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SAE TECHNICAL
PAPER SERIES 2000-01-2805

KIVA Simulation for Mixture Formation

Processes in an In-Cylinder Injected
LPG SI Engine
Gisoo Hyun, Daeyup Lee and Shinichi Goto
Mechanical Engineering Laboratory, AIST, MITI

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2000-01-2805

KIVA Simulation for Mixture Formation Processes in an

In-Cylinder Injected LPG SI Engine
Gisoo Hyun, Daeyup Lee and Shinichi Goto
Mechanical Engineering Laboratory, AIST, MITI

Copyright © 2000 Society of Automotive Engineers, Inc.

ABSTRACT even near the stoichiometric mixing condition. Then LPG

fuel is more promising as an alternative fuel for In-
This is a preliminary work for the development of a cylinder injection engines. However, It is necessary to
stratified combustion engine using liquefied petroleum find a suitable combustion chamber shape for LPG,
gas(LPG) as an alternative fuel. The main objective of because the physical properties of LPG are different from
this research is to find out the optimizing engine gasoline. Therefore, numerical simulation was performed
parameters from the viewpoint of mixture formation with using the KIVA _ code to search for optimized engine
the aid of simulation, where the KIVA_ code was used. parameters and combustion chamber geometry from the
The combustion characteristics of LPG and gasoline are viewpoint of mixture formation.
different because of their different physical properties.
Therefore, the numerical simulation was performed for CALCULATION METHOD AND CONDITION
optimizing engine parameters by changing the piston and
cylinder geometry, as well as injection conditions. Result A numerical simulation concerning the mixture formation
showed that geometry of combustion chamber has a process was performed in this work by using the KIVA _
great influence on mixture stratification. Also, weaker code, developed as an engine combustion analysis
swirl seems to be better for mixture formation in the program in the United States Los Alamos laboratory[7].
vicinity of the spark plug. The KIVA _ code has been developed to do unsteady
numerical analysis of the spray behavior and combustion
INTRODUCTION process of the internal combustion engine. The analysis
can be done by giving the initial and boundary conditions.
The main purpose of this research is to develop a low
emission and high efficiency engine system from the Type1 Type2
standpoint of energy security and environmental aspects.
Offset 10mm Offset 10mm
Up to now, authors have conducted several researches
concerning the LPG-fueled lean-burn spark-ignition(SI)
engine and LPG direct-injection(DI) diesel
engine[1][2][3]. A great NOx reduction can be achieved in
the former, and the suggestion of LPG as a fuel for low
NOx and particulate matter(PM) is obtained in the latter. Type3 Type4 Offset 3mm

On the other hand, several works have been carried out

for injecting the fuel directly into the combustion chamber
to meet the low emission standard and high
efficiency[4][5][6]. Recently, those methods have been
Type5 spark plug
used in practical gasoline engines. Mixture stratification
is achieved by using swirl and tumble in the cylinder spray nozzle
because the gasoline direct injection(GDI) engine chiefly
operates in a lean condition. As a result, rapid and stable
combustion can be achieved. However, a large amount of
unburned hydrocarbon emission is a new problem with
GDI engines, when they operate near the stoichiometric Fig.1 Vertical view of combustion chamber,
mixing condition. and position of spark plug and spray nozzle
As for LPG, the evaporation rate is higher than for
gasoline, and unburned hydrocarbon emission is low

1
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Table 1. Engine specifications and calculation conditions combustion chamber shape. To that end, the geometry of
the piston cavity was changed as shown in Fig.1. And
the detailed fuel-air mixture formation process in each
cavity was observed with respect to the flow. The
parameters and fuel injection conditions of the engine
are shown in Table1.

CALCULATION RESULTS AND DISCUSSION

MIXTURE FORMATION PROCESSES IN EACH

CAVITY GEOMETRY – Fuel injection has a great
influence on mixture formation and stratified combustion
in the cylinder. Therefore, it is important to control
adequately the fuel fluid in association with the flow in the
combustion chamber. Therefore, the velocity vector
distribution in various geometries of the combustion
chamber was examined. Moreover, to consider the
mixture formation process in more detail, the distribution
of fuel, fuel vapor and equivalence ratio were observed
simultaneously. Results on the vertical and horizontal
The mixture stratification is the most important factor in cross section are shown in Fig.2.
In-cylinder injection engine. Therefore, it is necessary to
examine the mixture formation process by changing the

Type1
lean rich
30° BTDC 20° BTDC 15° BTDC

(a)velocity vector

(b)fuel

(c)fuel vapor

(d)equivalence ratio

Figure 2-I. Distribution of (a) velocity vector, (b) fuel, (c) fuel vapor and (d) equivalence ratio in case of Type1
(Base case: injection direction; central axis direction, Injection angle; 45° from axis, swirl; 1.0)

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Type2
lean rich
30° BTDC 20° BTDC° 15° BTDC

(a)velocity vector

(b)fuel

(c)fuel vapor

(d)equivalence ratio

Type3
lean rich
30° BTDC
20° BTDC 15° BTDC

(a)velocity vector

(b)fuel

(c)fuel vapor

(d)equivalence ratio

Figure 2-II. Distribution of (a)velocity vector, (b)fuel, (c)fuel vapor and (d)equivalence ratio in case of Type2 and 3
(Base case: injection direction; central axis direction, Injection angle, 45° from axis, swirl; 1.0)

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Type4
lean rich
30° BTDC
20° BTDC 15° BTDC

(a)velocity vector

(b)fuel

(c)fuel vapor

(d)equivalence ratio

Type5
lean rich
30° BTDC 20° BTDC 15° BTDC

(a)velocity vector

(b)fuel

(c)fuel vapor

(d)equivalence ratio
Figure 2-III. Distribution of (a)velocity vector, (b) fuel vapor and (d) equivalence ratio in case of Type4 and 5
(Base case: injection direction; central axis direction, Injection angle; 45 from axis, swirl; 1.0)

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A large vortex is formed at the periphery of the injected density liquid fuel and the fuel vapor are both present at
fuel fluid by shear with surrounding air; the vortex grows the vicinity of the spark plug. Therefore, it is thought that
while entraining surrounding air. It is considered that Type5 is the ideal combustion chamber geometry with
surrounding air and small droplets, as well as the fuel respect to mixture formation.
vapor which has already evaporated, are entrained into
Fig.3 represents the local relative equivalence ratio within
the fuel fluid by these vortices, and move with the fuel
15mm of the spark plug, so that mixture distribution at the
fluid. Fuel fluid of this kind impinges on the bottom of the
vicinity of the spark plug may be considered in more
piston cavity, and progresses along the wall. This
detail. Where, relative equivalence ratio is the value that
characteristic of the flow can be observed with all
equivalence ratio was divided by the maximum value.
combustion chamber geometries. The piston cavity does
not show any effect on fuel fluid before impingement. The local equivalence ratio for Type1, Type2 and Type4
However, different behaviors can be observed after is extremely small in the vicinity of the spark plug.
impingement with different combustion chamber Therefore, it can be concluded that these geometries of
geometries. In the case of Type1, the vortex flow after the combustion chamber are not suitable for stratified
impingement is comparatively weak, because the swirl combustion.
flow is attenuated on the other side wall of the nozzle. As
On the other hand, though a good value is obtained for
a result, the flow toward the central axis becomes weak.
Type3, the case of Type5 has a remarkably large value
In the case of Type2, the first vortex rolls up at the piston
which is maintained even until ignition timing. Therefore,
cavity center, and then the flow moves towards the upper
this geometry is the most suitable combustion chamber
side of the combustion chamber. However, the flow
shape for the purpose of this research. Therefore, the
toward the spark plug is weak, because the vortex flow
combustion chamber geometry of Type5 is chosen from
cannot be maintained to top dead center and then the
the above-mentioned results.
flow collapses. For Type3, a wall has been installed at the
piston cavity center, so that the entire flow may proceed
IN FL UE N CE O F I NJ E CT IO N D IR E CTI O N – The
to the cylinder center. The vortex flow is observed even in
influence of injection direction on mixture formation is
the vicinity of the spark plug though the scale of vortex is
determined by utilizing the combustion chamber selected
small. In the case of Type4, though growth of a large
from the above-mentioned results.
scale vortex continues without collapsing after
impingement on the piston cavity wall, the scale is still Fig.4 shows the distribution of the local equivalence ratio
small. In the case of Type5, the entire combustion in each injection direction. (a) is injected in the reverse-
chamber is influenced by the flow of the large scale swirl direction 10° from the central axis, (b) is injected in
vortex. Moreover, the influence of squish is added to the the direction of the central axis, and (c) is injected in the
swirl flow in the vicinity of top dead center, and the flow swirl direction 10° from the axis.
toward the central axis of the piston cavity is
In case of (a), rich mixture is formed in the vicinity of
strengthened. It seems that this large scale vortex flow
the spark plug at 20°BTDC. Also, a high equivalence
forms an ideal mixture for stratified combustion with the
ratio distribution has been observed in the vicinity of the
swirl flow, which is seen from the velocity distribution on
spark plug from the cross section. However, the high
the horizontal cross section.
equivalence ratio distribution observed at 20°BTDC has
It is understood from the figure of the fuel and fuel vapor weakened by 15°BTDC. The reason is as follows. The
distribution that fuel fluid progresses getting on the mixture progresses toward the spark plug till 20°BTDC
above-mentioned flow. For Type1, after forming a rich due to the inertia force of liquid fuel. Afterwards, this
mixture in vicinity of the wall on the opposing side of the inertia force is lost, and the mixture at the vicinity of the
nozzle, the fuel fluid does not advance inward. And also, spark plug is pushed out due to the influence of swirl flow.
the fuel vapor does not arrive at a central axis, though the
In the case of (b), rich mixture is formed in the place
fuel vapor distribution has extended more than the fuel
where some comes off at 20°BTDC, and it is formed far
concentration. The mixture formation process for Type2 is
from the spark plug at 15°BTDC.
almost the same as for Type1. A wall has been installed
at the piston cavity center aiming to form rich mixture in In the case of (c), rich mixture is widely distributed in
the vicinity of the spark plug for Type3. However, its effect the vicinity of the spark plug at 20°BTDC. As time
is not strong. The mixture progresses along the cavity advances, though it becomes thin at 15°BTDC, the
wall with swirl flow as is shown in the horizontal cross mixture is concentrated in the vicinity of the spark plug.
section, but it does not arrive at the vicinity of the spark
Fig.5 is the distribution of the local relative equivalence
plug.
ratio within 15mm of the spark plug.
In the case of Type4, though the fuel concentration
The results for case(a) and (b) are similar. However,
distribution keeps growing up along the piston cavity wall,
case(c) indicates a larger value compared to the others.
both liquid fuel and fuel vapor do not move to the vicinity
Therefore, it is thought that fuel injection into the swirl
of the spark plug. Type5, remarkably, has the desired
direction is advantageous for the mixture formation of
mixture formation for stratified combustion in the piston
stratified combustion.
cavity geometry. It can be seen from Fig.2 that high

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Fig.3 Relative equivalence ratio near the spark

plug for each combustion chamber

20° BTDC 15° BTDC 20° BTDC 15° BTDC

(a) Injection to reverse-swirl direction (b) Injection to the
for 10°from a central axis direction

20° BTDC 15° BTDC

(c) Injected to swirl direction
for 10°from a central axis

Fig.4 Distribution of the local equivalence Fig.5 Relative equivalence ratio near the
ratio in the injection direction spark plug for each injection direction

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INFLUENCE OF INJECTION ANGLE – Injection angle 20°BTDC. On the other hand, even though the
also has an effect on the mixture formation, when the fuel distribution has changed at 15°BTDC, rich mixture is
from the above-mentioned results is injected into the swirl formed in the vicinity of the spark plug.
direction 10° from a central axis. The results are shown in
In the cases of (b) and (c), though the rich mixture
Fig.6 and 7. (a) is case of injection at 35°, (b) case of
distribution has concentrated in the vicinity of the spark
injection at 45° and (c) case of injection at 55° from the
plug like case(a) at 20°BTDC, It is attenuated a little at
cylinder central axis.
15°BTDC compared with case(a). Moreover, rich mixture
In the case of (a), that is, 35° injection, rich mixture is is formed in a place somewhat away from the spark plug.
distributed very well in the vicinity of the spark plug at

20° BTDC 15° BTDC 20° BTDC 15° BTDC

(a) Injection at 35°from a central axis (b) Injection at 45°from a central axis

20° BTDC 15° BTDC

(c) Injection at 55°from a central axis

Fig.6 Distribution of the local

equivalence ratio in the injection Fig.7 Relative equivalence ratio near the
angle spark plug for each injection angle

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These results are shown quantitatively in Fig.7. Rich In the case of swirl intensity 0.5, rich mixture in the
mixture is formed well in the order of 35°, 45° and 55°. vicinity of the spark plug is formed at 20°BTDC and
These results are consistent with Fig.6. 15°BTDC, but the tendency with the stronger swirl
intensity is that more goes away from the spark plug.
Therefore, It is thought that it is more advantageous with
respect to injection angle to inject the fuel into the Fig.9 shows the quantitative results concerning Fig.8.
direction of the cavity wall for mixture stratification. The stronger the swirl intensity is, the earlier the rich
mixture reaches the vicinity of the spark plug. However,
INFLUENCE OF SWIRL INTENSITY – Fig.8 and 9 are there is a tendency in the case of stronger swirl intensity
the result of observing the influence which swirl intensity for rich mixture to leave early from the spark plug.
gives to the mixture formation process. (a) is case of swirl Moreover, the weaker the swirl intensity is, the more rich
intensity 0.5, (b) is case of swirl intensity 1.0, (c) is case mixture is formed in the vicinity of the spark plug.
of swirl intensity 2.0 and (d) is case of swirl intensity 3.0,
respectively.

20° BTDC 15° BTDC 20° BTDC 15° BTDC

(a) Swirl 0.5 (b) Swirl 1.0

20° BTDC 15° BTDC 20° BTDC 15° BTDC

(c) Swirl 2.0 (d) Swirl 3.0

Fig.8 Distribution of the local equivalence ratio in the swirl intensity

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Fig.9 Relative equivalence ratio near the spark

plug for the swirl intensity

CONCLUSION REFERENCES

A numerical simulation was performed by using the KIVA 1. S. Goto, D. Lee, Y. Wakao, H. Honma, M. Mori, Y.
III code concerning the mixture formation process in an Akasaka, K. Hashimoto, M. Motohashi, and M.
in-cylinder injected LPG SI engine for the purpose of the Konno, "Development of an LPG DI Diesel Engine
low emission and high efficiency. using Cetane Number Enhancing Additives", SAE
Paper 1999-01-3602, 1999.
In particular, the geometry of the combustion chamber is 2. S. Goto, D. Lee, J. Shakal, N. Harayama, F. Honjyo,
varied in this work, because it seems that its influence is and H. Ueno, "Performance and Emissions of LPG
the largest for the mixture stratification. The mixture Lean Burn Engine for Heavy Duty Vehicles", SAE
formation process is considered in various geometries of Paper 1999-01-1513, 1999.
combustion chamber. And then the following results were 3. D. Lee, J. Shakal, S. Goto, H. Ishikawa, H. Ueno, and
obtained. N. Harayama, "Observation of Flame Propagation in
The case of Type5 has the remarkably large value of an LPG Lean Burn SI Engine", SAE Paper 1999-01-
equivalence ratio in the vicinity of the spark plug that is 0570, 1999.
maintained even until the ignition timing. Therefore, this 4. Dennis N. Assanis, S.-J. Hong, A. Nishimura, George
geometry is the most suitable combustion chamber Papageorgakis, and Bruno Vanzieleghem, ”Studies
shape from the respect of the mixture formation process. of Spray Breakup and Mixture Stratification in a
Gasoline Direct Injection Engine Using KIVA-3V”,
Fuel injection into the swirl direction is advantageous with ASME, No.99-ICE-161, 1999.
respect to the injection direction for the mixture formation 5. Barry R. Lutz, Rudolf H. Stanglmaier, Ronald D.
of stratified combustion. Matthews, Jim ”Turbo” Cohen, and Ryan Wicker,”The
Effects of Fuel Composition, System Design, and
It is more advantageous with respect to injection angle to
Operating Conditions on In-System Vaporization and
inject the fuel into the direction of the cavity wall for Hot Start of a Liquid-Phase LPG Injection System”,
mixture stratification. SAE Paper 981388, 1999.
The stronger the swirl intensity is, the earlier the rich 6. M. Kanda, R. Shimizu, T. Kobayasi, S. Matsushita, M.
mixture reaches the vicinity of the spark plug. However, Koike, and A. Saito,”New Concept of a Direct
there is a tendency for it to leave early from the spark Injection SI Gasoline Engine”, JSAE paper 9939604,
plug. And the weaker the swirl intensity is, the more rich 1999.
mixture is formed in the vicinity of the spark plug. 7. Amsden, A.A., “KIVA-3V : A Block-Structured KIVA
Program for Engines with Vertical or Canted Valves”,
Los Alamos National Laboratory Report LA-13313-
MS, 1997.