Development and test of combustion chamber for Stirling engine heated by natural gas

The combustion chamber is an important component for the Stifling engine heated by natural gas. In the paper, we develop a combustion chamber for the Stifling engine which aims to generate 3-5 kWe electric power. The combustion chamber includes three main components： combustion module, heat exchange cavity and thermal head. Its feature is that the structure can divide ＂combustion＂ process and ＂heat transfer＂ process into two appar- ent individual steps and make them happen one by one. Since natural gas can mix with air fully before burning, the combustion process can be easily completed without the second wind. The flame can avoid contacting the thermal head of Stifling engine, and the temperature fields can be easily controlled. The designed combustion chamber is manufactured and its performance is tested by an experiment which includes two steps. The experi- mental result of the first step proves that the mixture of air and natural gas can be easily ignited and the flame burns stably. In the second step of experiment, the combustion heat flux can reach 20 kW, and the energy utiliza- tion efficiency of thermal head has exceeded 0.5. These test results show that the thermal performance of com- bustion chamber has reached the design goal, The designed combustion chamber can be applied to a real Stifling engine heated by natural gas which is to generate 3-5 kWe electric power.     

Thermal model of a dish/Stirling systems

This paper presents a global thermal model of the energy conversion of the 10 kW_el Eurodish dish/Stirling unit erected at the CNRS-PROMES laboratory in Odeillo. Using optical measurements made by DLR, the losses by parabola reflectivity and spillage are calculated. A nodal method is used to calculate the heat losses in the cavity by conduction, convection, reflection and thermal radiation. A thermodynamic analysis of a SOLO Stirling 161 engine is made. The Stirling engine is divided in 32 control-volumes and equations of ideal gas, mass and energy conservation are written for each control-volume. The differential equation system is resolved by an iterative method developed using Matlab^™ programming environment. Temperature, mass, density of working gas, heat transfers and the mechanical power are calculated for one Stirling engine cycle of 40 ms and for a constant direct normal irradiation (DNI). The model gives consistent results correctly fitting with experimental measurements.     

Exergetic analysis and performance evaluation of parabolic dish Stirling engine solar power plant

In this communication, a 50 MW_e design capacity parabolic dish Stirling engine solar power plant (PDSSPP) has been modeled for analysis, where 2000 units of parabolic dish Stirling engine each having capacity of 25 kW_e were considered to get desired capacity. An attempt has been made to carry out the energetic and exergetic analysis of different components of a solar power plant system using parabolic dish collector/receiver and Stirling engine. The energetic and exergetic losses as well as efficiencies for typical PDSSPP under the typical operating conditions have been evaluated. Variations of the efficiency of Stirling engine solar power plant at the part‐load condition are considered for year‐round performance evaluation. The developed model is examined at location Jodhpur (26.29°N, 73.03°E) in India. It is found that year‐round energetic efficiency varies from 15.57% to 27.09%, and exergetic efficiency varies from 16.83% to 29.18%. The unit cost of electric energy generation (kW_eh) is about 8.76 Indian rupees (INR), with 30 years life span of the plant and 10% interest rate on investment. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermochemical two-step water splitting by internally circulating fluidized bed of NiFe2O4 particles: Successive reaction of thermal-reduction and water-decomposition steps

Thermochemical two-step water splitting using a redox system of iron-based oxides or ferrites is a promising process for producing hydrogen without CO₂ emission by the use of high-temperature solar heat as an energy source and water as a chemical source. In this study, thermochemical hydrogen production by two-step water splitting was demonstrated on a laboratory scale by using a single reactor of an internally circulating fluidized bed. This involved the successive reactions of thermal-reduction (T-R) and water-decomposition (W-D). The internally circulating fluidized bed was exposed to simulated solar light from Xe lamps with an input power of 2.4-2.6 kW_th for the T-R step and 1.6-1.7 kW_th for the subsequent W-D step. The feed gas was switched from an inert gas (N₂) in the T-R step to a gas mixture of N₂ and steam in the W-D step. NiFe₂O₄/m-ZrO₂ and unsupported NiFe₂O₄ particles were tested as a fluidized bed of reacting particles, and the production rate and productivity of hydrogen and the reactivity of reacting particles were examined.     

An experimental investigation of a household size trigeneration

A household size trigeneration based on a small-scale diesel engine generator set is designed and realized in laboratory. Experimental tests are carried out to evaluate the performance and emissions of the original single generation (diesel engine generator); and the performances of the whole trigeneration including the diesel generator within the trigeneration system, the heat exchangers which are used to recover heat from engine exhaust, the absorption refrigerator which is driven by the exhaust heat; and the emissions from the whole trigeneration.Comparisons of the test results of two generations are also performed. The test results show that the total thermal efficiency of trigeneration reaches to 67.3% at the engine full load, comparing to that of the original single generation 22.1% only. Within the range of engine loads tested, the total thermal efficiencies of trigeneration are from 205% to 438% higher than that of the thermal efficiency of single generation.The CO₂ emission per unit (kW h) of useful energy output from trigeneration is 0.401 kg CO₂/kW h at the engine full load, compared to that of 1.22 kg CO₂/kW h from single generation at the same engine load. Within the range of engine loads tested, the reductions of CO₂ emission per unit (kW h) of trigeneration output are from 67.2% to 81.4% compared to those of single generation.The experimental results show that the idea of realizing a household size trigeneration is feasible; the design and the set-up of the trigeneration is successful. The experimental results show that the innovative small-scale trigeneration is able to generate electricity, produce heat and drive a refrigeration system, simultaneously from a single fuel (diesel) input.     

Performance assessment of a Stirling engine plant for local micro‐cogeneration

In this paper, we evaluate the viability of a 9.5‐kW_e wooden pellet‐fueled Stirling engine‐based micro‐cogeneration plant as a substitute for small‐scale district heating. The district heating systems against which the micro‐cogeneration plant is compared are based either on a pellet‐fueled boiler or a ground‐source heat pump. The micro‐cogeneration and district heating plants are compared in terms of primary energy consumption, CO₂ emissions, and feasibility of the investment. The comparison also considers an optimally operated individual 0.7‐kW_e pellet‐fueled Stirling engine micro‐cogeneration system with exhaust gas heat recovery. The study is conducted in two different climates and contributes to the knowledge base by addressing: (i) hourly changes in the Finnish electricity generation mix; and (ii) uncertainty related to what systems are used as reference and the treatment of displaced grid electricity. Our computational results suggest that when operated at constant power, the 9.5‐kW_e Stirling engine plant results in reduced annual primary energy use compared with any of the alternative systems. The results are not sensitive to climate or the energy efficiency or number of buildings. In comparison with the pellet‐fueled district heating plant, the annual use of primary energy and CO₂ emissions are reduced by a minimum of 25 and 19%, respectively. Owing to a significant displacement of grid electricity, the system's net primary energy consumption appears negative when the total built area served by the plant is less than 1200 m². On the economic side, the maximum investment cost threshold of a CHP‐based district heating system serving 10 houses or more can typically be positive when compared with oil and pellet systems, but negative when compared with a corresponding heat pump system. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of an experimental test rig for cogeneration based on a Stirling engine and a biofuel burner

A system consisting of a last-generation Stirling engine (SE) and a fuel burner for distributed power generation has been developed and experimentally investigated. The heat generated by the combustion of two liquid fuels, a standard Diesel fuel and a rapeseed oil, is used as a heat source for the SE, that converts part of the thermal energy into mechanical and then electric energy. The hot head of the SE is kept in direct contact with the flame generated by the burner. The burner operating parameters, designed for Diesel fuel, were changed to make it possible to burn vegetable oils, not suitable for internal combustion engines. The possibility of adopting different configurations of the combustion chamber was taken into account to increase the system efficiency. The preliminary configurations adopted allowed to operate this integrated system, obtaining an electric power up to 4.4 kW_el with a net efficiency of 11.6%.     

Performance of a twin power piston low temperature differential Stirling engine powered by a solar simulator

This paper provides an experimental investigation on the performance of a low-temperature differential Stirling engine. In this study, a twin power piston, gamma-configuration, low-temperature differential Stirling engine is tested with non-pressurized air by using a solar simulator as a heat source. The engine testing is performed with four different simulated solar intensities. Variations of engine torque, shaft power and brake thermal efficiency with engine speed and engine performance at various heat inputs are presented. The Beale number, obtained from the testing of the engine, is also investigated. The results indicate that at the maximum simulated solar intensity of 7145 W/m², or heat input of 261.9 J/s, with a heater temperature of 436 K, the engine produces a maximum torque of 0.352 N m at 23.8 rpm, a maximum shaft power of 1.69 W at 52.1 rpm, and a maximum brake thermal efficiency of 0.645% at 52.1 rpm, approximately.     

Experimental evaluation of the sensitivity to fuel utilization and air management on a 100 kW SOFC system

The tubular SOFC generator CHP-100, built by Siemens Power Generation (SPG) Stationary Fuel Cells (SFC), is running at the Gas Turbine Technologies (GTT) in Torino (Italy), in the framework of the EOS Project. The nominal load of the generator ensures a produced electric power of around 105 kW_e ac and around 60 kW_t of thermal power at 250 °C to be used for the custom tailored HVAC system.     

Combustion and emission characteristics of a swirling fluidized-bed combustor burning moisturized rice husk

Burning of rice husk in a swirling fluidized-bed combustor (SFBC) was the focus of this experimental study. Swirl motion of a fluidized bed in this combustor was induced by an annular spiral distributor of primary air and also promoted by tangential injection of secondary air into the bed splash zone. “As-received” rice husk was moisturized with the aim to control NO emission from the combustor. The SFBC was tested at a constant fuel feed rate (of about 80 kg/h) for six fuel-moisture contents (from 8.4% to 35%). In each test series for the particular fuel quality, excess air was ranged from about 20% to 80%. Radial and axial profiles of temperature and gas concentrations (O₂, CO and NO) were plotted for different fuel options and operating conditions with the aim to study pollutants formation and reduction in different regions of the SFBC. With increasing the fuel-moisture content, the emission of NO from the combustor apparently reduced, while the emission of CO was adjusted at a quite low level due to the effects of secondary air. An effective least-cost control of both NO and CO emissions and high (over 99%) combustion efficiency are achievable when firing moisturized rice husk in this SFBC.     

流化床炉内温度场的虚拟表示

介绍了以VC^ 6．0为平台，结合Intra3D技术，研究流化床锅炉燃烧温度场的三维动态可视化虚拟表示．在流化床锅炉燃烧温度场的动态全面仿真的基础上，运用计算机图形学的理论和方法，利用数字仿真的大量数据，借助粒子运动系统的规律，建立流化床虚拟火焰，并实现动态显示和基本的人机交互，该技术的研究，可拓展热力系统性能研究的思路，弥补试验或中试研究投资大和周期长的不足，开拓出新型热力系统的虚拟再现研究手段。     

Characterization of ashes from a 100 kWth pilot-scale circulating fluidized bed with oxy-fuel combustion

Oxy-fuel combustion experiments have been carried out on an oxygen-fired 100 kW_th mini-circulating fluidized bed combustion (CFBC) facility. Coal and petroleum coke were used as fuel together with different limestones (and fixed Ca:S molar ratios) premixed with the fuel, for in situ SO₂ capture. The bed ash (BA) and fly ash (FA) samples produced from this unit were collected and characterized to obtain physical and chemical properties of the ash samples. The characterization methods used included X-ray fluorescence (XRF), X-ray diffraction (XRD), char carbon and free lime analysis, thermogravimetric analysis (TGA), and surface analysis. The main purpose of this work is to characterize the CFBC ashes from oxy-fuel firing to obtain a better understanding of the combustion process, and to identify any significant differences from the ash generated by a conventional air-fired CFBC. The primary difference in the sulfur capture mechanism between atmospheric air-fired and oxy-fuel FBC, at typical FBC temperatures (∼850 °C), is that, in the air-fired case the limestone sorbents calcine, whereas the partial pressure of CO₂ in oxy-fuel FBC is high enough to prevent calcination, and hence the sulfation process should mimic that seen in pressurized FBC (PFBC). Here, the char carbon content in the fly ash was much higher than that in the bed ash, and was also high by comparison with ash obtained from conventional commercial air-firing CFBC units. In addition, measurements of the free lime content in the bed and fly ash showed that the unreacted Ca sorbent was present primarily as CaCO₃, indicating that sulfur capture in the oxy-fuel combustor occurred via direct sulfation. Limestone utilization for oxy-fuel combustion in this unit was generally lower than that in industrial-scale air-firing CFBCs, with better limestone performance found during combustion of petcoke running at relatively higher temperatures. The Brunauer–Emmett–Teller (BET) surface area and also the pore volume in the fly ash were much higher than in the bed ash and smaller size pores predominated in the fly ash samples.     

Design and performance optimization of GPU-3 Stirling engines

To increase the performance of Stirling engines and analyze their operations, a second-order Stirling model, which includes thermal losses, has been developed and used to optimize the performance and design parameters of the engine. This model has been tested using the experimental data obtained from the General Motor GPU-3 Stirling engine prototype. The model has also been used to investigate the effect of the geometrical and physical parameters on Stirling engine performance and to determine the optimal parameters for acceptable operational gas pressure. When the optimal design parameters are introduced in the model, the engine efficiency increases from 39% to 51%; the engine power is enhanced by approximately 20%, whereas the engine average pressure increases slightly.     

Experimental study on N2O emission in O2/CO2 combustion with high oxygen concentration in circulating fluidized bed

To characterize the N₂O formation and fuel nitrogen conversion in an oxy-fuel circulating fluidized bed (CFB) combustor with high oxygen concentration, tests were carried out by analysing the axial concentrations of N₂O in a 50 kW_th CFB combustor. The conversion ratios from fuel nitrogen to gaseous N-containing pollutants were calculated. The initial N₂O concentrations in the bottom of the combustor were similar between oxy-fuel firing and air-firing. The axial N₂O formation was more in oxy-fuel combustion than in air-firing, improving the N₂O emission during 50% O₂/50% CO₂ combustion. The atmospheric variation significantly affected the conversion ratio from fuel nitrogen to N₂O. In addition, the conversion from fuel nitrogen to N₂O was much higher than that to NO. As a result, the N₂O emission during oxy-fuel CFB combustion cannot be ignored. Gas staging little influenced the N₂O emission. With the increasing ratio of secondary gas, the initial N₂O formation in the dense zone increased, while the axial N₂O formation along the combustor declined. By analysing the conversion ratios of fuel nitrogen, it was also found that gas staging obviously affected the conversion ratio from fuel nitrogen to NO by enhancing the NO to N₂ conversion. However, gas staging did not impact the conversion ratio from fuel nitrogen to N₂O.     

小型斯特林发动机不同外加热工况下运行的探索性实验

该文就其微型化可能产生的一系列问题,如：输出频率过高、产生转矩过小、冷热端差过小等进行了分析。提出自由活塞式斯特林发动机比热声式更具微型化的优势。并对一台长12cm、直径2．5cm的小型活塞式斯特林发动机进行了实验。实验中发动机热端温度范围64～626℃,通过测量其外壁面温度和声信号随时问的变化,得到发动机的稳定性和输出功率随外加热功率变化规律。该发动机的理论最高功率密度为102kW／m^3。     

CFB combustion of low-grade lignites: Operating stability and emissions

This work presents the results of a comprehensive experimental investigation on the combustion of the low grade Turkish lignites in a 30 kW_th circulating fluidized bed combustor. This is the first study of this kind has ever been undertaken on these coals. Eighteen lignite samples procured from various lignite sites of Turkey have been burned under similar combustion conditions in order to access to their combustion stability and to determine the emissions of the major pollutants such as CO, NO_X and SO₂ in the flue gas from combustor. The qualities of lignites were evaluated based on van Krevelen graph which was highly scattered and diverse in respect to the degree of ageing. A steady and stable combustion was observed in the temperature range of 725–950 °C with an average operating temperature of around 850 ± 50 °C for all lignites. Under the operating condition applied in the study, CO, NO_X and SO₂ emissions varied mostly in the ranges of 120–600 mg/Nm³, 90–420 mg/Nm³ and 1100 mg/Nm³ - 18000 mg/Nm³, respectively. From the experimental results it seems that the most challenging problem may be faced during the CFB combustion of most of these lignites will be SO₂ emissions.     

Design and performance evaluation of an innovative small scale combined cycle cogeneration system

This paper deals with an innovative natural gas (NG) combined cycle cogeneration system (150-kW_e, 192 kW_t). The system is made up of a combination of two interconnected combined heat and power (CHP) systems: a reciprocating internal combustion engine cogenerator (ICE CHP) as the topping cycle and a Rankine cycle cogenerator (RC CHP) which operates as the bottoming cycle on the exhaust gases from the ICE. The expander technology chosen for the Rankine cycle prime mover is a reciprocating single expansion steam engine with three cylinders in a radial architecture. The ICE is an automotive derived internal combustion engine with a high part-load electrical efficiency, due to a variable speed operation strategy and reduced emissions.     

回收垃圾填埋气发电的热气机燃烧系统研究

针对热气机连续燃烧的特点,采用稀薄燃烧和燃气再循环技术,开发了一套新型旋流扩散燃烧系统和燃烧控制逻辑,建立了利用热气机回收填埋气发电的试验系统,在垃圾填埋场进行了现场系统性能试验.结果表明,改装了燃烧垃圾填埋气燃烧器的热气机系统启动容易,对甲烷浓度适应范围广,燃烧完善,燃烧室内温度分布均匀合理,污染物排放低,并且实现了热气机发电系统无人值守运行.     

Effect of operating parameters on sulphur capture in a pressurized circulating fluidized bed combustor

Experiments are conducted to investigate the effect of system pressure, Ca/S ratio and primary air velocity on sulphur capture in a pressurized circulating fluidized bed (PCFB) combustor. The pressure inside the PCFB combustor is varied from 200 to 700 kPa. The Ca/S ratio is varied from 1.6 to 3.0. The primary air velocity ranges from 3 to 7 ms^?1. The bed temperature is maintained at 750°C. The sulphur capture increases with system pressure in the present range of experimental investigations. The sulphur capture also increases with Ca/S ratio up to a certain ratio and then shows a decreasing trend for the given operating conditions. A semi‐empirical model is developed for explaining the sulphur capture mechanism in the pressurized circulating fluidized bed combustor under batch combustion conditions. The experimental data are validated with the model predictions and a reasonable agreement has been observed. Copyright © 2002 John Wiley & Sons, Ltd.