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Full-Text Articles in Mechanical Engineering
Autoignition Of N-Decane Under Elevated Pressure And Low-To-Intermediate Temperature Conditions, Kamal Kumar, Gaurav Mittal, Chih-Jen Sung
Autoignition Of N-Decane Under Elevated Pressure And Low-To-Intermediate Temperature Conditions, Kamal Kumar, Gaurav Mittal, Chih-Jen Sung
Dr. Gaurav Mittal
. The current experiments span a temperature range not fully investigated in previous autoignition studies on n-decane. Two-stage ignition, characteristic of large hydrocarbons, is observed over the entire range of conditions investigated, as demonstrated in the plots of raw experimental pressure traces. In addition, experimental results reveal the sensitivity of the first-stage and total ignition delays to variations in fuel and oxygen mole fractions, pressure, and temperature. Predictability of two kinetic mechanisms is compared against the present data. Discrepancies are noted and discussed, which are of direct relevance for further improvement of kinetic models of n-decane at conditions of elevated …
Aerodynamics Inside A Rapid Compression Machine, Gaurav Mittal, Chih-Jen Sung
Aerodynamics Inside A Rapid Compression Machine, Gaurav Mittal, Chih-Jen Sung
Dr. Gaurav Mittal
The aerodynamics inside a rapid compression machine after the end of compression is investigated using planar laser-induced fluorescence (PLIF) of acetone. To study the effect of reaction chamber configuration on the resulting aerodynamics and temperature field, experiments are conducted and compared using a creviced piston and a flat piston under varying conditions. Results show that the flat piston design leads to significant mixing of the cold vortex with the hot core region, which causes alternate hot and cold regions inside the combustion chamber. At higher pressures, the effect of the vortex is reduced. The creviced piston head configuration is demonstrated …
A Rapid Compression Machine For Chemical Kinetics Studies At Elevated Pressures And Temperatures, Gaurav Mittal, Chih-Jen Sung
A Rapid Compression Machine For Chemical Kinetics Studies At Elevated Pressures And Temperatures, Gaurav Mittal, Chih-Jen Sung
Dr. Gaurav Mittal
A rapid compression machine (RCM) has been designed and fabricated for the purpose of chemical kinetics studies at elevated pressures and temperatures. The present RCM is pneumatically driven and hydraulically actuated and stopped. Stroke of the machine varies from 7 to 10 inches and clearance is also adjustable. Compression ratio of up to 21 can be obtained. The optically-accessible reaction chamber is equipped with sensors for the measurements of pressure and temperature. In addition, a rapid sampling apparatus is incorporated in the reaction chamber for determining species concentration at specific post-compression time. A deliberately machined crevice on the cylindrical surface …
Computational Fluid Dynamics Modeling Of Hydrogen Ignition In A Rapid Compression Machine, Gaurav Mittal, Mandhapati Raju, Chih-Jen Sung
Computational Fluid Dynamics Modeling Of Hydrogen Ignition In A Rapid Compression Machine, Gaurav Mittal, Mandhapati Raju, Chih-Jen Sung
Dr. Gaurav Mittal
In modeling a rapid compression machine (RCM) experiment, a zero-dimensional code is commonly used along with an associated heat loss model. However, the applicability of such a zero-dimensional modeling needs to be assessed over a range of accessible experimental conditions. It is expected that when there exists significant influence of the multidimensional effects, including boundary layer, vortex roll-up, and nonuniform heat release, the zero-dimensional modeling may not be adequate. In this work, we simulate ignition of hydrogen in an RCM by employing computational fluid dynamics (CFD) studies with detailed chemistry. Through the comparison of CFD simulations with zero-dimensional results, the …
Homogeneous Charge Compression Ignition Of Binary Fuel Blends, Gaurav Mittal
Homogeneous Charge Compression Ignition Of Binary Fuel Blends, Gaurav Mittal
Dr. Gaurav Mittal
The present experimental investigation aims to understand the homogeneous combustion chemistry associated with binary blends of three surrogate components for practical fuels, including toluene, isooctane, and diisobutylene-1 (DIB-1). Specifically, high-pressure autoignition characteristics of the three neat fuel components as well as the fuel blends of toluene + isooctane and toluene + DIB-1 are studied herein. Experiments are conducted in a rapid compression machine at compressed pressures varying from 15 to 45 bar and under low to intermediate temperatures. To obtain insights into interactions among fuels, the relative proportion of the two neat fuels in the reactive mixtures is systematically varied, …
Autoignition Of Toluene And Benzene At Elevated Pressures In A Rapid Compression Machine, Gaurav Mittal, Chih-Jen Sung
Autoignition Of Toluene And Benzene At Elevated Pressures In A Rapid Compression Machine, Gaurav Mittal, Chih-Jen Sung
Dr. Gaurav Mittal
Autoignition of toluene and benzene is investigated in a rapid compression machine at conditions relevant to HCCI (homogeneous charge compression ignition) combustion. Experiments are conducted for homogeneous mixtures over a range of equivalence ratios at compressed pressures from 25 to 45 bar and compressed temperatures from 920 to 1100 K. Experiments varying oxygen concentration while keeping the mole fraction of toluene constant reveal a strong influence of oxygen in promoting ignition. Additional experiments varying fuel mole fraction at a fixed equivalence ratio show that ignition delay becomes shorter with increasing fuel concentration. Moreover, autoignition of benzene shows significantly higher activation …
Cfd Modeling Of Two-Stage Ignition In A Rapid Compression Machine: Assessment Of Zero-Dimensional Approach, Gaurav Mittal, Mandhapati Raju, Chin-Jen Sung
Cfd Modeling Of Two-Stage Ignition In A Rapid Compression Machine: Assessment Of Zero-Dimensional Approach, Gaurav Mittal, Mandhapati Raju, Chin-Jen Sung
Dr. Gaurav Mittal
In modeling rapid compression machine (RCM) experiments, zero-dimensional approach is commonly used along with an associated heat loss model. The adequacy of such approach has not been validated for hydrocarbon fuels. The existence of multi-dimensional effects inside an RCM due to the boundary layer, roll-up vortex, non-uniform heat release, and piston crevice could result in deviation from the zero-dimensional assumption, particularly for hydrocarbons exhibiting two-stage ignition and strong thermokinetic interactions. The objective of this investigation is to assess the adequacy of zero-dimensional approach in modeling RCM experiments under conditions of two-stage ignition and negative temperature coefficient (NTC) response. Computational fluid …
Interpretation Of Experimental Data From Rapid Compression Machines Without Creviced Pistons, Gaurav Mittal, Mickael Chromier
Interpretation Of Experimental Data From Rapid Compression Machines Without Creviced Pistons, Gaurav Mittal, Mickael Chromier
Dr. Gaurav Mittal
Over the last two decades, experimental data of the nature of species evolution profiles and ignition delays from rapid compression machines (RCMs) has been used to develop and validate chemical kinetic mechanisms at low-to-intermediate temperatures and elevated pressures. A significant portion of this overall dataset is from RCMs that had not employed a creviced piston to contain the roll-up vortex. The detrimental influence of the roll-up vortex and the thermokinetic interactions due to the resulting temperature non-homogeneity during the negative temperature coefficient (ntc) regime have been documented in the literature. However, the adequacy of the homogeneous modeling of RCMs without …
Ignition Delay Study Of Moist Hydrogen/Oxidizer Mixtures Using A Rapid Compression Machine, Apurba Das, Chih-Jen Sung, Yu Zhang, Gaurav Mittal
Ignition Delay Study Of Moist Hydrogen/Oxidizer Mixtures Using A Rapid Compression Machine, Apurba Das, Chih-Jen Sung, Yu Zhang, Gaurav Mittal
Dr. Gaurav Mittal
Autoignition of moist hydrogen/oxidizer mixtures has been studied experimentally using a rapid compression machine (RCM). This work investigated the effect of water addition on ignition delays of stoichiometric hydrogen/oxidizer mixtures in the end of compression temperature range of TC = 907–1048 K at three different end of compression pressures viz. PC = 10 bar (1 MPa), 30 bar (3 MPa), and 70 bar (7 MPa). RCM experiments were conducted with 0%, 10%, and 40% molar percentages of water in the reactive mixture. At PC = 30 bar and 70 bar, the presence of 10% and 40% water vapor was shown …
Computational Assessment Of An Approach For Implementing Crevice Containment In Rapid Compression Machines, Gaurav Mittal, Sudhir Gupta
Computational Assessment Of An Approach For Implementing Crevice Containment In Rapid Compression Machines, Gaurav Mittal, Sudhir Gupta
Dr. Gaurav Mittal
In Rapid compression machines (RCMs), creviced pistons are often employed to suppress the formation of the roll-up vortex. The use of a creviced piston, however, can enhance other multi-dimensional effects especially during the first-stage of the two-stage ignition. Such multi-dimensional effects can be avoided by using ‘crevice containment’ in which the crevice zone is separated from the main reaction chamber at the end of compression. In this work, an approach for the implementation of ‘crevice containment’ in RCMs is assessed through reactive and nonreactive CFD simulations for a stepped combustion chamber geometry in which ‘crevice containment’ is achieved by using …
A Rapid Compression Machine With Crevice Containment, Gaurav Mittal, Anil Bhari
A Rapid Compression Machine With Crevice Containment, Gaurav Mittal, Anil Bhari
Dr. Gaurav Mittal
A rapid compression machine (RCM) incorporating ‘crevice containment’ is designed and fabricated. ‘Crevice containment’ maintains the advantage of suppression of piston-motion induced roll-up vortex while avoiding undesirable multi-dimensional effects of crevice. The geometry of the combustion chamber is optimized with computational fluid dynamic simulations. The designed RCM is demonstrated to provide highly reproducible experimental data at compressed gas pressures up to 100 bar. Pressure traces also reveal that ‘crevice containment’ leads to significant reduction in the post-compression pressure drop. Further, the importance of ensuring instrumentation calibration and avoiding thermal shock of pressure sensor is highlighted to avoid systematic errors in …
A Computationally Efficient, Physics-Based Model For Simulating Heat Loss During Compression And The Delay Period In Rcm Experiments, S. Goldsborough, Colin Banyon, Gaurav Mittal
A Computationally Efficient, Physics-Based Model For Simulating Heat Loss During Compression And The Delay Period In Rcm Experiments, S. Goldsborough, Colin Banyon, Gaurav Mittal
Dr. Gaurav Mittal
A computationally efficient, physics-based model is developed to account for the heat loss that occurs during the compression process and delay period in rapid compression machine (RCM) experiments. The model is formulated using multiple zones (MZs) and accounts for conductive losses in the main reaction chamber as well as convective losses in the piston crevice and ringpack regions. Blowby past the piston ringpack is also considered. The loss terms can be incorporated into the widely-utilized ‘adiabatic core’ model in order to perform ‘volumetric expansion’ calculations during chemical kinetic simulations that correct for pressure and temperature reductions resulting from these energy …
Autoignition Of Ethanol In A Rapid Compression Machine, Gaurav Mittal, Sinead Burke, Varun Davies, Bikash Parajuli, Wayne Metcalfe, Henry Curran
Autoignition Of Ethanol In A Rapid Compression Machine, Gaurav Mittal, Sinead Burke, Varun Davies, Bikash Parajuli, Wayne Metcalfe, Henry Curran
Dr. Gaurav Mittal
Ethanol is a renewable source of energy and significant attention has been directed to the development of a validated chemical kinetic mechanism for this fuel. The experimental data for the autoignition of ethanol in the low temperature range at elevated pressures are meager. In order to provide experimental data sets for mechanism validation at such conditions, the autoignition of homogeneous ethanol/oxidizer mixtures has been investigated in a rapid compression machine. Experiments cover a range of pressures (10–50 bar), temperatures (825–985 K) and equivalence ratios of 0.3–1.0. Ignition delay data are deduced from the experimental pressure traces. Under current experimental conditions …
Effect Of Crevice Mass Transfer In A Rapid Compression Machine, Gaurav Mittal, Mickael Chromier
Effect Of Crevice Mass Transfer In A Rapid Compression Machine, Gaurav Mittal, Mickael Chromier
Dr. Gaurav Mittal
Rapid Compression Machines (RCMs) often employ creviced pistons to suppress the formation of the roll-up vortex. However, the use of a creviced piston promotes mass transfer into the crevice when heat release takes place in the main combustion chamber. This multi-dimensional effect is not accounted for in the prevalent volumetric expansion approach for modeling RCMs. The method of crevice containment avoids post-compression mass transfer into the crevice. In order to assess the effect of the crevice mass transfer on ignition in a RCM, experiments are conducted for autoignition of isooctane in a RCM with creviced piston in the temperature range …
Vortex Formation In A Rapid Compression Machine: Influence Of Physical And Operating Parameters, Gaurav Mittal, Mandhapati Raju, Chih-Jen Sung
Vortex Formation In A Rapid Compression Machine: Influence Of Physical And Operating Parameters, Gaurav Mittal, Mandhapati Raju, Chih-Jen Sung
Dr. Gaurav Mittal
The performance of a rapid compression machine (RCM) with a creviced piston is assessed over a range of operating conditions through computational fluid dynamics simulations with systematic demonstration of the effects of compressed gas pressure, temperature, stroke length, and clearance on altering vortex formation and temperature homogeneity inside the reaction chamber. Simulated results show that as compressed gas pressure is reduced, the temperature homogeneity deteriorates due to the combined effect of thicker boundary layer and increased flow velocities. A further optimization of the creviced piston geometry is then required to completely suppress the roll-up vortex. Stroke length and clearance volume …
A Numerical Assessment Of The Novel Concept Of Crevice Containment In A Rapid Compression Machine, Gaurav Mittal, Mandhapati Raju, Anil Bhari
A Numerical Assessment Of The Novel Concept Of Crevice Containment In A Rapid Compression Machine, Gaurav Mittal, Mandhapati Raju, Anil Bhari
Dr. Gaurav Mittal
Rapid compression machines (RCMs) typically incorporate creviced pistons to suppress the formation of the roll-up vortex. The use of a creviced piston, however, can enhance other multi-dimensional effects inside the RCM due to the crevice zone being at lower temperature than the main reaction chamber. In this work, such undesirable effects of a creviced piston are highlighted through computational fluid dynamics simulations of n-heptane ignition in RCM. Specifically, the results show that in an RCM with a creviced piston, additional flow of mass takes place from the main combustion chamber to the crevice zone during the first-stage of the two-stage …