Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2010
Sept. 27-30, 2010, Cincinnati, Ohio USA

Mixing and Combustion Performances of a Baffle-Plate-Type
Miniature Confined Multijet
Kazuya Tatsumi1,2, Yasuhiro Rai1, Yusuke Nibayashi1 and Kazuyoshi Nakabe1,2
1: Mechanical Engineering and Science, Kyoto University,
Sakyo-Ku, Kyoto 606-8501, Japan
2: Advanced Research Institute of Fluid Science and Engineering, Kyoto University
Nishigyo-Ku, Kyoto 615-8530, Japantatsumi@me.kyoto-u.ac.jp

ABSTRACTThe mixing and combustion performances of abaffle-plate-type millimeter-scale confined multijet were
investigated experimentally by measuring the blow-off limitof the flames, exhaust gas components and two-dimensional
unburned flow velocity profiles in the chamber. Two typesof multijet, parallel- and swirl-type nozzles, were examinedin this study. In the parallel-type multijet case, a smallchange in the distance between the fuel and air nozzles
showed significant effects on the blow-off limit. When the
air nozzles were closely located around the center of thechamber, the flame was easily extinguished and a pair ofelongated flow recirculation was observed near the chambersidewalls. When the distance was increased, the reverse
flows were observed in the central region that led to a stableand efficient combustion. In the swirl-type multijet case, theswirl made the flame to be more stable. Some cases ofexcessive swirl, however, deteriorate the fuel-and-air
mixing performance and increase the CO concentration.

Fig. 1

Schematic of baffle-plate type multijet
decreased markedly withoutb impairing the stability evenunder fuel-lean conditions. Woodfield et al. [2] carried out athree-dimensional numerical simulation for this baffle-plate
type multijet combustor under low Re condition in the rangeof 50 < Re < 200. They showed that fluid mixing between
the central and surrounding jets is increased compared withthe conventional co-axial jet case. This was attributed to thereverse flow generated at the downstream of the central jet
caused by the momentum difference between the central
and surrounding jets. Yahagi et al. [3] studied the influenceof the central/surrounding jet mass flow ratio mainly bychanging the diameter of the nozzles.
In this study, two types of the multijet combustors are
discussed. One is a multijet similar to those mentioned
above that has surrounding jets flowing parallel to thecentral jet (parallel-type). The other is a swirl-type, which
has the same shape with the parallel-type except that thesurrounding nozzles are inclined in the circumferential
direction (cf. Fig. 1(c)). To examine the mixing
performance of the swirl type before combustion
experiments, Tatsumi et al. [4] carried out numericalsimulations and predicted that a strong swirl can beproduced by the inclined surrounding jets. The swirl not
only generated a reverse flow at the chamber centerline toenhance the fluid mixing in some degree, but also made theflow stable.
In the present experiment, the measurements of flame

1. INTRODUCTION
Fluid mixing is one of the most important processes influid engineering and is applied in numerous industrial
applications such as chemical processing in reactors,
fuel-oxidizer mixing in combustors, and high/low
temperature fluids mixing in air conditioners. There is anincrease in the demand for developing a new mixing
technique that has high mixing efficiency and requires
compact mixing chambers. One of the important issues
attributed to the decrease of the characteristic length of the
combustor is the decrease of the flow Reynolds number, Re.
When the Reynolds number decreases, the flow becomeslaminar that will lead to a deterioration of fluid mixing
attributed to the lack of turbulence diffusion and mixing.
This will incur incomplete combustion reactions in the
combustor, and exhausts of carbon monoxide and soot.
In order to tackle this problem, the authors previously
proposed a miniature combustor consisted of a baffle-platewith multiple jet-nozzles (cf. Fig. 1 (a) and 1 (b)). The
central nozzle, from which the fuel is supplied, issurrounded axisymmetrically by six jets, from which theoxidizer is supplied. Choi et al. [1] experimentally
evaluated the flame characteristics of the multijet
combustor and showed that the flame length can be1

Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2010
Sept. 27-30, 2010, Cincinnati, Ohio USA

Table 1Case

R60-s0R75-s0R60-s20

R60-s40

R75-s20R [mm]

6

7.5

6

6

7.5

θ [°]

0

0

20

40

20

Sw

0

0

0.20

0.46

0.25

Fig. 2surrounding jet, respectively. Here, we ignored themomentum of the central jet because of its relatively small
mass flow rate, and assumed the flow of the surrounding jet
are all supplied along the centerline of the nozzle in thecomputation.

Experimental conditions.

2.2 Measurement of blow-off condition
In order to evaluate the flame stability, blow-off
condition of the combustion was measured in this study.
Measurement was made by first setting the mass flow rate of
the fuel, Qf, to a certain value, and igniting at a relatively
small air flow rate. The fuel flow rate Qf was varied in therange from 0.5L/min ≤ Qf ≤ 2.5L/min during the blow-off
measurements.
While keeping Qf constant, the mass flow rate of the air
Qa [L/min] was increased every 5s at the rate of 1L/min until
the flame blew off. The blow-off limit was defined when the
flame blew off at a certain air flow rate Qa for each Qf.
2.3 Gas mixture components analysis
The mixture components of the exhaust gas wereanalyzed by using a gas chromatograph (Shimadzu, Co.
GC-8A). Sample gas was collected by a vacuum bottle,
which was connected to a sampling tube and probe inserted
into the combustion chamber. The tube was made ofstainless steel, and its inner and outer diameters were 6 and4mm, respectively. The diameter of the probe installedinside the sampling tube was 0.2mm to freeze gaseous
reactions. The sampling tube was connected to a tube packed
with silica gel, which was placed upstream of the vacuum
bottle to remove the vapor from the sampling gas.
The sampling gas was collected at the three radial
location, |r| < 2mm, 2mm < r < 6mm, and 6mm < r at thestreamwise location of 30mm upstream the exit of the
combustion chamber. Flow velocity distributions at these
positions were measured with the PIV (particle image
velocimetry) system. The average values of the gas
concentration were calculated by first multiplying theconcentration with the flow rate at each measuring positions,and then dividing it with the total flow rate of the chamber.
The gas components of N2, CO, and CO2 were measured
in this study. In the discussed shown in the Section 3, thefollowing two values, reaction rate α and preferential
generation rate of CO, γ, will be considered.
QCO + QCO2
(1)

Experimental apparatus.

blow-off condition, flow velocity and exhaust gas
component are carried out. The effects of the radial positionof the surrounding nozzles in the parallel-type case, and theinclination angle in the swirl-type case on the combustion
and flow performances are discussed.

2. EXPERIMENTAL METHOD
2.1 Experimental apparatus
Figure 2 shows the experimental apparatus. Methane
was used as fuel, and was supplied to the central nozzle ofthe baffle-plate. Air was supplied to the surrounding nozzles
as oxidizer. Mass flow rates of these gases were controlled
by mass flow controllers (Yamatake Co., MQV0020 and
MQV0200), respectively. A tube made of fused quartz withthe length of L = 300mm was placed at the downstream ofthe baffle-plate as the combustion chamber.
The dimensions of the baffle-plate are shown in Fig. 1(b) and Table 1. The position of the surrounding nozzle, R,
and the inclination angle of the nozzle in the swirl-type
multijet, θ, were varied in this study: R = 6.0mm or 7.5mm
and θ = 0° (no swirl), 20°, or 40°. The other values were
kept constant; df = 4mm, da = 4mm, D = 22mm, and tb =7mm. In the swirl-type case, the nozzles were made so thatthe holes were inclined in the circumferential direction
against the chamber axis as shown in Fig. 1 (c). The
diameter of the hole in the baffle-plate was kept as da =4mm, therefore, the shape of the nozzle exit was elliptic.
Sw in Table 1 is the swirl number defined as Sw =2Ga/GtD. Ga [kg⋅m2/s2] and Gt [kg⋅m/s2] are the angularmomentum and the translation momentum of the

α=

γ=

QCH 4

QCO
QCO + QCO 2(2)

QCO [L/min], QCO2 [L/min], and QCH4 [L/min] are thevolume flow rate of CO, CO2 and CH4 included in theexhaust gas, respectively. α is increased as CH4 isconsumed in the reaction. γ shows a smaller value as thecomplete combustion reactions occur in the combustor.
2.4 PIV measurement2φ=0.2
60

20

20

φ=0.5

50

U [m/s]

15

40
30

φ=1.0

10

10

5

5

20
10
0.5

1.0

1.5

-10-8 -6 -4 -2 0 2 4 6 8 10

2.5(a-1) x-y planey [mm]

Fuel mass flow rate, Qf [L/min]Fig. 30.00-4.00

R60-s0R75-s0
2.0

8.00
4.00

0
0.0

12.0

15

x [mm]Air mass flow rate, Qa [L/min]

Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2010
Sept. 27-30, 2010, Cincinnati, Ohio USA-10-8 -6 -4 -2 0 2 4 6 8 10z [mm](a-2) x-z plane(a) Qf = 0.5L/min and Qa = 40L/min

Blow-off limit in parallel-type multijet case.

Flow velocity distributions in the area close to thebaffle-plate were measured using the PIV method. It should
be noted that the measurement was made for a
non-combustion state, in which air was supplied from thecentral and surrounding nozzles. Therefore, the influences ofthe buoyancy and fluid property variation due to thetemperature and gas component change are not considered.
This may lead to some discrepancy with the practical flow
field in the combustion. However, we believe that the results
will provide some insight into the understanding of the flow
characteristics in the baffle-plate type multijet combustor.
The PIV system is composed of a double pulse Nd:YAG
laser (New Wave Research Solo3) and high resolution CCD
camera (TSI, Powerview Plus, 4MP). The laser light wasshaped in sheet form. This light sheet was aligned with the yand z axes during the measurement in order to measure thevelocity fields at the x-y and x-z planes, respectively. The
frame rate was 15frames/s and a sufficient number of framesof instantaneous particle image were taken to calculate thetime mean velocity field. PIV analysis software (TSI, Insight6.0) was used to obtain the flow velocity from the recorded
images. When the PIV measurement was conducted, aparticle generator (TSI, model 9306) was installed in the
upstream of the settling chamber, and a small amount of oil
mist (Di-Ethyl-Hexyl-Sebacate, 1.0μm in nominal diameter)
was supplied into the air as tracing particles.

20

20

15

15

12.0

10

10

8.00

5

5

x [mm]

U [m/s]4.00
0.00-10-8 -6 -4 -2 0 2 4 6 8 10

y [mm]-4.00-10-8 -6 -4 -2 0 2 4 6 8 10z [mm](b-2) x-z plane(b-1) x-y plane(b) Qf = 1.5L/min and Qa = 20L/min

Fig. 4 Streamwise velocity U contours and velocity
vectors in R60-s0 case.
20

20

U [m/s]12.0

15x [mm]

15

8.00

10

10

5

5

4.00
0.00
-4.00

-10-8 -6 -4 -2 0 2 4 6 8 10

y [mm](a) x-y plane-10-8 -6 -4 -2 0 2 4 6 8 10z [mm](b) x-z plane

Fig. 5 Streamwise velocity U contours and velocity
vectors in R75-s0 case (Qf = 1.5L/min and Qa =3. RESULTS AND DISCUSSION

40L/min).

3.1 Parallel-type multijet caseIn this section, the discussion will be made on the
results of the parallel-type multijet cases, R60-s0 and
R75-s0, to evaluate the effect of the distance between thefuel and air nozzles, R = 6.0mm or 7.5mm under no swirl
condition. The air nozzles are not inclined and are parallelto the x-axis.
Figure 3 shows the blow-off conditions in the cases of
R60-s0 and R75-s0. The dash line shown in the figure
presents a constant equivalent ratio, φ, for thecorresponding conditions of Qf and Qa. In R60-s0 case(open circle), a relatively stable flame is observed even forlean combustion conditions of φ < 0.2 when the fuel flowrate Qf is small. As Qf increases, the air flow rate Qa of theblow-off limit decreases markedly showing thedeterioration of the flame stability. The blow-off limit willthen increase moderately along the line of φ < 1.0.
In R75-s0 case, the blow-off limit with the Qf =0.5L/min condition shows a similar value with the one
observed in R60-s0 case. The blow-off limit, on thecontrary to R60-s0, increases as Qf increases. Then, theblow-off limit remains nearly constant in the range of φ >0.2. Comparing the above two results, it can be concluded
that a higher combustion stability is obtained in R75-s0 casethan in R60-s0 case.
Figures 4 and 5 show the contour maps of thestreamwise velocity U and velocity vectors at the x-y and3

Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2010
Sept. 27-30, 2010, Cincinnati, Ohio USA

R75-s0R60-s00.9
0.8

αAir mass flow rate, Qa [L/min]

1.0

0.7
0.6
0.5
0.4
0.0
0.00

Fig. 6

0.05

0.10

γ

0.15

0.20

φ=0.2

60

φ=0.5

50
40
30

φ=1.0

R60-s0R75-s0R60-s20
R60-s40
R75-s20

20
10
0
0.0

0.5

1.0

1.5

2.0

2.5

Fuel mass flow rate, Qf [L/min]

Reaction rate, α, and preferential generation rateof CO, γ, in the cases of parallel-type multijet(Qf = 0.5L/min and Qa = 30L/min).

Fig. 7Blow-off limit in swirl-type multijet case.

near the chamber sidewalls decreases, and a large reverse
flow region is generated at the downstream of the central
nozzle. The center-located reverse flow of the fluids
supplied from the surrounding jet will impinge the central
jet. An effective mixing of the fuel and air is expected inthis area which will be discussed in the following paragraph.
In addition to this mixing effect, the reverse flow helps themixed fluid and flame to hold close to the baffle-plate. Thiscan be the reason why a more stable flame was observed in
R75-s0 case, compared with R60-s0 case.
In Fig. 6, the reaction rate, α, is plotted against thepreferential generation rate of CO, γ, for the cases of
R60-s0 and R75-s0. The flow rates are Qf = 0.5L/min and
Qa = 30L/min. R60-s0 case shows relatively smaller α andlarger γ that means an incomplete combustion is producedin the combustor. In the R75-s0 case, on the contrary, αincreases and γ decreases, compared with the R60-s0 case.
Thus, not only the reaction rate is increased, but also larger
rate of complete combustion reaction is occurring in the
combustor.
From these results, we can conclude that the generationof the reverse flow in the downstream of the central nozzle
is more effective in enhancing the fuel and air mixing andproducing a stable flame than the generation of the reverse
flow near the sidewalls. Considering that these different
flow structure can appear by slightly changing the value R,
the distance between the central and surrounding nozzles,
therefore, should be carefully decided so that a large reverse
flow region in the center of the combustor be effectively
formed in the parallel-type multijet case. The reverse flow
may bring an additional effect of exhaust gas recirculation(EGR) to stabilize and enhance the combustion reactions.

x-z planes. Figure 4 shows the results of two different mass
flow rate conditions, (a) Qf = 0.5L/min and Qa = 40L/minand (b) Qf = 1.5L/min and Qa = 20L/min, in R60-s0 case,while Fig. 5 shows the results of R75-s0 case.
In Fig. 4 (a-1), U shows positive values in the area
between the surrounding jets. On the other hand, near the
sidewalls of the combustion chamber, the areas withnegative U are observed showing that a reverse flow is
generated in this area. In the flow distribution at the x-z
plane that crosses between the air jets as shown in Fig. 4(a-2), the area size of the reverse flow increases, and aradial flow heading toward the chamber centerline isobserved near the surface of the baffle-plate. These results
show that a portion of the surrounding jets flows upstream
toward the baffle-plate along the sidewalls, and then heads
toward the chamber centerline. The flow will then mix withthe central jet.
Although not shown here, the transition from luminous
flame to blue flame was observed together with a marked
decrease of the flame length as the air flow rate Qa wasincreased while keeping the fuel flow rate Qf = 0.5L/min.
We believe that as Qa increases, the strength of the reverse
flow and radial flow that are previously mentioned isincreased. This enhances the fuel and air mixing in the area
near the central jet that can be the reason why blue flame
was observed for larger Qa conditions.
In the case of (Qf, Qa) = (1.5L/min, 20L/min) shown in
Fig. 4 (b), the reverse and radial flows same as those in Qf =0.5L/min case are observed. These reverse and radial flows
are considered to enhance the fluid mixing near the central
jet. Indeed, under this flow condition, a blue flame wasobserved in the combustor. However, compared to Fig.4 (a),the flow velocity downstream of the central nozzle is large.
As Qa increases, the velocity of the flow increases and theflame cannot be held close to the baffle-plate. This isconsidered to be the reason why the blow-off limit appears
with relatively small Qa condition.
In R75-s0 case shown in Fig. 5, the flow field largely
differs with those observed in R60-s0 case. Reverse flow

3.2 Swirl-type multijet case
Figure 7 shows the blow-off conditions in the cases of
R60-s20, R60-s40 and R75-s20. The results of R60-s0 and
R75-s0 are additionally depicted in the figure forcomparison. In R60-s20 case, the blow-off limit increases
linearly as Qf increases. In the R60-s40 and R75-s20 cases,
the blow-off limit decrease slightly around Qf = 0.75L/min,and shows a minimum value. It then increases with Qf. The
blow-off limit lines of all swirl-type cases cross the line of4

Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2010
Sept. 27-30, 2010, Cincinnati, Ohio USA

1.0
20

20

10

10

5

5
-10-8 -6 -4 -2 0 2 4 6 8 10

y [mm]

12.0

0.8

8.00

0.7

α

15

x [mm]

15

0.9

U [m/s]

4.00

0.6

0.00

0.5

-4.00

0.4
0.0
0.00

-10-8 -6 -4 -2 0 2 4 6 8 10z [mm](b) x-z plane(a) x-y plane

15

15

10

10

5

5

x [mm]

20
12.0
8.00
4.00
0.00

-10-8 -6 -4 -2 0 2 4 6 8 10(a) x-y plane(b) x-z planey [mm]

Fig. 9x [mm]-4.00

z [mm]

Streamwise velocity U contours and velocity
vectors in R60-s40 case (Qf = 1.5L/min and Qa= 40L/min).

20

20
U [m/s]

15

15

10

10

5

5

-10-8 -6 -4 -2 0 2 4 6 8 10

-10-8 -6 -4 -2 0 2 4 6 8 10(a) x-y plane(b) x-z plane

12.0
8.00
4.00

y [mm]

0.10

γ

0.15

0.20

sidewalls in the downstream area. The latter flow is
attributed to the centrifugal force caused by the swirl.
Comparing Figs. 8 (a) and (b) with Figs. 4 (b-1) and (b-2),
one can find that these flows decrease the strength of thereverse and radial flows that were observed near the
sidewalls and baffle-plate, respectively. On the other hand,a reverse flow around the central region becomes dominant
due to the swirl flow causing the decrease of the pressure in
the area along the centerline.
In Figs. 9 and 10, velocity distributions similar to theR60-s20 case are observed in both figures. However, since
Sw is larger in R60-s40 case than in R60-s20 case, greater
centrifugal force works on the surrounding jets, and the jets
flow toward the sidewalls in a shorter streamwise distance.
A stronger reverse flow is, thus, observed at the centerline.
In the case of R75-s20, the increase in R enhances theeffects of the flow momentum difference obtained between
the surrounding and central jets. This leads to theenhancement of the reverse flow generation in the area
along the centerline. On the other hand, same as in R60-s40
case, the magnitude of the flow heading toward thecenterline near the central nozzle exit is decreased
compared with the R60-s20 case.
Figure 11 shows the plots of α versus γ in R60-s20,
R60-s40 and R75-s20 cases. The results of R75-s0 with theflow rates of Qf = 1.5L/min and Qa = 40L/min are alsoplotted in the figure for comparison. The values of theR60-s20, R60-s40 and R75-s20 cases are located close witheach other. Among them, the results of R60-s40 and
R75-s20 cases are nearly identical, and the values of γ in
R60-20 case are smaller than the other two cases. On theother hand, comparing these cases with the cases of R75-s0,
α in the swirl-type cases shows a larger value. Furthermore,
γ is nearly the same among the R60-s40, R75-s20 and
R75-s0 cases.
Considering the velocity distributions previously
discussed, we believe that the flow fields can be divided
into two types in the swirl-type multijet case. The first type
is the cases of R60-s40 and R75-s20 (cf. Figs. 9 and 10),where the swirl generates a relatively large reverse flow
region at the chamber centerline that increases the fuel-air
fluid mixing near the exit of the central nozzle. Such flow

U [m/s]-10-8 -6 -4 -2 0 2 4 6 8 10

0.05

Fig. 11 Reaction rate, α, and preferential generation rateof CO, γ, in the cases of parallel-type multijet(Qf = 1.5L/min and Qa = 35L/min).

Fig. 8 Streamwise velocity U contours and velocity
vectors in R60-s20 case (Qf = 1.5L/min and Qa =40L/min).
20

R60-s20
R60-s40
R75-s20
R75-s00.00-4.00

z [mm]

Fig. 10 Streamwise velocity U contours and velocity
vectors in R75-s20 case (Qf = 1.5L/min and Qa= 40L/min).
R75-s0 case at around Qf ≅ 1.75L/min, and a larger
blow-off limit is observed in these swirl cases for larger Qf
conditions.
Figures 8, 9, and 10 show the U contour maps andvelocity vectors of each swirl case with the flow rate
conditions of Qf = 1.5L/min and Qa = 40L/min. Focusing on
the surrounding jet flows shown in Fig. 8 (a) presenting thex-y cross-sectional velocity distribution of R60-s20 case,
one can see that the surrounding air jets first head toward
the centerline in the area adjacent to the central nozzle
outlet, and then flow outwards toward the chamber
5Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2010
Sept. 27-30, 2010, Cincinnati, Ohio USA

of CO and the reaction rate of the fuel.

structure seems similar with both two cases, except that thereverse flow at the centerline is weaker than in R75-s0 case.
The swirl, however, shows another significant influenceon the flame characteristic, not shown in the PIV
measurements. That is, the flame forms an axisymmetricshape and remains close to the chamber centerline, whereas
the flame in the R75-s0 case happens to fluctuate in the
spanwise direction in the chamber. This is considered to be
attributed to the fact that the swirl reduces the radial flow
flowing between the surrounding nozzles and helps theflame to move outwards toward the sidewalls. From theseresults, γ is larger in R60-s40 and R75-s20 cases than in
R75-s0 case possibly attributed to the relatively poor fluid
mixing at the exit of the central nozzle due to the weak
reverse flow. However, since the flame remains stable near
the centerline, a higher rate of complete combustion
reaction is relatively easy to take place in the flame.
On the contrary, R60-s20 case shows a different flow
structure and combustion performance (cf. Fig. 8). In thiscase, the flow of the surrounding jets heading toward thechamber centerline in the area adjacent to the central nozzle
exit produces a strong interaction between the surround jets
and the central jet. This largely increases the fuel-air fluid
mixing in that area. The mixed gas will then spread widelyin the chamber as it flows downstream owing to the swirl.
These are considered to be the main reasons why larger α,
smaller γ, and more stable combustion than the other swirl
cases were observed in the R60-s20 case.

MAIN SYMBOLS
di
do
D
Ga
Gt
L
Qa
Qf
R
Re
Sw
tb
U
x
y, z

Diameter of the central nozzle [mm]Diameter of the surrounding nozzles [mm]Diameter of the combustion chamber [mm]Angular momentum [kg⋅m2/s2]
Translation momentum [kg⋅m/s2]
Length of the combustion chamber [mm]Flow rate of the air jets [L/min]
Flow rate of the fuel jet [L/min]
Distance between the surrounding and central
nozzles [mm]Reynolds number
Swirl number
Thickness of the baffle plate [mm]Streamwise velocity [m/s]
Coordinate in stream direction [ mm]Coordinates in radial direction [ mm](Greeks)
fuel reaction ratio
preferential generation rate of CO
inclination angle of the surrounding nozzle
Equivalent ratio

α
γ
θ
φ

(Subscripts)
CH4 value of the CH4 componentCOvalue of the CO component
CO2 value of the CO2 component

4. CONCLUSIONSThe combustion and flow characteristics of abaffle-plate-type millimeter-scale confined multijet were
evaluated in this study. Blow-off condition, flow velocity,and gas components were measured for the parallel- andswirl-types of multijet. The influences of the distance
between the central and surrounding nozzles, and theinclination angle of the surrounding nozzles were described.
The main conclusions obtained are as follows:(1) In the parallel-type multijet, a reverse flow was
generated along the chamber centerline when the
distance between the surrounding and central nozzles,
R, was large. This led to the generation of a stable
flame and a higher reaction rate with possible EGR
effect. On the other hand, when R was small, no reverse
flow was observed along the centerline, and the flame
became unstable.
(2) In the swirl-type multijet, a reverse flow was observedat the chamber centerline. The area of the reverse flow
was increased as the swirl number or R was increased.
The swirl decreased the size of the reverse flow insome degree, compared with the parallel-type multijet.
However, a stable flame with axisymmetric shape wasobtained near the centerline. This led to a slightincrease in the value of the preferential generation rate

REFERENCES[1] Choi, H. S., Katsumoto, Y., Nakabe, K. and Suzuki, K.,
An Experimental Investigation of Mixing andCombustion Characteristics on the Can-type Micro
Combustor with a Multi-jet Baffle Plate, Fluid
Mechanics and its Applications Turbulent, Mixing andCombustion, Vol. 70 (2002), pp. 367 – 375, Kluwer
Academic Publisher.
[2] Woodfield, P. L., Nakabe, K. and Suzuki, K., Numerical
Study for Enhancement of Laminar Flow Mixing using
Multiple Confined Jets in a Micro-can Combustor, Int. J.
of Heat Mass Transfer, Vol. 46 (2003), pp. 2655 – 2663.
[3] Yahagi, Y., Sekiguti, M. and Suzuki, K., Flow Structure
and Flame Stability in a Micro Combustor with a Baffle
Plate, Applied Thermal Engineering, Vol. 27 (2007), pp.
788 – 794.
[4] Tatsumi, K., Tanaka, M., Woodfield, P. L. and Nakabe,K., Swirl and Buoyancy Effects on Mixing Performanceof a Baffle-Plate-Type Miniature Confined Multi-Jet,
Int. J. Heat and Fluid Flow, Vol. 31 (2010), pp. 45 – 56.

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