Journal of Power and Energy Engineering, 2015, 3, 458-466
Published Online April 2015 in SciRes. http://www.scirp.org/journal/jpee
How to cite this paper: Ehsan, M., Sarker, M., Mahmud, R. and Riley, P.H. (2015) Performance of a Score-Stove with a Ke-
rosene Burner and the Effect of Pressurization of the Working Fluid. Journal of Power and Energy Engineering, 3, 458-466.
Performance of a Score-Stove with a
Kerosene Burner and the Effect of
Pressurization of the Working Fluid
Md Ehsan1, Manabendra Sarker1, Rifath Mahmud1, Paul H. Riley2
1Department of Mechanical Engineering, Bangladesh University of Engineering and Technology (BUE T),
2Department of Electrical Engineering, University of Nottingham, Nottingham, UK
Received January 2015
Score-S tove TM a clean-burning cooking stove that also generates electricity was tested using a
pressurized kerosene burner. The Score-Stove works on the principle of thermo-acoustics to gen-
erate small-scale electricity. The device having hot-end, cold-end and regenerator acts in a way
similar to a stirling cycle generating acoustic power, which is then converted to electricity using a
linear actuator. It can supply small power for applications such as LED lighting, mobile phone
charging and radios particularly in rural areas without grid electricity as well as improving house-
hold air pollution. After assessing the needs of the rural communities through a survey, tea-stalls
and small restaurants owners were identified as clients with the most potential of using the stove
in Bangladesh. Bangladesh University of Engineering and Technology ((BUET) modified a Score-
Stove to use both wood and a pressurized kerosene burner of a design that is widely used for
cooking in rural areas of Bangladesh. The design was adapted to meet performance needs such as:
heating rate, cooking efficiency, energy distribution, electric power generation, exhaust emissions
and time taken to boil water using standardized water boiling tests. Performance was also com-
pared with conventional (non-electrically generating) stoves that use a pressurized kerosene burn-
er. The Score-Stove performance was then evaluated while increasing the pressure of the sealed
working fluid (air in this case) from atmospheric to about 1.4 bar. The pressurization was found to
almost double the power generation. An arrangement for utilizing cooling water waste heat was
also devised in order to improve the thermal performance of the stove by 18%. Technical defi-
ciencies are documented and recommendations for improvements and future research in order to
obtain wider end-user acceptance are made.
Score-S tove , Small-Scale Power, Therm o-Ac oustic s, Clean Cooking Stove, Kerosene Burner,
M. Ehsan et al.
Developing a low pollution, fuel efficient and affordable cooking stove can change the life of billions of people
around the world, particularly in Sub-Saharan Africa, the Indian subcontinent and South America where people
cook on open fire stoves and are largely deprived of grid electricity as well. Inefficient burning causes thousands
of tons of carbon emission as well as serious health hazards to the users, which causes almost four million peo-
ple to die prematurely each year due to household air pollution (HAP) . The Lancet  states that household
air pollution is the leading risk factor for premature deaths in south Asia.
Despite the high death rates, the problem continues to be intractable for a variety of reasons . The World
Bank  states “…In short, many approaches to introducing improved stoves have been tried, with some suc-
cesses and many failures…”. There is a growing body of opinion that more radical approaches are needed .
Riley  argues that the addition of electrical generation to cooking stoves increases the affordability and hence
social acceptance of clean cooking. Studies in Malawi  using thermo-electric technology have made some
progress, although the power produced is low, about three Watts of electricity. Another thermo-electric stove
that is commercially available for use in developed countries and has had trials in Laos is the Biolite  that
produces about 2 to 3 Watts. It only takes small pieces of wood and so is thought unsuitable for areas where cut
wood is long . Recent developments in thermo-acoustic technology have shown potential to provide solutions
to the problems set out above -. This paper describes the use in Bangladesh of the Score-Stove TM that
incorporates the thermoacoustic principle to generate electricity whilst cooking by converting excess thermal
energy into electrical energy before releasing waste energy to the atmosphere . With the use of a chimney
and proper combustion of air-fuel, the stove can provide a non-smoky and healthier environment inside the kit-
chen. After assessing the needs of the rural communities through a survey, tea-stalls and small restaurants own-
ers were identified as people with the most potential of using the stove in Bangladesh. Later the pressure of the
sealed working fluid was increased to see the effect on the power generated.
2. Background and Working Principle
Byron Higgins (1777) first documented the themoacoustic phenomenon . A century later Lord Rayleigh ex-
plained the phenomenon qualitatively , in the 1960s’. From then until the 1990’s others progressed under-
standing   until progress became much more rapid through the theoretical work of Swift  at Los
Alamos laboratories  and the practical realizations of deBlok from Aster . F ig ur e 1 below shows the ba-
sic components of a dual full wavelength, looped tube travelling wave engine as used in the Score-Sto ve™ .
In a thermoacoustic engine (TAE), heat is supplied from a source to a gas (air in Score-Stove) via the hot heat
exchanger (HHX), heat is removed via the ambient heat exchanger (AHX) and the gas undergoes repetitive
Figure 1. Functional diagram of Score-Stove.
M. Ehsan et al.
thermal expansion and rarefaction to produce acoustic energy. Between the HHX and AHX a temperature gra-
dient is formed in a porous material called the regenerator that sustains a resonant acoustic wave. A linear alter-
nator (a loudspeaker working in reverse for the field trials) within the closed loop converts the acoustic wave
into electricity. Previous works reported change in onset temperature  and increase of power generated when
pressure of the sealed working fluid was increased . However, this requires stronger materials and better
joint seals, which tend to increase the cost of the stove.
3. Modification of the Score-Stove
The basic stove design described in reference   was modified in two ways. Firstly, the TAE working gas
was pressurised and secondly, the waste heat from the TAE was used to pre-heat water for cooking as described
in the following paragraphs. The increase in pressure was modest and within the limits of the low cost materials.
4. Score-Stove Performance Analysis
Stove performance was tested during typical water boiling tests (WBT) and the heat input rate was calculated
from the gravimetric measurement of the fuel consumption rate and the lower heating value. Temperatures of
the flue gas, TAE, HHX and AHX were recorded using K-type thermocouples and a National Instruments com-
pact data acquisition system. Mass flow rate and temperatures of the cooling water and the exhaust leaving the
chimney were recorded to estimate the heat losses. The electric power voltage and current produced from the
linear actuator was measured using a watt -meter with either LED lights or a variable resistance as a load in order
to check the sensitivity at different loads. The major parameters recorded during the laboratory water boiling test
are given in Ta ble 1. For the WBT, two identical water pots each filled with 2 litres of water were placed on the
stove. Resonance started after about 11 minutes of heating at about 64 Hz and the lights came on within 12 min-
utes. The first pot reached a temperature of 80˚C after about 39 minutes, while the water in the second pot
reached 64˚C. It took 15 minutes more to get another pot of hot water at 80˚C if the preheated water of the sec-
ond pot was used to replace the water in the first pot. More details of the WBT results are given in . Later
increasing working fluid pressure and recovery of cooling water heat were studied to improve stove perform-
Being a heat engine the Score-Stove TAE is limited by the second law of thermodynamics and Carnot’s law
so TAE efficiency is a function of the temperature difference between HHX and AHX. Figure 2 shows heat
flows of the stove under test and Table 2 shows the component shares of energy distribution during a WBT test.
It was noted that the time requirement for boiling in the Score-Stove was longer (in about 39 min) compared to
boiling the same pot of water directly using the conventional pressurised kerosene burner (typically in about 10
min). This is because in the conventional stove, the flame directly comes in contact to the pot and the tempera-
ture difference across the water in the pot and the flames are higher which facilitated a greater rate of heat trans-
fer and faster heating. In the case of Score-Stove, the flame from the burner first passes by the TAE and then
reaches the boiling pots in sequence, which reduces flame temperature thus reducing the temperature gradient
and the rate of heat transfer. In the unit tested, waste heat from the AHX is vented to atmosphere and so is not
doing useful work.
Table 1. WBT results of the Score-Stove.
Amount of water 2 kg water in each of two pots
Temperature From 26˚C room temperature to 80˚C, took 39 min for pot-1
Resonance initiation (onset) 11 min 17 seconds after start-up, Frequency: 64 Hz
Power output About 3.5 watts (2 LED lamps)
Maximum current 0.7 Amp at 5 volts
Fuel consumed 0.36 Lit/hr
TAE hot-end temp 700˚C
Exhaust temp 175˚C
Exhaust condition Clear exhaust, almost invisible
M. Ehsan et al.
Table 2. Energy distribution during a WBT test.
INPUT ENERGY COMPONENT Value
Fuel consumption at 26˚C r oom 0.194 kg
Assumed burning efficiency 95%
Input heating rate 3325W
Total energy during WBT (100%) 7780 kJ
ENERGY CONSUMPTION kJ Share
Pot-1 (conv. 80˚C + evap, 50 mg) 565 11.4%
Pot-2 (conv. 64˚C + evap, 0 mg) 319
Heat absorbed by cooling water 1297 16.7%
Heat lost from exhaust gases 986 12.7%
Heat loss from cooking pot 140 1.8%
Heat loss from hot stove surface 1193 15.3%
Heat loss from chimney surface (open) 387 5%
Radiation loss from exposed flame 790 10.2%
Heat absorbed by ~90 kg metallic mass 1377 17.7%
Energy as sound (estimated) considering 5% alternator efficiency 180 2.3%
Unaccounted energy losses 555 7.2 %
Figure 2. Energy balance of Score-S to ve.
Higher flame temperatures would have been achieved by restricting the airflow and keeping combustion
closer to stoichiometric conditions (less excess air). However, laboratory experiments showed that this higher
flame temperature caused gradual overheating of the fuel tank as more heat started to be conducted through the
M. Ehsan et al.
metallic fuel line up to the burner. This increased the vaporisation of kerosene fuel, which increased the fire risk
significantly and so was considered unsafe for field trials. The problem also could be solved by reorienting the
fuel tank and connecting it with a non-metallic high-temperature withstanding pressure hose. However this
would compromise the simplicity of the present design and convenience of directly plugging in the very popular
pressurised kerosene stove. So in practice the common pressurised kerosene burner design at present has limita-
tion regarding increasing of flame temperature  hence the heat transfer rate decreases causing longer time
requirement of the Score-Stove for performing the WBT.
5. Score-Stove with Pressurization
5.1. Theoretical Considerations
The characteristic acoustic impedance of a pipe Z0, is:
where c is the speed of sound in the pipe, A is the pipe area and the density of the gas ρ varies with mean pres-
sure so that the density of the working gas ρw is:
where Pm is the mean pressure in the pipe and P0 is the pressure at the defined density ρ0. Giving:
Acoustic power in a travelling wave travelling is:
where p is the dynamic pressure variation, v is the particle velocity and A is the pipe area.
The drive ratio Dr has a value of around 5% to 10% in practical thermo-acoustic engines, defined as:
Substituting p from 5.3 into 5.2 gives:
Pressure is related to velocity by the pipe impedance:
Equation (5.6) shows that for a fixed pipe diameter and drive ratio, acoustic power is proportional to the
square of the mean pressure. Furthermore, Equation (5.8) shows that for a fixed drive ratio and pipe area, veloc-
ity is constant and independent of Pm.
M. Ehsan et al.
There are two main sources of loss in a TAE: pipe losses that are mainly a function of particle velocity, and
losses in the regenerator that are a function of velocity, gas density (i.e. pressure) and gas viscosity. As the re-
generator has a larger area than the pipe, velocity through it is lower than pipe velocity. Increasing Pm by small
amounts increases pipe acoustic power, but losses stay the same, therefore we predict efficiency to improve. For
larger increases in Pm, losses in the regenerator increase and so efficiency will level off.
5.2. Experimental Results
The pressurizing apparatus consisted of a small reciprocating compressor fitted with a pressurized air tank. Fig-
ure 3 shows the set-up used for pressurizing the stove using compressed air from a reciprocating compressor.
The sealing at this stage was only capable of safely withstanding up to 1.5 bar of air pressure in the resonance
tube. The initial surge of air from the compressor caused a rapid rise of air pressure in the resonance tube and it
was difficult to attain and maintain a particular pressure level. Therefore, the tank was filled with compressed air
and the compressor turned off. A precision flow control valve was fitted between the tank and the resonance
tube. The stove was heated up and pressure of air in the system was raised to about 1.5 bars then by gradually
releasing air from the tank, readings were recorded at resonance from 1.35 bar to about atmospheric level.
However, the stove performance of the pressurized kerosene burner and the linear alternator showed some
variations in repeating runs, which is showed as a band as in Figure 4(a). Variations in-heating rate of the typi-
cal kerosene burner, condensation of some water vapours in the resonance tube, performance of linear alternator,
are jointly responsible for such differences. The general trend showed a non-linear (2nd/3rd order) increase of
electric power developed with the increase of air pressure of the resonance tube. With air pressure from atmos-
pheric to about 1.35 bar the average rise of power output from the linear alternator almost doubled as shown in
Figure 4(b) and is in line with the theoretical predictions. However, higher air pressure caused larger forces
acting on the tube joints and at the present condition of sealing, the pressure could be sustained only for about 20
6. Score-Stove the Cha-Wala Version
The regular version of the Score-Stove uses a supply of cooling water around the cold-end of the regenerator
mesh and the auxiliary heat exchanger or a radiator heat exchanger to keep the temperature of the cold-end close
to room temperature. For application like small tea stalls a water reservoir can be used for this purpose, which
could also be a source of preheated water for boiling using waste heat. This originated the idea of the “Cha-Wala”
(it means the vendor who sells tea) version of the Score-Stove, where the cold end of the TAE was submerged in
an additional water tank eliminating the use of radiator or line supply of cooling water. During the operation of
Figure 3. Pressurizing the system with compressed air.
M. Ehsan et al.
Figure 4. (a) Variation of power with air pressure; (b) Trend
of increase in power generated.
the stove the water in this tank gets gradually heated up, which can be tapped as pre-heated feed in the boiling
water container. This reduces the time required for boiling as well as improving the thermal efficiency of the
system. In this process, some of the waste heat is recovered, reducing the overall heat losses.
The “Cha-Wala” in Figure 5 Stove performance was also evaluated using typical WBT. Parameters were re-
corded as the water temperature in the cooking pot reached 80˚C and 100˚C from room temperature of 22˚C.
The first of the two pots reached a temperature of 80˚C after about 32 minutes and 100˚C after about 44 min-
utes, while the water in the second pot reached 52˚C and 64˚C at the respective times. It took 14 minutes more to
get another pot of hot water at 100˚C if the preheated water of the second pot was used to replace the water in
the first pot. The water in upper portion of the water tank was warmer than the water in the lower portion be-
cause of the nature of convection. This preheated water gained a temperature of about 33˚C (in upper portion)
and an average temperature of about 28˚C at the time of the boiling of water in the first pot. This preheated wa-
ter was then used in the second pot to make the cooking even faster. The Cha -Wala version could heat the first
pot 7 minutes (18%) earlier compared to the standard version described before, reflecting the utilization of
The Score-Stove provides a unique solution using thermoacoustic technology regarding the use of waste heat
during cooking and the potential to produce small-scale electricity, especially for the people who do not have the
access to mains electricity.
The current design is capable of using multiple fuels and acceptable for limited field trials to obtain end-user
feedback. However, its performance is lower than that required to compete with conventional pressurized kero-
sene cooker. Further adaptations are required to improve performance and ensure safety under typical end use.
Two features for improving the performance investigated are: increase of pressure of the working fluid and
reusing the waste heat. The increase of pressure by 1.4 times almost doubled the power produced and fits well
9001000 11001200 1300 1400
Electric Power (W)
90010001100 12001300 1400
Electric Power (W)
M. Ehsan et al.
Figure 5. Cha-Wala version of the sto ve.
with the theoretical predictions. The recovery of heat lost in cooling the cold-end is incorporated in the Cha-
Wala version of the stove, which reduces the cooking time by 18%. These are rich areas for further research and
development and provided the changes give sufficient improvement, the Score-Stove has the potential to make
an impact on the target users.
The authors would like to thank University of Nottingham UK and Bangladesh University of Engineering and
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