Gautam Biswas Professor Department of Mechanical Engineering Indian Institute of Technology Guwahati Guwahati, Assam-781039, India July, 2018 I am grateful to the Department of Mechanical Engineering at IIT Guwahati, especially my sincere thanks go to Dr.
List of Publications
Mishra, Analysis of LPG combustion in a household cooking appliance with a porous radiant burner, 23rd National combustion in a household cooking appliance with a porous radiant burner, 23rd National and 1st International ISHMT-ASTFE Heat and Mass Transfer Conference, Trivandrum, Kerala, India, 17- December 20, 2015. Mishra, Analysis of Combined Mode Conduction and Radiation in a Porous Matrix Using Lattice Boltzmann Method, 23rd National and 1st International ISHMT-ASTFE Heat and Mass Transfer Conference, Trivandrum, Kerala, India, December 17-20 2015 .
The present work aims at the numerical and experimental analyzes of the combustion of gaseous and liquid fuels inside the PIB. Towards validating the developed solver, the numerical model is compared with experimental data from the present work.
PERFORMANCE EVALUATION OF DME AS AN ALTERNATIVE FUEL
7.2 (a) Stable flammability range of kerosene-fueled PIB, (b) comparisons of measured and calculated maximum temperature inside PIB as a function of ignition rate. 7.4 (a) Comparisons of FF and PIB temperature profiles and soot particle size variations along the combustor (b) Combustor FV and ND distribution at 1.8, under thermal load of Qth = 2.57 kW.
LIST OF TABLES
Work Done in the Area of PIB
With combustion modeled as a localized volumetric heat generation zone, they incorporated nonlocal thermal equilibrium between the gas and solid phases of PM by using separate energy equations for them. The flame was stabilized only in the upstream half of the PM and was not sustained in the downstream half.
Motivation for the Proposed Work
They investigated the thermal efficiency and emission characteristics of the conventional domestic LPG cooking stoves with various PM such as metal balls, pebbles and metal chips. Similar observation of a decrease in thermal efficiency with the increase of DME mixture in the conventional coke stoves was reported by Anggarani et al.
Problem Statement and Roadmap
From the literature survey it is also revealed that, despite the negative impact of soot components on public health and environment, no studies have been done on the evolution process of soot particles in the PIB. With a detailed survey on the various works done so far with PMC technology, the motivation for the current doctoral study was presented, and based on the overview of the available literature, the aim and problem statement of the current research work. defined along with the road map.
NUMERICAL MODELING OF PIB
Numerical Method and Radiation Formulation
- Radiation formulation
- Solution method
The radiative source term of the PM can be calculated using the FVM  for solving the quasi-steady radiative transfer equation (RTE). With from the emissivity of the PM, the boundary intensities are calculated from the following.
Results and Discussions
- Ray independent test
- Heat release rate
- Stability range
- Heat flux
- CO emission
Stable burner operating range for LPG and CH4 combustion in PM and FF mode v. Comparison of stability region with respect to (a) flame speed and (b) ignition speed for LPG and CH4 combustion in PIB.
With LPG combustion in PM, an average reduction of 1224.67 ppm in CO emission can be achieved, whereas an average reduction of 725.25 ppm can be achieved if CH4 is allowed to burn in PIB instead of its combustion in FF -condition.
COMBUSTION OF LPG IN TWO-LAYER PIB
Results and Discussions
- Effects of thicknesses of porous layers
- CO emission of the burner
- Effect of conductivity and scattering albedo
For each it is observed that the CO emission for each burner increases with the increase of Qth. It also applies that for each , the higher the thickness of the SiC matrix, the lower the CO emissions. The combustion of LPG in two-layer PIB 39 CB4 burners is lower than the CO emissions of the stove when using CB1 and CB2 burners.
This causes an increase in the preheating temperature of the incoming LPG air mixture, which reduces CO emissions.
EFFECT OF DME ADDITION TO LPG FLAME
Kinetic Model Selection
- Stable operating range of LPG-DME flame inside the PIB
- Effect of DME addition on temperature profiles and total heat release rate To further explore the flame structure of LPG and DME mixtures ( 0.0, 0.5 and 1.0)
- Reaction mechanism of various LPG-DME blend flames inside the PIB
- Species concentration Profiles and ROP analysis
- Soot suppression study in DME flame
- Effect of DME addition on H 2 /syngas production
- Flame thickness of different LPG-DME blends inside the PIB
- Sensitivity analyses
- Parametric sensitivity
However, no study was reported to understand the effect of DME addition on LPG flame behavior under enthalpy excess combustion conditions achieved within PIB. This is due to the increased reaction rate and higher filtration rate of DME than that of LPG, as previously discussed. From Table 4.2 it can be seen that, for all values of and , the combustion in PIB shows a thinner flame width than that of laminar FF.
The sensitivity of these reactions was enhanced by the addition of DME to the LPG-air mixture, which increased the filtration rate of the flame in the burner.
This is due to the fact that medium with high porosity has a low extinction coefficient, and therefore by absorbing more radiant energy, it increases the burner reactivity. This leads to an improvement in the incoming fuel-air mixture temperature, which ultimately increases the V0 of the PIB. However, the filtration velocity is found to be insensitive to the porous burner density and specific heat capacity, as seen in Fig.
In addition, the effect of different levels of DME in the fuel-air mixture on the sensitivity of the filtration rate and the thickness of the PIB reaction zone was also analyzed.
PERFORMANCE EVALUATION OF DME AS AN ALTERNATIVE FUEL
Results and Discussions
- Stable operating ranges of DME-air flames within the PIB stove
- Heat recirculation mechanism of the PIB
- Chemical structure of DME flames in the PIB under ultra-lean conditions From the above experimental and numerical investigations, it can be established that from
For all values of it is found that the Qth for the PIB furnace is higher than for the conventional burner. CO emission is sensitive to flame temperature and flame location in the PIB. While only one peak (Peak-II2.28 kW) can be observed for the heat release rate at the PIB interface at high heat load (Qth = 2.28 kW).
Then the resulting CH3 recombines to produce ethane (C2H6) or reacts with CH2O, HO2 and DME to generate methane (CH4) in this area of the PIB.
SOOT FORMATION IN PIB
Numerical Method and Kinetic Model Selection
In an instant, combustion spreads throughout the PIB and eventually the flame stabilizes at a specific location within the burner, depending on the velocity and equivalence ratio of the incoming C2H4-air mixture. This model is solved by the RTE solver to account for volumetric radiation from the PIB solid phase, and the effect of H2O, CO2 and soot particle radiation is calculated considering the optical thin model and the gray gas approximation . To explain the effect of PIB on soot development, this chapter uses a comprehensive kinetic mechanism  consisting of 156 chemical species and 5600 different reactions.
At each grid point, the temperature-dependent Planck average absorption coefficient for all species is calculated by.
Model Results and Discussions
- Soot inception within the PIB
- Influence of equivalence ratio on soot formation
- Influence of flame velocity on soot evolution
- Effects of thermo-physical and optical properties on soot production
It is found that the mole fractions of all BINs formed within the PIB along the burner axis are much smaller than the FF value. These results indicate that the combustion of the C2H4-air mixture inside the PIB could reduce the soot volume fraction and particle diameter at the burner exit. In addition, due to the high dependence of the burner temperature distribution on the behavior of the soot, the temperature profiles of the gas and solid phases inside the PIB are also shown in fig.
Likewise, as seen, the reduction in thermal conductivity of the PIB increases the soot formation process.
Moreover, the PIB with lower porosity matrix (Case-IIa) reduces the route evolution, due to the lower gas temperature inside the burner caused by the faster heat transfer by conduction and radiation in the solid matrix of the PIB. Furthermore, the effects of various thermophysical and optical properties of PIB on the soot growth parameters were investigated. Sensitivity analyzes of different thermal and optical properties of the PM indicated that a PIB with low porosity, scattering albedo, extinction coefficient, pore diameter and high thermal conductivity can reduce the PAHs and soot formation.
The results from this chapter showed that PIB not only reduced CO emissions, but was also able to inhibit soot formation and delay the soot formation process.
LIQUID FUEL COMBUSTION WITHIN PIB
To initiate evaporation of the liquid fuel, the evaporator must be preheated with little oil burning for 2-3 minutes in the mixing chamber housing below the evaporator. Once combustion within the PIB is stabilized, the evaporation process of kerosene continues due to the radiant heat transfer from the highly radiating SiC medium to the evaporator, and the combustion mechanism of the kerosene-air mixture is self-sustaining in the PIB without the use of an external heat source for evaporation. The temperature distributions in the PIB were measured using chromel-alumel and Pt-Pt/10%Rh thermocouples, which were connected to a data acquisition system, as illustrated in Fig.
A chromel-alumel thermocouple was inserted near the burner inlet (T1) to measure the temperature of the inlet air-fuel mixture, while two Pt-Pt/10%Rh thermocouples were placed at 1.0 cm intervals along the SiC section (T2, and T ) to measure the temperature of the combustion zone inside the PIB.
Results and Discussions
It is also seen, as expected, for a certain equivalence ratio, with the increase in firing rate, the peak temperature of PIB increases. The size of the soot particle formed at the exit of PIB is DSP = 2.9 nm, while the calculated particle diameter for premixed FF state is around DSP = 8 nm under the same. Moreover, the lower temperature at the downstream section of SiC PM inhibits the soot growth mechanism, resulting in the decrease of particle number density (ND) and soot volume fraction FV. As seen in the figure, DSP, ND and FV are decrease continuously with increasing thermal load of the burner.
114 Combustion of liquid fuel inside the PIB. a) Comparisons of FF and PIB temperature profiles and soot particle size variations along the combustor (b) Combustor FV and ND distribution at.
Influence of thermal load input on the concentrations of major soot precursors and soot particles at 1.8.
CONCLUSIONS AND FUTURE SCOPE
The numerical model developed as part of this thesis provides valuable insight into improving the thermal performance of gas and liquid fueled PIBs, as well as allowing constructive theoretical guidance for the experimental analysis. Based on the current research, more studies can be conducted in the future for the further improvement of the PIB. In this study, ceramic foam (SiC) and alumina beds were used as burner material for the bilayer PIB.
In this regard, a complete numerical model, including the evaporation process, needs to be developed to obtain an accurate approximation for the combustion of liquid fuels inside the PIB.
Ellzey, A numerical and experimental study of methane to hydrogen conversion in a porous media reactor, Combust. Saffar Avval, Numerical evaluation of combustion in porous media using EGM (Entropy Generation Minimization), Energy. Wagner et al, Effect of pressure and temperature on soot formation in premixed flames, Proc.
Riedel, Application of an improved PAH growth model to soot formation in a laminar coflow ethylene/air diffusion flame, Combust.
Pressure regulator (Compressed air)
Data acquisition unit (DAQ)