

Power density characteristic analysis and multi-objective optimization of an irreversible porous medium engine cycle

Based on irreversible Porous Medium cycle model established in the previous literature, this paper investigates cycle optimal performance by taking cycle power density as optimization objective and applying finite time thermodynamics. Various parameters are used to examine relationships among power density and thermal efficiency versus compression ratio. The cycle performance is compared under maximum power density circumstance and maximum power output circumstance. Compared with condition of maximum power output, the Porous Medium cycle engine gets higher thermal efficiency and smaller size under the maximum power density condition. One-, two-, three- and four-objective optimizations of the cycle are performed by using NSGA-II algorithm, choosing compression ratio as design variable, and choosing dimensionless power density, dimensionless power output, thermal efficiency, and dimensionless ecological function as optimization objectives. Using three decision schemes, LINMAP, TOPSIS and Shannon entropy, deviation indices under different optimization objective combinations are compared. For six two-objective optimizations, power output and thermal efficiency optimization has the smallest deviation index, 0.1215. For four three-objective optimizations, power output, ecological function and power density optimization has the smallest deviation index, 0.1235. For four-objective optimization, the deviation index is 0.1419. The appropriate solution should be selected according to the actual application.

Performance analysis and optimization of an irreversible Carnot heat engine cycle for space power plant

In this paper, an irreversible Carnot heat engine cycle model for space power plants is built by using finite time thermodynamics. A radiator panel is considered between low temperature heat sink and space environment, expressions for power output and thermal efficiency of the plant are derived. Influences of internal irreversibility effect and thermal leakage loss on the optimal power output performance are analyzed when thermal conductivity of hot- and cold-sides heat exchangers are given. For the fixed total area of three heat exchangers the double-maximum power output and double-maximum thermal efficiency are obtained further by optimizing area distributions of hot- and cold- side heat exchangers and radiator, and by optimizing temperature of low-temperature heat sink. Influences of internal irreversibility effect and thermal leakage loss on the optimal performances are investigated. The results show that when taking power output as optimization objective, if considering thermal leakage and irreversibility effect, internal irreversibility effect increases from 1.1 to 1.3, double maximum power output decreases from 216.38 kW to 139.85 kW and decreases by 35.37%, the optimal the temperature the low-temperature heat sink decreases from 556K to 501.1K and decreases by 9.87%, and the optimal area allocations of hot- and cold-side heat exchangers decrease from 0.213 to 0.182 and decreases by 14.55%, from 0.213 to 0.207 and decreases by 2.82%, respectively, and that of radiator increases from 0.563 to 0.611 (an increase of 8.35%). Such temperature and area distribution condition ensure the future design of plant conversion system that aligns better performances and compactness.

Thermodynamic Analysis of General Heat Engine Cycle with Finite Heat Capacity Rates for Power Maximization

Thermodynamic Analysis of General Heat Engine Cycle with Finite Heat Capacity Rates for Power Maximization

Thermodynamic analysis of chemical precooled turbine combined engine cycle

The precooling technology is an effective way to expand the flight envelope of the turbine engine. To solve the problem of engine performance degradation caused by excessive fuel consumption, a new type of chemical precooled engine cycle is proposed, in which part of the heat energy from the incoming air is converted into the chemical energy by pyrolytic reaction. To evaluate the engine performance, a thermodynamic model is established. Based on this model, the experiments are performed to obtain the chemical heat sink of selected fuels. Through the simulation, it is found that the specific impulse is greatly improved because the fuel consumption is effectively reduced by introducing the chemical precooling process. Moreover, the highest operating Mach number (HOMN) of the precooled turbine channel is effected by different component parameters, among which the increase of the turbine inlet temperature has the most significant effect on rising the HOMN. Furthermore, the optimal fuel ratio can be obtained when the equivalence ratio is equal to 1.0, and the fuel consumption can be saved by 42% ~ 52% at this time. In general, the results in this paper are beneficial for developing high-performance turbine combined engines.

Influence of Bioethanol Blends on Performances of a Micro Turbojet Engine

This paper proposes a study regarding the use of bioethanol as fuel for turbine engines used in aviation. For this purpose, three blends of 5, 10, and 15% concentrations of bioethanol mixed with Jet A fuel were tested on JET CAT P80 microturbo engine. During the engine testing, the following parameters were monitored: engine speed, generated force, temperature in front of the turbine, fuel volumetric flow rate, and vibration levels measured both on axial and radial direction. The tests were performed by maintaining the microturbo engine for about 1 min at three operating regimes: idle, cruise, and maximum speed. In addition, a comparative analysis between fuels for a test with the microturbo engine from the idle position to maximum position is presented. After the tests were conducted, a jet engine cycle analysis was performed at the max regime and the fuel specific consumption, the efficiency of the combustion chamber, and the thermal efficiency of the engine for each fuel blend were calculated. The tests were made without making any modifications to the engine components or automation system.

Computationally efficient prediction of cycle-to-cycle variations in spark-ignition engines

Cycle-to-cycle variations are important to consider in the development of spark-ignition engines to further increase fuel conversion efficiency. Direct numerical simulation and large eddy simulation can predict the stochastics of flows and therefore cycle-to-cycle variations. However, the computational costs are too high for engineering purposes if detailed chemistry is applied. Detailed chemistry can predict the fuels’ tendency to auto-ignite for different octane ratings as well as locally changing thermodynamic and chemical conditions which is a prerequisite for the analysis of knocking combustion. In this work, the joint use of unsteady Reynolds-averaged Navier–Stokes simulations for the analysis of the average engine cycle and the spark-ignition stochastic reactor model for the analysis of cycle-to-cycle variations is proposed. Thanks to the stochastic approach for the modeling of mixing and heat transfer, the spark-ignition stochastic reactor model can mimic the randomness of turbulent flows that is missing in the Reynolds-averaged Navier–Stokes modeling framework. The capability to predict cycle-to-cycle variations by the spark-ignition stochastic reactor model is extended by imposing two probability density functions. The probability density function for the scalar mixing time constant introduces a variation in the turbulent mixing time that is extracted from the unsteady Reynolds-averaged Navier–Stokes simulations and leads to variations in the overall mixing process. The probability density function for the inflammation time accounts for the delay or advancement of the early flame development. The combination of unsteady Reynolds-averaged Navier–Stokes and spark-ignition stochastic reactor model enables one to predict cycle-to-cycle variations using detailed chemistry in a fraction of computational time needed for a single large eddy simulation cycle.

분리형 로터리엔진 사이클 해석

분리형 로터리엔진 사이클 해석

Performances and Emissions Evaluation of a Microturbojet Engine Running on Biodiesel Blends

This paper analyzes the performances and the emissions of the JETCAT P80 microengine, when jet A jet A + 10% biodiesel (BD), jet A + 20% biodiesel, and jet A + 30% biodiesel are utilized as fuel, and to each of these combinations is added 5% of Aeroshell Oil 500. The performances will be assessed based on the engine speed, for the generated thrust force, the temperature in front of the turbine, and on the fuel flow. The paper will investigate the performances and the emissions generated by the four fuel blends burning when the engine is idle, at the cruise and at the max regime. This will be realized by maintaining each of these regimes for approximately a minute and a half. During the tests, the vibrations were monitored both radially and axially for the observation of the engine function regimes. From the measurements, the concentrations of SO2, NOx, and CH4 will be analyzed, highlighting the emissions of SO2. There were performed measurements to determine the fuel blend's density in order to transform the values of the fuel flow from liter per hour into kilogram per second. Having these data registered from the engine, a jet engine cycle analysis at max regime will be performed based on the combustion efficiency, the thermal efficiency of the engine, and the specific fuel consumption.

Optimal Approximations of Coupling in Multidisciplinary Models

This paper presents a methodology for identifying important discipline couplings in multicomponent engineering systems. Coupling among disciplines contributes significantly to the computational cost of analyzing a system and can become particularly burdensome when coupled analyses are embedded within a design or optimization loop. In many cases, disciplines may be weakly coupled, so that some of the coupling or interaction terms can be neglected without significantly impacting the accuracy of the system output. Typical practice derives such approximations in an ad hoc manner using expert opinion and domain experience. This work proposes a new approach that formulates an optimization problem to find a model that optimally balances accuracy of the model outputs with the sparsity of the discipline couplings. An adaptive sequential Monte Carlo sampling-based technique is used to efficiently search the combinatorial model space of different discipline couplings. An algorithm for selecting an optimal model is presented and illustrated in a fire-detection satellite model and a turbine engine cycle analysis model.

Thermodynamic analysis and multi-objective optimisation of endoreversible Lenoir heat engine cycle based on the thermo-economic performance criterion

ABSTRACTA thermodynamic model of a steady-flow endoreversible Lenoir heat engine cycle (a ‘three-point’ cycle) coupled with constant-temperature heat reservoirs is established in this paper by using finite-time thermodynamic theory. The cycle consists of one isochoric heating branch, one adiabatic expansion branch and one isobaric cooling branch. A mathematical approach based on the finite-time thermodynamic is proposed to obtain thermal efficiency, the output power and the entropy generation rate throughout the Lenoir system. In this study, an irreversible Lenoir engine is analysed thermodynamically in order to optimise its performance. In this regard, the optimal values of the ecological coefficient of performance and dimensionless thermo-economic objective functions of the Lenoir heat engine are determined. Multi-objective evolutionary algorithms based on Non-dominated Sorting Genetic Algorithm II algorithm is applied to the aforementioned system for calculating the optimal values of decision variables. Decision variables considered in this paper include the ratio of fluid temperature (), the effectiveness of the cold-side heat exchanger, the effectiveness of the hot-side heat exchanger, the temperature of state 1 and relative investment cost parameter of the hot-side heat exchanger. Moreover, Pareto optimal frontier is applied and an ultimate optimal answer is chosen via three competent decision-making approaches comprising Linear Programming Technique for Multidimensional Analysis of Preference, fuzzy Bellman-Zadeh and Technique for Order of Preference by Similarity to Ideal Solution.

Study on multi-cycle coupling mechanism of hypersonic precooled combined cycle engine

Propulsion system is a crucial issue of hypersonic civil aviation. Precooled engine shows attractive advantages in high flight Mach numbers, and the hypersonic precooled combined cycle engine (HPCCE) is one of the most potential plans. Multi-cycle coupling is the most remarkable feature of HPCCE, reflected by the large-scale frequent energy exchange among subsystems, i.e. opened cycle, closed cycle and propellant system, and the interaction between the designs for different working conditions. The mechanism is studied through engine cycle analysis with enthalpy-entropy relations. Quantitative discussion on major design parameters based on a component level simulation model shows the trends of inter-impact among subsystems and parameters, and sketches the multi-cycle mechanism and energy transfer relations in detail. Vital issues that should be emphasized through the design process are pointed out.

Improving the performance of LOX/kerosene upper stage rocket engines

Improved liquid rocket engine cycles were proposed and analyzed via comparison with existing staged combustion and gas-generator cycles. The key features of the proposed cycles are regenerative cooling of thrust chamber by oxygen and subsequent use of this oxygen for driving one or two oxygen pumps. The fuel pump(s) are driven in a conventional manner, for example, using a fuel-rich gas-generator cycle. Comparison with staged combustion cycle based on oxygen-rich pre-burner showed that one of the proposed semi-expander cycles has a specific impulse only on 0.4% lower while providing much lower oxygen temperature, more efficient tank pressurizing system and built-in roll control. This semi-expander cycle can be considered as a more reliable and cost-effective alternative of staged combustion cycle. Another semi-expander cycle can be considered as an improvement of gas-generator cycle. All proposed semi-expander cycles were developed as a derivative of thrust chamber regenerative cooling performed by oxygen. Analysis of existing oxygen/kerosene engines showed that replacing of kerosene regenerative cooling with oxygen allows a significant increase of achievable specific impulse, via optimization of mixture ratio. It is especially the case for upper stage engines. The increasing of propellants average density can be considered as an additional benefit of mixture ratio optimization. It was demonstrated that oxygen regenerative cooling of thrust chamber is a feasible and the most promising option for oxygen/kerosene engines. Combination of oxygen regenerative cooling and semi-expander cycles potentially allows creating the oxygen/kerosene propulsion systems with minimum specific impulse losses. It is important that such propulsion systems can be fully based on inherited and well-proven technical solutions. A hypothetic upper stage engine with thrust 19.6kN was chosen as a prospective candidate for theoretical analysis of the proposed semi-expander cycles. The newly-developed software RECS was used for the comparative analysis of engine cycles.

Performance optimization of a regenerative Brayton heat engine coupled with a parabolic dish solar collector

In this study, a detailed thermodynamic analysis of a regenerative Brayton heat engine cycle coupled with a parabolic-dish solar collector is conducted. The analysis examines the thermal performance of the coupled system for power generation applications. Important non-dimensional parameters that govern the optimized performance of the coupled system are identified. The efficiency of the coupled system is expressed in terms of three parameters namely the Brayton cycle pressure ratio, the concentration ratio of the parabolic dish collector, and the maximum temperature ratio of the Brayton cycle. The efficiency of the coupled system is then optimized with respect to the aforementioned parameters by solving the resultant system of three coupled non-linear algebraic equations using a MATLAB(R) program. Optimal values for Brayton cycle pressure ratio, concentration ratio of the parabolic dish collector, and maximum temperature ratio of the Brayton cycle are obtained corresponding to the optimal efficiency of the coupled system. Effects of variation of heat exchanger efficiency, total concentrator error, rim angle and non-dimensional radiation flux parameter on the optimal performance of the coupled system are investigated. Impact of these parameters on the engine size is also presented. In addition, a procedure for preliminary design of the coupled system using performance charts is developed. Results are presented in the form of performance charts that display the effects of changing the heat exchanger efficiency, total concentrator error, rim angle and non-dimensional radiation flux parameter on the optimal efficiency of the coupled system. The analysis show that higher optimal efficiency of the coupled system is achieved for lower values of total concentrator error and higher values of the heat exchanger efficiency. It is also seen that a solar thermal power generation system using the regenerative Brayton cycle results in migration of the optimal efficiency point towards lower values of engine pressure ratio.

A full engine cycle analysis of a turbofan engine for optimum scheduling of variable guide vanes

This paper proposes a full engine cycle analysis to derive the schedule of variable guide vanes (VGVs) in a multi-stage axial compressor for improving the performance of a turbofan engine with required surge margin. Most researchers assumed the operating line of a compressor in process of scheduling of VGVs. However, it has been known that the performance of a compressor is influenced by the angle of VGVs. As a result, the performance variation of a compressor can affect an engine. Therefore, a full engine cycle analysis is conducted to consider the effect of VGVs on a turbofan engine. The VGVs are applied to the front stages of the high pressure compressor in the low-bypass ratio turbofan engine. The compressor of the front stages is transonic three-stage axial flow compressor. The commercial engine simulation program, NPSSTM is employed to analyze the on- and off-design performance of the turbofan engine. 1D meanline analysis is used for performance prediction of a multi-stage axial flow compressor with VGVs. The engine simulation program is coupled with the compressor performance prediction tool to consider the engine performance variation with application of the VGVs. The proposed scheduling algorithm of the inlet guide vane (IGV) and stator vanes (SV) is adjusting the vanes angle to have the minimum loss incidence angle at all rotor blades and to satisfy the required surge margin at off-design condition. The result shows that the proposed algorithm can obtain the scheduling of the IGV, 1st and 2nd SVs angle with stable operation and improved specific fuel consumption of the engine.

Calibration-free, high-speed, in-cylinder laser absorption sensor for cycle-resolved, absolute H2O measurements in a production IC engine

The performance of a hygrometer based on calibration-free direct tunable diode laser absorption spectroscopy (dTDLAS) for in-cylinder H2O measurements is demonstrated in a nearly unmodified production internal combustion engine. The H2O concentration is a proxy for the residual gas fraction remaining in the cylinder after intake-valve closure. One challenge for in-cylinder measurements, especially in multi-cylinder engines, is to obtain optical access to the combustion chamber. The measurements here were performed in the flywheel-side cylinder of a four-cylinder engine with small access ports that were previously designed for endoscopic imaging. Due to their position these ports prohibit the usual collinear arrangement of the optical elements typical for line-of-sight measurement techniques. Therefore, we developed a new “angled” fiber-optical interface, which allows a trans-illumination of the engine at a 90° angle. The optical fiber interface uses a scattering target inside the combustion chamber with its 84mm bore achieving an absorption length of about 70mm. With this arrangement, crank-angle resolved measurements of the H2O concentration during early compression could be realized with a temporal resolution of 250μs and a H2O detection limit of 0.074vol.%. This allows detailed analysis of single engine cycles as needed for residual gas investigations. Measurements were performed over a range of loads (25–100Nm) and speeds (1400–3650rpm), over which the residual gas fraction was expected to vary significantly. H2O concentrations were measured between 3.3 and 5.0vol.%. The results were compared with a simple model of residual gas content and were found to agree within the combined uncertainty of both methods, which gives an indication that dTDLAS can be used to validate more complex engine models beyond what is possible by pressure-trace analysis.

Entransy analysis of irreversible Carnot-like heat engine and refrigeration cycles and the relationships among various thermodynamic parameters

Because of the energy needs of the world and the issues involved with global warming, analyzing and optimizing power cycles have increased in importance. In this paper, the concepts of entransy dissipation, entropy generation, power output, exergy output, energy, exergy efficiencies for irreversible heat engine cycles and entransy dissipation, entropy generation, power inputs, exergy input, entropy generation, COP and the exergy of efficiency for the irreversible refrigeration cycle are applied as a means of analyzing them. The results are obtained numerically, and the optimum or critical values are determined for a dimensionless temperature ratio and a dimensionless heat conductance ratio. Finally, recommendations on the design and range of operating conditions for the cycles are presented. Values of TC/TE (x), can be selected between 0.5 and 0.55 and values of kE/kC (y) in the range of 0.3–0.5 can be selected for high performance and low losses in a heat engine. Choosing values of TC/TE (x) and kC/kE (y) as low as possible for high performance, besides low thermodynamic losses (entropy generation and entransy dissipation) for the refrigeration cycle.