=Paper=
{{Paper
|id=Vol-452/paper-31
|storemode=property
|title=Experimental Analysis of the effect of very early pilot injection on pollutant formation for a PCCI Diesel engine
|pdfUrl=https://ceur-ws.org/Vol-452/poster11.pdf
|volume=Vol-452
}}
==Experimental Analysis of the effect of very early pilot injection on pollutant formation for a PCCI Diesel engine==
https://ceur-ws.org/Vol-452/poster11.pdf
Experimental Analysis of the effect of very early pilot injection
on pollutant formation for a PCCI Diesel engine
A. Vanegas, N. Peters
Institut für Technische Verbrennung
RWTH Aachen University, Aachen, Germany
In the present work, the influence of a very early pilot injection on pollutant formation was investigated in
a Common-Rail DI Diesel engine. The engine was operated at conventional part-load conditions at 2000
rpm, an EGR variation was done and the injected fuel mass was 15 mm^3/cycle. The Nozzle type were
conical and flow optimized geometries (ks nozzle) with hole diameters of 0.141 mm, length of hole of
1mm and the Spray Cone Angles were 148° and 120°
Introduction a Common-Rail DI Diesel engine was carried out
In Common-Rail DI Diesel Engines, a low on a production-type GM FIAT 1.9 l CDTI ECOTEC
combustion temperature process is considered as Diesel engine. The 4-cylinder engine utilizes a
one of the most important possibilities to achieve Common-Rail fuel injection system, variable ge-
very small emissions and optimum performance. ometry turbocharger (VGT), an exhaust gas recir-
To reduce NOx and Soot strongly, it is necessary culation system, and an intake throttle valve. The
to achieve a homogenization of the mixture in or- engine has four valves per cylinder, centrally lo-
der to avoid the higher local temperatures which cated injectors, and a re-entrant type combustion
are responsible for the NOx formation [1]. Through chamber. All relevant engine data are given in
the homogenization it is also possible to obtain a Table 1. The mounting of the engine on the test
stoichiometric air-fuel ratio in order to significantly bench is shown in Fig. 1. The production of this
reduce the Soot emissions. One way to achieve engine is certified to meet EURO IV emission
this homogeneous condition is to start injection standards.
very early together with the use of higher EGR
rates. The direct effect of these conditions cause a DI, 4-cylinder,
Engine Type
longer ignition delay (this is the time between start charged, 4-stroke
of the injection and auto-ignition during physical Bore [mm] 82.0
and chemical sub processes such as fuel atomiza- Stroke [mm] 90.4
tion, evaporation, fuel air mixing and chemical pre-
3
Displacement [cm ] 1900
reactions take place) so that the mixture formation
has more time to achieve a homogeneous state. Compression Ratio 18.3
However there are some problems that must be Combustion Chamber Re-entrant type
solved before this concept can be use completely.
Max. Power [kW (PS)] 110 (150) @4000rpm
The first problem consists on the higher production
-1
of HC and CO emissions, due to spray is impinging Max. Torque (Nm / min ) 320 / 2000-2750
onto the wall surface. The second problem con- Injection System Bosch Common Rail
sists on the position of the combustion phasing,
Max. Rail Pressure [bar] 1600 bar
which take place before the top death center and
this situation influences negatively the engine effi- Nozzle hole diameter [mm] 0.141
ciency. Therefore is necessary to develop many Injector Nozzle 7 holes
strategies in order to solve mainly these two prob- 3
Hydraulic flow rate [cm
lems. [2]. In Previous Works was found optimal (30s) at 100 bar]
440
spray cone angle and piston bowl geometry, now
this work try to find an optimal injection strategy.
Table 1. Engine specifications and injection sys
tem specifications
Experimental Setup and Measurement Tech-
niques
The experimental investigation of the effect of
a very early pilot injection on pollutant formation in
along with an EGR valve. An intake throttle valve
supports high flow rates of exhaust gas recircula-
tion. According to conditioning modules for engine
testing, the following applications were used:
- Intake Air Conditioning - Fuel Conditioning and
Measurement - Engine Oil Conditioning and
Engine Coolant Conditioning.
The air-flow rate was measured using a laminar
flow element. AVL 733, a dynamic fuel meter, was
used for fuel metering. An air-conditioning system
determined and maintained the preset temperature
and pressure of the intake air. Pressure data was
collected for one cylinder. Measured emission data
included smoke number, NOX, HC, and CO. AVL
415, a variable sampling smoke meter, provided
exhaust smoke levels. An engine dynamometer
(AC/DC type) was used to measure engine torque.
The measuring equipment used in the experiments
Figure 1. Engine test bench
is summarized in Table 3.
The engine is equipped with a second-generation
Advance Options Ana-
Bosch Common-Rail injection system that was CO, CO2
lysatormodul Magnos 16
used for all experiments reported in this study. ECO Physics CLD 700
NOX
Regular Diesel fuel was used in the experiments. A EL ht
Advance Options FID-
summary of the most important properties of the HC Analysatormodul Multi-
used Diesel fuel is shown in Table 2. FID 14 (THC C3)
Variable Sampling
Particulate matter
Smoke Meter AVL 415
Fuel AVL 733
Cetane number 53.6
Density at 288K
834.2
(kg/m3) Table 3: Emission and fuel consumption measur-
Viscosity at 313K ing equipment
2.892
(mm2/s)
Distillation T 50% (K) 539.7 A Bosch-type flow bench [3, 4] was used to meas-
ure the fuel injection rate. Fuel is injected into a
Distillation T 95% (K) 619.0 tube of constant diameter and known length, filled
Sulphur (mg/kg- with liquid fuel. Then, a pressure wave propagates
9.0
fuel) through the tube and provides a signal which is
Lower Heating detected by a Kistler piezo electric pressure trans-
43.163
Value (MJ/kg-fuel) ducer (type 70061B) mounted close to the nozzle
exit. This signal correlates to the instantaneous
Table 2. Fuel properties injection flow-rate. The Piezo signal, fuel delivery
pipe pressure, injector energizing time, injector
A Common-Rail fuel system allows for vari- current, and voltage are measured with a fast data
able pressures (up to 1600 bar), timing, and num- acquisition system (sample = 30 kHz, IMTEC com-
bers of injections. Second-generation Bosch injec- pany). All measurements are carried out over 2000
tor systems allow for up to five injections (for ex- single injection events, where the injected fuel is
ample, two pilot, one main, and two post injections) collected and weighted. The measured pressure
per cycle. VGTs have flexible vanes, which move wave signal is calibrated by the time-integral of the
and let more air into the engine, depending on the signal which is equal to the averaged injected fuel
load. This technology increases both performance mass per injection. From a comparison of the in-
and fuel economy. Turbo lag is reduced, as the jection rate and the current signal, the injection
turbo impeller inertia is compensated using VGT delay and duration can be derived.
spray cone angle 148 and 120 are showed in the
figure 3 and 4.
Description of experiments
The investigations were carried out for a conven-
tional medium-load point at 2000 rpm, a fuel
amount of 15 mm^3/cycle, an external EGR rate
variation and 700 bar rail pressure.
In order to get a reference point in the first experi-
ment the fuel mass of 15 mm^3/cycle was injected
via a single injection. Secondly, 1/15 of the total
fuel mass was pre-injected at a distance (dSOI) of
the 70 CA deg respect to the SOI main injection or
80 deg. BTDC, in this case the fuel mass of the
main injection was 14 mm^3/cycle and Thirdly, a
pilot injection was done 60 deg. BTDC also with a
mass fuel of 1 mm^3/cycle and a Main injection
with 14 mm^3/cycle. See figure 2 Figure 3. Soot and NOx emissions for SCA 148°.
At a SOI pilot injection by 60 deg. BDTC the Soot
and NOx emissions were reduced in comparison to
the single injection event, for the second case with
SOI 80 deg. BTDC the situation was similar. If the
Soot emissions of this experiment with the SCA
148 are compared to the SCA 120 results is possi-
ble to see that the Soot and NOx emissions in-
crease due at the higher temperatures resultants
of a better quality of the combustion. In the figure 4
is showed that the Soot emissions are reduced by
using a pilot injection at 80 deg. BTDC in compari-
son to the single event. These results could be
mean that through the pilot injection the mixture
Figure 2: Duration between the starts of two injec- formation is more homogeneous with respect to
tions the single injection.
All experiments were carried out first with the spray
cone angle 148° and the same experiments also
were done with the spray cone angle 120°. See
Figure 3.
Figure 3. Spray Cone Angle Variation
Figure 4. Soot and NOx emissions for SCA 120°.
Results and Discussion For the pilot injection events the HC and CO emis-
sions are increased. These results were expected
This work was only experimental but numerical because at very early injection times like 60 or 80
support is expected. A very early pilot injection has deg. BTDC the pressure, temperature and density
the intention to prepare good conditions for the in the combustion chamber are very lower and
combustion. The Soot and NOx emissions for the therefore the spray penetration is longer, that
means, the fuel spray is impinging on the cylinder- Due a better quality of the combustion the HC and
wall. In the figure 5 and 6 the HC and CO emis- CO are lower but unfortunately the NOx emission
sions are showed for a SCA 148°. increases due at the high temperature. In relation-
ship to the pilot events there are not advantages
with respect to the HC and CO emissions.
Figure 5. HC and NOx emissions for SCA 148°
Figure 8. CO and NOx emissions for SCA 120°
For the nozzle with the SCA 148° the IMEP is for
the single injection the largest. That means, the
fuel consumption is higher for the cases with pilot
events. This is a consequence that the spray of the
pilot injections is impinging on the cylinder walls. In
the figure 9 is showed the IMEP versus NOx for
the SCA 148.
Figure 6. CO and NOx emissions for SCA 148°
However the HC and CO emissions for the SCA
120 are decreased with respect to the SCA 148°.
See figure 7 and 8.
Figure 9. IMEP and NOx emissions for SCA 148°
For the nozzle with SCA 120 the IMEP for the sin-
gle injection event is similar to the experiment with
the SCA 148. However, the pilot injection at 60 deg.
BTDC showed a similar value of IMEP in compari-
son to the single injection.
Figure 7. HC and NOx emissions for SCA 120°
Summary and Conclusions
An optimal injection strategy is necessary in order
to reduce the NOx, Soot, HC and CO emissions
and to move the combustion phasing after the top
death center. Therefore is necessary to do a lot of
experiments using different start of injection times
for the main- and pilot injections in order to find the
optimal.
Use of a very early pilot injection reduces mainly
the Soot and NOx emissions but increase the HC
and CO emissions.
A drastic reduction of HC and CO is possible by
using of one smaller Spray Cone Angle.
References
[1] Merker, G., Schwarz, C., Stiesch, Otto, F.
“Verbrennungsmotoren“ , 2004.
[2] H. Won, A. Vanegas, “Experimental Study of
HC Emissions Using Narrow Spray Cone An-
gles and Different Surrogate Fuels in Low
Temperature Diesel Combustion Systems
FISITA 2008 World Automotive Congress,
September 2008 Munich Germany.
[3] Bosch, W., ”Der Einspritzgesetzindikator – ein
neues Messgerät zur direkten Bestimmung
des Einspritzgesetzes von Einzeleinspritzun-
gen”, MTZ-Motortechnische Zeitschrift, 25(7),
1964
[4] Smith, W. J., and Timoney, D. J., “Fuel Injec
tion Rate Analysis - A New Diagnostic Tool for
Combustion Research”, Paper No. SAE
92224, 1992.