Simulation of a Syngas - Diesel Dual Fuel Engine for Small-Scale Power Generator Le Anh Tuan *, Pham Hoang Luong Hanoi University ofScience and Technology.. 2013; accepted: April 22, 2
Trang 1Simulation of a Syngas - Diesel Dual Fuel Engine for Small-Scale
Power Generator
Le Anh Tuan *, Pham Hoang Luong Hanoi University ofScience and Technology No 1, Dai Co Viet Str., Hai Ba Trung, Ha Noi, Viet Nam
Received: September 17 2013; accepted: April 22, 2014
Abstract
The paper presents findings from numerical simulation on utilization of syngas in 3 cylinder diesel engine, 8.75 kW power, used in a small gen-set, based on the concept of syngas-dieset dua! fuel It is the first step
of the process of applying syngas produced by biomass gasification system to the diesel gen-set to be used
in rural areas
The simulation model was created on AVL Boost software, of which Vibe 2 zone combustion model was used for the prediction of combustion characteristics, Woschni 1978 was selected for heat transfer model, while NOx, CO and soot emission calculation was based on models developed by Pattas & Hefner, Onoiati and Schubiger, respectively With the constant rates of the syngas containing of 11.63%, H2, 24.47% CO,
0 01%, CH4, 0.08%, O2, 1.79%, CO2 and 62 02%, N2, the simulation results show that at the engine speed ol
1500 rpm and indicated mean effective pressure, IfvlEP = 6.54 bar (at the full load condition), the syngas emissions including CO and NOx were raised while soot emission decreased with the syngas quantity of the dual fuel cases
Keywords: Syngas-diesel dual fuel, Small d ^1 gen-set, Biomass gasification, AVL Boost simulation
1 Introduction
The gasification technology is i kind of
thermochemical technologies that can efficiently
destroy biomass and generate synthesis gas in a very
ash and synthesis gas which can be applied both
and electricity power) [2] In case of power production
purpose, the intemal combustion engine has been
considered for integrating with gasification system in
small scale power plant (< 1 MW) that can be beneficial
in the areas like islands, mral areas, industrial areas,
etc [3]
Syngas has been using as an additive fuel for
compression ignition engines (CI engines) or the main
fiiel on spark ignition engines (SI engines) There are
a numerous paper investigated about using syngas on
[4,5] investigated the performance and NO emission
formation of a SI engine fueled with syngas under
various loads by using a multi-dimension combustion
and emissions of a SI engine driven generator on
biomass based syngas The experiment was earned out
on a commercial 5,5 kW generator modified for
" Corresponding author; Tel,: (•f84) 4386.3176
Operation with 100% syngas, the mass flows of this gas were adjusted to obtaining same electrical power with those got for gasoline operation The CO and NOx
higher for the syngas operation R G Papagiannakis
et al [7] evaluated the perfonnance and cxhausi emissions of a SI engine operating on syngas and
natural gas at the same lambda (X) value The engine
engines The brake specific fuel consumption (BSFC)' was significant increased NO and CO emissions concentiation were higher for syngas operation
On CI engme, A S Ramadhas et al [8] used producer gas from coir-pith as a supplement fuel for diesel and rubber seed oil The brake thermal efficiencies (BTE) were decreased when operatmg at
dual fuel engine were higher than that of the original engine; the smoke density had the same trends with the addition of coir-pith producer gas,
B B Sahoo et al [9,10] evaluated the effects
of H2/CO ratio on the performance of dual fuel diesel engine There were four ratios of H2:C0 in syngas fiiel, 100:0, 75:25, 50:50 and 0:100 The BTE of dual fuel
modes raised with an increase in HiVo of syngas
composition The HC, CO and CO2 emissions improved with the increase of CO content in syngas, whereas NOx emission had an opposite tiend
Trang 2R Uma et al [ I I ] also used producer gas
supplying to a diesel generator engine The
experimental results showed that BTE reduced in the
dual fuel mode, CO and HC emissions surged, while
NOx, SO2 and PM emissions declined
The low energy density of the producer gas/air
mixture and the engine's volumetnc efficiency are the
main factors causing the engine's power derating [12]
Besides, the cost for production same engine power
while using biomass is much cheaper than that of the
conventional diesel engine Hence, using dual fuel
syngas-diesel mode is one of the ways to reduce the
expense per unit of engine power In addition, the
environment by using agriculture wastes (rice husk,
rice straw) or forest/wood residues (wood chips,
sawdust, coir-pith ,)
This paper focuses on numerical study of a 3
cylinder diesel engine, 8.75 kW max power, used in a
small gen-set which is operated with single diesel fuel
and syngas-diesel dual fuel modes It is aimed to
investigate the diesel replacement potential by syngas
as well as effects of syngas-diesel dual fiiel modes to
exhaust behaviors
2 Model Setup And Parameterization
2.1 Engine Specifications
The test engine used in this study is the S3L2,
3 cylinder diesel engine with the specifications listed
in table I
Table ! Specifications of the test engine
Model
Type
Bore
Stroke
Compression ratio
Actual power/speed
S3L2 Four-stioke, CI engine
78 mm
92 mm
22:1
8.75 kW/I500 rpm
This engine is located in 12 kVA small gen-set
The max power at 1500 rpm of this engine at brand
new condition is 9.6 kW Of the cunent status, it was
measured as 8.75 kW at 1500 rpm,
2.2 Simulation Model and Procedure
The simulation model of the test engine was
created on AVL Boost It is showed in Fig I
The combustion model used is the Vibe 2 zone
which has the same input as for the single Vibe
temperature, two temperatures (burned and imbumed
zone) are calculated
The rate of heat release, and thus the mass fraction burned, is specified by a Vibe function However the assumption that bumed and unbiuned charges have the same temperature is dropped Instead the first law of thermodynamics is applied to the bumed charge and unbumed charge, respectively [14]
Fig 1 The simulation model
'Il^=-p^^+^- 2^-l-hJ/^-hBB.b^^ (I)
(2)
uu '^ iia "'' ""
index b: bumed zone index u: unbumed zone
The term ' i u ~ T ^ covers the enthalpy flow from the unbumed to the bumed zone due to the conversion of a fresh charge to combustion products Heat flux between the two zones is neglected In addition the sum of the volume changes must be equal
to the cylinder volume change and the sum of the zone volumes must be equal to the cylinder volume
da da da Vi,+K =
(3) t4)
The heat tiansfer to the walls of the combustion chamber is calculated by:
Qm and A, are wall heat flow and surface area
(cylinder head, piston, liner), respectively; «„ is heat transfer coefficient, is calculated by Woschni in 1978
model [14]; Tc and T^, are gas temperahire in the
cylinder and wall temperature
The NOx formation in CI engines is calculated based on a reaction-kinetic model developed by Pattas
Trang 3and Hafher [15] The concentiatton of N2O is obtained
by the following relation:
J ^ l l S O S l O - r - e x p i ^ (6)
N,40, - H r
The NO formation rate is calculated by:
The CO value can be computed by solving a
differential equation based on two reactions and
expressing the resulting CO reaction rate as [16]'
CO
dCO
R R, I
* ^ ' CO
(8)
with [CO]e is the predicted equilibrium concentration
of CO
The soot foimation model based on Schubiger
et al [17] used two steps equation approach (formation
and oxidation) The net rate of change in soot mass
msooi is the difference between the rates of soot formed
msooiform and oxidized
m^ooi.ox-dm , <^'tn m^ooi.ox-dm ,
with
dm
(10)
(11)
^ ct.a P0,r.f
- A/orm soot formation factor [-]
- Ao, soot oxidation factor [-]
- Tchar characteristic mixing time ["CA]
- ffifte/ mass of fuel bumed [kg]
- Ta-/orm actlvatioo temp: soot formation [K]
- Ta-ox activation temp: soot oxidation [K,]
- Tavi: average m-cylinder temperatiu-e [K]
- Pcyi/pref noimalizcd in-cylinder press [-]
-j7o3/po:re/normalized oxygen partial press [-]
- ni, ni, n-i model factor [-]
The simulation was conducted at the speed of
ISOOrpm and full load (with the diesel fuel quantity
supplied to the engine was 3.14 l/h or 2.10 kg/h)
At the first step, only diesel fuel was used Then
20%, 30% to 60% while syngas was supphed (diesel-syngas dual fuel) to the intake manifold aiming to maintain the indicated mean effective pressure (IMEP
= 6.54bar) The engme performance, combustion charactenstics and exhaust emissions were investigated to evaluate the potential of diese] replacement by syngas
2.3 Syngas Compositions
The syngas was produced by a small-scale down draft gasifier which used charcoal as a raw material Detail of this gasifier and its energy performance were elaborated elsewhere [13] The measured syngas compositions consist of 11.63% H2,
62.02% N2 The tar content of 20.89 mg/m^ ensures the usage possibility of the produced syngas in the engine
Table 2 Syngas compositions and properties
Properties
% by vol
% by mass Density*
A/F ratio
CH4 0.01 0.01 0.71
4 17.2
CO 24.4
7 27.1
5 1.25
0 2.5
H2
11.6
3 0.92 0.08
9 34.3
N j 62.0
2 68.8
1 1.25
0
0
COi 1.79 3.12 1.96
4
0 '
*atO°C and I atm
Based on the data in Table 2, properties of syngas can be calculated as follow:
- Density: 0.995 [kg/m3]
- Stoichiometric A/F ratio: 1.127 [-]
- Low heating value (LHV): 4.75 [MJ/kg] The global lambda (A.) value for dual-fuel engine'
is calculated as following:
(12)
where dmAir, dmd,esei and dmsy„gas are mass flow rates of
intake air, diesel and syngas, respectively [kg/h];
(A/F)diesei and (A/F)syngai are in tum the stoichiometric
A/F ratio of diesel and syngas,
3 Results a n d Discussions
3.1 Model Calibration
At the flill load condition and engine speed of I500rpm, the measured engine power with diesel fuel was 8.75 kW, 9,7% lower that of the designed power
As simulated at the actual condition, tiie brake power was obtained as of 9.27 kW for single diesel M
Trang 4one This uncertainty is acceptable as there are quite
many assumptions applied for the simulation model
3.2 Diesel Replacement Rate
Table 3 shows mass flow of ambient au, diesel
fuel, syngas and global lambda values of 7 simulation
fromO% (single diesel) to 60% (dual fuel)
Table 3
Cases
case I
case 2
case 3
case 4
case 5
case 6
case 7
Mass flow of air
Diesel
replace ment
0
10
20
30
40
50
60
A h
[ k g * ]
59.39
56.99
54.97
52.55
50.33
47.53
44.90
md fiiel and global lambda
Diesel
[kg/h]
2.70
2 43
2.16
1.89 1.62 1.35 1.08
Syngas [kg/h]
0.00 2.92 5.08 7.78 11.34 14.26 17.28
Global lambda [-]
1.517 1.569 1.648 1.733 1.814 1.907 2.027 Table 3 expresses that when diesel fiiel was
replaced 60% (case 7), the mass flow of syngas must
be 17.28 kg/h This value is within the supporting
capacity of the gasifier as this system can supply up to
21.78 kg/h syngas
Higher diesel fuel mass flow replacement was
also tned in the simulation model, however due to very
high global lambda (higher than 2.027), the mixture
was too lean which can inversely affect the diesel
autoignition time and the flame propagation, more fuel
was post combusted which contributed to high
effective energy EvenUially the IMEP was reduced
despite of any syngas mass flow
3.3 Engine Performance
The specific energy consumption (SEC) was calculated based on the diesel and the syngas energy inputs and their heating values as following:
3dieset ^HVdiesel+ Ssyngai Ltf V^ynggs
where gdtesei and gsyngm are mass flow of diesel and syngas in kg/s; LHV,iK.,d and LHVsy„ga^ are lower
heating values of diesel and syngas, respectively Fig 2 shows the specific energy consumption
of 7 simulation cases
It is observed in Fig 2 that the SEC of the engine increases with the mass flow of the syngas, and
diesel fuel are replaced from 40% to 60%, This proofs that diesel replacement up to 30% can maintain high
more than 7.29% compared to that of the case 1 - the case (single diesel tiiel) which gives the lowest specific energy consumption
As the IMEP was fixed, the in-cylinder pressure profiles of all cases are similar However due to high
syngas, when the mass flow of the syngas was raised, higher rate of heat release (ROHR) could be resulted Fig 3 illustiates the ROHR of the 3'^ cylinder versus crank angle of the case 1, case 4 and case 7 It
case 7 has caused the highest ROHR This contributes
to move a little bit backward the position of the pressure peak, nevertheless it is not necessary to adjust the diesel advanced injection time at this medium engine speed of 1500rpm
''""
• • ^ —Case 1
N \ —Case 4
^ v —Case 7
510 530 angle (deg) Fig 2 Specific energy consumption of the engine Fig 3 Rate of heat release versus crank angle of the
case I, case 4 and case 7
Trang 54000
— 3500
a 3000
.9 2500
I 2000
g 1500
CrankAngtefdeg]
^^-^
^ r ^ A-NoK • C O
p - * = ^
i
300 1
250 •?'
ll
200 •^'
^i
100 gi
50 8:
Diesel replacement rate (%) j
Fig 4 in-cyiinder temperature versus crank angle of Fig 5 NOx and CO concentration versus diesel
the case I, case 4 and case 7 replacement rate
Higher ROHR of the case 4 and case 7, due to
more homogeneous combustion, comparing to the case
been converted to high in-cylinder temperature This is
also showed clearly in Fig 4
3.4 Exhaust Emissions
Fig 5 and Fig 6 express the exhaust emissions
at the different diesel replacement rates
It is observed in Fig 6 that the higher the syngas
mass flow the more reduction of soot emission due to
more homogeneous combustion This expresses the
important role of syngas in reducing the particulate
syngas-diesel dual fiiel mode
As mentioned in Fig 4, the in-cylinder
temperature was surged with the mass flow of syngas,
thus high NOs concentration was resulted in Fig 5 In
this figure, the CO concentration was also increased It
the mixture too lean to have a good condition for
converting CO to COi
Diesel replacernent_raje(%) j
Fig 6 Soot emission versus diesel replacement rate
4 Conclusion and Outlook
The simulation study has shown that the syngas
60% of diesel fuel supphed to the tested engine at fiill load condition and I500prm speed The diesel replacement rate up to 30% can maintain high energy economy however from the rate of 40%, the specific
compared to that of the of the single diesel case (base case)
As a result of high flame speed of hydrogen and^ homogeneous combustion the rate of heat release of dual fiiel cases is higher than that of the base case The higher the diesel replacement, the higher the rate of heat release and the higher the in-cylinder temperature are
When the syngas flow rate was raised the NOx and CO concentration in the exhaust gas were surged while soot emission reduced remarkably
Acknowledgements
This work was part of the Vietnam-Thailand bilateral collaborative research work on development
of biomass gasifier system for small-scale energy production which was funded by Ministry of Science and Technology (MOST, Vietnam) and implemented
in close collaboration with National Metal and Materials Technology Center (MTEC, Thailand)
References [1] T,B, Reed, A Das, Handbook of Biomass Downdratt Gasifier Engine Systems, The Biomass Energy Foundation Press, Colorado, 1988
[2] P Quaak, H Knoef, H Stassen, Energy from Biomass:
A Review of Combustion and Gasification Technologies, Energy Series: WTP 422, WashingtOD, D,C Library of Congress Catalonging-in-Pub!ication Data, 1999
[3] Pham Hoang Luong, Promoting an efficient and clean use of biomass for energy production in Vietnani, Project final report submitted to Flemish Interuniverslty Council (VLIR OUS, Belgium), April 2007
Trang 6[4] CD Rakopoulos and C.N Michos, Development and
validation of a multi-zone combustion model for
performance and nitric oxide formation in syngas fueled
spark ignition engine Energy Conversion and
Management 49, (2008), pp 2924-2938
[5] CD Rakopoulos et al Availability analysis of a
syngas fueled spark ignition engine using a multi-zone
combustion model Energy 33, (2008), pp, 1378- 1398
[6] A Shah el al,, Perfonnance and emissions of a
spark-ignited engine driven generator on biomass based
4656^661
[7] R.G Papagiannakis et al Study of the performance and
exhaust emissions of a spark-ignited engine operating
Propulsion, Vol 1,(2007) 190-215
[8] A.S Ramadhas et al Dual fiiel mode operation in
diesel engines using renewable fuels Rubber seed oil
and coir-pith producer gas Renewable Energy 33,
(2008)2077-2083,
[9] B.B Sahoo et al, Effect of H2:C0 ratio m syngas on
the performance of a dual fuel diesel engine operaUon,
Applied Thermal Engineering, (2011),
[10] B.B Sahoo et al., Effect of Load Level on the
Performance of a Dual Fuel Compression Ignition
H2/C0 Content, Joumal of Engineering for Gas
Turbines and Power 133, (2011) 122802-1-122802-12
[II] R, Uma etal Emission characteristics of an electricity
generation system in diesel alone and dual fuel modes,
Biomass and Bioenergy 27, (2004) 195-203,
[12] J D, Martinez, et al,, Syngas pro-duction in downdraft
biomass gasiiiers and its application using intemal
combustion engines Renewable Energy 38, (2012) 1-9
[13] Pham Hoang Luong, Van Dinh Son Tho and Nguyen
Tien Cuong, Effect of air-intake on energy perfomiaoce
of a biomass down draft gasifier, submitted to Joumal
of Science and Technology (Technical Universities),
Hanoi University of Science and Technology,
September 2013 (in Vietnamese)
[14] AVL Boost version 2011, Boost theory, AVL LIST
GmbH
[15] Pattas and Hafiier, Stickoxidbildung bei der
ottomotorischen Verbrennung, MTZ 12, (1973)
397-404
[16] A, Onorati et al., ID Unsteady Flows with Chemical
Reactions in the Exhaust Duct-System of S.I Engines:
Predictions and Experiments, SAE paper 2001-01-0939,
(2001)
[17] R, A Schubiger et al, RulJbildung und Oxidation faei
der dieselmotorischen Verbrennung, MTZ 5, (2002)
342-353