Kunal Karan - Academia.edu (original) (raw)
Papers by Kunal Karan
ABSTRACT Abundant supply and existing infrastructure makes diesel a favorable candidate for porta... more ABSTRACT Abundant supply and existing infrastructure makes diesel a favorable candidate for portable energy supply. Diesel generators are widely used in locations where there is no reliable electric grid, but they are noisy, have emission issues, and often have poor fuel efficiency in practical operations. Because of these drawbacks, there is interest in developing Solid Oxide Fuel Cell (SOFC) systems which use diesel fuel, but which deliver electricity quietly and with lower emissions and higher efficiency. The current study is part of a larger effort aimed at developing 1-5 kW diesel fed solid oxide fuel cells at SOFC-Canada and is mainly focused on understanding and deconvoluting the mechanism of diesel surrogate auto-thermal reforming in an experimental packed bed reactor. Gas phase kinetics play an important role during auto-thermal reforming and this study employs a detailed kinetic model developed using the automated Reaction Mechanism Generator (RMG) software. The generated model has about 9500 reactions and 450 species incorporating updated parameters from experiment and theory. The model has been validated against ignition delay data at different equivalence ratios and was found to perform reasonably well. The model has also been validated against the packed bed reactor steady state concentration data at different operating conditions. Coupling the fluid dynamics and heat transfer effects defined above with the large number of reactions and species was found to be very difficult using currently available commercial software such as Fluent and COMSOL. Hence an iterative approach was used in which simplified packed bed plug flow reactor model with heat transfer was solved using a finite element solver while the kinetics equations were solved using the CHEMKIN plug flow solver. The generated model shows the importance of entrance region effects for auto-thermal reformer design. Gas phase oxidation/pyrolysis consumes a large part of the hydrocarbon leading to lower molecular weight products that reach the catalyst surface and participate primarily in steam reforming reactions dominant on the surface of the catalyst.
Bookmarks Related papers MentionsView impact
Electrochemistry Communications, Mar 31, 2010
Bookmarks Related papers MentionsView impact
Ind Eng Chem Res, 2004
Bookmarks Related papers MentionsView impact
Electrochemical and Solid State Letters, 2007
This experimental study was undertaken to resolve the contrasting viewpoints on the role of a mic... more This experimental study was undertaken to resolve the contrasting viewpoints on the role of a microporous layer (MPL), attached to carbon paper porous transport layer (PTL), on the net water transport in a polymer electrolyte membrane fuel cell (PEMFC). Experimental results on ...
Bookmarks Related papers MentionsView impact
Meeting Abstracts, Mar 8, 2013
Bookmarks Related papers MentionsView impact
Meeting Abstracts, Aug 1, 2011
Bookmarks Related papers MentionsView impact
In regions where electricity is supplied using diesel generators (e.g., Northern territories of C... more In regions where electricity is supplied using diesel generators (e.g., Northern territories of Canada) and regions where diesel engines are used as a standby system when there is no electric power from grid (e.g., India, Pakistan), diesel reforming coupled with a Solid Oxide Fuel Cell (SOFC) system is a promising technology to efficiently convert the chemical energy of the fuel into electricity with less pollution issues. The present work will discuss the technical issues related to diesel reforming and research undertaken by SOFC Canada and SECA to address these issues. Experimental studies have been performed to characterize and screen two catalysts for diesel reforming. Fundamental surface science studies have been carried out using a Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) cell to study surface reactions as well as gas phase species formed during the catalytic reforming of small molecules such as methane and carbon monoxide. A blank reactor study us...
Bookmarks Related papers MentionsView impact
1st International Fuel Cell Science, Engineering and Technology Conference, 2003
ABSTRACT
Bookmarks Related papers MentionsView impact
SPE Annual Technical Conference and Exhibition, 2000
Copyright 2000, Society of Petroleum Engineers Inc. This paper was prepared for presentation at t... more Copyright 2000, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 2000 SPE Annual Technical Conference and Exhibition held in Dallas, Texas, 14 October 2000. This paper was selected for presentation by an SPE Program Committee following ...
Bookmarks Related papers MentionsView impact
ABSTRACT Understanding the detailed physicochemical mechanisms for the electro-oxidation of fuel ... more ABSTRACT Understanding the detailed physicochemical mechanisms for the electro-oxidation of fuel at the triple phase boundaries (TPBs) in solid oxide fuel cell (SOFC) anodes is a key step towards improving SOFC performance. Significant efforts have been directed toward this goal via both experimental and computational modeling studies. In particular, patterned Ni anode on a planar YSZ substrate has been examined because of its well-defined two-dimensional geometry that in principle offers the advantages of known TPB length and minimization of mass transport effects. A common formulation for such patterned anodes considers modeling of surface reactions and diffusion on both electrode and electrolyte surfaces, along with charge-transfer reactions at the TPBs based on elementary kinetics. In this study, we review the theoretical approaches proposed by several authors and offer a critique of their methods.
Bookmarks Related papers MentionsView impact
ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology, 2012
ABSTRACT The effect of ionomer loading on ultra-thin polymer electrolyte membrane fuel cell (PEMF... more ABSTRACT The effect of ionomer loading on ultra-thin polymer electrolyte membrane fuel cell (PEMFC) electrodes fabricated using an inkjet printer is studied under a variety of temperatures and relative humidity conditions. Catalyst layer inks with varying amounts of Nafion were prepared and loaded in inkjet cartridges. The inks were then jetted on a Nafion membrane using an inkjet printer in order to produce fuel cell electrodes with low loadings. The Pt loading for the fabricated electrodes was estimated to be in the range of 0.009–0.01 mg/cm2 per printer pass. SEM imaging shows that the thickness of a catalyst layer fabricated using 10 passes is approximately 3 microns and the catalyst layer agglomerates are about 200nm in radius. In order to determine the optimal Nafion content for this fabrication method, the electrochemical active area and steady state performance for the fabricated catalyst coated membranes (CCMs) was measured and also compared to a conventional CCM fabricated using spray deposition. Results show that optimal performance is achieved with a 40wt% Nafion loading under the operating conditions tested. The improved performance can be attributed to decrease in cell resistance and increase in proton conductivity.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Advanced Materials Research, 2007
Bookmarks Related papers MentionsView impact
ECS Transactions, 2013
Bookmarks Related papers MentionsView impact
ECS Transactions, 2008
ABSTRACT The influence of humidity of supplied gases on on electrochemically active surface area ... more ABSTRACT The influence of humidity of supplied gases on on electrochemically active surface area and charge transfer resistance in cathode process of PEM fuel cell was studied. Impedance spectra for cells operated with various gas stream combinations - H2/Air, H2/O2, H2/H2 and H2/N2 - was analyzed to determine the physical/chemical origin of the spectra features. Cathode charge transfer resistance increased with a decrease in the humidity of supplied gases. As well, a reduction in the electrochemically active surface area with a decrease in relative humidity was observed.
Bookmarks Related papers MentionsView impact
ECS Transactions, 2009
Bookmarks Related papers MentionsView impact
ECS Transactions, 2006
ABSTRACT A test station was modified to collect water from the anode and cathode exhaust streams ... more ABSTRACT A test station was modified to collect water from the anode and cathode exhaust streams of a PEM fuel cell. Various combinations of cells were built and tested with (SGL10BA) and without microporous layers (SGL10BB) on the electrodes. Cells with a MPL at the cathode performed much better compared to cells with no MPL and the degradation rates were decreased. Water balance experiments were conducted with two combinations of inlet relative humidities (RH): 100% anode-60% cathode and 60% anode-100% cathode at current densities of 300, 500 and 700 mA/cm2. For the range of current densities studied, the net drag coefficient at 60{degree sign}C was -0.08-+0.08 mol H2O/mol H+ for RH 60% anode and 0.01-0.2 mol H2O/mol H+ for RH 100% anode. There was no significant change in the drag coefficient attributable to the presence of the MPL on the cathode. A MPL on the anode did affect the net water drag.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
The Journal of Physical Chemistry C, 2015
ABSTRACT The unique behaviors of Nafion nanothin films with thicknesses of 10 nm (ultrathin) and ... more ABSTRACT The unique behaviors of Nafion nanothin films with thicknesses of 10 nm (ultrathin) and 160 nm (thin) were evaluated using variable-temperature and variable-humidity solid-state H-1 NMR spectroscopy. These unprecedented measurements of nanothin films stacked within an NMR rotor represent a remarkable experimental achievement and demonstrate that H-1 NMR spectroscopy of such minute amounts of ionomer might be possible within active catalyst layers in polymer electrolyte fuel-cell electrodes. This study was motivated by the observation, in a separate work, of thickness-dependent and highly suppressed conductivity in nanothin films of Nafion (4-300 nm) compared to counterpart free-standing Nafion membranes. Trends in the line width and, more precisely, the T2 relaxation, as probed using a Hahn echo, showed that the local mobility within the hydrogen-bonded domain is equivalent for 10 and 160 nm films and is governed by the fast exchange limit in terms of NMR time scales. Subtle differences in the chemical shift trends provide insight into the domain structures, where the 10 nm films show no changes whereas the thicker 160 nm films exhibit chemical shift trends that indicate a rearranging hydrogen-bonded network. Thus, it is inferred that domain structure formation is influenced by film thickness and that the interaction with the substrate becomes limiting as the film becomes thinner.
Bookmarks Related papers MentionsView impact
ECS Transactions, 2009
Bookmarks Related papers MentionsView impact
ABSTRACT Abundant supply and existing infrastructure makes diesel a favorable candidate for porta... more ABSTRACT Abundant supply and existing infrastructure makes diesel a favorable candidate for portable energy supply. Diesel generators are widely used in locations where there is no reliable electric grid, but they are noisy, have emission issues, and often have poor fuel efficiency in practical operations. Because of these drawbacks, there is interest in developing Solid Oxide Fuel Cell (SOFC) systems which use diesel fuel, but which deliver electricity quietly and with lower emissions and higher efficiency. The current study is part of a larger effort aimed at developing 1-5 kW diesel fed solid oxide fuel cells at SOFC-Canada and is mainly focused on understanding and deconvoluting the mechanism of diesel surrogate auto-thermal reforming in an experimental packed bed reactor. Gas phase kinetics play an important role during auto-thermal reforming and this study employs a detailed kinetic model developed using the automated Reaction Mechanism Generator (RMG) software. The generated model has about 9500 reactions and 450 species incorporating updated parameters from experiment and theory. The model has been validated against ignition delay data at different equivalence ratios and was found to perform reasonably well. The model has also been validated against the packed bed reactor steady state concentration data at different operating conditions. Coupling the fluid dynamics and heat transfer effects defined above with the large number of reactions and species was found to be very difficult using currently available commercial software such as Fluent and COMSOL. Hence an iterative approach was used in which simplified packed bed plug flow reactor model with heat transfer was solved using a finite element solver while the kinetics equations were solved using the CHEMKIN plug flow solver. The generated model shows the importance of entrance region effects for auto-thermal reformer design. Gas phase oxidation/pyrolysis consumes a large part of the hydrocarbon leading to lower molecular weight products that reach the catalyst surface and participate primarily in steam reforming reactions dominant on the surface of the catalyst.
Bookmarks Related papers MentionsView impact
Electrochemistry Communications, Mar 31, 2010
Bookmarks Related papers MentionsView impact
Ind Eng Chem Res, 2004
Bookmarks Related papers MentionsView impact
Electrochemical and Solid State Letters, 2007
This experimental study was undertaken to resolve the contrasting viewpoints on the role of a mic... more This experimental study was undertaken to resolve the contrasting viewpoints on the role of a microporous layer (MPL), attached to carbon paper porous transport layer (PTL), on the net water transport in a polymer electrolyte membrane fuel cell (PEMFC). Experimental results on ...
Bookmarks Related papers MentionsView impact
Meeting Abstracts, Mar 8, 2013
Bookmarks Related papers MentionsView impact
Meeting Abstracts, Aug 1, 2011
Bookmarks Related papers MentionsView impact
In regions where electricity is supplied using diesel generators (e.g., Northern territories of C... more In regions where electricity is supplied using diesel generators (e.g., Northern territories of Canada) and regions where diesel engines are used as a standby system when there is no electric power from grid (e.g., India, Pakistan), diesel reforming coupled with a Solid Oxide Fuel Cell (SOFC) system is a promising technology to efficiently convert the chemical energy of the fuel into electricity with less pollution issues. The present work will discuss the technical issues related to diesel reforming and research undertaken by SOFC Canada and SECA to address these issues. Experimental studies have been performed to characterize and screen two catalysts for diesel reforming. Fundamental surface science studies have been carried out using a Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) cell to study surface reactions as well as gas phase species formed during the catalytic reforming of small molecules such as methane and carbon monoxide. A blank reactor study us...
Bookmarks Related papers MentionsView impact
1st International Fuel Cell Science, Engineering and Technology Conference, 2003
ABSTRACT
Bookmarks Related papers MentionsView impact
SPE Annual Technical Conference and Exhibition, 2000
Copyright 2000, Society of Petroleum Engineers Inc. This paper was prepared for presentation at t... more Copyright 2000, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 2000 SPE Annual Technical Conference and Exhibition held in Dallas, Texas, 14 October 2000. This paper was selected for presentation by an SPE Program Committee following ...
Bookmarks Related papers MentionsView impact
ABSTRACT Understanding the detailed physicochemical mechanisms for the electro-oxidation of fuel ... more ABSTRACT Understanding the detailed physicochemical mechanisms for the electro-oxidation of fuel at the triple phase boundaries (TPBs) in solid oxide fuel cell (SOFC) anodes is a key step towards improving SOFC performance. Significant efforts have been directed toward this goal via both experimental and computational modeling studies. In particular, patterned Ni anode on a planar YSZ substrate has been examined because of its well-defined two-dimensional geometry that in principle offers the advantages of known TPB length and minimization of mass transport effects. A common formulation for such patterned anodes considers modeling of surface reactions and diffusion on both electrode and electrolyte surfaces, along with charge-transfer reactions at the TPBs based on elementary kinetics. In this study, we review the theoretical approaches proposed by several authors and offer a critique of their methods.
Bookmarks Related papers MentionsView impact
ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology, 2012
ABSTRACT The effect of ionomer loading on ultra-thin polymer electrolyte membrane fuel cell (PEMF... more ABSTRACT The effect of ionomer loading on ultra-thin polymer electrolyte membrane fuel cell (PEMFC) electrodes fabricated using an inkjet printer is studied under a variety of temperatures and relative humidity conditions. Catalyst layer inks with varying amounts of Nafion were prepared and loaded in inkjet cartridges. The inks were then jetted on a Nafion membrane using an inkjet printer in order to produce fuel cell electrodes with low loadings. The Pt loading for the fabricated electrodes was estimated to be in the range of 0.009–0.01 mg/cm2 per printer pass. SEM imaging shows that the thickness of a catalyst layer fabricated using 10 passes is approximately 3 microns and the catalyst layer agglomerates are about 200nm in radius. In order to determine the optimal Nafion content for this fabrication method, the electrochemical active area and steady state performance for the fabricated catalyst coated membranes (CCMs) was measured and also compared to a conventional CCM fabricated using spray deposition. Results show that optimal performance is achieved with a 40wt% Nafion loading under the operating conditions tested. The improved performance can be attributed to decrease in cell resistance and increase in proton conductivity.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Advanced Materials Research, 2007
Bookmarks Related papers MentionsView impact
ECS Transactions, 2013
Bookmarks Related papers MentionsView impact
ECS Transactions, 2008
ABSTRACT The influence of humidity of supplied gases on on electrochemically active surface area ... more ABSTRACT The influence of humidity of supplied gases on on electrochemically active surface area and charge transfer resistance in cathode process of PEM fuel cell was studied. Impedance spectra for cells operated with various gas stream combinations - H2/Air, H2/O2, H2/H2 and H2/N2 - was analyzed to determine the physical/chemical origin of the spectra features. Cathode charge transfer resistance increased with a decrease in the humidity of supplied gases. As well, a reduction in the electrochemically active surface area with a decrease in relative humidity was observed.
Bookmarks Related papers MentionsView impact
ECS Transactions, 2009
Bookmarks Related papers MentionsView impact
ECS Transactions, 2006
ABSTRACT A test station was modified to collect water from the anode and cathode exhaust streams ... more ABSTRACT A test station was modified to collect water from the anode and cathode exhaust streams of a PEM fuel cell. Various combinations of cells were built and tested with (SGL10BA) and without microporous layers (SGL10BB) on the electrodes. Cells with a MPL at the cathode performed much better compared to cells with no MPL and the degradation rates were decreased. Water balance experiments were conducted with two combinations of inlet relative humidities (RH): 100% anode-60% cathode and 60% anode-100% cathode at current densities of 300, 500 and 700 mA/cm2. For the range of current densities studied, the net drag coefficient at 60{degree sign}C was -0.08-+0.08 mol H2O/mol H+ for RH 60% anode and 0.01-0.2 mol H2O/mol H+ for RH 100% anode. There was no significant change in the drag coefficient attributable to the presence of the MPL on the cathode. A MPL on the anode did affect the net water drag.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
The Journal of Physical Chemistry C, 2015
ABSTRACT The unique behaviors of Nafion nanothin films with thicknesses of 10 nm (ultrathin) and ... more ABSTRACT The unique behaviors of Nafion nanothin films with thicknesses of 10 nm (ultrathin) and 160 nm (thin) were evaluated using variable-temperature and variable-humidity solid-state H-1 NMR spectroscopy. These unprecedented measurements of nanothin films stacked within an NMR rotor represent a remarkable experimental achievement and demonstrate that H-1 NMR spectroscopy of such minute amounts of ionomer might be possible within active catalyst layers in polymer electrolyte fuel-cell electrodes. This study was motivated by the observation, in a separate work, of thickness-dependent and highly suppressed conductivity in nanothin films of Nafion (4-300 nm) compared to counterpart free-standing Nafion membranes. Trends in the line width and, more precisely, the T2 relaxation, as probed using a Hahn echo, showed that the local mobility within the hydrogen-bonded domain is equivalent for 10 and 160 nm films and is governed by the fast exchange limit in terms of NMR time scales. Subtle differences in the chemical shift trends provide insight into the domain structures, where the 10 nm films show no changes whereas the thicker 160 nm films exhibit chemical shift trends that indicate a rearranging hydrogen-bonded network. Thus, it is inferred that domain structure formation is influenced by film thickness and that the interaction with the substrate becomes limiting as the film becomes thinner.
Bookmarks Related papers MentionsView impact
ECS Transactions, 2009
Bookmarks Related papers MentionsView impact