Dual-compression, dual-expansion piston engine assessment and optimization
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A dual-compression, dual-expansion engine concept utilizing thermal insulation, piston compressors and expanders is presented and analyzed to determine the potential for improved efficiency and performance. The engine design takes advantage of the ability to separate and optimize the different processes occurring in the cycle and to recover energy that otherwise would have been lost. Gains of approximately 10% over the baseline modern turbodiesel engine were realized at mid- to high loads due to more efficient pumping, expansion and heat transfer improvements. At low loads, the increased friction of the piston dual-compression, dual-expansion concept hurt the efficiency in comparison to the baseline.Keywords:
Piston (optics)
Expansion ratio
Thermal efficiency
A dual-compression, dual-expansion engine concept utilizing thermal insulation, piston compressors and expanders is presented and analyzed to determine the potential for improved efficiency and performance. The engine design takes advantage of the ability to separate and optimize the different processes occurring in the cycle and to recover energy that otherwise would have been lost. Gains of approximately 10% over the baseline modern turbodiesel engine were realized at mid- to high loads due to more efficient pumping, expansion and heat transfer improvements. At low loads, the increased friction of the piston dual-compression, dual-expansion concept hurt the efficiency in comparison to the baseline.
Piston (optics)
Expansion ratio
Thermal efficiency
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Authors Rusinov R.V., Hoodorozhkov S.I., Dobretsov R.Yu., kgm-spb@mail.ru. Estimation of the efficiency of the thermal cycle of a piston internal combustion engine The article proposes a simplified technique for the operational assessment of the efficiency of the heat cycle of a piston internal combustion engine. A feature of the developed computational model is the release of the amount of heat consumed for the production of only mechanical energy in the form of a separate component of the heat balance of the cycle. The value of this component is determined by calculation (or according to the results of experiments) in advance, which makes it possible to reduce the number of pre(determined initial data. The methodology is based on a mathematical description of thermodynamic processes occurring during the development of the thermal cycle of an engine with ignition of the working mixture from compression (diesel engine), which allows it to be expanded to new engines of design, including those operating under electronic control. The objects for the application of the calculation method can be diesel engines installed on transport vehicles, both individually and as part of a hybrid power plant, as well as engines of stationary or transportable power plants. The very principle underlying the model can be implemented for engines of other purposes and other thermal cycles. Keywords: heat cycle; the working process; diesel; heat content of the working fluid; expansion
Piston (optics)
Thermal efficiency
Thermodynamic cycle
Heat Engine
Working fluid
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Optical engines allow for the direct visualization of the phenomena taking place in the combustion chamber and the application of optical techniques for combustion analysis, which makes them invaluable tools for the study of advanced combustion modes aimed at reducing pollutant emissions and increasing efficiency. An accurate thermodynamic analysis of the engine performance based on the in-cylinder pressure provides key information regarding the gas properties, the heat release, and the mixing conditions. If, in addition, optical access to the combustion process is provided, a deeper understanding of the phenomena can be derived, allowing the complete assessment of new injection-combustion strategies to be depicted. However, the optical engine is only useful for this purpose if the geometry, heat transfer, and thermodynamic conditions of the optical engine can mimic those of a real engine. Consequently, a reliable thermodynamic analysis of the optical engine itself is mandatory to accurately determine a number of uncertain parameters among which the effective compression ratio and heat transfer coefficient are of special importance. In the case of optical engines, the determination of such uncertainties is especially challenging due to their intrinsic features regarding the large mechanical deformations of the elongated piston caused by the pressure, and the specific thermal characteristics that affect the in-cylinder conditions. In this work, a specific methodology for optical engine characterization based on the combination of experimental measurements and in-cylinder 0D modeling is presented. On one hand, the method takes into account the experimental deformations measured with a high-speed camera in order to determine the effective compression ratio; on the other hand, the 0D thermodynamic analysis is used to calibrate the heat transfer model and to determine the rest of the uncertainties based on the minimization of the heat release rate residual in motored conditions. The method has been demonstrated to be reliable to characterize the optical engine, providing an accurate in-cylinder volume trace with a maximum deformation of 0.5 mm at 80 bar of peak pressure and good experimental vs. simulated in-cylinder pressure fitting.
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Thermal efficiency
Characterization
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Introduction. The relevance lies in the use of a motor with an external heat supply to convert solar radiation into electrical energy, while the source of thermal energy is a solar collector. Aim. To develop an alternative energy source for remote consumers based on a low-temperature Stirling engine capable of converting low-grade heat of heated water into mechanical energy with subsequent generation of electric current of industrial frequency. In contrast to the classical design of the well-known Stirling engine, the presented DVPT has a significant displacer volume, which exceeds the volume of the working piston by more than 20 times; this allows it to operate at a lower temperature difference between the heater and the cooler. The operating temperature of the heater is 90–100 °C, which is 7–9 times less than the known Stirling engine. Materials and methods. To work out the results of full-scale experiments, computer modeling was used; the dependence graphs for the change in the pressure of the working fluid and its volume when compressed by the working piston are presented. Results. A brief description of the design features of a low-temperature engine with an external heat supply operating according to the Stirling cycle is given, as well as some results of research and computer modeling. Conclusion. The use of air as a working fluid is not justified, since when using it, the mass and size dimensions of the DVPT per unit of power produced are larger than that of internal combustion engines. For a low-temperature DVPT, a prerequisite is the difference in the volumes of the displacer and the working piston; for a heater temperature within 90 °C, the displacer must be 20 to 40 times larger in volume. The efficiency is influenced by the temperature difference between the heater and the cooler and the pressure of the working fluid.
Piston (optics)
Stirling cycle
Working fluid
Heat Engine
Mechanical energy
Thermal energy
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Performance characteristic of a new type rotary internal combustion engine was investigated analytically. The new type rotary engine named as Separate type Rotary Engine consists of a compressor, an expander, and an air path. Engine cycle analysis program developed for the SRE was utilized as a performance analysis tool and the effects of the three SRE design parameters such as the ratio of air path volume to combustion chamber volume, air path cooling, and over expansion ratio on the engine performance have been studied analytically. It was found in this study that although the air path from compressor to combustion chamber is indispensable, it is better to be as small as possible for engine performance. Air path cooling is a good method to increase power output in the limit of max combustion chamber temperature even at some cost to the thermal efficiency. Ease of getting over expansion in the expander is a special feature of this SRE and it is possible because compression and expansion do not occur in one cylinder, but in two separate cylinders, a compressor and an expander. As the expansion ratio increase, thermal efficiency was increased and as a result, the power output also increased. Within the limit of this study, 15% increase of expansion ratio has resulted in about 5% increase of thermal efficiency, as well as power.
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Thermal efficiency
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The Stirling engine is an alternative solution to produce cleaner energy in order to achieve the reduction of the fossil fuel consumption and the CO2 emissions. It comprises an external combustion engine that can convert any external heat source into mechanical power, through cyclic expansion and compression of a working gas in a closed-regenerative cycle, with or without driving mechanisms. The free-piston Stirling Engine is significantly preferred because of the absence of any mechanical linkage resulting in longer operating life, lower noise pollution, maintenance and vibration free, self-starting and high thermal efficiency. The aim of this paper is to summarize the research works on the free-piston Stirling engine technologies and models. First, the working principles of the free-piston Stirling engine are described, identifying different configurations. Then, several applications are presented. Finally, a detailed review of the models available in literature is given, pointing out the main assumptions and equations.
Piston (optics)
Stirling cycle
Thermal efficiency
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The performance of the single stage free piston air compressor of the Junkers type has been investigated by analysing the indicator diagrams. From the results of experiments, the following factors were ascertained. i) In the power cylinder, combustion occurs at nearly constant volume and the indicated thermal efficiency of 52.5% is obtained in case the effective compression ratio is higher than 16 : 1. ii) The frictional mean effective pressure in power cylinder increases rapidly with the increase of fuel rate and compression ratio. iii) The compression efficiency in the compressor cylinder decreases rapidly with the increase of clearance volume, provided that pressure ratio is high.
Piston (optics)
Overall pressure ratio
Air compressor
Thermal efficiency
Volumetric efficiency
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The current paper investigates two particular features of a novel rotary split engine. This internal combustion engine incorporates a number of positive advantages in comparison to conventional reciprocating piston engines. As a split engine, it is characterized by a significant difference between the expansion and compression ratios, the former being higher. The processes are decoupled and take place simultaneously, in different chambers and on the different sides of the rotating pistons. Initially, a brief description of the engine’s structure and operating principle is provided. Next, the configuration of the compression chamber and the sealing system are examined. The numerical study is conducted using CFD simulation models, with the relevant assumptions and boundary conditions. Two parameters of the compression chamber were studied, the intake port design (initial and optimized) and the sealing system size (short and long). The best option was found to be the combination of the optimized intake port design with the short seal, in order to keep the compression chamber as close as possible to the engine shaft. A more detailed study of the sealing system included different labyrinth geometries. It was found that the stepped labyrinth achieves the highest sealing efficiency.
Piston (optics)
Reciprocating motion
Port (circuit theory)
Rotary engine
Volumetric efficiency
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Upcoming stringent Euro-6 emission regulations for passenger vehicle better fuel economy, low cost are the key challenges for engine development. In this paper, 2.2L, multi cylinder diesel engine have been tested for four different piston bowls designed for compression ratio of CR 15.5 to improve in cylinder performance and reduce emissions. These combustion chambers were verified in CFD at two full load points. 14 mode points have been derived using vehicle model run in AVL CRUISE software as per NEDC cycle based on time weightage factor. Base engine with compression ratio CR16.5 for full load performance and 14-mode points on Engine test bench was taken as reference for comparison. The bowl with flat face on bottom corner has shown reduction 25% and 12 % NOx emissions at 1500 and 3750 rpm full load points at same level of Soot emissions. Three piston bowls were tested for full load performance and 14 mode points on engine test bench and combustion chamber ?C? has shown improvement in thermal efficiency by 0.8%. Combinations of cooled EGR and combustion chamber ?C? with geometrical changes in engine have reduced exhaust NOx, soot and CO emissions by 22%, 9 % and 64 % as compared to base engine at 14 mode points on engine test bench.
Piston (optics)
Thermal efficiency
Test bench
Engine efficiency
Naturally aspirated engine
Four-stroke engine
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A reciprocating engine without a crank-slider mechanism is called a free-piston engine. If the piston is directly connected to a linear alternator, it is called a free-piston linear alternator. Free-piston engines and free-piston linear alternators have the potential to offer solutions for future hybrid electric vehicles and stationary power generation, by enabling direct conversion of mechanical energy to electricity. They benefit from reduced friction losses compared to conventional engines and can have variable compression ratio, which enables combustion control and optimization. Their widespread application has been limited by the necessity for high-speed control strategies. However, their operating characteristics can provide high efficiency, especially when used with low temperature combustion strategies. Low temperature combustion combines the high thermal efficiency of diesel engines, with the low soot emissions of spark-ignition engines, and low NO x emissions because of low burned gas temperatures. This article provides a comprehensive review of free-piston engine technology, with a focus on advanced combustion processes and their potential for use in future powertrain systems.
Piston (optics)
Alternator
Reciprocating motion
Four-stroke engine
Thermal efficiency
SPARK (programming language)
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Citations (30)