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International Symposium on Computational and Experimental Investigations on Fluid Dynamics CEFD’2013, March 18-20, 2013, Sfax, TUNISIA

DESIGN OF NEW INTAKE MANIFOLD FOR SPARK IGNITED ENGINE TO RUN WITH HYDROGEN FUEL Saaidia Rafaa *, G. Kantchev, Mohamed Salah Abid Laboratory of Electro-Mechanic Systems (LASEM), National School of Engineers of Sfax (ENIS), University of Sfax (US), B.P. 1173, Road Soukra km 3.5, 3038 Sfax, TUNISIA

Received June 5, 2012 / Accepted September 9, 2012 / Published January 8, 2013. Abstract: Since the creation of the first automobile in the 19th century, internal combustion engines have largely evolved to become more efficient, less polluting, while having a limited consumption. Hydrogen production, energy carrier, from environmentally friendly sources and consumption in new energy systems is one of the answers to the current problems, for this reason, the study examines the conversion of a ignition engine with dual petrol hydrogen. The work focuses on the changes to the intake manifold at the end of its geometry to improve engine performance. Key words: bi-fuelled engine gasoline-hydrogen, natural overeating, manifold

1. Introduction The thermal engines essentially provides training and transportation fuel [3],[9] to the combustion chamber where it burns to give birth to the thermal heat witch the originally received work on the crankshaft [4], [5], [6]. Before arriving in the cylinders, fresh air crosses several restrictions formed by various engine components: air filter, carburetor, the motorized butterfly, intake manifold, intake pipe and intake valve [5], [6]. Diet is an important factor that can significantly influence the performance of engines especially the intake manifold [7], whose geometry must be carefully chosen while interpolating between the nature of the fuel and the operating speed of the engine.

2. Formation and transport of the mixture

atmospheric pressure in the reservoir (for gasoline and diesel) or it is stored under pressure (for gases: LPG, Hydrogen).The amount should be introduced in relation to the air mass in which it will be mixed with the relationship defined stoichiometry. The dosage takes place at the carburetors while respecting stoichiometry issued to ensure proper combustion Elemental analysis provides quantitative fuel mass content of carbon, hydrogen and optionally oxygen, so it can write the overall formula (CxHyOz).

2.2 Transport of the mixture The fresh gas circuit behaves essentially five major modules for the preparation of the fuel, they defined the coefficient of the engine permeability (the rate of gas admitted). The intake system can be represented by the following diagram:

2.1 Formation process The fuel should be at a pressure higher than the pressure in the mixing chamber so as to be introduced which is generally provided by a pump if the fuel is at * Corresponding author: Rafaa Saaidia E-mail: [email protected]. 1

Saaidia R. / CEFD’2013, March 18-20, 2013,

2

hypothesis that the temperature variations are relatively slow compared to other dynamic faceoffs The model (1) is then called isothermal and can be rewritten as [1] [2]:

Pcol 

rTcol Vcol

ncyl     m pap   mcyli  (2). i 1  

Given the influence of the intake manifold on the Fig.1: Diagram of the supply circuit (1: air filter, 2

flow of gas, that is to say, according to its nature and

carburetor, 3 butterfly valve, 4 intake manifold)

composition, the losses and the filling of the cylinders, we will be interested to study the optimal design for this body, through the modeling of flows in the intake

In the previous system it is clear that we can not make changes only on the intake manifold which is

manifolds for tender to good engine performance for operation in the case of gasoline and hydrogen.

given by the following figure

3. Study of flow in the intake pipe We know that the macroscopic variables that characterize the state of thermodynamic equilibrium of a

fluid

are

related

by

the

equation

of

state: f ( p,V , T )  0, p , p is the pressure, V is volume, and T is the absolute temperature. Usually

defined

two

types

of

coefficient

of

compressibility, one isothermal and isentropic other [11]:

Fig. 2: An intake manifold.

To model the pressure in the intake manifold (Fig.2), representing the most frequently used is that of modeling the intake manifold as a reservoir containing a gas mixture considered perfect. The pressure which reigns in the intake manifold can be written as the following form [5] [6]: ncyl    T col  m pap   mcyli   pcol Tcol i 1  

1 V 1 V ( )T et Ks   ( ) S V p V p

(3).

For a perfect gas, the equation of state of a gas mass is: pV = nRT = mrT ou p = rT n is the number of moles. In addition, such a gas, changing isentropic satisfies the Laplace equation pV   Cte Compressibility coefficients apply in this case:



rT Pcol  col Vcol

KT  

(1)

Where Vcol is the volume of the intake manifold and ncylinder is the number of cylinders of the engine. The second term of (1), containing the derivative of the temperature, is often overlooked in considering the

1 nRT 1 1 V 1 Kt   ( )  et K s   ( )  V p² p V p p

(4).


pCD  pe ( x  dx, t ) 

3

1  ( ) x  dx ,t K s x

(10)

We deduce the pressure difference pCD - pAB pCD  p AB  pe ( x  dx, t )  pe ( x, t ) 

1        (11)      Ks  x  x  dx ,t  x  x ,t 

So: Fig. 3: slice of gas

pCD  p AB  pe ( x  dx, t )  pe ( x, t ) 

Forces to consider are also occasional forces Foc with gravity, pressure forces exerted on the bases AB and CD. projecting along Ox so we have[12]:

  dx 

The equation of motion can be written as:  Sdx

 ² ( x, t )  Sp AB  SpCD  FOC t ²

 Sdx

1   ²  K s  x ²

 ² S   ²   Spe ( x  dx, t )  Spe ( x, t )   t ² K s  x ²

  dx  FOC 

(12)

(5). As, in the static state, we have:

It is therefore necessary to express the pressure difference pCD - pAB depending of  (x, t). Note first

0 = Spe(x, t) - Spe(x + dx, t) + FOC, it comes in

that the fluid displacement is accompanied by an

equilibrium value  e .

expansion which is

[12] [11]:

V  S  ( x  dx)  ( x  dx)  ( x)  x   S (d  dx)  Sdx(1 

 ) x

simplifying and neglecting the small variations

 Sdx

 ² S   ²     dx t ² K s  x ² 

 ²   ²    Ks   x ²  t ² 

(6) Hence the relative expansion of the slice: V S (d  dx)  Sdx    V Sdx x

(7)

 around its

or (13)

3.1 - Nature of movement The differential equation is characteristic of a previous wave phenomenon. However, unlike the propagation along a string where the wave is transverse,

However, a relative expansion of the fluid involves a pressure fluctuation p * = p - p

e,

p e is the pressure at

longitudinal wave is here because displacement  ( x, t ) occurs in the direction of propagation.

equilibrium. Give p* 

p  pe  

1 Ks

(

V V

)

1 V Ks V



1  K s x

soit p*  

1 Ks

(

 x

3.2 Resolution with the impedance method [5] [12]

)

(8)

So between A0B0 and AB, at the same time t, the pressure difference as follows: p AB

1   pe ( x, t )  ( ) x ,t K s x

portion of fluid from a pipe of finite length during the propagation of a sound wave due to the superposition of

( 9)

Similarly, between C0D0 and CD the pressure difference, at the instant t, is:

The pressure disturbances that affect speed and a

two effects of simple waves progressing in the opposite direction from each of a different end of the pipe. These simple waves are generated either directly by a device driver (eg piston) by the reflection of another simple wave, in this case, the properties of the reflected wave


4

depends not only those of the incident wave which it result, but also the characteristics of the section where the reflection took place.

k0 l 

2 N  l  ( 2n  1 ) c0 2



f 

2n  1 c0 4l

et



Or

Boundary condition such section requires the fluid flow (boundary condition on the pressure and speed in general) is superimposed on the response the middle by specific impedance 0 c0 . Brings to the acoustic

 ( 2 n 1 0) c l  ( 2 n 1 )  4 4 f

(15)

This equation is the base for the determination of the optimum length of the intake manifold. [14] [12]

disturbance generated by a wave. To reflect this situation and saw that the pipe section has finite dimensions, we reduce this section, that is to say the flow variation

A U * what

produces the acoustic

fr 

 2k  1 c0

4L c0 c   0  L  4 L2 k 1 4   2k  1 

c0   L  4 f r  L  L  2 k 1 2k  1

wave, the response of the medium at a pressure Where k is the harmonic vibration and c0 = (γRT)1/2

disturbance p* . Hence

the

notion

of

characteristic

acoustic

c0: sound speed

impedance[12]: Z

p* AU *

4. Determination of the optimal length

(14)

When opening the intake valve of a pressure difference

3.3 Case of a pipe open at one end and closed at the other [12] [13] An acoustic disturbance is created in the length of a pipe cross-section A, open at its end were x = 0, closed at its end were x = l.

-

At x = 0 open was

is much greater than that present in the combustion chambers (effect of displacement of the piston), so a potential difference of pressure takes place and the fuel mixture provided in the intake manifold moves guided by the pipes to the area chamber of combustion is the

We have the boundary conditions: p*( x0 )  0

of pressure will occur and the pressure in the manifold

intake phase in the engine cycle.  Z0  0

,

* To the abscissa x =l is closed U ( xl )  0  Zl   .

Fig. 5: intake phase Fig.4: Tube closed at one end, open at the other

The pressure of the volume of air inside the intake manifold is about atmospheric pressure. This pressure is much higher than the pressure in the end of the intake

Under these conditions, we have:

pipe around the valve.

4l 2n  1


When closing the valve the flow of the fuel mixture s'

5

k : Harmonic vibration.

stop at the seat of the valve but at the end of the tubing connected with the fluid manifold e s t yet driven and

Where f r is the frequency of wave propagation which

under the effect of compressibility of the mixture one

can be determined from the frequency of opening and

pressure wave shape profile in the tubing causes extrémitéde air masses will rush enprésence.Celles simultaneously latubulure resonance so that the wave sepropage e to the inlet valve. Optimal length should be

closing the valve, which is in turn, dependent on engine speed (position of the crank angle) whose it can be determined as follows:

calculated under the condition of closing instant the intake valve so that the appropriate model E is that of a

T tf 

tube open on one side and closed on the other

720   a 720  250 470   N 6  n 6 N 360  60

fr 

1 6N  tf 470

Where

(16)

N (rev / min) is the speed of rotation of the motor The speed of propagation of the wave is given by : c   mel RT 

12

Fig. 6 : Wave pressure in the tubing

The depression wave arrival at the end of the duct is

the inlet valve to enjoy the large pressure difference and improve filling.

 x cp  x cv i

i

i

i

So the optimum length can be written as

L

c0 4 fr

L

( RT) 4 fr

transformed into a pressure wave which goes down to the valve. This is when it would be interesting to open

 mel 

And

So

1/2

( 

x cv i

 x cp i

i

RT)1/2 (17)

i

4 fr

- For a gasoline-air fuel mixture :

At the time of opening of the inlet pipe valves are open on one side and closed on the other side and from the equation (15), the model suitable is that of a quarter wave-length from which the resonance Frequency

 mél 



a

   cpe  c  r  cpa 

 a    cve  c 

r  c va 

- For a hydrogen-air fuel mixture :

response of the model is: fr

 2k  1 c 

4L c c    L  4 L2 k 1 4   2k  1 

 R c  R c '

c  L  4 fr   L  L  2 k 1 2k  1 

 mél 

pe

'

ve

 cpa 

 cva 

So the optimum length is given by equation (17) for admission can be written in the form :


6

  a    cpe  c  r  c pa   2  1  L  RT       a    c ve  c  r  c va    4 fr    1

can conclude that in the case of operation with gasoline

(18)

has no influence on the length. The equivalence ratio of the fuel mixture at a gasoline-air

When operating with gasoline

affects the length negligible rather than hydrogen-air as

  R '  c pe  c pa   2  1    L  RT    R '  c ve  c va    4 fr    1

shown in Fig.7 can influence but not tight and we can

(19)

conclude that when operating with hydrogen and is found in conditions or the ideal mixture does not meet

When operating with hydrogen

the stoechometry, engine performance will degrade.

4.1 Determination of the optimum length for the engine subject of study

Gasoline engine Cycle

RENAULT Express (C15E) Four-stroke petrol carburettor

Number of cylinders

four

Rated power

35kW

Rated speed

5250 rev / min

Fig.7: Variation in length according to the ratio (hydrogen)

We note that the composition of the mixture can Bore

70mm

Race

72mm

Total Displacement

1108cm 3

Compression ratio

9.5

Table1 : Characteristics of the engine studied

3.1. Influenced of the ratio on the optimum length

intervene in the choice of the geometry if the machine is scanning off level of equivalence ratio during operation. The influence of this parameter is clear from the range of ns has low levels of equivalence ratio but if the mixture is to turn one unit of equivalence ratio level influence is not large enough that can be counted an advantage for sizing pipes for our engine as a fixed geometry can be

First we will try to identify the influence of the

accepted the following criteria.

equivalence ratio of the value of the optimum length From equation (18) while setting the engine at the end well only variable whose length depends is the equivalence ratio (φ) we can draw the different value of the pipe length that is presented in Fig. 7. The graph below shows the variation of the length of the tubing following the change in equivalence ratio and we

3.2. Influenced engine speed on the optimum length The length of admission clearly depends on engine speed for both fuels Fig.8 and 9


7

In our case the frequency that delivers maximum torque is 3200 rev / min that require the optimum length for a equivalence ratio unit, the following : Harmonic

0

1

2

3

essence

2,096

419.2

299.43

213.87

hydrogen

2,090

418

298.57

213.26

k Fuel Fig. 8: Variation length depending on the speed (petrol)

Table 2 : L s ongueurs optimum for admission

The collector current in the motor given by Fig.10 carries the following features :

Fig.9: Variation length depending on the speed (hydrogen)

For high engine lengths for hydrogen and fuel values are near but diets low differential geometry is clear and we cannot accept a common length for both fuels instead for large systems such as shows the following curve illustrates the difference in length of the two fuels depending on engine speed.

5. Design of the new intake manifold

Fig. 10: Intake manifold

The geometry of the existing collector does not respond

First we choose a single length which corresponds to the

to the e presented in Table2 as the external piping are

frequency that delivers a maximum torque and justified

320 (mm) and two interior is 250 (mm) hence the need to

the choice is made by that time most of u engine

develop a new geometry back to a good filling for both

operating on this frequency is also the frequency of the

fuels.

motor it corresponds to minimum specific fuel consumption.

The solution proposed is to split the manifold in two equal volume and length of tubing and the end which

It is interesting to determine the geometry that takes

corresponds to a harmonic k = 2 and the two internal

advantage of the natural boost to turn this frequency

harmonic for k = 3

while the contribution and the economic and mechanical.


8

The simulation is done for the time opening the valve in this case it is 0.0093 seconds is the time that corresponds to the regime of study (3200tr / min). 

The velocity profile for the first cylinder

The following Fig. carries the change in velocity in the first pipe in the intake phase Durant le cylinder fill time. Fig. 11: Intake manifold proposed

The filling time = cycle time - time of closing of the

5.1. CFD validation

valves

The flow in this configuration is symmetrical

(The time of closing of the valves should be that of the

configuration meets the boundary conditions in the next

wave propagation in the tubing)

step, the software Floworks, we will simulate the flow in this geometry in order to verify the choice of this solution. The boundary conditions are taken as follows : - Closing the opening of the valves is instantaneous - The pressure at the input E of the manifold - A volume flow in the pipe corresponding to the

Fig. 13: The pressure profile for the old geometry

cylinder in the intake phase - The mixture is a perfect gas. The characteristics of the manifold mesh are given by the following table below : Mesh level = 4

Fig. 14: The pressure profile for the proposed geometry

examining the trajectories of fluid along the manifold and combustion chamber shows that the proposed geometry provides a more uniform flow without much Fig. 12: M esh fluid domain


9

variation which have an advantage in the case of operation in hydrogen.

Fig. 18: The pressure evolution on the proposed geometry

Fig. 15: The velocity evolution on the old geometry

Fig. 19: The turbulent energy evolution on the old geometry

Fig. 16: The velocity evolution on the proposed geometry

Fig. 20: The turbulent energy evolution on the proposed geometry

We note that the proposed geometry seems better for Fig. 17: The pressure evolution on the old geometry

operation in hydrogen. From fig.15 and fig.16 it is clear that the flow rate attain greater value than that in manifold mounted in the

10


engine which allows a better filling in the cylinders. The reflection of the fluid on the piston surface which appears in the geometry that exists at the instant t = 0.002s the reflection of the fluid on the piston surface geometry that appears in the designed time t = 0.002s but it occurs at the last moment of filling in the collector mounted on the engine which can be a major effect to increase amount of residual fuel in tubing which may obstruct the operation of the engine in the case of hydrogen particular appearance of the phenomenon of back-fire.

6. Conclusions Bi-fuel hydrogen-gasoline seems an effective solution to deal with problems relating to fuel supplies, economic and environmental ones but bi should ensure good performance for engines. One of the modules has a great influence on these benefits is the power system. The choice of a new geometry that takes advantage of the existence of acoustic waves which have a propagative is a solution that provides a natural boost in addition to the improvement of the filling. To achieve a better fill rate, using the impedance method and while setting the engine speed to the value corresponding to the maximum torque and equivalence ratio unit, it was verified that the collector current of the engine does not good filling of the cylinders. Then we designed a new one that takes advantage of the natural charge which is managed by the propagation acoustic wave pressure. Then we checked the choice of this solution for a new intake manifold using the COSMOS Flow simulation. The intake manifold is selected so dimensioned that the filling is better. Also with this solution can reduce the amount of fuel remaining in the intake pipe and the problems back-fire and auto-ignition in can be reduced in the case of operation with hydrogen.

Acknowledgments We recall that the modifications to the collector are not a total solution for operating the engine with hydrogen there are still many problems to be solved, such as: - Hydrogen is very sensitive to the auto ignition and flashback to the intake manifold and study necessary to avoid this effect. - The combustion chamber is about six times faster than that of gasoline; a precise adjustment of the motor is required. - The materials constituting the power system must be selected resistant to hydrogen, in particular to avoid the risk of corrosion cracking and leakage problems.

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Sound and Vibration 278 (2004) 975–1011