Linear Stirling Engine with a Buffer Tube

家用热电联产系统是一种既能高效发电，又能减轻电网和地区配电网压力的明显方式。转向电动和插电式混合动力汽车将给电网带来额外的需求，并使当地配电系统不堪重负，目前只能满足约10%的家庭为汽车充电。对于国内的热电联产系统，需要一种不同的思维方式，因为有必要将发电视为供暖需求的副产品，因为电力可以出口。虽然一个小型家用锅炉的额定功率可能为12千瓦，但夏季的供暖需求当然要小得多，这导致对斯特林发动机的功率(但效率)要求较低。考虑下面的例子，它假设常规锅炉的基准效率为90%：对于1 kW的电力输出，斯特林发动机的“指示功率”需要为1.3 kW(以考虑发电机和电力电子设备中主要是电气损耗的损耗)。以悲观的28%的效率假设(净输出功率/热量输入)，这将需要3.6千瓦的热输入，以及4千瓦的燃料能量。发动机产生的废热将为家庭供暖提供2.3千瓦的能量，而在传统锅炉中，这将需要2.6千瓦的燃料能量。因此，燃料能源消耗增加了1.4千瓦(=4.0-2.6)，产生了1千瓦的电力；假设需要加热，总的电力效率为71%。如果考虑到电网传输效率，这大约是传统发电厂效率的两倍。最终目标是开发一台电力输出至少为1千瓦的斯特林发动机，但作为示范单位，目前的工作将生产一台电力输出为100瓦的斯特林发动机。之所以选择这个较小的尺寸，是因为我们有一台额定功率为100瓦的移动磁铁电机，可以用作发电机。这将避免扩大电机设计的需要，并将大大降低项目成本。这个100W的系统将足够大，可以安装压力传感器、热电偶和位移传感器，实验数据可以用来验证模型，这样就可以对更大的发动机的模型预测有信心。较小的尺寸也将降低制造成本。电加热将有助于准确测量热输入，并避免开发燃烧系统的需要。从长远来看，催化燃烧系统将在足够低的温度下运行，从而使NOx排放可以忽略不计，并适用于一系列气体燃料。热电联产系统的吸引力已经导致小型线性斯特林发电机的开发(例如SunPower/Microgen和Infinia/QEnergy系统)。尽管这个想法已经得到了很好的证明，但由于高昂的拥有成本和可靠性问题，这些技术并没有成功。传统置换器配置的低成本制造极具挑战性。这里提出的研究的一个非常重要的好处是展示了一种新的发动机配置，它从根本上简化了置换器的设计和制造--置换器是关键部件。可能的成本降低将极大地增强斯特林热电联产系统的前景。美国能源部最近资助了几个斯特林发动机项目，用于国产热电联产(https://arpa-e.energy.gov/?q=news-item/department-energy-announces-18-new-projects-accelerate-technologies-efficient-residential).尽管大众市场被设想为国内热电联产，但还有其他可供开发的无声发电利基市场，这些市场将支持与小规模制造相关的更高成本。这方面的例子包括游艇上的辅助发电和军事应用。

Domestic CHP systems are an obvious way of both generating electricity with a high efficiency and reducing strain on the grid and local distribution systems. The move to electric and plug-in hybrid vehicles will place additional demand on the grid and overload the local electrical distribution system that can currently only cope with about 10% of households recharging vehicles. With domestic CHP systems a different mind-set is needed as it is necessary to consider the electricity generation to be a by-product of the heating demand, as the electricity can be exported. Although a small domestic boiler might have a rating of 12 kW the heating demand in the summer is of course much smaller and this leads to a lower power (but high efficiency) requirement for the Stirling engine. Consider the following example which assumes a baseline efficiency for a conventional boiler of 90%:For an electrical output of 1 kW the 'indicated power' of the Stirling engine would need to be 1.3 kW (to allow for losses that are mostly electrical losses in the generator and power electronics). With a pessimistic 28% efficiency assumption (Net W[e] out/Heat in), this will require a heat input of 3.6 kW, with 4 kW of fuel energy. The waste heat from the engine will provide 2.3 kW for domestic heating, and in a conventional boiler this would have required 2.6 kW of fuel energy. So, 1kW of electricity has been generated from an increased fuel energy consumption of 1.4 kW (= 4.0 - 2.6); an overall electrical efficiency of 71% assuming the heat is needed. This is about double the efficiency of a conventional power plant, once allowance is made for the grid transmission efficiency.The ultimate aim is for a Stirling engine with an electrical output of at least 1 kW, but as a demonstration unit the current work will produce a Stirling engine with an electrical output of 100 W. This smaller size has been chosen because we have a moving magnet motor of this rating that can be used as a generator. This will avoid the need to scale-up the motor design and will give a significant reduction in the project cost. This 100 W system will be large enough to install pressure transducers, thermocouples and displacement transducers, and the experimental data can be used to validate the modelling, so that there will be confidence in the model predictions of the larger engines. The smaller size will also reduce the manufacturing costs. Electrical heating will facilitate accurate measurements of the heat input, and avoid the need to develop a combustion system. Longer term, a catalytic combustion system would operate at a sufficiently low temperature so as to make NOx emissions negligible, and be suitable for a range of gaseous fuels.The attraction of CHP systems has already led to small linear Stirling generators being developed (e.g Sunpower/Microgen and Infinia/QEnergy systems). Although the idea has been well demonstrated these technologies have not been successful due to high ownership costs and reliability issues. The low cost manufacture of conventional displacer configurations is extremely challenging. A very significant benefit of the research proposed here will be the demonstration of a new engine configuration that radically simplifies the design and manufacture of the displacer - a key component. The cost reductions possible will greatly enhance the prospects of Stirling CHP systems.The US Department of Energy has recently funded several Stirling engine projects for domestic CHP (https://arpa-e.energy.gov/?q=news-item/department-energy-announces-18-new-projects-accelerate-technologies-efficient-residential). Although the mass market is envisaged to be domestic CHP there are other niche markets for silent power generation that can be exploited, and these would support greater costs associated with small scale manufacture. Examples of this include auxiliary power generation on yachts and military applications.