International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
CFD Simulation and Geometrical Optimization of
Producer Gas Carburetor
Shirish L. Konde1, Dr. R. B. Yarasu2
1
M. Tech.Student at GCOE, Amravati
2
Asso. Proff. at GCOE, Amravati
Abstract— In this paper Computational Fluid Dynamics (CFD)
analysis has been carried out to study the flow characteristics
and mixing performance of producer gas and air in the specially
designed producer gas carburetor for 15 kw capacity engine. The
model is made up of a mixer chamber that has the essential inlets
i.e. three inlets for air and one inlet for fuel to generate stable
stoichiometric mixture at near to ambient conditions using the
induction of the engine as the driving pressure differential for the
flow, Then based upon the results obtained from the above
analysis a new prototype carburetor designes having two, four
and five air inlets keeping inlet area ratio of air and fuel constant
were designed. Further analysis was then performed on the
prototype carburetors to study the effect on the air-fuel ratio.
The results of the simulation shows that a four hole carburetor
give better fuel distribution characteristics than the designed
carburetor.
Keywords— computational fluid dynamics, producer gas,
carburetor, air/fuel ratio, turbulence.
I. INTRODUCTION
This Producer gas is the best fuel for substituting conventional
fuels because of low pollutants and Carbon dioxide emission.
Recently sky-rocketing fuel cost, energy security and
environmental pollution issues are very important concerns
worldwide so amongst the various alternatives fuels, producer
gas is the most practical solution. Air/fuel ratio characteristic
exert a large influence on exhaust emission and fuel economy
in Internal Combustion engine. With increasing demand for
high fuel efficiency and low emission, the need to supply the
engine cylinders with a well defined mixture under all
circumstances has become more essential for better engine
performance. This paper examined the effect of air placement
technique on the flow behavior of the producer gas in the
specially designed carburetor for a 15 kw capacity engine.
The geometry of the existing carburetor has been slightly
modified to meet the air and fuel requirement to achieve
stoichiometric A/F ratio. The CFD’s predictions showed that
the uniformity of fuel distribution was heavily affected by the
location of air inlets. An ideal carburetor would provide a
mixture of appropriate air-fuel (A/F) ratio to the engine over
its entire range of operation from no load to full load
ISSN: 2231-5381
condition. To ensure proper performance, Carburetors should
be reproducible and have unequivocal adjustment procedures.
CFD software used for cold flow analysis is CFX 14.5. 3-D
RANS CFD code is used for the flow analysis and a
computational model with suitable mesh is generated. The k-ε
turbulence model is most commonly used and is considered to
be the best model between computational time and precision.
The geometric model is built using Ansys ICEM CFD.
II. PRODUCER GAS CARBURETOR
One of the important things considred while designing mixing
chamber of producer gas carburetor is simplicity and
ruggeddness as basic requirements that would achieve
reproducible and good performance. The air and fuel flow
through air-fuel regulator and then entering into a mixing
chamber of the carburetor enables to produce stoichiometric
ratio with good mixing of air and fuel. Carburetor is being
designed to have air and fuel flow near ambient conditions of
working pressure. The carburetor is as shown in the Fig.1 and
it has air and fuel inlets such that the A/F ratio at ambient flow
condition should maintained stoichiometry for a 15 kW engine.
The amount of fuel flow inside the carburetor is controlled by
air-fuel regulator which are located prior to the air and fuel
inlets. The pressure balancing electronic control module
drives suitably the valves with the help of a AC motor that
brings the valves for a null pressure differential across the
manifolds of the fuel and air. In a practical system, the
variation of air-fuel ratios are indicated by a differential
pressure sensor and the valves movements are controlled
based on this feedback towards maintaining the stoichiometric
airfuel ratio. The effective area reduction of gas and air entry
holes is considered by taking a suitable coefficient of
discharge. In order to overcome the problems associated with
the use of zero pressure regulators and to maintain the
stoichiometry A/F mixture, carburetor uses the entry area ratio
of 1.2 at both side of airline and gas line. areas are designed
based on the mass flow rate of producer gas requires for IC
engine A reported work also mentions the need for
homogeneity in mixing and maintenance of the air-fuel ratio
in the gas carburetors. Continuous tetrahedron meshed model
considered for CFD analysis and which is shown in Fig.2,
with 1.3 lakh computational nodes.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014

(1)
  ( U )  0
t
And the momentum equation becomes.
U
t
  ( U  U )   ( eff U )
T
 p '   ( eff U )
(2)
B
The flow–solver CFX-14.5 used for the analysis uses the
differential transport equation for the turbulence kinetic
energy and turbulence dissipation for analysis.
The equation for kinetic energy K is given by
   
t

 


Fig.1 - Geometric Model of Carburetor
   Uk  

t
k


k  Pk

(3)
 
The equation for ε without compressibility is given by.
   
    U   
t
 t       C P
  
    K  1 K

(4)
 C  2  
Where μ is molecular viscosity, μT is turbulent viscosity and
Cε1 & Cε2 are constants with values 1.45 &1.9 respectively. σk is
turbulent model constant for kinetic energy which is 1 and σε
is constant for k-ε model which is 1.3.
IV. RESULTS
Fig. 2 – Meshed model of Carburetor
III. COMPUTATIONAL APPROACH
Turbulence consists of fluctuations in the flow field in time
and space. It is a complex process, mainly because it is three
dimensional, unsteady and consists of many scales. It can
have a significant effect on the characteristics of the flow.
Turbulence occurs when the inertia forces in the fluid become
significant compared to viscous forces, and is characterized by
a high Reynolds Number. The k-ε model of turbulence is
widely chosen for fluid flow analysis. k is the turbulence
kinetic energy and is defined as the variance of the
fluctuations in velocity. ε is the turbulence eddy dissipation
(the rate at which the velocity fluctuations dissipate). To
simulate the turbulence parameters, a standard k-ε model has
been chosen with isothermal heat transfer condition at 300 K.
The Solver uses k-ε model with two new variables and the
continuity equation is then.
A.Results of Designed carburetor
Designed carburetor means carburetor with three inlets for air
and one inlet for producer gas. Fig. 3 indicate the pressure
variation contour along the length of carburetor i.e in YZ
direction and it is found that pressure variation is around
403.945 pa.
Fig. 3 –Pressure Variation along Length
ISSN: 2231-5381
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
Fig. 4 indicate the show the average air-ideal gas mass
fraction at carburetor outlet is found to be 0.5287 which is
good as per stoichiometric requirement.
Fig.7
Fig.4- Average air mass fraction at outlet
Fig.8
Fig. 9,10,11 shows 2,4,5 entry holes of air. From figures it
can be interpreted that most desired air mass fraction is at 4
entry hole carburetor as compared to others. Air mass fraction
for 4 air entry hole carburetor is 0.5404 which makes best
stoichiometric air-fuel ratio.
From Fig. 5 shows the mixing of streamlines of air and
producer gas. It can be inferred that there is homogeneous
mixing of producer gas and air at area near to outlet carburetor.
Fig. 9
Fig. 5 – Mixing of air and producer gas
B. CFD Analysis Results of Proposed Carburetor Geometries
Fig. .6,7,8 shows the plane in YZ direction showing pressure
variation contour along the length of carburetor for 2,4,5 entry
holes of air with respect to single entry hole of fuel. From
Figure it is evident that the Pressure variation in this
configurations are found to be 403.945 Pa, 358.011 Pa,
514.453 Pa. Minimum pressure loss is for geometry with 4
entry holes for air and 1 entry hole of fuel.
Fig. 10
Fig. 11
Fig.12,13,14 indicate the amount of effect on mixing pattern
of air and producer gas in three different configuration. From
figures it can be said that most homogeneous mixing is
happening in geometry with 4 air entry holes and 1 entry hole
pg gas.
Fig. 12
Fig. 6
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
Fig. 13
Fig.14
TABLE I
COMPARISON CHART
Air
inlet
position
3 hole
Gas
inlet
position
1 hole
Air
mass
fraction
0.5287
Pre.
Drop
Results
641.49
proper mixing,
very high pr
drop
Not proper
mixing,
considerably
high pr drop
Fig. 16 Air mass fraction Vs No. of air entry holes
2 hole
1 hole
0.5282
403.94
4 hole
1 hole
0.5404
358.01
Good mixing,
very low pr
drop
5 hole
1 hole
0.5268
514.45
Not proper
mixing,
considerably
high pr drop
V. CONCLUSIONS
CFD simulation of existing carburetor shows that required airfuel ratio can be achieved but pressure losses within plane of
carburetor are major. Which are attempted to minimise by some
changes in geometrical shape and results are as per the
expectation. Geometry with 4 inlets for air and 1 inlet for
producer gas shows the best results. Pressure losses are almost
minimum with required air mass fraction at outlet and good
mixing of both air and gas at outlet.The work is carried out with
an objective to achieve optimum design for a carburetor for
engine application with fuels of low energy contents, mentioned
earlier. Turbulent model based on k-ε theory with a RANS
code has been used for the CFD predictions of the producer
gas mass fraction and the carburetor performance has been
evaluated leading to bringing out of an optimal design of the
PG carburetor that can be used for prototype testing and real–
time testing.
GRAPHS
REFERENCES
Fig. 15 Pressure variation Vs No of air entry holes
ISSN: 2231-5381
[1] Anderson, John D. Jr., “Computational Fluid Dynamics: Basics with
Applications”, Mcgraw-Hill Inc., 1995.
[2] Klimstra J “Carburetors for Gaseous Fuels –on Air to Fuel ratio,
Homogeneity and Flow restriction. SAE paper 89214, pp 23-29.
[3] Mukunda H S and Paul P J, “Fundamental Combustion and Gasification
Aspects of Biomass and Biomass Derived Gaseous Fuels”, Proceedings of the
First ISHMTASME, Heat and Mass Transfer Conference, Jan 1994.
[4] G.Sridhar, P.J Paul, H.S. Mukunda “Simulation of fluid flow in a high
compression ratio reciprocating internal combustion engine”.SAE paper,
0857 ,vol.1, 1999.
[5] Master Contents of software Ansys CFX-14.5.
[6] S.S.Vinay, S.D.Ravi, G.PremaKumar and N.K.S.Rajan. “Numerical and
Experimental Modelling of Producer Gas Carburettor” Proc. of the
International Conference on ‘Advances in Mechanical Engineering’,2008.
[7] T.R.Anil, S.D.Ravi, M.Shashikanth, N.K.S.Rajan and P.G.Tewari. “CFD
Analysis of
a Mixture Flow in a Producer Gas Carburetor” International Conference on
Computational Fluid Dynamics, Acoustics, Heat Transfer and
Electromagnetics CFEMATCON- 06,2006.
[8] T.R.Anil, P.G.Tewari, N.K.S.Rajan . “An Approach for Designing of
Producer Gas Carburetor for Application in Biomass based Power Generation
Plants”, Proceedings of the national conference of Natcon, 2004, pp. 27-31.
[9] Yoshishige Ohyama, “Air /fuel ratio control using upstream models in the
intake system.” SAE paper, 0857 ,vol.1, 1999.
[10] G Sridhar, H V Sridhar, S Dasappa, P J Paul, N K S Rajan, and H S
Mukunda, “Development of Producer Gas Engine”, Proc. Imeche, Vol.219
Part D: Automobile Engineering,2004.
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