This document summarizes an experimental study on the characterization and emission analysis of premixed and preheated porous radiant burners during LPG combustion. Experiments were conducted on 13 different burners made of brass and cast iron with varying geometric parameters like diameter, thickness, pore size, number of pores, and pore distribution. The maximum thermal efficiency obtained was 64.59% for a cast iron burner with the largest diameter and pore distribution. Material, pore geometry, and firing rate significantly affected thermal efficiency and emissions. Burner material, precise pore design, and optimal firing rate are important to improve efficiency while meeting emission standards.

1. adfa, p. 1, 2011.
© Springer-Verlag Berlin Heidelberg 2011
CHARACTERIZATION AND EMISSION ANALYSIS
OF PREMIXED AND PREHEATED POROUS
RADIANT BURNERS DURING LPG COMBUSTION
Premananda Pradhan 2, a
, Purna C Mishra1
and Bibhuti B. Samantaray1
1School of Mechanical Engineering, KIIT University, Bhubaneswar-24, Odisha
2ITER, S’O’A University, Bhubaneswar-30, Odisha
(a
Email: pradhanpremananda@gmail.com)
Abstract. Experiments were conducted in porous radiant burners of different
configurations. Each of the burner used in the investigation was characterized
with array of pores, number of pores, pore diameter and porosity geometry. The
fuel used in the studies was Liquefied Petroleum Gas (LPG). The experimental
results are presented in-terms of the performance and emission from PRBs of
different configurations available in the market used for cooking. This work fo-
cuses to characterize the performance and emission analysis of PRBs. The char-
acterization of each burner was carried out by the help of a horizontal floor type
profile projector (Metzer-M, Model: 806A). The temperature field at various
flame zones was measured by the help of both FLUKE IR camera (Model: Ti32)
and K-type thermocouples. Thermal efficiency of each of the burner was deter-
mined by calculating the heat gained by the water and the container subjected for
heating and the amount of fuel consumed during the process. Parameters like
convective heat transfer coefficient (h), fuel density, firing rate and thermal effi-
ciency, were computed by using suitable empirical formulae. The maximum ther-
mal efficiency obtained was 64.59% and found good agreement with the previous
data in the open literature.
Keywords: Characterization, Emission, LPG, PRB
1 Introduction
The heating systems used for domestic purposes that operate on free flame, leads to
relatively low thermal efficiency. Energy conversion aspects between flowing gas en-
thalpy and thermal radiation by using porous medium becomes an interesting approach
for improving the overall performance of these systems. Proper parametric control may
lead to better enhancement of burner performance. In India, LPG (liquefied petroleum
gas) is the most commonly used conventional fuel for cooking. Depletion of fossil fuel

2. and drastic deterioration of climatic conditions forced to improve porous media tech-
nology, catalytic conversion technology and metal morphology to control air pollution
and to enhance fuel efficiency due to complete combustion as a result of energy feed-
back by thermal radiation and conduction through porous matrix. N.K. Mishra et al.[1]
tested Medium-Scale (5-10 kw) Porous Radiant Burners for LPG Cooking applications
and found the PRB with 5kw thermal load yielded the maximum thermal efficiency of
about 50%, which is 25% higher than the efficiency of the conventional burner with the
emissions much lower than the conventional burner. V.K Pantangi et al. [2] studied the
porous radiant burner for LPG cooking application. In his study he found that the max-
imum thermal efficiency of PRB is found to be 68% which is 3% higher than the con-
ventional burner with less CO & NOX emission. P.Muthukumar and P.I Shyamkumar
[3] developed a novel porous radiant burner for LPG cooking applications. They tested
PRBs having different porosity with different equivalence ratio & wattages. The re-
ported maximum thermal efficiency is about 75% which is 10% higher than the con-
ventional burners. S.B. Sathe et al. [4] studied both theoretically & experimentally the
thermal performance of the PRB. The results indicate that the heat release and radiant
output are found to increase as the flame is shifted toward the middle of the porous
layer. Akbari, M. H., Riahi, P. and Roohi, R. [5] carried out a study to investigate the
lean flammability limits of the burner and the unstable flash-back/blow-out phenomena.
Hayashi et al. [6] presented a three-dimensional numerical study of a two-layer porous
burner for household applications. They solved the mathematical model using CFD
techniques which accounted for radiative heat transport in the solid, convective heat
exchange between solid and fluid. Talukdar et al. [7] presented the heat transfer analysis
of a 2-D rectangular porous radiant burner. Combustion in the porous medium was
modeled as a spatially-dependent heat generation zone. A 2-D rectangular porous
burner was investigated by Mishra et al. [8]. Methane–air combustion with detailed
chemical kinetics was used to model the combustion part. Mishra et al. [9] studied the
Performance improvement of self-aspirating porous radiant burner by controlling pro-
cess parameters. They characterized the heat transfer phenomena of Porous radiant
burner using IR Thermography and achieved the maximum thermal efficiency as 64%.
2 Experimental Set-up
A schematic of the experimental set-up used for testing the performance of PRBs is
shown in Fig.1. The experimental setup was very flexible and it consisted of a LPG
setup, LPG Rotameter, pressure gauge, six k-type thermocouples, a data acquisition
system, an IR camera, a computer, a digital weighing machine, a flue gas analyzer
(FGA) and burners with different configurations and arrays. The gas cylinder is con-
nected to the burner through flexible tubes of 0.6m inner diameter. LPG from the cyl-
inder is made to pass through a pressure gauge and a Rotameter to measure the density
as well as the velocity of the fuel. A suitable valve was used to control the flow veloc-
ities. Combustion zone was formed with high porosity, highly radiating porous matrix,
and the preheating zone was made of cylindrical passage carrying air and mixture.

3. Three thermocouples were arranged horizontally to measure radial temperature distri-
bution from the center of the burner and other three are positioned vertically for the
measurement of the flame temperature along vertical axis of the burner. All the ther-
mocouples data are continuously assessed by CHINO data acquisition system (model-
KR2000). DAS was connected with a computer for analyzing the data in real time. Also
the surface temperatures of the exposed part of the burners (porous matrix) were meas-
ured with the help of IR camera to observe the radiation effect from the solid surface.
Fig. 1. Schematic of the experimental set-up
Fig. 2. Schematic view of Thermocouple Arrangements
COMPUTER DAS
LP
G FGA
Pressure Gauge
Burner
Rotameter
Thermo
-couple
T-3
T-1
115mm
64mm
28mm
T-2
12mm
25mm
35mm
T-6
T-4
T-5
VERTICAL ARRANGEMENT
OF THERMOCOUPLES
RADIAL ARRANGEMENT
OF THERMOCOUPLES

4. 3 Experimental Procedure
The whole experiment was conducted in both controlled and open atmosphere. The gas
velocity was measured by LPG Rotameter. It was positioned before the fuel nozzle with
a pressure gauge. The experiment was conducted in five different fuel velocities viz.
3.6 m/s, 3.0 m/s 2m/s, 1m/s and 0.4 m/s. The temperature of the flame was measured
by the thermocouples arranged both vertically and horizontally on the top surface of
the burner. The temperature data were assessed by the data acquisition system. Also the
surface and flame temperatures are measured by IR camera. There are thirteen different
types of porous burners were collected and used in this investigation. Fig 4 shows the
burners used in this work.
Fig. 3. Real Images of the different configuration of the Burners

5. 3.1 Characterization Porous Burners:
Open literature revealed that there is a significant effect of the burner configuration
on the performance. Hence, it was decided to characterize the LPG burners to study the
effect of geometric parameters such as diameter, thickness, pore diameter, no. of pores
and distribution pattern on heat transfer, thermal efficiency and emission from the burn-
ers.
Pore size was measured with the help of Profile Projector [Model: Metzer M, 806A,
horizontal floor type]. The profile projector consisted of Projector Screen, three range
of magnification, contour illuminator and surface illuminator. Average pore diameter
of each burner was noted for the analysis of result. The design parameters measured
from profile projector for all types of burners are depicted in Table 1.
Table 1. Salient features of all types of burners
Burner No.
#
Out.Dia
(mm)
Thickness
(mm)
Array/No of
Pores
Pore size
(mm)
Material
1 66.33 3.9 53+34+23 = 110 1.39 Brass
2 62.47 5.26 49+24+19 = 92 1.95 Brass
3 68.32 5.9 61+32+24 = 117 1.53 Brass
4 77.35 5.9 60+25+28 = 113 2.21 Brass
5 82.3 1.5 55+28+20 = 103 1.56 Brass
6 69.61 5.4 60+30+30 = 120 1.93 CI
7 75.75 3.9 64+30+25 = 119 2.16 Brass
8 84.29 5.5 70+36+34 = 140 2.21 CI
9 84.92 5.0 79+31+30 = 130 2.07 Brass
10 114.42 6.0 60x3+22 = 202 2.61 CI
11 103.32 3.7 54x3+16 = 178 3.46 Brass
12 70.07 4.35 43+30+21 = 94 2.0 Brass
13 75.58 4.6 60+30+18 = 108 3.36 CI
3.2 Performance Tests
3.2.1 Thermal Efficiency Test
The following figure (Fig.3) is showing the schematic of the thermal efficiency test of
different burners. The thermal efficiency was obtained by the water boiling test pre-
scribed by BIS 4246:2002. The procedure of the water boiling test is simple. First some
known quantity of water was taken (say 5.0kg) in an aluminum vessel. Initial tempera-
ture (T1) of water and the container was noted before keeping it on the burner. The
distance of the burner surface to the bottom of the vessel should be 50 mm. Then the
water was stirred to maintain uniformity of temperature throughout until it reaches the
final temperature (T2) about 80 . Now the burner should be switched off. So the ther-
mal efficiency is being calculated using the formula given below. The calorific value
of the fuel (CV) is 45780 kJ/kg. Specific heats of aluminum and water are Cpv = 0.8959

6. kJ/kg K and Cpw = 4.1868 kJ/kg K, respectively. The mass of the fuel consumed mf is
the result of weight of the LPG cylinder before the test and weight of the cylinder after
the test (W1-W2), where W1 is the initial weight of the cylinder and W2 is the final
weight of the cylinder. mw and mv are calculated by the digital weighing machine.
η= 2 1( )( )w pw v pv
f
m c m c T T
m CV
 
Where,
mw = mass of water used for heating, Kg
mv = mass of the utensil used for heating, Kg
mf = mass of fuel used for heating, Kg
Cpw= Specific heat of water, Kj/Kg
Cpv= Specific heat of the utensil, Kj/Kg
D = Hydraulic Diameter, m
ρ = Mass density of LPG, kg/m3
∅ f= Porosity
V = Gas Velocity, m/s
CV = Calorific Value of Fuel
Fig. 4. Schematic of standard Porous Burner
Thermometer
Burner
Fuel Nozzle
Flue Gases
Vessel
Mixing Chamber
Regulator
LPG
To FGA

7. 3.2.2 Emission Test.
The emission test was conducted in a confined environment. In our experimental
setup it is being designed such that it can be closed all around except the exhaust outlet
whenever required. So in the emission test the experimental setup is closed all around
and the probe of the Flue gas analyzer (AVL DIGAS 444 model) was kept in the ex-
haust outlet of the hood. After some seconds it automatically shows the percentage of
the CO, NOx, CO2, HC & O2 etc.
4 Results and Discussion
4.1 Thermal Efficiency
The thermal efficiency of the different burners was measured at different firing rates.
i.e. 0.4 m/s, 1.0 m/s, 2.0 m/s, 3.0 m/s, 3.6 m/s. The maximum thermal efficiency was
varying from 58 % for burner #6 (cast iron) to 64.59 % for burner #10 (cast iron).
4.1.1 Effect of Burner Material on Thermal Efficiency
From Table 1 it was clear that burner #10 was having maximum space (outer diam-
eter 114.42 mm) with an average pore diameter equal to 6mm and 202 pores with a
completely different arrangement of pores as compared to others. There might be more
uniform distribution of fuel-air mixture in this burner and hence the maximum effi-
ciency was obtained. It was also confirmed from the experiments that the burner mate-
rial had great effect on the heat transfer and thermal efficiency during burning. From
the results, it is clear that the burners made of brass were not capable to give significant
efficiency even though the outer diameter and number of pores were approximately
close to the cast iron burners.
4.1.2 Effect of geometry of Porous Medium on Thermal Efficiency
The effect of geometry of Porous Medium (pore size, no. of pores and uniform dis-
tribution of pores) might be a significant effect on the heat transfer characteristics of
the burners. The maximum thermal efficiency was 58 % for burner #6 (cast iron) (outer
diameter = 69.61 mm with 120 pores), 62.3% for burner #8 (cast iron) (outer diameter
= 84.29mm with 140 pores) and for burner #10 (cast iron), it was 64.59 %. Hence it is
obvious that geometry of porous medium significantly influences thermal efficiency as
well as the heat transfer characteristics of the burners.
4.1.3 Effect of Firing Rate on Thermal Efficiency
The effect of firing rate on thermal efficiency was investigated. It was found that at
the firing rate 2 m/s, the thermal efficiency was obtained as 64.59 % which was maxi-
mum among all other firing rates taken into consideration in the experiments. The ef-
ficiency value was reduced when the firing rate was 0.4 m/s and 3.6 m/s. Therefore, the
firing rate 2 m/s was taken as the optimum value for the optimal thermal efficiency in
this work. This might be due to the reason that at the minimum firing rate the fuel

8. supply might be not sufficient to propagate over the burner area and number of pores
involved in the burner while, at the maximum firing rate i.e, 3.6 m/s, there was a huge
loss of fuel and fuel blown off over the heat transfer area on the burner. It may be
concluded that to achieve more thermal efficiency there might be a need of precision
design of burner so as to recover the fuel loss at maximum firing rate.
4.2 Emission
The emission test gives the value of CO and NOx different at different firing rate. The
value of NOx and CO for the maximum firing rate (V=3.6 m/s) were found to be 101
ppm and 2.12 % respectively. Similarly in the minimum firing rate (V=0.4 m/s) the
value of NOx and CO were found to be 73 ppm and 1.25 %. The emission values are
well above the WHO standards.
5. Conclusion:
Experiments were carried out on existing domestic and commercial cooking burners to
study the performance and emission. It was revealed that material used for porous me-
dium, pore geometry, firing rate plays vital role for influencing the Thermal efficiency
and emission characteristics of the burners. Hence it may be concluded that change in
material and pore geometry are the important factors to be considered while designing
porous burners for improved thermal efficiency within the limit of stringent climatic
regulations.
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