Agarwal2013

Effect of fuel injection pressure on diesel particulate size and number distribution
in a CRDI single cylinder research engine
Avinash Kumar Agarwal ⇑
, Atul Dhar, Dhananjay Kumar Srivastava, Rakesh Kumar Maurya,
Akhilendra Pratap Singh
Engine Research Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India
h i g h l i g h t s
" Particulates were investigated in a research engine at varying fuel injection pressures and timings.
" Particulate number concentration in the exhaust increases with increasing engine load.
" Increasing Pinj reduces the number and mass of particulates at all loads.
" At higher Pinj, advancing the injection timing reduces the particulate number concentration.
" Particulate surface area and volume distribution increases with load and decreases with increasing Pinj.
a r t i c l e i n f o
Article history:
Received 9 January 2012
Received in revised form 9 May 2012
Accepted 30 January 2013
Available online 14 February 2013
Keywords:
Diesel exhaust particulate
Size–number distribution
Gravimetric emissions
Fuel injection pressure
Injection strategies
a b s t r a c t
Particulate and NOx emissions from diesel engine are the biggest challenges faced in making diesel
engines environmentally benign. Measures adopted for reducing gravimetric particulate emission to
meet the prevailing emission regulations necessarily always do not reduce particulate number concentra-
tion, which has profound adverse health effects. Therefore it is important to investigate effect of fuel
injection parameters, especially fuel injection pressure and start of injection timings on particulate size
and number distribution in diesel exhaust. In the present study, a single cylinder research engine is used
for experimental assessment of the effects of fuel injection strategies and start of fuel injection timing on
particulate size–number, surface area, and volume concentration distributions by using engine exhaust
particulate sizer (EEPS) spectrometer. Investigations have been conducted at three different fuel injection
pressures (300, 500, 750 bar) and four different start of injection timings. The experimental data indicates
that the particulate size–number concentration increases with increasing engine load (BMEP) and it
reduces with increasing fuel injection pressure.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
A large number of diesel engines are used as power plants for
mobility as well as stationary applications due to their excellent
fuel economy and robustness. However they suffer with the
drawbacks of higher particulate and NOx emissions and trade-off
between them. Mass of particulate emitted from diesel engines is
generally 10–100 times higher than SI engines [1–3]. Diesel partic-
ulates are of grave concern from engine performance, durability as
well as harmful environmental and health impact standpoint.
Higher particulate formation and emission results in reduced fuel
economy due to incomplete combustion. Interaction of these
particulate with engine components results in increased engine
wear. Environmental effects of diesel particulates are poor visibil-
ity, soiling of buildings and adverse health effects on humans, live-
stock, etc. These effects are inﬂuenced greatly by the particulate
size distribution e.g. smaller particulates are more harmful for hu-
man health (due to their larger surface to volume ratio) however
they do not adversely impact visibility. While attempting the en-
gine calibration/ mapping, one is required to consider particulate
number–size distribution as well, along with particulate mass
emission to meet the emission norms of immediate future. Preva-
lent emission regulations globally limit emission of particulate
mass in terms of grams per kilometer (g/km) or grams per kilo-
watt-hour (g/kW h) and they do not take into account the particu-
late size and number distribution as of now. There are several
methods/techniques/after-treatment systems used for reducing
the particulate mass emission such as increasing fuel injection
pressures, variable geometry turbochargers and diesel particulate
0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.fuel.2013.01.077
⇑ Corresponding author. Tel.: +91 512 259 7982; fax: +91 512 259 7408.
E-mail address: akag@iitk.ac.in (A.K. Agarwal).
Fuel 107 (2013) 84–89
Contents lists available at SciVerse ScienceDirect
Fuel
journal homepage: www.elsevier.com/locate/fuel

Fig. 1. Schematic of the experimental setup.
Fig. 2. Particulate size–number distribution with varying fuel injection pressure and start of injection timing.
A.K. Agarwal et al. / Fuel 107 (2013) 84–89 85

filters. However, sometimes these techniques tend to increase
particulate numbers by reducing their size in an effort to control
particulate mass emission, which may turn out to be more harmful
for human health, inspite of significant reduction in particulate
mass emissions [4,5]. Effectiveness of after-treatment technologies
as well as in-cylinder technologies like fuel injection parameters,
turbocharging, EGR, etc. in reducing particulate size-number
distribution needs to be experimentally investigated.
Diesel exhaust particulates can be completely characterized by
gravimetric measurements, particle size–number distribution, par-
ticle surface area–size distribution, particle volume/mass–size dis-
tribution, soluble organic fraction, elemental carbon fraction, total
carbon fraction, trace metals, PAH concentration, etc. [6–12]. Diesel
oxidation catalyst (DOC) causes the number concentration of par-
ticles under 30 nm diameter to significantly increase with
500 ppm sulfur diesel, however the number of the particles in
the same size range didn’t increase with 12 ppm sulfur diesel [5].
On the other hand, surface functionalised activated carbon fiber
based filter used in the exhaust reduces the particulate number
concentration significantly [13]. Particulate number concentration
decreased with increasing concentration of diesel–diethyl-adipate
in the blends and this number concentration was further decreased
by DOC [14]. Agarwal et al. reported increase in particle number
concentration at lower engine load and reduction at higher engine
load with addition of 20% biodiesel to the mineral diesel [15].
Number concentration has been reported to increase with biodie-
sel concentration with respect to mineral diesel in the test fuel
[16,17]. Harris and Maricq reported increase in particulate number
concentration and shifting of peak concentration towards larger
diameter with increasing EGR [18]. As the fuel injection pressure
increases, the number of nano-particles ranging from 10–60 nm
diameter increases while the number of the relatively large parti-
cles decreases [5]. Millo et al. investigated the particulate forma-
tion during DPF regeneration [19]. They performed experiments
with biodiesel using a Euro 5 common rail automotive diesel en-
gine, during both normal operating mode and DPF regeneration
mode. They suggested that under normal operating mode, particu-
late number-size and mass-size distributions with biodiesel were
similar to conventional fuels, while in regeneration mode, particle
numbers increase by an order of magnitude, with a substantial
shift in the number distribution peak towards larger diameters
[19].
Reduction of particulate formation inside the combustion
chamber is preferred because it enhances the fuel efficiency
slightly by re-burning the particles formed, in comparison to ex-
haust gas after-treatment approach. Changing the fuel composi-
tion, EGR and optimization of fuel injection strategies are the
most commonly used methods for in-cylinder particulate mass
control. Very few studies have been conducted to investigate the
effect of fuel injection pressure on real time particulate size–num-
ber distribution. Therefore in this study, effect of fuel injection
strategies on particle number–size distribution is experimentally
investigated for varying fuel injection pressure and injection tim-
ings in a state-of-the-art single cylinder research engine.
2. Experimental setup
For this experiment, a single cylinder research engine (AVL,
5402) equipped with a modern common rail direct injection sys-
tem coupled to a transient AC dynamometer was used. Detailed
technical specifications of the test engine are given in Table 1.
The experimental setup was equipped with fuel conditioning,
lubricating oil conditioning and coolant condition systems for con-
ducting investigations under controlled environment. This experi-
mental facility has provision for control and measurement of fuel
injection pressure, injection timings, and injection duration. The
engine was coupled with an AC transient dynamometer (Wittur
Electric Drives, 2SB 3), state-of-the-art intake air measurement
system (ABB Automation, Sensyflow P), and gravimetric fuel flow
meter (AVL, 733S.18) for performing various tests. Detailed sche-
matic of the experimental setup is shown in Fig. 1.
For particulate size–number characterization, Engine Exhaust
Particle Sizer™ Spectrometer (EEPS) (TSI Inc., EEPS3090) was used.
Table 1
Detailed technical specifications of the test engine.
Engine parameter Specifications
Engine type AVL 5402
Number of cylinders 1
Cylinder bore/stroke 85/90 mm
Swept volume 510.7 cc
Compression ratio 17.5
Inlet ports Tangential and swirl inlet port
Maximum power 6 kW
Rated speed 4200 rpm
Fuel injection pressure 200–1400 bar
Fuel injection system Common rail direct injection
High pressure system Common rail CP4.1 BOSCH
Engine management system AVL-RPEMS + ETK7 BOSCH
Valves per cylinder 4 (2 inlet, 2 exhaust)
Valve train type DOHC cam follower
Fig. 3. Total particulate concentration with varying fuel injection pressure and start
of injection timing.
86 A.K. Agarwal et al. / Fuel 107 (2013) 84–89

This instrument can measure particle sizes ranging from 5.6–
560 nm with a maximum concentration of 108
particles/cm3
of
exhaust. It has sizing resolution of 16 channels per decade com-
prising of total 32 channels. Number concentration of particulates
in the raw engine exhaust was higher than the maximum measur-
ing range of the EEPS hence the exhaust is diluted by sheath air
(560 times for the present investigations) using a rotating disk ther-
mo-diluter (Matter Engineering AG, MD19-2E). Concentration of
the particulates in the diluted exhaust was measured and concen-
tration in engine out exhaust was calculated by multiplying the
measured concentrations in diluted exhaust by the dilution factor.
EEPS spectrometer performs the particle size classiﬁcation based
on differential electrical mobility of particles of different sizes. For
each data set, measurements were done for 1 min at a frequency
of 1 Hz. Particle size–number distribution data presentenced in
the graphs shown in the results and discussion section are average
of these 60 measurements taken and the error bars shown corre-
spond to the standard deviation of the experimental data.
3. Results and discussion
Particulate size–number distributions were measured at vari-
ous engine loads (1.4, 2.8 and 3.6 bar BMEP) for varying fuel injec-
tion pressures (300, 500 and 750 bar). Start of injection was varied
from 9.375° BTDC to 0.375° BTDC. Particulate size–number distri-
bution was measured after thermal stabilization of the engine at
each test condition. Fig. 2 shows the variation of particulate num-
ber concentration at these three fuel injection pressures and four
different ‘start of injection’ timings at three different engine load
conditions.
Particle number concentration increases with increasing engine
load at fuel injection pressures and all injection timings. With
increasing engine load, air/fuel ratio decreases and fuel-rich condi-
tions favor soot formation and agglomeration. This trend was also
reported by Zhu et al., Virtanen et al. and Mathis et al. [16,20,21].
With increasing engine load, peak of highest particle concentration
shifts towards higher size, which conﬁrms that these conditions
are also more favorable for agglomeration of particulates formed.
At lower engine load and relatively lower fuel injection pressures,
particulate number concentrations are lowest at retarded injection
timings and this number concentration increases with advanced
injection timings. With increasing fuel injection pressures, total
particulate number concentration in the exhaust decreases due
to better mixing of air and fuel (Fig. 3). At higher engine loads,
advancing fuel injection timing reduces the total particulate num-
ber concentration. Minimum particulate concentration was ob-
served at 750 bar fuel injection pressure at 9.375° BTDC ‘start of
Fig. 4. Particulate surface area distribution with varying injection pressure and start of injection timing.

injection’ timing. At lower injection pressures, in-cylinder pressure
and temperature are very critical for fuel atomization and air fuel
mixing. If fuel is injected at higher in-cylinder pressures (i.e. re-
tarded injection timings), smaller fuel droplets are formed due to
improved atomization. Process of air–fuel mixing also depends
on time available for fuel droplets to mix with surrounding air after
atomization and before start of combustion. The available time for
atomized fuel droplet to mix with surrounding air increases with
advanced fuel injection however fuel droplet size also increases
simultaneously due to lower in-cylinder temperature and pressure
at the time of fuel injection. These two counter effects affect the
particulate formation in mutually opposite directions. At 300 bar
fuel injection pressure, particulate number concentration ﬁrst in-
creases with retarding the injection timings then decreases due
to combined effect of these two factors mentioned above.
Particle surface area was calculated by assuming exhaust par-
ticulates to be perfectly spherical.
ds ¼ dN Á pD2
p
where ds is the area concentration of size range with mean diameter
Dp and dN is the number concentration of particulates. Particulate
surface area distribution with size is more directly related to the
toxic potential of particulate as it is a measure of active sites avail-
able for adsorption of volatile hydrocarbon fractions and PAHs.
These species are largely toxic species. Particulate surface area dis-
tribution is also an indicator of effectiveness of interaction of partic-
ulates with respiratory system of living beings, which in-turn
determines their effect on the health. Surface area distribution of
the exhaust particulates increases with increasing engine load. This
trend is similar to the one observed for particulate number-size dis-
tribution. Particulate surface area concentration was found to be
decreasing with advanced fuel injection timing at 500 and 750 bar
fuel injection pressures (Fig. 4). It can be observed from Fig. 4 that
with increasing fuel injection pressure, peak of area distribution
curve shifts towards relatively smaller particles while height of sur-
face area peak decreases. Increasing the fuel injection pressure re-
sults in improved mixing of fuel droplets with surrounding air,
which results in lower number concentration of particulates and
formation of smaller particulates. Advancing the fuel injection tim-
ing increases the time available for oxidation of particulates formed
inside the combustion chamber, which reduces the surface area
concentration of the particulates [21].
Particulate volume/mass distribution with size depends on the
mean diameter, number and fractal dimensions of particulates
[11]. Particulate volume distribution in the diesel engine exhaust
Fig. 5. Particulate volume concentration distribution with varying fuel injection pressure and start of injection timing.
88 A.K. Agarwal et al. / Fuel 107 (2013) 84–89

increases with increasing engine load (Fig. 5). Peak height of partic-
ulate volume distribution was observed to decrease with increas-
ing fuel injection pressure at the same engine load. At 500 and
750 bar fuel injection pressures, peak height of particulate volume
distribution curve decreases with advancing the fuel injection tim-
ings. At lower fuel injection pressure (300 bar), volume distribu-
tion with size of particulate first increases and then decreases
with retarding the injection timing.
4. Conclusions
Particulate size–number, surface area, volume distributions
were investigated in a diesel fuelled single cylinder research en-
gine operating at 1500 rpm. The experiments were carried out at
different engine loads and fuel injection pressures were varied
from 300, 500 and 750 bar at various start of injection timings. Par-
ticulate number concentration in the exhaust increases with
increasing engine load. Increasing the fuel injection pressure re-
duces the number concentration of particulates along with mass
of particulates at all loads. At higher fuel injection pressures,
advancing the injection timing reduces the particulate number
concentration because advanced injection timings provide more
time for mixing of fuel droplets with surrounding air before start
of combustion. At lower fuel injection pressures, number concen-
tration first increases and then decreases with retarding the injec-
tion timings because fuel–air mixing at lower fuel injection
pressures is more sensitive to in-cylinder pressure and tempera-
ture along with time available for mixing before start of combus-
tion. Particulate surface area and volume distribution also
increases with increasing engine load and decreases with increas-
ing fuel injection pressure.
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