Browse Topic: External combustion engines
Thermoacoustic heat engines (TAHEs) are external combustion engines primarily designed to convert thermal power into acoustic power and, eventually, into mechanical, electric or other forms of high grade power. TAHEs rely on the presence of a porous core, often referred to as “stack”. A temperature gradient is established along the porous core and quasi-adiabatic heat exchanges occur between the solid walls of the pores and the surrounding gaseous medium undergoing pressure fluctuations. The internal geometry of the stack has tremendous impact on the efficiency of thermal-to-acoustic power conversion. In this study, the selective laser melting (SLM) has been used to produce stacks. The SLM is an additive manufacturing (AM) technique designed for 3D metal printing. It is based on high power- density laser which melts and fuses metallic powders together. Three sets of stacks, provided with different hydraulic radii and internal geometries, have been produced. Each set is constituted by
Investigations on alternative fuels and new hybrid powertrain architectures have recently undergone significant efforts in the automotive industry, in attempt to reduce carbon emissions from passenger cars. The use of these fuels presents a potential for re-emerging the deployment of external combustion non-conventional engines in automotive applications, such as the Stirling engines, especially under the current development context of powertrain electrification. This paper investigates the potential of fuel consumption savings of a series-parallel hybrid electric vehicle (SPHEV) using a Stirling machine as fuel converter. An exergo-technological explicit analysis is conducted to identify the Stirling system configuration presenting the best compromise between high efficiency and automotive implementation constraints. The Stirling engine with combustion chamber preheater is prioritized. A SPHEV model is developed based on the Prius power-split hybrid electric architecture. Energy
Higher fuel economy of the vehicle is a critical concern in automobile industry. Traditional internal combustion (IC) engines waste a large portion of the available fuel energy as heat loss via exhaust gas. This proposal aims at recovering the available exhaust heat of the IC engines using stirling engine (SE) as an add-on device. SE is a type of cyclic heat engine which operates by compression and expansion of the working fluid, at different temperature levels resulting in a conversion of the heat energy into mechanical work. A thermodynamic analysis is performed on the chosen beta SE rhombic drive configuration with different combinations of design parameters like working fluid mass, total dead volume, thermal resistance, and hot side and cold side temperatures. A regenerator temperature model is developed to account for first law consistency in the regenerator section of SE, along with heat transfer in accordance with mass flow within the regenerator. In conclusion, the results
The Stirling engine is a device that has great potential for being used in applications where energy (heat) is available in the system. As an example, a Stirling motor can use the energy available in the gases from the combustion process of an automotive engine by using exhaust manifold as hot source. The Stirling motor consists of a piston that can move along a cylinder that is fulfilled by a working fluid and a displacer installed between the hot and cold chambers. Due to the large temperature difference between the chambers, it becomes feasible to use the corresponding energy to drive the Stirling engine. For design purposes, a multi-objective problem is formulated so that the maximization of thermodynamic efficiency, the minimization of energetic loss associated with the movement of the displacer set, and the minimization of energetic loss related to the fluid displacement between the two chambers is obtained for the optimal configuration of the system. To solve this optimal design
The world today is majorly dependent upon fossil fuels for power generation, of which diesel forms an integral part. Diesel engines, having the highest thermal efficiency of any regular internal or external combustion engine, are widely used in almost all walks of life and cannot be dispensed with in the near future. However, the limited availability of diesel and the adverse effects of diesel engine emissions like nitrogen oxide (NOx) and soot particles raise serious concerns. Hence, their performance and emission improvement continues to be an avenue of great research activity. In this research work, the effects of blending Diethyl Ether with diesel in various proportions (5%, 10%, 15% and 20% by volume) were evaluated on engine performance and emissions of an industrial internal combustion engine. Several properties of DEE such as its low viscosity, high volatility, high cetane number, low auto ignition temperature and high solubility in diesel make it favorable for use in
The amount of energy wasted through the exhaust of an Internal Combustion Engine (ICE) vehicle is roughly the same as the mechanical power output of the engine. The high temperature of these gases (up to 1000°C) makes them intrinsically apt for energy recovery. The gains in efficiency for the vehicle could be relevant, even if a small percentage of this waste energy could be regenerated into electric power and used to charge the battery pack of a Hybrid or Extended Range Electric Vehicle, or prevent the actuation of a conventional vehicle's alternator. This may be achieved by the use of thermodynamic cycles, such as Stirling engines or Organic Rankine Cycles (ORC). However, these systems are difficult to downsize to the power levels typical of light-vehicle exhaust systems and are usually bulky. The direct conversion of thermal energy into electricity, using Thermoelectric Generators (TEG) is very attractive in terms of minimal complexity. However, current commercial thermoelectric
A unique engine, based on the regenerative principle, is being developed with the goal of achieving high brake efficiency over a wide power range. It can be characterized as an internal combustion Stirling engine (ICSE). The engine is a split-cycle configuration with a regenerator between the intake/compression cylinder and the power/exhaust cylinder. The regenerator acts as a counter-flow heat exchanger. During exhaust, the hot gases are cooled by the regenerator. The regenerator stores this heat. On the next cycle, compressed gases flow in the opposite direction and are heated by the regenerator. The gases coming from the regenerator into the power cylinder are very hot (~900°C), which provides the necessary gas temperature for auto-ignition of diesel and other fuels. A simplified Air Cycle analysis of the ICS engine is presented to validate the concept thermodynamics and to show the inherent difference between the ICS and conventional internal combustion engine (ICE) indicated
The device illustrated in Figure 1 is designed primarily for use as a regenerative heat exchanger in a miniature Stirling engine or Stirling-cycle heat pump. A regenerative heat exchanger (sometimes called, simply, a “regenerator” in the Stirling-engine art) is basically a thermal capacitor: Its role in the Stirling cycle is to alternately accept heat from, then deliver heat to, an oscillating flow of a working fluid between compression and expansion volumes, without introducing an excessive pressure drop. These volumes are at different temperatures, and conduction of heat between these volumes is undesirable because it reduces the energy-conversion efficiency of the Stirling cycle. Hence, among the desired characteristics of a regenerative heat exchanger are low pressure drop and low thermal conductivity along the flow axis
The editors of Automotive Engineering International highlight some of the more innovative new products and technologies on display at the SAE 2006 World Congress, based on the latest information provided by exhibiting companies. The TurboDISI engine from FEV is a 1.8-L turbocharged gasoline direct-injection engine that offers impressive low-end torque and a fuel economy typically associated only with diesel engines. The engine, which can replace larger, heavier naturally aspirated engines, also promises reduced emissions compared to naturally aspirated and port-fuel-injected turbocharged engines. Compared to the larger 2.6-L naturally aspirated engine that it replaces, the TurboDISI engine produces the same peak torque and power, but reaches peak torque more quickly while offering better specific fuel consumption throughout the engine map. It minimizes the traditional turbo-lag drawback experienced by conventional turbocharged engines, which is characterized by a delay in the torque
Experiments have shown that an assembly of multiple free-piston Stirling engines can be designed and constructed in such a way as to both (1) make the vibrations of the engines balance each other to minimize the overall level of vibration, and (2) enable the engines to operate independently of each other, so that if one fails, the other(s) can continue to provide power. Prior to these experiments and to the research and development effort that preceded them, it was not possible to achieve both redundancy and suppression of vibrations: The only previously demonstrated method to balance out vibrations of multiple Stirling engines was by use of counter-oscillating pistons coupled to each other via a common thermodynamic hot space, with the engines driving linear alternators connected electrically in series. This older scheme precludes redundancy because the common thermodynamic interaction and the series electrical connection causes both engines to fail when one fails
An important secondary topic addressed in the research and development effort described in the preceding article is the use of artificial neural networks to improve the monitoring and thus the control and safety of multiple free-piston Stirling engines. Information collected by monitoring subsystems constitutes essential feedback for use by control and safety subsystems. This information includes such externally measurable quantities as heater-head temperatures, motions of engine housings, and output currents and voltages
The figure illustrates an apparatus for measuring heat-transfer and pressure-drop characteristics of porous plug specimens in oscillating flows. The apparatus is built around an oscillating-flow test rig that was originally designed for pressure-drop (but not heat-transfer) measurements and has since been modified and refined. The flows and specimens are chosen to be representative of those encountered in the regenerators of Stirling engines
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