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CONSEIL INTERNATIONAL
DES MACHINES A COMBUSTION
20th INTERNATIONAL CONGRESS ON COMBUSTION
ENGINES 0111
MEASUREMENT OF DIESEL
COMBUSTION BY OPTICAL FIBER
THERMOMETER
byDr Masahiro Ilshida and Mr Noboru Matsu-Muth, Nagasaki University Dr Shuhei lzumi, MEITEC Corporation
and
'MFI-lideo.Suetsugii, Nagasaki institute of Applied Science, Japan
LONDON 1993
11
OICIMAC°1993
D38
INTERNATIONAL COUNCIL
Dr. Masahiro ISHIDA
Dr. Shuhei IZUMI
Mr. Noboru MATSUMURA Mr. Hideo SUETSUGU
Measurement of Diesel Combustion by Optical Fiber Thermometer
Professor, Mechanical Systems Engineering, Nagasaki University
Executive Advisor, MEITEC Corporation Graduate Student, Nagasaki University Associate Professor, Nagasaki Institute of Applied Science
Japan
ABSTRACT
Reducing exhaust NOx and smoke of diesel engines, in-cylinder combustion
process was analyzed experimentally. Especially, the soot formation and
oxidization processes have been tried to make clear. The authors have
proposed new techniques for measuring combustion behavior locally in a direct
injection diesel engine combustion chamber by means of the optical fiber
thermometer in combination with two types of light-pipe sensor. The temporal
and spatial distributions of flame temperature and soot concentration were
measured accurately through a simple and easy procedure applying the infrared
two-color method.
Influences of several combustion parameters on flame temperature and soot
concentration were investigated comparing with engine performance and the exhaust NOx and smoke concentrations. Parameters were engine speed, mean
effective pressure, fuel injection timing, suction air temperature and so on.
It was also shown that the proposed measuring technique was useful and effective for evaluating the combustion behavior in diesel engines, and an
improved trade-off relationship between NOx and particulate emission was
attained by an appropriate combination of timing retard and high pressure
injection.
Measures de la Combustion Diesel Par le Thermometre e Fibres Opt ique
RESUME
Pour reduire remission d'echappement tel que NOx et la fume des
moteurs diesel,
les processus de combustion inter-cylindrique ont
ete analyses experimentalement. Des essais ont ete entrepris pour analyser,surtout, la formation de la side et le prosessus d'oxydation. L'auteur a
propose des techniques nouvelles pour mesurer les comportements des
combustibles localement dans la chambre de combustion d'un moteur diesel
injection direct au moyen du thermometre e fibres optique dans la combinaison
avec deux types de light-pipe-sensor.
Les distributions temporelle et
spatiale de la temperature de la flamme et is concentration de la suie sont
mesurees avec precision d'une facon simple et facile en appliquant une
methode infra-rouge de deux couleurs.
Les influences de quelques parametres du combustion sur is temperature de is flamme et sur is concentration de la suie ont ete etudies en comparant
le fonctionnement du moteur, les gchappements NOx et is concentration de
fume. Les parametres sont is vitesse du moteur,
la pression moyenne
effective,
le chronometrage de l'injection du fuel,
la temperature
d'aspiration d'air et ainsi de suite. Ii a ete aussi demontre clue cette technique demesure propose etait utile et efficace pour
evaluer les comportements de is combustion dans les moteurs diesel et une relationd'echange amelioree entre NOx et les emissions particuliers
keit
atteint parune combinaison du reglage du retard et de l'injection adequate sous forte
pression. NOMENCLATURE be Ds or Smoke Dry Soot dB/de dO/de NB NOx Particulate Pcomb Pm.. PNmax Ps q. SOF Tc2 Te Ts V11 ft 0 or CA 0
Specific fuel consumption rate (g/kWh or g/PSh)
Smoke densj.ty (Bocsh)
Dry soot in particulate (mg/Ne)
Fuel injection rate (mg/deg) Rate of heat release (J/deg)
Rotational speed of turbocharger (rpm)
Nitrogen oxides concentration (ppm or g/PSh)
Particulate concentration (mg/Nm3 or g/PSh) Combustion pressure (bar)
Maximum combustion pressure (bar) Maximum fuel injection pressure (bar)
Suction air pressure at engine inlet (bar) Specific air consumption rate (kg/PSh)
Soluble organic fraction in particulafe (mg/Ne) Cooling water temperature at engine inlet
( C)
Exhaust gas temperaturecc
)Suction air temperature ( re )
Needle valve lift (mm) Crank angke (deg)
Fuel injection timing (deg of CA)
: : : A : : :
1. INTRODUCTION
Numerous studies in the past have been focused on evaluation of the
performance and durability of diesel engines. At the present, the extremely low levels of exhaust emissions such as smoke and nitrogen oxides #(N0x) are required without deteriorating engine performance not only in the land plant diesel engine but also in the marine diesel engine. Particularly with regard
to emission control, it is necessary to obtain more fundamental knowledges of
the diesel combustion process because NOx formation and soot formation and
oxidation are influenced by temperature, pressure, fuel/air ratio and time.
Matsui, et al. [1] examined the diesel combustion process in detail by
the both visible and infrared two-color methods. Furthermore. Van & Borman[2]
also tried to get a good accuracy of the two-color method by improving a device of the radiant energy sensor. Nagase & Funatsu[3] have proposed the multi-color method in which flame temperature is estimated from more than three wavelengths of the radiant energy. Recently Mohammad & Borman[4] and
Dresen-Rausch[5] measured the local flame temperature and soot concentration at many points simultaneously using plural sensors. In all those cases, the
sensor was too big to insert into the combustion chamber. It should be,
therefore, installed outside of the combustion chamber wall to prevent
disturbance and a special device was required to avoid contamination of the
sensor top surface.
The authors have proposed here new technique for measuring the
combustion behavior locally and accurately. It is a simple and easy procedure by means of the optical fiber thermometer with the light-pipe sensor made of a small sapphire rod. The infrared two-color method was applied for real time measurement of flame temperature and soot concentration. One technique is to
utilize two types of light-pipe sensor which has the different observation
space respectively. The other is to vary the measuring space only by rotating
the axis of the beveled-edge type light-pipe sensor.
Ahead of the first stage of experiment, the sensor characteristics were checked on their view angle, which were about J:10 degrees in both sensors.
Also the influence of sensor contamination due to combustion on the OFT output was examined and an appropriate correction method was applied for
compensation of the decreased OFT output.
Cyclic variation of combustion was measured and compared in two types of
sensor respectively. The temporal and spatial distributions of flame
temperature and soot concentration were measured by the beveled-edge type
sensor in the several measuring spaces which cover almost the whole region of
a DI diesel engine combustion chamber. At the second stage of experiment, influences of engine speed, mean effective pressure, injection timing and suction air temperature were investigated on the flame temperature and the soot concentration, and those were compared with the engine performance,
especially with NOx concentration and smoke density measured in the exhaust
gas. At the final stage, a lower level of the trade-off relationship between
NOx and particulate was attained in a DI diesel engine by means of an
appropriate combination of timing retard and high pressure injection which
2.1 Temperature Measuring System
Test engine shown in Fig.1 was a four-cylindered high-speed turbocharged
direct injection diesel engine with the intercooler system; 4D31-T type
manufactured by Mitsubishi Motors Corporation; a bore of 100mm, a stroke of
105mm and a maximum output of 95.6kW(130PS)/3500rpm. Test fuel was an
automotive diesel oil having a cetane index of about 60.
Figure 2 shows the configuration of the beveled-edge type light pipe.
sensor, which is a 1.27mm diameter smooth sapphire rod with its head inclined
50 degrees to the sensor rod. On the other hand, the flat-edge type light-pipe sensor has a top surface vertical to the sensor rod. The sensor was inserted into the combustion chamber utilizing the glow-plug hole of the engine. The temperature measuring system consists of the light-pipe sensor,
the optical fiber thermometer #(OFT) Model 100C manufactured by Accufiber Corp., the multi-channel combustion analyzer Model CB-466 by Ono Sokki Co.
Ltd. and a personal computer system as shown in Fig. 2.
Two infrared
wavelengths of 950 and 800nm were selected in this system for the two-color
method. The radiant energy of the two wavelengths detected by the OFT was
transmitted to the combustion analyzer as a couple of voltage output, and it was collected and recorded as data for every 0.25 degrees of the crank angle
on floppy disk. errY7
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2. TEST ENGINE AND' MEASURING SYSTEM
Sensor Personal Computer PC-9801 . . 177 Sensor
°silos! neer Cants
CO:C1:1 CID CEO rffl-r-1ocren7 co col cern co co
:
LEMMnclgiEffl'g: 41° actlikUritT e
Engine Analyzer 03-466Fig.1 Section of Test Engine Fi .2 Sensor Configuration and
Temperature Measuring System
I q OFT
Model 100C
Combustion Chamber use.
4
Soo,.,.
0.60 um/
0 i 2 4 5 6 7 8 ' 1 0 11 II ntensity0103W/m2pms) ,1 10. 1 II I, 3 4. ''S 6 7 B 9 10 095 pm Outpul(9) ii I Wavelength
a-
0.90 (Pm)0 0.95 (pm )
0.009m Output 1 0.95wn0u1pui P 095 100 l.05 2.2 Two-Color 'MethodThe calibration between the detector-output and the temperature is
usually done by a black body furnace, however the OFT system has a function which calculates the brightness temperature from the detector-output voltage.
Figure 3 shows the calibrated result between the OFT output and the intensity
of the radiant energy. And it also shows a completely linear relationship
for the respective wavelength where the correlation coefficient was 0.9999.
If the monochromatic emissivity of the flame is E (A ).the monochromatic radiance N( A,T ) of the flame is written as follows;
N(A,T ) = CI (A)
A5
eXP(C2/AT) 1 11-1= CI '"
A-5*
4 exp(C2/AT.) - 11-'
(1)where A is the wavelength (um), T is the absolute temperature, T. is the
brightness temperature and C/, C2 are Planck's radiation constants. In the
case of diesel flames,
E(A) is given by the following Hottel and
Broughton's empirical equation.
E CA) = I - expf - KL/Ac4; -(2)
where K is the absorption coefficient, L is the flame thickness in the
direction of observation and a is a constant; 0.95 is usually used for the infrared range[1]. Assuming to be equal KL for the selected two wavelengths
A L A 2, the true temperature T is calculated numerically from the two
measured brightness temperatures Tai. T32.
Fig.3 Relationship between the OFT Fig. 4 Estimated Error in the output and Radiant Intensity Infrared Two-Color Method'
-J 0 15 to 2400 2300 2200 2000 05 010 2
-Figure 4 shows the calculated flame temperature and XL value for a given OFT output voltage and also shows the estimated error range due to an error
in measurement. According to the estimated results, if there is an error
within± 5% in the difference between the two OFT output voltages,
thecalculation error is at most 70 17., or so. If the OFT output decreases 20%
because of contamination of the sensor top surface, the error is 30 °C.: or so.
These errors are much smaller than the measured temperature level, 2,300K. On the other hand, the XL value, which represents the soot concentration, changes
in proportion to the OFT output, so the contamination of the sensor top
surface leads to measurement error. For example, if the output decreases 20% due to contamination, the error becomes 20% or so. In the case whichincludes a 5% error in the difference of the voltage output, the error of theKL value
can be assumed to be 25% or so.
In order to maintain a good accuracy of measurement, the influence of sensor contamination on the OFT output was examined in detail and the OFT
output under the clean sensor surface condition was estimated from the results
calibrated before and after experiment. However, sensor contamination was
less in this method than other methods applied in the past because the sensor
leading edge was inserted into the combustion chamber and it was in the flame. 2.3 Measuring Space
Figure 5 shows variations of the OFT output due to incidence angle. In
this calibration, an approximate 0.3 mm diameter laser beam was used. (a)
shows the view angle of the flat-edge type,
(b)shows the yaw angle
characteristics of the beveled-edge type and (c) shows the pitch angle characteristics of the beveled-edge type. The direction of measuring space is
equal to the sensor rod axis in the case of the flat-edge type and it is vertical to the sensor rod in the case of the beveled-edge type. And the
measuring space is within about ±10 degrees in each case.
00
0
co00
o o o o o o00
o 0.40Oo o o o o o o o oo oo ca o o co o I IPt
1 1 1 -30 -20 -10 0 10 20 -20 -10 0 10 20 30View Angle (deg) Yaw Angle (deg) Pitch Angle (deg)
(a) Flat-Edge Type (la) Beveled-Edge Type (c) Beveled-Edge Type Fig.5 View Angle of the Light-Pipe Sensor
I 1 1 t -20 -10 0 10 20 100 7
a 50
70
1 0 If 1-I00
000
0Figure 6 shows configuration of combustion chamber of the test engine, measuring spaces which are indicated by hatching regions with the view angle
of ±10 degrees, and also shows five spray axes by solid lines with an arrow
from the five-hole nozzle. The sensor leading edge was inserted 1.7 mm below from the fire side of the cylinder head in the case of the flat-edge type and
7.0 mm below in the case of the beveled-edge type.
In Fig. 6(b), thebeveled-edge type sensor was rotated around the sensor axis every 40 degrees
from the reference direction No. 1 to No. 9. These nine measuring spaces
almost cover the entire combustion chamber. Especially one of five fuel spray
axes includes almost wholly in the reference measuring space No. 1.
3. EXPERIMENTAL RESULTS AND DISCUSSION
3.1 Temporal and Spatial Behavior of Combustion (1) Cyclic Variation of Combustion:
Figures 7(a) and (b) show cyclic variations of the OFT output and the
flame temperature measured by the flat-edge type and the beveled-edge type respectively, and the ensemble averaged cycle over 360 cycles was shown in
the figures. Cyclic variation in Fig.7(a) is significantly large because its
measuring space is quite local and includes only a part of the spray.
oioo
(a) Flat-Edge Type Sensor
Sensor
(b) Beveled-Edge Type sensor
Fig.6 Combustion Chamber Configuration and Measuring Space
Nozzle
o: E2400 a, W 2100 -LI-1800 111500 , 10 700 ICY 70
Speed 318Srpm ,Pme=8.30 bar
Einj=-11°, Ts = 45°C CA (deg) 3X0 C,
MIMIC=
=
=MEM
Min
=MEW=
=MEM
15X-40 50 W -10r TX MI 20 i 40 SO 60 CA' (deg)' (a) Flat-Edge Type Sensor (b) Beveled-Edge Type Sensor=
Fig. Cyclic Variation of Combustion
'On the other hand, cyclic variation in Fig.7(b) is smaller than that in Fig.7(a) and the onset point of the OFT output is significantly stable in any
cycle because one of five sprays is included wholly in its measuring space
No. 1. The cyclic variation of combustion might be caused by the temporal and
local variation of the turbulence scale in the combustion chamber due to a
complicated three dimensional flow with swirl and squish. k2) Local Behavior of Combustion:
Figures 8(a), (b) and (c) show the temporal and spatial distributions of the OFT output, the flame temperature and the KL value. These are measured in the nine measuring spaces and the ensemble averaged cycle over successive 360
cycles under the condition of engine speed of 3,185 rpm and mean effective
pressure of 8.3 bar.
The temperature field is almost uniform in the
combustion chamber but the KL value which represents soot concentration is
not uniform especially in the initial stage of combustion_
These phenomena are confirmed quantitatively in Figs. 9(a), (b) and (c)
which are separated into three characteristic groups which have a similar
history of the flame temperature and the KL value respectively. The
difference of combustion behavior among three groups seems to be dependent on the relative positions between the measuring space and the fuel spray
axis. That is, one of five spray axes is almost included in the spaces No. 1, B and 9 but none of them is in the spaces No. 5. 6 and 7. It is also assumed to be due to the relative position of the measuring space and the combustion;
chamber wall and the size of the measuring
space.-3000 2 700 10 Cycle Aye 360 10 6 2
10
Speed 3185rpm1 Pme=8.30 bar einj=-11%, Ts= 45°C
(a) OFT Output
-ID IOC AO 70 701 40 SO 61
CA (deg
Fig. 8 Two-dimensional Display of Combustion Behavior
Speed 3185rpm1 Pme='8.30 bar
Ginj = .110, Ts= 45°C
-10 TX '01 70 70 40 SO 60 CA (dell
(a) Spaces No. 11, 8, 9 (b) Spaces No. 2, 3, 4
b) Flame Temperature and KL value
44
0
0.
0
Fig.9 Local Characteristics of Combustion Behavior
(3) Beginning of Soot Formation:
The measured OFT output is based on strong radiant energy from soot particles. That is,
the onset point of the OFT output is equal
to thebeginning of soot formation, In general, the soot formation is said to he
I Space 5 -to MC 10 20 10 40 SO 60 CA (deg) (c) Spaces No. 5.6. 7 0 1.0 -\60 2W 2000 00 1.0 -1.0 0.5 0- 10 5 0 Sooce I Soace 1 2500 2000 1500 -MM -2000
dominant in the diffusion combustion process if the heat release rate curve is separated into two parts, that are, the premixed combustion period after ignition and the diffusion combustion period after the premixed one. Judging from the distributions of the flame temperature in Fig.9, the spike on the
temperature curve showing at the beginning of combustion is obviously the
radiant energy from the premixed combustion. It is, therefore, assumed that some soot particles are produced in the premixed combustion process because of a locally rich mixture in that process. Judging from that the spike form
temperature is temporal, the soot particles oxidize and disappear.
Figure 10 shows a correlation between the ignition point and the onset point of the OFT output measured in the space No.1 where the onset point was observed earliest among the nine measuring spaces. Ignition point was defined as the first zero-cross crank angle of the heat release rate curve. Judging
from Fig. 10, soot 'formation begins at a crank angle of about two degrees
after ignition under the wide engine operation condition: engine speed, 1,750
^41,1185 rpm, the brake mean effective pressure, 3.97,-4.30 bar.
3185 rpm
110 -5 TOC 5
Ignition Point (deg))
Fig. 10 Correlation between Ignition Timing and.
Onset Point of the OFT Output
3.2 CoMbustion Process and Exhaust Emission Level 1(1) Injection Timing Retard:
Figure 11(a) shows the flame temperature and the XL value measured in the
space No.1 and Fig. 11(b) shows engine performance when the injection timing was retarded from 11 to 5 deg.BTOC every two degrees without changing other
engine operational condition. The onset point of the OFT output delays and the flame temperature falls in both the maximum and the level in accordance
with the delay of injection timing. The maximum XL value increases with
timing retard, and the later the injection timing, the higher the XL value becomes at the end of combustion. This increasing tendency in the XL value at the end of combustion coincides with that of the exhaust smoke density. And
the decreasing tendency of the flame temperature level corresponds well to that of the exhaust NOx concentration_ Similar results have been shown in
other literatures.
2765 romi rorri
5a
U-0
Speed 3185 rpm, Pme=8.30 bar Ts 45C
7910C
5.13TDC
I. '
-10 MC 20 30
Speed 3185 rpmcGinj=-11° ,Ts=45°C
Fig. ¶1 Fuel Injection Timing Variation'
CA (deg), 8 800r KO-a. mr .5 51- 1CCO--800 600 4002-60 -0' 0
0 /la
.1a -10 ;11;fa
al .a 200 S 1180Er---
4 -1m einj(deg) (b) Engine Performancet
2
& p 600 8001 40ooO
t"..oi 120 9 3 15 100 2 011
I
5 .-. 2 a o 0 110 8 2- 15r Jo cY 1,L o
o o c;10600
2soo , 2 0-2 0.---.---.tC1.---100 00 r; 1000 2I
ZOOO 11' a a 800 1 d,a
z 600 Or---"---Cr---4-- -Z. 0 ZO ---000_,-.:.C.---C
/
1.0 co a .a ti 24 0,g
2
in 220 .54 al 200t
.a 180 /60 6126i 6.30 Prne(bar)i(a) Flame Temperature and' KL-value (b) Engine Performance
Fig. 12 Mean Effective Pressure Variation <3,185 rpm)
-10 TDC 10 20 30 40 50 SO
CA (deg)
4a) Flame Temperature and KL-value
40 50 601 3.97 120 100 80 a. 10 1.0 5-.. 0-5 10 Pme(bar) 8.30 6.26 3.97 0 10 -2500 2000 1500
°
-0 1 -1400 a -9 -7 -5 01.0-i.e
0.5
Speed 175Orpm Ainj=-10°,Tsa- 45°C
IF PmeAco I 8.30 6.26
-.
3-97 2000 ,± 500 4 1iL 0.
xx
°---°
TOO 2 1603 200 2500 1400 1 1200 g a moo o BOOZ
z 600 4W 0a
-1 t0I
Eot A. 4 180 JO 3 4 140 1 -10 TUC 10 20 30 40 50 60 197 6.26 8.30 CA (deg) iPrne(bar)(a) Flame Temperature and KL-value (t), Engine Performance
Fig. 13 Mean Effective Pressure Variation (1,750 'rpm)
Mean Effective Pressure Variation:
Figures 12 (a) and (b) show the measured flame temperature and' engine
performance respectively when the brake mean effective pressure Pme decreased from 8.30 to 3.97 bar while engine speed was kept constant at 3,185 rpm. And Figs. 13(a) and (b) show those in the case of engine speed of 1,750 rpm. In
accordance with decreasing Pme, fuel consumption rate and air consumption rate increase a lot and, on the other hand, NOx concentration and exhaust smoke density decrease. This corresponds well to decreases of the flame
temperature level and the KL value at the end of combustion. It is natural
that the flame temperature level drops due to increase of air consumption rate when Prim decreases. A significant difference under two engine speed
condition appears in the history curve of the KL value, that is, in Fig. 12(a)
the KL value increases temporarily during combustion when Pme decreases, on
the other hand,
there is no such temporal increase of the KL value in
Fig. 13(a). It might be caused by the time effect in reaction rates of soot
formation and oxidation.
Suction Air Temperature Variation:
Figures 14(a) and (b) show the measured results of the flame temperature
and engine performance when the suction air temperature was raised from 45
o 75
T...; by adjusting the cooling water flow-rate of the intercooler. Airconsumption rate decreases because the volumetric efficiency becomes worse,
therefore, fuel consumption rate, NOx concentration, exhaust smoke density and exhaust gas temperature increase a little. This corresponds to minor
increases of the flame temperature and the KL value at the end of combustion_
BO 60 mf
C}---0-_o
5 _ -g 0 ..Acr --0---0
]1.0 k 0 0. 10r-5 0 C. a 0 0 100 200-Speed 3185 rpm, Pme.8. 30bar, 8inj=-11° e o 17-0 17.. -E. .00 EL Jo ,....r., 1, 15[ o m 2500 7c 10 ... 2 o i600 ... o V
I400
200 )-2000 0,, 1200[ E U-1500 r.,o 800 2 Z 600 u 12.0 g .c -I 1. 0 tn 18010 0'
a o. Cil 160 a; .to i I 45 60 75 Ts(C )(a) Flame Temperature and KL-value (b) Engine Performance
Fig. 14 Suction Air Temperature Variation
3.3 Simultaneous Reduction of NOx and Smoke
Effect of Injection Pressure:
In order to investigate the effect of fuel injection pressure, three fuel
injection pumps were used in this test. In those pumps, the constant pressure delivery valve was adopted to avoid the secondary injection, and cam velocity
was increased in the pump type VE2 by 19% and in the pump type VE3 by 38% compared to the standard pump type VE1 while the plunger diameter was the
same 12mm in three pumps. In the combustion test, particulate emission was measured by means of the mini-dilution tunnel[61.
Figure 15(a) shows fuel consumption rate and the concentrations of
exhaust emissions such as NOx, smoke, total particulate, dry soot and SOF.
Figure 15(b) shows the histories of combustion pressure, heat release rate
and fuel injection rate for the three pumps. In accordance with increasing
injection pressure, fuel consumption rate, smoke density and particulate
emissions decreased because of decreases in the fuel injection duration and the combustion period. It is clear that better atomization leads to better combustion_ However, NOx increased significantly because of increase in the
premixed combustion quantity due to increase of the initial injection rate. Effect of Nozzle Hole Diameter:
Figures 16(a) and (b) show the exhaust emission concentration and the combustion history when the nozzle hole diameter was reduced from 0.30mm
(type A) to 0.24mm (type D). Particulate emission has a tendency to decrease
gradually in accordance with reducing nozzle hole diameter, however, NOx and smoke show the maximum temporarily at the nozzle type B (0.28 mm dia.). Two factors are assumed for the effect of nozzle hole diameter reduction; one is
the effect of reducing NOx due to decrease of the initial fuel injection
0 -o -1 120 o .o -,-, a Jim E m 0 0 10 I Ts (C 3 I 45
---I
50 I 75 2 5 -1.0 0.5 0 I I i ! I -10 TDC 10 20 30 40 SO 60 CA (deg) a E2
rate and the other is the effect
of
increasing NOx due to better atomizationand better mixture formation. It is clearly shown in Fig. 16(b) that even
though the injection duration increased by reducing the nozzle hole diameter,
the premixed combustion quantity decreased and combustion period changed
little. According to Fig 16, simultaneous reduction of NOx and particulate
can be attained by an appropriate combination of nozzle and pump.
tn, a_ sal 180r 1701-1.0[ 0 180[ 170 2 0 10[ 0
ccc
10
40 320 10 0(a) Exhaust Emission (b) Combustion History
Speed 3185rpm, Pme=8.30 bar
einj.-11°,Pump Type VE2
0---0---0----0
Fig. 15 Effect of Fuel Injection Pressure
C SOF 250 ]240 230 -1400 1 1300 1200 100 a 000 g 900 BOO E 5
]
250 260 230 11-11200 1100 a 1000 x goo!fE]=="14
130 20 10 0 a 130 120 110 100 .`"?"so 880 a 70 60 so 130 120 110 100 90 eel SO 50 1. 2 Speed 3185rpm, Pme=8.30bar einj,-.-11° , Nozzle Type APump Type VEI Type VE2 Type VE3 1100
50;
a 0 064 0.75 057 100 -20 -10 TOC 10 20 30Area Ratio CA (deg)
(a) Exhaust Emission (b) Combustion History
Fig. 16 Effect of Nozzle Hole Diameter
I 1 1 10 20 X) CA (deg) -10 -20 VE I VE2 YE)
Type of Injection Pump
NO ') Dry Soot 2 .0 4 71, -0 o TDC
Speed 3185 rpm . Pme=8.30 bar
Nozzfe Typek3 , Pump Type VE 3
2
iscr o__o__o__o
r
o 1 uo "En 1.7 1701_no 2
41 0 tn -9-
-7 -5 igirli(deg) MO 1200 MO OM MO MO 700 -600 a 0. 0.3 0.1 / 0 0 2 4 6 B 10 NOx(g/ P 5 h) 11 Fig. 17 Effect of Fuel Injection fig: 18 An Improved Trade-offTiming Relationship
Effect of Timing Retard:
Figure 17 shows changes of the fuel consumption rate and the exhaust
emission concentration due to timing retard in the improved fuel system of
the pump type VE3 and the nozzle type B. It is clearly shown that more
significant NOx reduction rate is obtained in comparison with the case shown in Fig. 11(b) whereas fuel consumption and particulate increase a little due
to timing retard.
Improved Trade-off Relationship between NOx and Particulate:
Figure 18 shows the trade-off relationship between NOx and particulate emission. Open circle marks indicate data obtained under the fuel injection
pump variation test and open triangles indicate data under the nozzle hole
diameter variation test and open squares indicate data under the injection timing variation test of the improved fuel injection system shown in Fig. 17;
in which a high injection pressure up to 900 bar was obtained by mean of the increased, cam velocity, the decreased nozzle hole diameter and the constant pressure delivery valve. By a combination of appropriate timing retard and a
high pressure injection, the lower level of the trade-off relationship
between NOx and particulate were attained.
8. CONCLUSIONS,
The authors have proposed new technique for measuring combustion
behavior locally in a DI diesel engine combustion chamber by means of an
optical fiber thermometer. Applying the infrared two-color method, temporal
and spatial behavior of combustion was made clear and the changes in
combustion temperature and soot concentration were measured and compared with'
1
20 10 0-9
1991 Limit -, 0.2 0 1 1994 Limit I-the exhaust emission levels in -the combustion test where parameters such as engine speed, mean effective pressure, fuel injection timing and suction air temperature were varied. And the authors have tried to attain the lower level of the trade-off relationship between NOx and particulate by improving fuel
injection system. Main results obtained in the present experiments are as
follows:
Cyclic variation of combustion differs significantly from space to
space in the combustion chamber; it might be caused by the temporal and
spatial difference of turbulence scale.
Flame temperature varies a little locally, however, soot concentration
changes considerably in a DI diesel engine combustion chamber especially at
the initial stage of combustion.
The soot formation process begins within the premixed combustion duration at a crank angle about two degrees after ignition under the wide
engine operation condition.
It was clearly shown by the OFT measurement that the exhaust smoke
density is dependent on the soot concentration at the end of combustion
process, and the exhaust NOx concentration is dependent on the flame
temperature level in the combustion process.
An improved trade-off relationship between NOx and particulate emission was attained by an appropriate combination of timing retard and a
high pressure injection.
ACKNOWLEDGMENTS
The authors would like to express their thanks to Mr. S. Kubota in
Nippon Mining Co. Ltd., Mr. H. Kondo in Daihatsu Diesel Co. Ltd., Mr. F. Yoshizu in ZEXEL Corporation, Mr. T. Maeda in Ono Sokki Co. Ltd. and to whom
it concerns in Mitsubishi Motors Corporation and Mazda Foundation for their assistance and kindness. All the experimental works were done by the authors'
colleagues in Nagasaki University and Nagasaki Institute of Applied Science.
REFERENCES
Matsui, Y. et al., SAE Paper No.800970(1980)
Yen, J., and Borman, G. SAE Paper No.891901(1989)
Nagase, K., and Funatsu, K., SAE Paper No.901615(1990)
Mohammad, I. S., and BormEm, G. L., SAE Paper No. 910728(1991)
Dresen-Rausch, J., et al., 19th CIMAC Paper No. D19(1991)
Maeda, T., et al., 18th CIMAC Paper No.D79(1989)
