mixture distribution and flame propagation in a heavy-duty liquid petroleum gas engine with liquid...

Mixture distribution and flamepropagation in a heavy-duty liquidpetroleum gas engine with liquidphase injection

SOh and C BaeDepartment of Mechanical Engineering,Korea Advanced Institute of Science andTechnology, Daejeon, Korea

Accepted 21 April 2004

Abstract: Enhanced mixture preparation by liquid phase It is especially apparent that most PM (particulate

matter) and NOx

(nitric oxides) emissions originateinjection on to the port could promote the applicationfrom the diesel engine. Therefore, LPG (liquefiedof liquefied petroleum gas (LPG) in spark ignition (SI)petroleum gas) is widely used as an alternative fuelengines. Mixture distribution and flame propagation ofin many countries throughout the world to reducethe liquid phase LPG injection (LPLI) engine with a largethe emissions. However, its use in heavy-duty vehiclebore size were investigated in a single-cylinder opticalapplications produces many difficulties such asengine which had optical accesses through both sides of theengine knock, thermal load and partial burning.cylinder liner and bottom of the piston. LPG fuel distri-Recently, a liquid phase LPG injection (LPLI) systembution was visualized quantitatively by the acetone planarwas introduced [1, 2], which injects LPG fuel into thelaser-induced fluorescence (PLIF) method. In addition,intake port in the liquid phase rather than in thea series of bottom-view images were taken by directgaseous phase.visualization using a high-speed camera. Flow conditions

The LPLI system has many advantages in itswere varied with the shapes of intake port and pistonapplication for a heavy-duty spark ignition enginegeometries characterized by different swirl and squishmodified from a diesel engine. Compared with aflows. The effects of fuel injection timings were also studiedconventional mixer system, it enhances volumetricto characterize the mixture preparation for open-valveefficiency by lowering intake air temperature andinjection and closed-valve injection.reduces toxic emissions such as NO

x. In addition,Stronger swirl with a swirl ratio of 3.4 and squish flow

power output increases and risks such as backfirewith a cylindrical piston bowl shape showed faster flamecould be reduced significantly as well. The knockpropagations under the open-valve injection condition withtendency in a spark ignition engine with a large borepreferable mixture formation. On the contrary, closed-valvesize can also be slightly relieved with the LPLI fuelinjection caused the undesirable mixture distribution ofsupply system.the mixture at the ignition, which led to a leaner mixture

To ensure fuel economy, performance and emissiondistribution near the spark plug.characteristics in the LPG engine, optimal combustion

chamber design should be investigated, which couldKey words: LPLI engine, mixture distribution, acetonebe accomplished by adopting a lean burn strategy.PLIF, fuel stratification, flame propagationLean burn generally causes unstable engine operation

due to combustion instability such as cyclic variation,

misfire or partial burning. There have been many1. Introductionattempts to extend the lean operation range in spark

A heavy-duty vehicle with a diesel engine has been ignition engines. Desirable mixture preparation and

rapid combustion can be achieved by flow fieldconsidered as a main source of urban air pollution.

513Int. J. Engine Res. Ω Vol. 5 Ω No. 6JER 01304 Ω © 2004 Ω IMechE

S Oh and C Bae

enhancement through optimal design of the intake access from the side and bottom, one at the upper

part of the cylinder liner and the other at the top ofport and piston shape.

The rich mixture in the vicinity of the spark plug the piston.

Figure 1 illustrates the schematic of the testedcould be formed through charge stratification by

controlling swirl intensity, squish flow and injection optical engine. A commercial heavy-duty diesel

engine, with a compression ratio of 17, was modifiedtiming [3, 4]. The injection strategy also affects the

stratification so that open valve injection usually to an LPG spark ignition (SI) engine with a lower

compression ratio of 9.3. A spark plug was mountedshows a better mixture preparation [5, 6]. It was

found that the axial stratification is maintained if the at the position of the diesel injector hole around the

centre of the combustion chamber. To minimizeradial component of the swirling motion is stronger

than the axial components [7]. The flow field in the vibration during operation of the single-cylinder

engine, the engine incorporated balance shafts withengine cylinder could be affected by the piston

geometry [8]. Inside the bowl-in-piston combustion counter-rotating weights. The optical engine was

driven by a d.c. dynamometer and controlled by achamber, the interaction between the swirl and

squish flow was intensively investigated [9–11]. programmable engine control unit (ECU). Table 1

shows the summary of its specifications.Planar laser-induced fluorescence (PLIF) using

acetone as a dopant has been used to visualize

2.2 LPLI fuel delivery systemfuel distributions in engines. Quantitative deter-

An LPLI fuel delivery system consists of injectormination of an air/fuel mixture was performed in

module, fuel pump, fuel tank and fuel lines, asengines [12, 13], direct injection engines [14] and

shown in Fig. 2. An LPG injector (DEKA-II injector,natural gas engines [14–16]. Pressure and temper-

Siemens-VDO), which is a bottom-feed type, wasature dependence of a fluorescence tracer was also

used and controlled by the programmable ECU.examined with acetone for an engine application

An injection nozzle specially designed for prevent-[17, 18].

ing ice formation around a nozzle hole due to latentIn the series of heavy-duty LPG engine develop-

heat of LPG fuel is attached at the end of the injector.ment, the optimized piston cavities for the LPLI system

The injector module is mounted 7 cm away from thewere investigated by experimental and numerical

cylinder head in the intake manifold. To keep themethods in a single-cylinder engine [19, 20]. In

fuel in the liquid phase, a fuel tank was alwaysaddition, mixture formation with a spray model for

pressurized with nitrogen gas up to 1.5 MPa. Toliquid LPG injection was simulated under closed-valve

circulate LPG, an external pump, originally readyinjection [21].

for gasoline fuel, was placed between the fuel tankIn the present work, mixture distribution and

and the injector module. The phase of liquid LPGflame propagation inside the LPLI optical engine

was monitored by measuring the temperature andcylinder were observed by direct imaging and the

pressure in the fuel supply line.acetone PLIF method. The fuel fluorescence with

doped acetone was visualized to recognize fuel2.3 Optical set-updistribution induced by port injection and flowFor the PLIF measurement, a broadband KrF excimerfield interaction prior to ignition. Two-dimensionallaser was used as the light source, which has a maxi-quantification of the equivalence ratio was performedmum energy of 400 mJ, wavelength of 248 nm andfor the purpose of clarifying the local variation ofpulse width of 20 ns. The laser sheet beam wasfuel distribution. The flame propagation imagesshaped both horizontally and vertically, as shownwere compared among various flow field conditionsin Fig. 3. The laser sheet beams were formed by aformulated by different intake port and piston shapes.combination of four different lenses. The beams wereThe effects of fuel injection timings on the mixturepartially masked by an iris at both edges beforepreparation were simultaneously analysed.

2. Experimental ApparatusStroke 140 mmBore 130 mmCompression ratio 9.32.1 Optical engineDisplacement volume 1858 cm3

The experiments were carried out in an optically Quartz piston window size in diameter 77.6 mmaccessible single-cylinder engine. The engine was

equipped with two quartz windows for optical Table 1 Engine specifications.

514 Int. J. Engine Res. Ω Vol. 5 Ω No. 6JER 01304 Ω © 2004 Ω IMechE

Mixture distribution and flame propagation in a heavy-duty LPG engine

Fig. 1 Schematic diagram for PLIF and flame propagation imaging.

Fig. 2 LPLI fuel delivery system for the optical single-cylinder engine.

Fig. 3 Laser sheet beam configuration for the bottom and side views.


S Oh and C Bae

entering the cylinder. The horizontal laser sheet fired for every cycle. While this appeared to be a

defect of these kinds of works, acetone has been pre-beam, the width of which is 43 mm, was passed

through the quartz liner approximately 8 mm below ferred as the best choice at least for qualitative fuel

tracing when considering an absorption band access-the bottom of the cylinder head. The vertical beam,

26 mm wide, was directed into the combustion ible with KrF excimer laser, collisional quenching

and toxicity.chamber.

An intensified charge-coupled device (ICCD) As mentioned above, pure LPG fuel does not

fluoresce in the excited electronic state by lasercamera (4Quik05A, Stanford Computer Optics) was

synchronized with the laser output to take images of excitation. The acetone, 20 per cent by volume of the

injected amount of fuel, was doped. To quantify fuelthe fluorescence at any given crank angle by the

delay generator and signal counter. The master signal concentration from the fluorescence signal, several

sources of error should be corrected, i.e. (a) variationfor the synchronization of all equipment came from

the optical encoder linked to the engine. A WG305 of the laser power, (b) spatial non-uniformity of the

laser sheet beam, (c) distortion due to the curvaturecut-off filter was attached in front of the camera to

suppress the undesirable signals such as Mie scatter- of the quartz window, (d) the variation of CCD

element sensitivities in the camera and (e) back-ing and stray light inside the cylinder. A high-speed

charge-coupled device (CCD) video camera (Kodak ground signal noise. A specially written program

was applied to process raw images with the detailedSR-c) was also used for direct flame imaging,

coupled with a high-speed gated image intensifier to considerations for quantification as follows.

compensate for the weak flame illumination. The3.1 Normalizationintensifier gain and the exposure time were adjustedWhile the average energy output of the laser is stablefor lean operation.over a long period of time, the shot-by-shot energy

can vary significantly. The variation of the laser

3. Acetone PLIF for LPG Fuel Imaging power output was usually measured directly with a

power meter. In this work, a portion of the laserA pure LPG, a mixture of butane and propane, emits output is diverted with a beam-splitter and comesno fluorescence. It needs the seeding of a fluorescing into the corner of view in the camera with attenuatedadditive. In the current study, acetone (dimethyl intensity. Because the fluorescence image and laserketone) was chosen as the dopant because it is much intensity were recorded simultaneously, every rawless dependent on oxygen quenching and is less toxic fluorescence image can be normalized using thethan other dopants [22]. The physical properties of reference intensity of the laser in the same image.LPG and acetone are summarized in Table 2.

Even though acetone may not be suitable as a flow 3.2 Background image subtraction

There are various sources of interference inside thefield tracer because its boiling point is higher than

that of LPG fuel, it should be noted that all the LPG cylinder that increase the uncertainty of quantification,

such as fluorescence from the quartz window itself,and acetone must be vaporized by the end of the

intake process. This was verified by fluorescence deposits on the wall and strayed light. These noises

were observed under an engine motoring conditionimaging without the optical filter. No elastic scatter-

ing from droplets was found in the tested images. without any fuel injection. To remove the background

noise, 50 images under the motoring condition wereTo minimize this kind of error due to unequal boiling

points, the temperature of the engine coolant was averaged at the corresponding crank angle and

subtracted from the raw image.kept at 80 °C and also the engine was simultaneously

Properties LPG Acetone

Molecular formula C3H8(60 wt%), C

4H10(40 wt%) CH

3KCOKCH

3Specific gravity at 25 °C 0.5247 0.7880Boiling point at 1 atm (°C) −34.30 56.13Vapour pressure at 20 °C (MPa) 0.61 0.02Density at 20 °C (kg/m3) 531.6 789.8Viscosity at 25 °C (cps) 0.1175 0.3075

Table 2 Physical properties of LPG and acetone.



3.3 Flat field correction investigate the effects of swirl intensity. The swirl

ratio was measured in a steady flow rig. The RicardoAfter normalization and background subtraction, it

is necessary to account for the variation of pixel swirl number (Rs) was defined by the following

equation [23]:sensitivity and non-uniformity of the laser sheet

beam. This correction was performed for every pixel

by dividing the fluorescence images of homogeneous

mixtures. During this quantification procedure a Rs=

LD P a2

a1

CfNR

da

AP a2a1

CfdaB2 (1)

mixing tank was placed between the intake manifold

and the fuel injector to improve air/fuel mixing [4].

After all corrections were made as described above,where L

Dis the engine shape parameter, C

fthe flow

the linear correlations between acetone fluorescencecoefficient, N

Rthe non-dimensional rig swirl, a

1the

intensity and the equivalence ratio were obtained atopening time of the intake valve and a

2the closing

each crank angle, as shown in Fig. 4.time of the intake valve.

In addition, flame propagation measurements

were performed only in the lean condition, with4. Experimental Conditionoverall equivalence ratios (w) of 0.8 but 1.0 for laser-

induced fluorescence (LIF) measurements becauseAll through this work, the optical engine was

its signal was too weak to acquire mixture distri-operated at an engine speed of 500 r/min, with an

bution in the lean region. Sometimes it is not easy tointake manifold pressure of 86 kPa and a coolant

distinguish the fluorescence signal from the noise.temperature of 80 °C. The LPG, formed as the mixture

Because the LIF signal is directly proportional toof 60 per cent propane and 40 per cent butane by

mixture concentration, the mixture distribution undermass, was used as a fuel. PLIF images were taken

lean conditions could be qualitatively representedduring the compression process, at BTDC (before

by observations under richer conditions. For bothtop dead centre) 120, 90, 60, 40 and 30° CA, described

measurements of mixture concentration and flameas the relative timings from compression TDC

propagation, ignition timings were always fixed at(top dead centre).

BTDC 20° CA.As for the injection timing, open-valve injection

Two geometrically different pistons were used(OVI) and closed-valve injection (CVI) were com-

to investigate the effects of piston geometry. Eachpared, which were BTDC 240 and 100° CA respect-

piston has a different squish area. Figure 5 illustratesively. The engine cylinder heads with different swirl

the shape of the pistons. One piston has a sphericalratios (Ricardo swirl number) of 2.3 and 3.4 were

bowl shape and the other has a cylindrical bowlimplemented by two different helical ports to

shape.

5. Results and Discussion

5.1 Mixture distribution

Figure 6 shows nine individual images selected

from a set of 50 images at BTDC 30° CA for w=1.0,

Rs=2.3 and open-valve injection. They show the

cyclic variations of the mixture distribution. In the

averaged images, a dominant trend in the mixture

distribution can be finally observed when the cyclic

fluctuating images are ensemble averaged.

The base engine used in the experiments is a

two-valve diesel engine with a helical intake port.

The flow field inside the cylinder mainly consists

of swirl flow that moves around the vertical axis of

the cylinder. Therefore, it is supposed that the fuel

Fig. 4 Relationship between the equivalence ratio (w) (or excess moves along the main stream, the swirling flow,

while the air/fuel mixing process proceeds.air ratio, l) and relative fluorescence intensity.


S Oh and C Bae

Fig. 5 Combustion chamber geometries of the tested pistons.

Fig. 6 Cyclic variation of fuel distribution at BTDC 30° CAFig. 7 The averaged bottom-view images of fuel distribution

for w=1.0, Rs=2.3 and open-valve injection.during the compression process at an engine speed of

500 r/min, overall equivalence ratio (w)=1.0, open-The images of LPG fuel distribution during com- valve injection and a spherical piston bowl.

pression from the bottom view are shown in Fig. 7

in the case of open-valve injection with w=1.0. Each

image at every crank angle was averaged from 50 fuel is found in the lower left side of the image at

BTDC 120° CA for Rs=2.3. The fuel is transportedsingle-cycle images to show the global effect of swirl

strength. Since the swirl flow moves in a clockwise to the upper side of the viewing area in the clockwise

direction. The cloud of fuel seemed to disappeardirection in this engine, the dense bulk motion of



in the window at BTDC 60° CA, but thick fuel injection period is accumulated in the intake port and

vaporized easily, its mixture preparation is relativelyconcentration is observed again at a later stage

(as in BTDC 40 and 30° CA). In the case of a high homogeneous. At the early stage of the intake pro-

cess the fuel in the volume of the intake port is firstswirl ratio, Rs=3.4, the dense fuel concentration is

observed at the upper side of the viewing area and induced into the cylinder and then the bottom of

the cylinder becomes richer than the other partsalso rotates clockwise. The overall fuel concentration

in the viewing area is much higher than that of of the cylinder [7]. As the compression process

advances, the homogeneity of the equivalence ratioRs=2.3. This indicates that a strong swirl flow

hinders air/fuel mixing. This can be observed in side is improved. However, it seems that the average

equivalence ratio near the spark plug is still lowerview measurements more clearly.

Images of the side view, as presented in Fig. 8, than that of the other parts of the cylinder. This

implies that the axial fuel distribution is not desirableshow vertical distribution of LPG fuel in the case of

open- and closed-valve injections with Rs=3.4 and and might cause a misfire or partial burn for a lean

operation. On the contrary, the open-valve injectionw=1.0. The closed-valve injection case shows a

higher equivalence ratio in the lower part of the demonstrates a higher concentration at the top of

the cylinder where the swirling motion governs theimages during compression, even though there is a

small spatial variation. Because LPG fuel during the formation of a rich mixture, as shown in Fig. 7. The

Fig. 8 The averaged side-view images of fuel distribution during the compression process at an engine speed of 500 r/min, Rs=3.4,

overall equivalence ratio (w)=1.0 and a spherical piston bowl.


S Oh and C Bae

cloud of fuel observed at BTDC 120° CA is steadily from the spark plug while it increases with closed-

valve injection (CVI). However, for (b) Rs=2.3, thesustained and the rich zone near the spark plug is

finally formed near TDC, as shown in the images of vertical fuel concentrations present are relatively

constant for both injection timings. As the swirlBTDC 60–30° CA in Fig. 8.

In the case of Rs=2.3, as shown in Fig. 9, even intensity becomes strong, the axial fuel concentration

varies to the extent that the equivalence ratio (w) nearthough there is small variation, the overall equivalence

ratio in the images is nearly homogeneous compared the spark plug is over 1.3 with Rs=3.4.

The comparison between open- and closed-valvewith the stronger swirl condition. The fuel cloud

found in the left side of the image at BTDC 120° CA injections shows that the fuel stratification could be

achieved by the injection timing control with a strongis also spread out during the compression process.

Figure 10 shows the averaged equivalence ratio for swirl flow of Rs=3.4. It is noted that the fuel distri-

bution is significantly sensitive with injection timingsBTDC 30° CA along the z direction from the spark

plug to describe the axial mixture stratification, where in the case of strong swirl. A low fuel concentration

is observed near the spark plug in the case ofeach value represents the averaged equivalence ratio

overall through the x direction. The axially stratified the closed-valve injection while a rich mixture is

distributed in the lower part of the cylinder. Thefuel distribution could be quantitatively obtained.

For (a) Rs=3.4 with open-valve injection (OVI), the overall fuel concentration in the vertical imaging

area, when Rs=3.4, also seems to be higher than forequivalence ratio shows a gradual decrease away

Fig. 9 The averaged side-view images of fuel distribution during the compression process at an engine speed of 500 r/min, Rs=2.3,

overall equivalence ratio (w)=1.0 and a spherical piston bowl.



geometry as for Rs=3.4. This again indicates that a

stronger swirl flow is more useful for rich mixture

formation near the spark plug. The cylindrical piston

bowl causes a stronger tumble motion than the

spherical piston bowl inside the cavity [21]. This

tumble motion pushes the mixture upwards with a

high equivalence ratio and finally results in a higher

fuel concentration near the ignition location. It is

supposed to enhance the combustion process for lean

operation.

5.2 Flame propagation

Raw flame images of different swirl ratios are pre-

sented in Fig. 11 for the cylindrical piston bowl under

the lean mixture condition (w=0.8). Flame images are

a series of frames in a cycle. The flame propagation

patterns are shown differently for both swirl ratios.

With Rs=2.3 the initial flame shape starts like a

circle and the flame front propagates towards the

exhaust valve side. The flame kernel is developed

around the spark plug and grows to larger flames in

an oval shape where the flame propagation direction

coincided with the swirl direction.

In the case of a high swirl ratio (Rs=3.4), the flame

continued to propagate in a circular shape. The initial

flame propagation is observed in the vicinity of the

spark plug. The flame is developed symmetrically

Fig. 10 The line averages of equivalence ratio along the vertical from the centre of the flame kernel. After the flame

direction from the spark plug at BTDC 30° CA with front exceeds the visualization limit, the piston

different injection timings and piston bowl shapes for window border, bright flames are observed around

w=1.0. the centre of the combustion chamber, rotating along

the swirl direction.

The flame stretches out along the major flow

direction in a weak swirl condition. However, whenRs=2.3. This means that, in the case of Rs=3.4, thelaid in a strong swirl flow field, trapped in the centre,rich region is centred and its fuel is not radially trans-the flame developed into the circular flame with aported as much as in case of Rs=2.3. This coincidesflame front in a saw-tooth shape. The flame withwith the results of the bottom-view images in Fig. 7.high swirl, Rs=3.4, shows a larger flame area thanIt is recognized that the advantage of strong swirl inRs=2.3. This implies that introducing a high levelopen-valve injection is due to the suppression ofof swirl increases the level of turbulence in theradial convection. A rich mixture remains in the

engine [24, 25].vicinity of the spark plug with the aid of a strong

Even though there are still uncertainties in theswirl flow. Mixing along the cylinder axis should be

flame images because they are two–dimensionaldelayed to retain axial stratification if the radial com-

projected ones of a three-dimensional propagatingponent of the swirling flow is stronger than the axial

flame, the flame propagation reflects the fuel distri-component. This confirms the report that the swirl

bution as presented in Figs 7 to 9. The late flameplays a key role in preserving axial fuel stratification

propagation in the centre with a high swirl ratio[7]. Figure 10 also shows the averaged equivalence

(Rs=3.4) is observed (e.g. 36° CA after ignition inratio with different piston bowl shapes. For both swirl

Fig. 11). It is supposed that the fuel burning isratios, the cylindrical piston bowl presents a higher

retained in the centre because the fuel concentrationequivalence ratio. For Rs=2.3, however, the fuel con-

centration is not affected as much by the piston in the centre of the cylinder is higher with a strong


S Oh and C Bae

Fig. 11 Flame images from ignition to 48° CA after ignition with overall equivalence ratio (w)=0.8, open-valve injection and a

cylindrical piston bowl.

swirl (Rs=3.4) and open-valve injection as shown in (Rs=3.4) is developed more rapidly than the weaker

swirl flow (Rs=2.3). However, the opposite trend isFig. 8b. In the case of a low swirl ratio (Rs=2.3), any

found in the case of closed-valve injection (CVI),noticeable burning flame in the centre is not found

even if a higher turbulence intensity for Rs=3.4 thannear the end of flame propagation.

for Rs=2.3 is supposed. As mentioned above, theFigure 12 shows the comparison of two-dimensional

axial fuel stratification under the strong swirl con-flame areas for two different swirl ratios, 2.3 and 3.4,

dition is strongly affected by fuel injection timing.at each crank angle. The flame area along the y axis

The flame propagation with Rs=2.3 does not dependrepresents the sum of the number of image pixels in

very much on its injection timing. The developmentthe inner region of the flame. The flame area was

of the flame area shows a very similar history forestimated by counting the pixels, the grey level of

each case, though the open-valve injection gives awhich is over the predetermined threshold value

slightly higher value. It should be noted that thererepresenting the clear border of the flame front with

is a large cyclic variation of the flame area formanifest contrast. In the case of open-valve injection

Rs=3.4 and closed-valve injection. It is most likely(OVI), the flame area for the stronger swirl flow

due to reverse stratification, as stated above. A leaner

mixture strength at the ignition timing may lead

to unstable initial flame development, resulting in

cyclic combustion variations. Unstable combustion,

such as misfire and partial burning, could be

expected in a real engine with this condition.

Figure 13 shows the flame areas for two different

piston geometries. Each piston has its own flow

characteristics, and it is squish intensity that causes

different flame propagations. The squish area of the

cylindrical piston bowl is 50 per cent larger than that

of the spherical piston bowl, as shown in Fig. 5. The

faster flame propagation of the cylindrical piston

bowl is clearly observed beyond variance. In addition

to a strong interaction between swirl and squish flow

Fig. 12 Flame areas from ignition to 30° CA after ignition for to accelerate in-cylinder combustion [3–6], it is con-

different swirl intensities and injection times with sidered that a higher concentration also exists near

overall equivalence ratio (w)=0.8 and a cylindrical the ignition location of the cylindrical piston bowl,

as shown in Fig. 10.piston bowl.



5. The cylindrical shape piston bowl with the larger

squish area showed faster flame propagation than

the spherical shape piston bowl with a smaller

squish area.

Notation

a1

opening time of the intake valve

a2

closing time of the intake valve

BTDC before top dead centre

Cf

flow coefficient

CVI closed-valve injection

ICCD intensified charge-coupled deviceFig. 13 Flame areas from ignition to 30° CA after ignitionLD

engine shape parameterfor two different piston geometries with overallLPG liquefied petroleum gasequivalence ratio (w)=0.8, open-valve injection andLPLI liquid phase LPG injectionRs=2.3.NR

non-dimensional rig swirl

NOx

nitric oxides

OVI open-valve injection6. ConclusionsPLIF planar laser-induced fluorescence

PM particulate matterFuel distribution and flame propagation character-

istics in a two-valve heavy-duty engine with an LPLI Rs Ricardo swirl number

fuel supply system were investigated in a single- SI spark ignition

cylinder optical engine. LPG fuel distribution was TDC top dead centre

measured by the acetone PLIF method quantitatively

l excess air ratioand the flame development was acquired by direct

w equivalence ratioflame imaging according to piston shape, swirl

intensity and injection timing. Fuel concentration was

quantified from the PLIF images and the flame areas

were also calculated from the direct flame images.

This study leads to the following conclusions: References

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mixture distribution and flame propagation in a heavy-duty liquid petroleum gas engine with liquid...

Engineering

lpg engine

diesel engine

lpg fuel distri

unstable engine operationdue

enhanced mixture preparation

spark ignition sipetroleum

lpli fuelinjection

directgaseous phase