Thermodynamics and Cumbustion
Mahdi Zakyani
Abstract
The paper presents Large Eddy Simulation (LES) Conditional Moment Closure (CMC) simulation of pilot stabilized methanol flame to study the effects of Conditional Scalar Dissipation Rate (CSDR). Two models are used in this research to evaluate CSDR: Conditional Volume Averaging (CVA) and Amplitude Mapping ...
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The paper presents Large Eddy Simulation (LES) Conditional Moment Closure (CMC) simulation of pilot stabilized methanol flame to study the effects of Conditional Scalar Dissipation Rate (CSDR). Two models are used in this research to evaluate CSDR: Conditional Volume Averaging (CVA) and Amplitude Mapping Closure (AMC). For the turbulence modelling, the dynamic Smagorinsky approach was adopted to allow for local adjustment of Smagorinsky constant. For turbulent combustion modelling, CMC is used. Conditional volume averaging is adopted for calculation of conditional velocity. The temperature, mixture fraction, and major species mass fraction are compared against experimental data along radial direction for both cases. The comparison showed reasonable agreement with the experimental measurements for the temperature. It is also observed that the AMC model is superior in predictions compared to CVA method. Additionally, carbon monoxide and carbon dioxide are predicted with remarkable accuracy. Moreover, the conditional temperature also is in good agreement with experimental data that shows CMC model capabilities in turbulent combustion modelling.
Thermodynamics and Cumbustion
Satyananda Tripathy; Manmatha K Roul; Akshaya K Rout
Abstract
Theoretical investigation of turbulent flame impinging normally on plane surfaces isdone to determine the average Nusselt number and the plate heat flux distribution as functions of jet Reynolds number, equivalence ratio, and separation distance. The analysis is established on the mathematical formulation ...
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Theoretical investigation of turbulent flame impinging normally on plane surfaces isdone to determine the average Nusselt number and the plate heat flux distribution as functions of jet Reynolds number, equivalence ratio, and separation distance. The analysis is established on the mathematical formulation of the governing equations for conservation of mass, momentum, and energy. The turbulence phenomenon is analyzed with the help of the RNG k-ε turbulence model. The radiative heat transfer model has been designed by using the Discrete Ordinates radiation model. Results show that the heat flux graduallyincreases with the radial distance towards the plate center and attains a maximum value at a location slightly away from the stagnation point. The peak value in the local heat flux comes closer to the stagnation point when the height between the plates and the nozzle increases. Effects of variation of dimensionless separation distance on heat transfer characteristics are investigated. It is observed that heat flux gradually improves when the value of separation distance changes from 12 to 8 and decreases near the stagnation region with the further decrease in separation distance from 8 to 4.
Thermodynamics and Cumbustion
A. A. Mirmohammadi; F. Ommi
Abstract
The purpose of this paper is to studying nonlinear k-ε turbulence models and its advantages in internal combustion engines, since the standard k-ε model is incapable of representing the anisotropy of turbulence intensities and fails to express the Reynolds stresses adequately in rotating ...
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The purpose of this paper is to studying nonlinear k-ε turbulence models and its advantages in internal combustion engines, since the standard k-ε model is incapable of representing the anisotropy of turbulence intensities and fails to express the Reynolds stresses adequately in rotating flows. Therefore, this model is not only incapable of expressing the anisotropy of turbulence in an engine cylinder, but also is unable to provide good performance when computing the swirling and tumbling flows is important in engine cylinders. Thus, in this paper, the results of nonlinear k-ε model are compared with those of the linear one. Results of diesel engine simulation with linear and nonlinear k-ε models in comparison show that turbulence intensity in the nonlinear model simulation is higher than that of the linear model; also, nonlinear k-ε models predict the second peak value because of the bowl shape in expansion stroke for turbulence intensity. Gas injection results show that nonlinear turbulence models predict spray penetration accurately because of correctly turbulence intensities predicting. Also, the results demonstrate that, for high pressure gas injection, turbulence intensity is high and predicted accurately using nonlinear models. Then, its spray penetration length is predicted accurately in comparison to experimental data’s. Although CPU time spending in the nonlinear model is more than that of the linear one, the non-linear stress model is found to increase computation time by 19%.
Thermodynamics and Cumbustion
M. V. S. Murali Krishna; R. P. Chowdary; T. Kishen Kumar Reddy; P. V. K. Murthy
Abstract
Investigations were carried out to evaluate the performance of direct injection diesel engine with medium grade low heat rejection (LHR) combustion chamber and 3 mm air gap insulated piston, 3 mm air gap insulated liner, and ceramic coated cylinder head [ceramic coating with the thickness of 500 µ ...
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Investigations were carried out to evaluate the performance of direct injection diesel engine with medium grade low heat rejection (LHR) combustion chamber and 3 mm air gap insulated piston, 3 mm air gap insulated liner, and ceramic coated cylinder head [ceramic coating with the thickness of 500 µ was made on the inside portion of the cylinder head].The engine had different operating conditions [normal temperature and pre–heated temperature] of crude waste fried vegetable oil (WFVO) which was collected from restaurants, hotels, etc. with varied injector opening pressure and injection timing. Performance parameters and exhaust emissions were evaluated at various values of brake mean effective pressure of the engine, while combustion parameters were determined at full load operation of the engine using special pressure–crank angle software package. Comparative studies were performed between vegetable oil operation and diesel operation in the engine with both versions of the combustion chamber with varied injection timing and injector opening pressure. Conventional engine (CE) showed deteriorated performance, while the engine with medium grade LHR combustion chamber had improved performance with waste fried vegetable oil operation at the recommended injection timing and pressure. Performance of both versions of the combustion chamber improved with advanced injection timing and at higher injector opening pressure compared with CE with pure diesel operation. The optimum injection timing was 32o bTDC (before top dead centre) with conventional engine, while it was 30o bTDC for the engine with LHR combustion chamber and vegetable oil operation. Compared with pure diesel operation in the conventional engine, at manufacturer's recommended injection timing of 27o bTDC, peak brake thermal efficiency increased by 9% at full load operation, brake specific energy consumption decreased by 2%, volumetric efficiency decreased by 13%, smoke levels decreased by 10%, and nitrogen oxide (NOx) levels increased by 44% with waste fried vegetable oil operation in the engine with LHR combustion chamber.
Thermodynamics and Cumbustion
A. H. Kakaee; J. Zareei
Abstract
Engine performance depends on two main factors of engine speed and ignition time. Ignition timing can affect engine life, fuel economy and engine power. In this paper, to study engine performance of Peugeot 206 TU3A with comparison ratio of 10.5:1 and displacement of 1361CC in MATLAB software, a two-zone ...
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Engine performance depends on two main factors of engine speed and ignition time. Ignition timing can affect engine life, fuel economy and engine power. In this paper, to study engine performance of Peugeot 206 TU3A with comparison ratio of 10.5:1 and displacement of 1361CC in MATLAB software, a two-zone burned/unburned model with the fuel burning rate described by aWiebe function was used for modeling in-cylinder combustion. For studying this issue, thermodynamic models such as Woshni, Isentropic, etc. were used. Then, the experiments were carried out to validate the calculated data. The objective of the present work was to examine effect of ignition timing on the performance of an SI engine. For achieving this goal, at the speed of 3400 rpm, ignition timing was changed in the range of 41 degrees before the top dead centre to 10 degrees after TDC. By changing the ignition timing, the results of some characteristics such as power, torque, indicatory pressure, exhaust emission and efficiency were obtained and compared. The results demonstrated that optimal power and torque and the maximum efficiency were achieved at 31 degrees before the top dead centre and engine performance was improved by changing timing angle. It was also indicated that the maximum thermal efficiency could be accomplished while peak pressure occurred between 5 and 15 degrees of ATDC. The amounts of O2, CO2 and CO were almost constant but HC increased with increase of ignition timing.
Thermodynamics and Cumbustion
M. V. S. Murali Krishna; V. V. R. Seshagiri Rao; P. V. K. Murthy; T. K. K. Reddy
Abstract
Experiments were conducted to evaluate the performance of a low heat rejection (LHR) diesel engine. Performance parameters and emission levels were determined at various magnitudes of brake mean effective pressure. Combustion characteristics of the engine were measured with TDC (top dead centre) encoder, ...
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Experiments were conducted to evaluate the performance of a low heat rejection (LHR) diesel engine. Performance parameters and emission levels were determined at various magnitudes of brake mean effective pressure. Combustion characteristics of the engine were measured with TDC (top dead centre) encoder, pressure transducer, console and special pressure-crank angle software package at peak load operation of the engine. Conventional engine (CE) and LHR engine showed improved performance at recommended injection timing of 27obTDC and recommended injection pressure of 190 bar, when compared with CE with pure diesel operation. Peak brake thermal efficiency increased by 18%, smoke levels decreased by 48% and NOx levels decreased by 38% with LHR engine relatively at its optimum injection timing and maximum induction of ethanol when compared with pure diesel operation of CE at manufacturer’s recommended injection timing.
