A quasi-dimensional two zone combustion model was employed to describe the working process of a spark ignition engine taking into multi-zone thermodynamic combustion model for the analys
Trang 1internal combustion engines
Juan Daniel Martíneza,b, Khamid Mahkamovc,*, Rubenildo V Andradeb, Electo E Silva Lorab
a Grupo de Investigaciones Ambientales, Instituto de Energía, Materiales y Medio Ambiente, Universidad Pontificia Bolivariana, Circular 1ra N 70 e 01, Bloque 11, Medellín, Colombia
b Núcleo de Excelência em Geração Termelétrica e Distribuída, Instituto de Engenharia Mecânica, Universidade Federal de Itajubá, Av BPS 1303, Itajubá, Minas Gerais, Brazil
c School of Computing, Engineering and Information Sciences, Northumbria University, Ellison Building, Newcastle upon Tyne, NE1 8ST, UK
a r t i c l e i n f o
Article history:
Received 6 August 2010
Accepted 23 July 2011
Available online 19 August 2011
Keywords:
Biomass gasification
Downdraft gasifier
Producer gas
Internal combustion engine
a b s t r a c t Biomass downdraft reactors, coupled with reciprocating internal combustion engines (RICEs), are
a viable technology for small scale heat and power generation This paper contains information gathered from a review of published papers on the effects of the particle size and the moisture content of biomass feedstock and the air/fuel equivalence ratio used in the gasification process with regard to the quality of the producer gas Additionally, data on the parameters of producer gas, such as its energy density,flame speed, knock tendency, auto-ignition delay period and the typical spark ignition timing, are sys-tematised Finally, information on the typical performance of various diesel and spark ignition RICEs fuelled with producer gas is presented
Ó 2011 Elsevier Ltd All rights reserved
1 Introduction
carbon-based material (feedstock) into gaseous fuel through its
partial oxidation with air, oxygen, water vapor or their mixture It
considered as a thermo-chemical treatment which unlike the full
combustion uses air/fuel ratios noticeably below the stoichiometric
the complete conversion of the carbon and the hydrogen present in
addition to those components, the producer gas also contains
Although the process takes place with a sub-stoichiometric amount
gasi-fication products Finally, hydrocarbons such as ethylene (C2H4) and
producer gas A detailed description of the thermo-chemical
[1e4,6e11]
Currently, small scale electricity generation using biomass
gasification is attracting increasing interest as a prospective way to
provide remote districts with electrical power using local
mechanism is the possibility of the utilization of various organic wastes from the local industry and agriculture with a considerable
tar and particulate matter generation Combustion properties of
of conventional hydrocarbon fuels, such as gasoline and natural gas However, they are satisfactory for this gas to be used as fuel in RICEs
or, in some cases, for gas turbines after an appropriate cleaning process[12]
reactors has been studied extensively and currently is considered to
most widespread reactors for small scale biomass and carbon
realization of the negative environmental and social effects caused
by a rapid depletion of resources of natural gas and crude oil, research and development projects on electricity generation with
Results of theoretical and experimental investigations of
parameters such as equivalence ratio, biomass particle size, its moisture content, etc., on gas composition, heating value, yield,
* Corresponding author.
E-mail address: khamid.mahkamov@northumbria.ac.uk (K Mahkamov).
Renewable Energy
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / r e n e n e
0960-1481/$ e see front matter Ó 2011 Elsevier Ltd All rights reserved.
Renewable Energy 38 (2012) 1e9
Trang 2power output and process efficiency are studied by Jain and Goss
[15], García-Bacaicoa et al.[18], Zainal et al.[19], Dogru et al.[20],
Jayah et al.[21], Wander et al.[22], Lv et al.[23], Wang et al.[24],
García-Bacaicoa et al.[25], Tiangco et al.[26], Yamazaki et al.[27],
Sheth and Babu[28], Tinaut et al.[29]and Ryu et al.[30]
The aim of this work is to present a review of theoretical and
employing downdraft reactors with air as an oxidation agent and
the application of producer gas in reciprocating internal
combus-tion engines
The main advantage of this type of reactor is the lower tar
concentration in the producer gas, which is very important for the
durability of RICEs The lower tar concentration is due to gas
passing through a high temperature zone (the combustion zone),
conversion and the lower ash carry over since gases pass through
response to any load change
in obtaining the homogeneous distribution of air in reactors with
in the range from 1.5 MWt to 5 MWt For reactors with a throat
a certain biomass consumption rate (or a chemical reaction rate), as
well as to maintain an acceptable pressure drop inside the reactor
without the formation of preferential channels (bridging) The
recommended maximum particle size to be used in the Imbert
diameter[20]
cate-gorized as open and close top designs, respectively The open top
design (or stratified) configuration, seeFig.1has an open top, forcing
air (by suction) to move downwards homogeneously throughout
process taking place in the reactor, as well as a possibility of the
formation of preferential channels and internal bridges The
strati-fied downdraft gasifier demonstrates high versatility and relatively
nature, such as rice husk of small particle size and low density A
number of authors have highlighted the ratio of the biomass mass
flow rate and the reactor area, called the specific rate of gasification,
at 58% cold efficiency Tiangco et al.[26]found this ratio to be 200 kg/
gasification to be 167 kg/(h,m2) at 70% gasification efficiency
with a conventional downdraft with a straight cylindrical reactor as shown inFig 2and one with a throat in the reactor core, seeFig 3,
plays an important role in reducing the tar concentration in the
dimensions, some low temperature zones appear in the throat zone
Fig 1 Gasifier with open top.
Fig 2 Conventional downdraft gasifier.
J.D Martínez et al / Renewable Energy 38 (2012) 1e9
Trang 3accordance with García-Bacaicoa et al [18], optimal conditions
exist if the ratio of the biomass consumption rate and the area of
pyrolysis, combustion and reduction) and the relevant equations
describing the chemical reactions in each of these stages are
The height of the reduction zone is very important for obtaining
conversion of the biomass and this results in a lower operational
throat should be greater than 0.5 m3/m2 According to Jayah et al
[21], a greater reactor length may increase its operational efficiency,
but this also results in an increase in the manufacturing cost
A further reduction of the tar concentration in the producer gas
stage air supply, seeFig 4 This type of reactor has been studied in
the Indian Institute of Science (IISc) and in Thailand in the framework
of the Energy Program of the Asian Institute of Technology (AIT)
undertaken at the Federal University of Itajubá in Brazil (UNIFEI) The
downdraft gasifier of the IISc is an open top reactor in which the first
stage of the air supply is provided at it stop, wherein the feedstock is
fed into the reactor The second stage of the air supply occurs at the
oxidation zone level where along with oxidation of a part of the char
the volatiles are released into the upper zone of the reactor The
closed top design Thefirst air supply stage is located near the top of
the reactor where the feedstock is partially oxidized and the thermal
energy is generated This is needed for the drying and pyrolysis
phases occurring above the combustion zone The second air supply
stage is in the middle of the reactor, more precisely, in the oxidation
zone where the tar decomposition into lighter compounds takes
place Bhattacharya et al stated in[33]that the gasifier of the AITalso
decrease the tar concentration during the warm-up period The designs described above are also known as two-stage
Viking, and developed by researchers at the Technical University of
partially oxidized products of pyrolysis This results in the reduc-tion of the tar content in the volatiles and in the generareduc-tion of
partially oxidized pyrolysis products pass through the char bed in
a factor of 100[34] Despite a comparatively low content of tar in the producer gas
using water scrubbers or special condensers in order to satisfy the requirements for the quality of gas used as fuel in RICEs
affect the quality of syngas fuel
used to maintain an acceptable level of the quality of syngas These
3.1 Equivalence ratio (ER)
In the gasification process it is the ratio of the actual air volume supplied per kg of biomass fuel and the volume of air which is necessary for stoichiometric combustion of the above amount of
Fig 3 Imbert gasifier.
Fig 4 Downdraft gasifier with double stage air supply.
J.D Martínez et al / Renewable Energy 38 (2012) 1e9
Trang 4biomass fuel Typical values of ER for biomass gasification vary
between 0.2 and 0.4 According to a number of studies, ER is one of
Yamazaki et al.[27]and Tinaut et al.[29]the amount of air fed into
rate The stoichiometric air/fuel ratio in cubic meters (at normal
conditions) per kg of biomass can be expressed in terms of the
chemical composition of the fuel and its typical value is between 5
3.2 Superficial velocity (SV)
production rate at normal conditions and the narrowest cross
the fuel consumption rate, the power output and char and tar
production rates It is independent of reactor dimensions, allowing
were obtained for SV values of about 0.4 Nm/s Low values of SV
result in a relatively slow pyrolysis process with high yields of char
values of SV cause a very fast pyrolysis process, formation of
tar cracking processes
The producer gas composition depends mainly on the temper-ature in the reactor, which in its turn is influenced by the ER value
are also controlled by the kinetics of the chemical reactions
reach a maximum value as ER increases and then the concentration
of these useful components decreases due to the combustion
with relatively high concentrations of nitrogen and this results in
reactor with air used as an oxidizing agent is as follows: 15e20% of
part is made of N2, O2and CxHy On the other hand, if oxygen or water steam or a mixture of both these is used, then the
the calorific value rises to 18 MJ/Nm3[35] 4.1.1 Yield
This parameter is usually used to measure the producer gas
4.1.2 Efficiency
on the type of biomass used, its particle size, the ER value and the
Table 1
Design characteristics of downdraft gasifiers and experimental results published in open literature.
Biomass Diameter (mm) Height of
reactor (m)
ER Combustion zone temperature ( C)
Gas composition (%)
Heating value (MJ/Nm 3 )
Yield (Nm 3 /kg)
Power (kW)
Cold efficiency (%)
Ref
Wood chips 1000 500 2.5 1.66 c n.a 26.5 7.0 2.0 5.06 b 1.44 448.04 48.77 h [2]
22.1 13.4 2.9 5.59 b , d 1.86 765.15 69.42 h Rice husk 152 n.a 0.40 n.a n.a n.a n.a 3.91 f 2.13 g 8.20 58.11 [3]
203 n.a 0.39 n.a n.a n.a n.a 4.02 f 2.10 g 14.83 58.78
244 n.a 0.40 n.a n.a n.a n.a 4.00 f 2.17 g 21.40 60.44
343 n.a 0.41 n.a n.a n.a n.a 3.98 f 2.22 g 43.89 61.49 Wood chips 600 200 2.5 0.287 1000 n.a n.a n.a 5.19 a n.a 44.93 76.68 [4] Hazelnut shells 450 135 0.81 1.51 e 1025 16.8 14.12 1.70 4.55 a 1.97 9.17 51.53 [5] Rubber wood 920 100 1.15 1.9 c 1000 20.2 18.3 1.1 n.a n.a n.a n.a [6] Sawdust 270 1.1 0.26 900 19.48 18.89 3.96 6.32 a 1.99 h n.a 62.5 h [7] Pine wood blocks 350 n.a 1.3 0.28 1108 25.53 28.93 6.82 4.76 n.a n.a n.a [8] Wood chips 440 350 2 1.3 c 1460 9.4 14.8 1.2 3.8 b n.a n.a n.a [10]
Wood chips 250 70 1.05 0.32 900 19.48 18.89 3.96 6.32 a n.a n.a 62.5 [12] Wood waste 310 150 1.1 0.205 1050 22 14 0.1 6.34 a 1.62 7.38 55 [13] n.a: not available.
a Higher heating value.
b Lower heating value.
c Air/Fuel ratio in Nm 3 /kg.
d Dry, inert free.
e Air/Fuel ratio (Nm 3 /kg), fuel is dry, ash free.
f Lower heating value at 25 C.
g At 25C.
h
J.D Martínez et al / Renewable Energy 38 (2012) 1e9
Trang 5reactor’s design The gasification efficiency, usually determined on
the lower heating value basis, can be calculated in two different
is calculated as the ratio of the total energy in the producer gas
(sensible and chemical) and the chemical energy in the feedstock
(the heating value) The cold efficiency calculations account only for
the heating value of the producer gas and neglect the value of the
avoid the uncertainty related to the calculations of the sensible heat
of producer gas discharged from the reactor since the high
temperature of this gas is very often not the objective in the
gasi-fication process Typical values of the cold efficiency for biomass
Table 1
in a downdraft reactor, namely the producer gas composition, its
process, depend on such physicalechemical properties of the
ratio which determines the temperature levels Finally, the
performance is affected by a number of design features of the
reactor, such as the locations of the air inlets, the volume of the
gasification zone[19]and the grate’s design[18].Table 1presents
downdraft reactors both with and without throat, as reported by
equivalence ratio varies between 0.2 and 0.4 In gas engine
Any further increase of the turndown ratio compromises the
quality of syngas in terms of the tar content and negatively affects
the durability of the engine
5 Reciprocating internal combustion engines fuelled with
producer gas
the operation of RICEs fuelled by producer gas The quality of
producer gas as a fuel is considerably poorer compared to gasoline
to be carried out in order to be able to run on producer gas Spark
ignition and diesel engines fuelled with artificial gas with a quality
similar to that of producer gas were studied by Muñoz et al.[37] The
operation of engines was also investigated using real producer gas
Wang et al.[24], Sridhar et al.[38], Shashikantha et al.[39],
Ram-achandra[40], Bhattacharya et al.[31], Uma et al.[41], Henriksen
of the air/fuel equivalence and the compression ratios
Alongside the experimental research, extensive theoretical
investigations have also been performed using various modelling
tools on the operation of RICEs fuelled by producer gas Thus
took into consideration 28 species to calculate the producer gas
composition as a function of the biomass-to-air ratio and its
temper-ature, the heat release and the auto-ignition period A quasi-dimensional two zone combustion model was employed to describe the working process of a spark ignition engine taking into
multi-zone thermodynamic combustion model for the analysis of
The model was calibrated using experimental data and applied for calculations of a multi-cylinder, four-stroke natural gas engine running on synthetic gas fuel The above engine was equipped with
a two zone combustion model for the description of the working process of an engine and concluded that the main parameter
unit volume) of the stoichiometric air/producer gas mixture The above model determines the fraction of the mass burnt, the vari-ation of the pressure and temperature over the cycle and values of
a parameter named as the Engine Fuel Quality (EFQ) the authors estimated the magnitude of the power de-rating in the engine fuelled by the producer gas
To use the producer gas obtained in the process of biomass
ignition engines it is necessary to ensure that the quality of gas is
dura-bility of major engine components, such as the valves, the
substances contained in producer gas that limit its application in
particle and tar concentration in producer gas for satisfactorily operation of the internal combustion engine must be less than 50
require-ments described in the literature should be interpreted with caution since the type of the engine used in tests and its design
engine operation was observed at higher tar concentration levels
gas was used in standard diesel engines in the dual-fuel mode operation and that diesel fuel savings up to 85% had been obtained However, in the case described above, the power produced by the engine cannot be considered as achieved entirely by the utilization
that engine was its capability to operate on diesel oil in the case when biomass was not available or when a malfunction occurred in
and, in some cases, the lower maintenance compared to
diesel engines in order to make these machines run on 100% producer gas include the installation of additional equipment incorporating spark ignition and air-gas mixing systems In spark ignition and diesel engines producer gas and air are usually mixed
in an intake collector and then the air-fuel mixture now ready for combustion enters the cylinders of the engine
Test results obtained using diesel engines running on low calorific gas produced in a biomass gasifier are presented by Sridhar et al.[38],
running RICEs in the dual-fuel mode of operation with a considerable reduction in the consumption of diesel oil was demonstrated in
J.D Martínez et al / Renewable Energy 38 (2012) 1e9
Trang 6[40], Bhattacharya et al.[31], Uma et al.[41], Ramadhas et al.[42],
an operational mode was between 20 and 30%
A case of fuelling modern spark ignition engines with producer
compression ratio of this type of engine, namely between 8 and 12
that in diesel engines According to Sridhar et al.[38], the reduction
in power in an engine run on producer gas is mainly attributed to
of the gas/air mixture which enters the engine cylinders The
amount of the combustible mixture supplied to a cylinder is
temperature conditions inside the cylinder and by the pressure and
temperature of the gas/air mixture The stoichiometric mass ratio in
the air/producer gas mixture is between 1.0 and 1.2, compared to 17
for methane and thus an adequate mixing and dosage device is
necessary for an engine to operate with high performance The
fuels, such as natural gas, and form a mixture with a high
energy density fuels This device with its improved control and
minimal pressure losses very accurately maintained the required
air/fuel ratio over a wide load range and provided the smooth
6 Parameters affecting the performance of RICEs fuelled
with producer gas
The parameters which mainly affect the performance of RICEs
are the energy density or the heating value of the producer gas/air
mixture, the displaced volume of the engine, the methane or octane
auto-ignition delay period, the compression ratio of the engine
(which is related to the knock tendency) and the spark timing
Some results reported in the open literature on RICEs fuelled with
6.1 Energy density
The energy density of any fuel/air stoichiometric mixture (HVm)
can be determined in terms of the volumetric heating value (kJ/Nm3)
The energy density of the producer gas/air mixture mainly depends
on the concentration of the combustible components in producer
gas The low heating value of the producer gas obtained from
With such concentrations of combustible substances the energy
value is lower than the energy density of a natural gas/air mixture
theoretical value of the power de-rating when a natural gas engine is switched to operate on producer gas is about 30% This value is consistent with the estimation made by Tinaut et al.[16] In this study the authors used the EFQ parameter to analyze the performance of an engine operating on a particular fuel They predicted that the power
of the engine fuelled with producer gas in the full load regime of operation will be approximately two-thirds of the maximum power
thermody-namic analysis demonstrated that a lesser value of power de-rating at the level of 15e20% could be achieved if the producer gas is used in
The current engine technology intensively exploits advantages
of lean combustion operation For producer gas/air mixtures the lean combustion condition is achieved when the actual air/fuel ratio is greater than 2 and in such conditions the relative energy density of the producer gas/air mixture may be higher than some
de-rating being lower when the producer gas/air mixture is used Producer gas is adequate for a lean burn and combustion of
a corresponding fuel/air mixture results in low NOx emissions due
consumption
6.2 Cylinder volume The amount of a combustible mixture which can be delivered to
tempera-ture Thus, to maintain the power level in a conventional natural gas engine switched to operate on low heating value fuel, such as
using a turbocharger for increasing the pressure of the air-fuel mixture in the beginning of the compression process in a cylinder 6.3 Flame speed and spark timing
fuel, the amount of air used in the combustion process, which is characterized by the parameter ER, and the pressure and
Table 2
Presence of pollutants in producer gas and used controlling mechanisms.
Pollutant Source Possible problems Control mechanism and/or
mitigation Particulates Ash, bed material Erosion, agglomeration and fouling.
Environmental pollution
Filtration, gas cleaning (scrubber)
Alkali metals (sodium,
potassium in the ash).
Ash Corrosion Cooling, condensation, filtration,
adsorption.
Nitrogen compounds
(NOx, NH 3 , HCN)
Reaction of nitrogen contained i
n air and feedstock
Corrosion, environmental pollution Treatment with substances of basic
character, use of pure oxygen
in the process Sulfur and chlorine
compounds (HCl, H 2 S)
Reaction of sulfur and chlorine contained in the feedstock
Cleaning, capture with CaCO 3 , MgCO 3
Tar (complex
hydrocarbon mixtures).
Low temperatures in the process, considerable amount of volatile
in the feedstock
Corrosion, agglomerations and fouling.
Health hazard
Removal, cracking J.D Martínez et al / Renewable Energy 38 (2012) 1e9
Trang 7depends on the turbulence intensity, which in its turn, is pre-defined
flame speed in its turn has a significant effect on the performance of
combustion of the producer gas/air mixture at ambient conditions
propagation varied from the mixture being lean (26% of fuel with an
ER value of 0.47) to rich (56% of fuel with an ER value of 1.65) The
ratio varied between 1.2 and 1.4 and this value is greater than that
for methane and carbon monoxide, but much less compared to that
was 0.5 m/s at 300K and 1 bar conditions in the burning process of
the stoichiometric air/producer gas mixture in a combustion bomb
The authors also used a software tool, namely CHEMKIN, together
different producer gas compositions at various pressure and
temperature conditions for a range of the producer gas/air
equiv-alence ratios For the stoichiometric air/fuel ratio at 300 K and 1 bar
found to be 0.42 m/s At typical engine operating conditions, which
are characterized by high pressures and temperatures, the
lower than that of isooctane but higher than that of methane
6.4 Spark timing
concen-tration in producer gas makes it necessary to use the smaller spark
advancement (retarding) in the spark timing to achieve a better
the cycle when the piston is very close to its top dead center (TDC) This is because of the high hydrogen concentration (around 20%) in
into account that the spark timing also depends on other variables,
at the permissible high position in the cylinder and when the fuel/
with the extraction of the maximum power Setting the correct
which corresponds to a higher power output from the engine and
a maximum brake torque (MBT) point and can be observed in the pressure vs crank angle (p-q) curve as a peak in the instance in the cycle corresponding to 16-17 degrees of crank angle after the
water cooled diesel engine with a compression ratio of 17 which was adapted to run as a spark ignition engine were carried out by
timings in engines fuelled by producer gas are retarded compared
to the spark timing for conventional spark ignition engines fuelled
in the spark timing is necessary for engines fuelled with producer
the ignition timing has to be retarded with an increase in the compression ratio in order to achieve the MBT point This is because the pressure and the temperatures are greater at the higher compression ratios and therefore the combustion process occurs
to the piston’s TDC
Table 3
Performance of some RICEs fuelled with producer gas.
Biomass Engine RPM CR Producer
gas fuelled (%)
Modifications
in the engine
Power (kW) Spark timing ( o BTDC
Power de-rating a (%)
Exhaust gas temperature ( C)
Engine’s thermal efficiency (%)
Combustion equivalence ratio
Overall Efficiency b (%)
Ref
Simulated
gas
Spark
ignition
2500 8.2:1 100 None 2.3 c n.a n.a 634
@ 2000 rpm
n.a n.a n.a [15] Wood Diesel 1500 11.5:1 100 Ignition
system d 12e16 e 35 n.a 360- 430 C 28e32 n.a 21e24 f [16] Wood Diesel 1500 17:1 100 Ignition
system g
2.3 c 10 20 h 310 e 370 C 19.05 i n.a n.a [17] Wood chips Diesel n.a n.a 100 Ignition
system
15e20 e n.a 20 n.a 28 i n.a 25 f [20] Coconut shell Diesel 1500 18.5:1 81 None 11.44 c n.a 21 488.2 14.7 j n.a 11.69 f [18]
13.22 e Wood Diesel 1500 50 17:1 100 Ignition
system
17.5 e 6 (MBT) 16.7 k n.a n.a 1.05 l 16.6 m [14] Wood Diesel 1500 17.5:1 65% None 4 c 27 20 410 22 i n.a n.a [23]
60% Ignition
system
a Calculated as a fraction of a nominal engine power.
b Gasification and engine system.
c Brake power.
d Combustion chamber was re-designed for the combustion with the turbulent flame propagation, CR was changed from 17 to 11.5.
e Electric power.
f From biomass to net electricity.
g The engine can operate in diesel and dual fuel mode.
h Assuming the alternator and transmission efficiency of 80% and 95% respectively.
i On the shaft.
j Engineegenerator system.
k In brake power.
l Fuel/air equivalence ratio.
m From biomass input to shaft output.
J.D Martínez et al / Renewable Energy 38 (2012) 1e9
Trang 86.5 Knock tendency
For gaseous fuels, the methane number is used to compare
knock properties and this is analogous to the octane number used
to quantify knock properties of liquid gasoline fuels Engines with
a high compression ratio require fuels with the high octane/
methane number in order to avoid an uncontrolled self-ignition of
cylinder after the start of such a combustion process Malenshek
used to blend simulated alternative gaseous fuels and measure
their methane number Numerous engines were run on natural gas
and the methane number was varied between 75 and 95 Producer
gas has a higher methane number than natural gas and therefore it
is not prone to detonation during the compression stroke
The knock is caused by a combination of factors, such as the
combustion chamber design, the equivalence ratio, the intake air
temperature and the pressure, the spark timing and fuel properties
a smooth engine operation at the compression ratio of 17 without
any traces of knocking when the engine was fuelled with producer
uncontrolled self-ignition in high compression ratio RICEs due to
the high concentration of the hydrogen in the gas was addressed by
the authors The high concentration of inert gases in producer gas,
as a knock suppressor and explains the high methane number
demonstrated the increased knock resistance within the extended
combustion of the fuel composition with the low methane number,
which otherwise would be prone to a high intensity knock
Nitrogen also demonstrates a similar knock suppressing quality,
gas is lower compared to conventional fuel such as methane and
therefore a better knock resistivity could be expected when an
the possibility of running RICEs on producer gas with a higher
compression ratio
Gaseous fuels with high hydrogen concentrations usually are
corresponding fuel/air mixture reduces the probability of knocking
speed, the portion of the air/fuel mixture that is heated above the
self-ignition temperature will be burnt off during the ignition delay
period and therefore the occurrence of knocking will be avoided
6.6 Auto-ignition period
The auto-ignition delay period of a fuel/air mixture is an
important parameter in the RICEs operation and also can be used to
time required for the mixture to spontaneously ignite at certain
temperature and pressure conditions The length of the ignition
delay depends on the producer gas composition and on the
time of a fuel/air mixture was theoretically determined by Lapuerta
demonstrated that at a constant cylinder pressure of 20 bar the
auto-ignition delay period for producer gas is much longer than that for gasoline in the low temperature range, namely below
the high temperature range With the pressure increased to the
50 bar the auto-ignition delay period for producer gas remains just slightly shorter than that for gasoline in the high temperature range
combustion temperatures, together with the longer auto-ignition delay period, for the producer gas/air mixture would make it possible to increase the compression ratio of the engine without increasing the knock tendency
Another problem associated with using producer gas in RICEs is
in the intake manifold and its burning in an explosive manner causing the engine to stop This is attributed to the relatively weak
present in the ignition cables could cause abnormal ignitions in the RICEs The authors recommended shielding the ignition cables to avoid these kinds of difficulties
7 Conclusions
biomass in downdraft reactors using air as an oxidizing agent were discussed The effects of the equivalence ratio (which should be kept between 0.2 and 0.4), the biomass particle size (which usually should be less than 5 cm), the moisture content (which should be
analyzed The literature review carried out in this subject area
respectively The average temperature in the combustion zone is
(diesel and spark ignition ones) were discussed The low energy
air mixture caused by the presence of hydrogen in the mixture it is necessary to retard the spark ignition time in order to achieve
possi-bility of using engines with a higher compression ratio when fuelled with producer gas without any increase in the knock tendency is highlighted The rise of the engine’s compression ratio results in the reduction of the power de-rating The use of air as an oxidizing agent
nitrogen (between 40 and 50%) in the fuel/air mixture and the
engines with the high compression ratio are employed
Acknowledgment The authors would like to express their gratitude to Companhia
through project PD153
Also we would like to thank the Committee on Coordination of Improvements in Higher Education (CAPES) for the allocation of
a scholarship and the National Research Council of Brazil (CNPq) for
Furthermore, we would like to acknowledge the Foundation of Science support from the Minas Gerais State (FAPEMIG)
Finally, we would like to thank the Royal Society (UK) for the financial support to perform this collaborative research between teams at Northumbria University (UK) and the Federal University of Itajuba (Brazil)
J.D Martínez et al / Renewable Energy 38 (2012) 1e9
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