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 two stacks with similar hydraulic radii, one with internal parallel plates and one with internal oblique pin array. The SLM provides precise control of the features of the printed object, allowing to explore geometries which are difficult to manufacture with conventional technologies but, possibly, more effective in the heat exchange process. This is the case of pin (and oblique pin) array geometries, which provide a reduced amount of viscous losses when the working fluid has Prandtl number Pr < 1, e.g. air. The printed stacks have been tested in a small scale standing-wave TAHE set up in Tallinn University of Technology (TalTech). Temperatures are monitored in proximity of the hot and cold heat exchangers, as well as the sound pressure within the engine resonator. The measured quantities are shown in time and frequency domain to analyze the onset and the stability of the thermoacoustic phenomenon.
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 consumption simulations are performed on the worldwide-harmonized light vehicles test cycle (WLTC) using dynamic programing as global optimal energy management strategy. Results show improved fuel consumption performance of the Stirling machine compared to the ICE. In addition, the Stirling offers other intrinsic advantages such as low noise and vibration operation and mainly multi-fuel use capability. Consequently, the studied Stirling presents a potential for implementation on SPHEVs.
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 indicate that a device based upon the typical tube fin type compact heat exchanger and Hydrogen as working fluid will have a working fluid volume of about 7.8 liters with 1016 W power at 12.65% thermal efficiency. For similar power output (1028 W), a smaller heat exchanger like the printed circuit heat exchanger (PCHE) requires 3.25 liters of working fluid volume at 10.85% thermal efficiency.
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 problem, the Non- dominated Sorting Genetic Algorithm is used. The preliminary results demonstrated that the methodology proposed represents a promising approach for the design of Stirling engines. The theoretical results were used to construct a prototype of a Stirling engine for evaluating the whole design process.
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 compression ignition engines. The data obtained from experimentation were carefully studied and a detailed theoretical analysis was carried out for each of the blends by comparing with baseline diesel performance data. The results were promising. The DEE blends showed a simultaneous decrease in carbon monoxide, unburned hydrocarbon, smoke emissions and brake thermal efficiency whereas the brake specific fuel consumption and the NOx emissions showed an increase. It was concluded that the 5% DEE-Diesel blend is the most effective combination from the performance and emission point of view.
Gustave de Ponton d'Amécourt, Gaspard Félix Tounachon and Guillaume Joseph Gabriel de La Landelle, dubbed the "Triumvirat Hélicoptèroidal" by French physicist Jacques Babinet, played indirect and subtle roles in the early history of the development of rotary-wing flight in the latter 19th century in Paris. Tournachon, adopting the professional name of 'Nadar', innovated aerial photography (from a balloon), forever changing the way people viewed the earth and significantly contributing to an enthusiasm for aviation, a term thought to have been coined by fantasy artist Gabriel de la Landelle. Landelle's appealing representations of just-possible future helicopter-ships caught the public fancy, also contributing to an awareness of such potential flight. Vicomte Gustave de Ponton d'Amécourt had begun working on a steam-powered coaxial rotary-wing design in 1853 - in the process, coining the word 'helicopter', and by 1863 a steam powered aluminum model had been produced by mechanic L. Joseph of Arras. Although the model aircraft failed, it represented the first use of aluminum in engine construction and was a milestone attempt to solve the weight/power issues necessary for manned flight that had been set forth by Sir George Caley, the "father of aerodynamics", in his 1809-10 series of papers under the collective title "On Aerial Navigation." These three, under the direction and promotion of Nadar, formed the 'Société d'Autolocomotion Aérienne' in 1862, the name of which was changed two years later to Société d'Aviation – the first organization to employ this term. These efforts resulting in a greatly increased public enthusiasm and awareness among the common people and notables of the time, and came to involve and inspire Jules Verne, who became the organization's secretary and promoter. Verne, in 1886, wrote Robur-le-Conquérant (Robur the Conqueror), known in English as The Clipper of the Clouds, the first helicopter novel, which would be read a young Russian boy and, much later, cited as a seminal inspiration – his name was Igor Sikorsky
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 modules based on Seebeck effect are temperature-limited, so they are unable to be in direct contact with the exhaust gases. A way to downgrade the temperature levels without significantly reducing the regeneration potential is to interpose Heat Pipes (HP) between the exhaust gas and the Seebeck modules in a controlled way. This control of maximum permissible temperature at the modules is achieved by regulating the pressure of phase change of the service fluid of the HP. In this way the system will be failsafe against overheating and will be able to operate efficiently under both low and high thermal loads. Such is the case of the range extender unit being developed by the team, which has a low (15 kW) and a high (40 kW) power mode of operation. Various designs concepts were evaluated by simulation, design and test. Although efficiencies were still moderate, it was possible to demonstrate the potential of this system for optimizing the output of commercially available temperature-limited TEGs.
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 efficiency. The ICE engine indicated efficiency increases with increasing compression ratio and is insensitive to peak temperatures, whereas in the ICS engine indicated efficiency increases with decreasing compression ratio and increasing peak temperature. This engine concept is a candidate for application of adiabatic engine technology which has been explored for many years. With materials that can withstand high temperatures, brake efficiencies of 60-70% are possible. Low heat transfer is important to the proper operation of the engine. A multi-step cycle computer indicated thermodynamic and fluid flow model of the ICS engine of increasing detail was used during the engine development. Finally, detailed perturbation studies were conducted to fully understand the ICS design sensitivities. An engine friction model was added to the computer model to be able to compare estimates of ICSE BSFC and BMEP with ICE engines. Important ICS engine innovations include elimination of throttling losses, low friction due to low compression ratio, and very high air cycle efficiencies (~80%) combined with low compression ratio. The engine is designed for the highest possible efficiencies. In addition to these advantages, the engine has nearly constant pressure combustion, which should help reduce NOx formation. The major findings were: the ICS engine is more efficient than either gasoline or diesel engines over the entire operating range especially at part power. At wide open throttle, an ICS engine is more efficient than either a gasoline or a diesel engine. This advantage increases at part power. On the negative side, the ICS engine has inherent low power density (volumetric efficiency) because of low compression ratio, late air intake and late combustion. A prototype engine and a modest engine test dynamometer and instrumentation are nearing completion to demonstrate the P&B Enterprises, Inc. (PBEI), ICSE concept. The prototype is a retrofitted two-cylinder diesel engine. The prototype uses the existing engine block, and the crankshaft and camshaft fit into existing spaces in the block. Anticipated problems to be addressed with the prototype engine are starting, combustion characteristics, regenerator temperature control and high turbocharging ratios to achieve reasonable power density.
As the buzz about space grows, and with the potential for government resurrection of funding, materials for space travel-and materials creation in space-are taking on new life. New materials for space applications can be exceptionally expensive to develop, and expensive has not been a positive concept in the space community for many years. Never mind the technology spin-offs from space exploration; give no consideration to the advances in metals, composites, electronics, you name it-all of which have moved ahead since the 1950s thanks to rocket and space research. The national dismay and envy around Sputnik translated into government dollars. Not surprisingly, project numbers rose when funding was the most free and the romance of space travel caught the fancy of the public. Today, time has dimmed the romance, national pride has taken a back seat to international projects, and there have been high-profile reminders that life in space is precarious. The result: relatively low research funding.
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 rise during acceleration, and applies technologies such as variable valve timing, an integrated charge air cooler in the intake manifold, and advanced charge air devices.
Caterpillar believes that a total revamp of its track-type tractors should trim operating costs by 30 to 70%. As Caterpillar's track-type tractors enter their second century, the OEM has dramatically revamped its undercarriage technology. The company claims its SystemOne upgrades extend operating life, reduce operating costs, and improve ride characteristics. A project team created in 1999 redesigned the undercarriage from the ground up, something that Cat hadn't done since the 1970s. That effort yielded more than two dozen patents.
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.
Items per page:
50
1 – 50 of 193