Importance of fuel injection system for low emissions, combustion noise and low fuel consumption

Abstract

Due to increasingly stringent global regulations on engine and noise emissions, the fuel injection system plays a key role in reaching the stricter limits. The performance, low level of emissions and noise of a diesel engine is directly influenced by the fuel injection system which the main purpose is to deliver fuel at high pressure into engine's cylinders. Another aspect of a diesel engine is that it generates much more noise compared to a gasoline one. For this problem, the appropriate fuel injection system, such as a common-rail system, has made it possible to reduce combustion noise. The strategy consists in the use of a split injection into the combustion chamber by splitting the main injection. The purpose of this paper is to emphasize the difference between servo-controlled electrohydraulic injectors and direct acting (piezoelectric) injectors of the common-rail injection system and to explain how they can support the engine in achieving stricter emissions and noise regulations.

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Importance of fuel injection system for low emissions, combustion noise
and low fuel consumption
To cite this article: N D Petrea and C Bujoreanu 2018 IOP Conf. Ser.: Mater. Sci. Eng. 444 042020
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The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
Importance of fuel injection system for low emissions,
combustion noise and low fuel consumption
N D Petrea1 and C Bujoreanu1
1Mechanical Engineering, Mechatronics and Robotics Department, “Gheorghe Asachi”
Technical University of Iasi, Iasi, Romania
E-mail: petrea_narcis09@yahoo.com
Abstract. Due to increasingly stringent global regulations on engine and noise emissions, the
fuel injection system plays a key role in reaching the stricter limits. The performance, low level
of emissions and noise of a diesel engine is directly influenced by the fuel injection system
which the main purpose is to deliver fuel at high pressure into engine's cylinders. Another
aspect of a diesel engine is that it generates much more noise compared to a gasoline one. For
this problem, the appropriate fuel injection system, such as a common-rail system, has made it
possible to reduce combustion noise. The strategy consists in the use of a split injection into the
combustion chamber by splitting the main injection. The purpose of this paper is to emphasize
the difference between servo-controlled electrohydraulic injectors and direct acting
(piezoelectric) injectors of the common-rail injection system and to explain how they can
support the engine in achieving stricter emissions and noise regulations.
1. Introduction
More and more stringent emission levels and noise regulations are forcing car manufacturers, fuel
injection system suppliers to develop new strategies to reduce the level of pollutant emissions and
noise coming from the internal combustion engine without compromising the actual performance and
fuel economy.
Figure 1 shows the worldwide emissions regulations [1], where each car manufactured according to
a specific implementation timetable must comply with the limits set for that year. The paper also
provides a summary of European Regulations on pollutant emissions and noise levels for passenger
cars and light commercial vehicles. For example in Europe, the transport sector is among the first
contributor to pollutant emissions released into the atmosphere, like CO, PM and NOx.
Since 2000 year, in the road transport sector, the level of pollutant emissions has been considerably
reduced by more than 25%, but for the non-road transport sector, such as agriculture, the level of
emissions has remained constant over the years [2].
On the other hand, the number of vehicles is increasing very rapidly from one year to another,
which means that the emissions regulations need to be updated more often in order to not lose out of
control pollutant emissions released into the atmosphere.
To achieve the required limits, appropriate equipment types are needed. In the past, to meet Euro 4
and 5 standards, the fuel injection systems were not as performant as they are today, and a system such
as Exhaust Gas Recirculation (EGR) has been used to meet the limits. For some engines to meet Euro
6 standard, it was added Selective Catalytic Reduction (SCR), which is an exhaust gas after-treatment
system.

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The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
Figure 1. Worldwide emissions regulations / Implementation calendar [1].
The purpose of developing EGR and SCR systems was to reduce NOx emissions. For particle
matter reduction, a diesel particulate filter (DPF) can be used as well, and for NOx and CO emissions
a fuel injection system that can accurately control the amount of fuel injected into the combustion
chamber.
In addition, the fuel injection system must be able to perform multiple injections to reduce
combustion noise and to facilitate different forms of advanced combustion (low temperature, premixed
or partially-premixed) to achieve very low NOx and soot formation for partial load conditions [3].
In order to get more injections into the combustion chamber, the common-rail system must be able
to carry very high pressures and, secondly, proper coding of the electronic control unit (ECU) is
required to precisely control the injectors. Injectors are one of the most important components of the
common-rail system; they directly influence the burning process inside the combustion chamber and
therefore the level of pollutant emissions is also affected.
Essentially, the purpose of our paper is to provide an analysis of the differences between servo-
controlled electrohydraulic (solenoid) injectors and direct acting (piezoelectric) injectors and how it
can improve the diesel engine performance, the level of emissions and the emitted noise.
2. Environmental and noise pollution standards for each vehicle category
Due to a multitude of categories of vehicles used in the transport sector, a single limit for this cannot
be implemented, as there are vehicles with a different purpose.
Table 1 shows the vehicle category based on the Gross Vehicle Weight (GVW) and vehicle
destination.
Table 2 sets out the emission limits to be complied with in accordance with the applicable standard
of that year.

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IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
Table 1. Vehicle Categories [4].
Category
Description
Subcategory
Number
of
persons
Mass limit
M
Carriage of
passengers, min
4 wheels, PC
M1
Up to 9
N/A
M2
>9
GVW ≤ 5000 kg
M3
GVW ≥ 5000 kg
N
Carriage of
goods, min 4
wheels, LCV
N1 CL1
N/A
GVW
≤ 3500 kg
Ref. M ≤ 1350 kg
N1 CL2
1305 kg < Ref. M ≤ 1760 kg
N1CL3
1760 kg < Ref. M ≤ 3500 kg
N2
3500 kg < GVW ≤ 12.000 kg
N3
GVW > 12.000 kg
Table 2. Euro 5 and 6 Standards - Emissions limits [5].
Emissions
Unit
Euro Standards - Compression ignition
emissions limits
Euro 5a
Euro
5b/b+
Euro 6b, 6c,
6d-Temp, 6d
PC M, LCV N1 CL1
NOx
mg/km
180
180
80
HC+NOx
230
230
170
CO
500
500
500
PM
5.0
4.5
4.5
PN
Nb/km
-
6×1011
6×1011
LCV N1 CL2
NOx
mg/km
235
235
105
HC+NOx
295
295
195
CO
630
630
630
PM
5.0
5.0
4.5
PN
Nb/km
-
6×1011
6×1011
LCV N1 CL3, N2
NOx
mg/km
280
280
125
HC+NOx
350
350
215
CO
740
740
740
PM
5.0
5.0
4.5
PN
Nb/km
-
6×1011
6×1011

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IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
According to World Health Organisation (WHO), noise pollution is the second dangerous
phenomenon influencing the environment, after the air pollution [6]. The main source of
environmental noise is the transportation noise which is pulled up by always increasing needs for
goods, energy, and personal transportation [7].
Table 3 and table 4 are showing European Regulations regarding the admissible noise levels
generated by vehicles with the effective dates in three stages, until 2026.
Table 3. European sound level limits of motor vehicles for carriage of passengers [8].
Vehicle
Category
Description of vehicle category
Limit values expressed in dB (A)
Phase 1
applicable for
new
vehicle types
from 1 July
2016
Phase 2 applicable
for new
vehicle type from
1 July
2020 and for first
registration from 1
July
2022
Phase 3 applicable
for new
vehicle type from
1 July
2024 and for first
registration from 1
July
2026
M - Vehicles used for the carriage of passengers
M1
Power to mass ratio
≤ 120 kW/1000 kg
72
70
68
M1
120 kW/1 000 kg < Power to
mass ratio ≤ 160 kW/1000 kg
73
71
69
M1
160 kW/1 000 kg < Power to
mass ratio
75
73
71
M1
Power to mass ratio > 200
kW/1000 kg number of seats
≤ 4 R point of driver seat ≤ 450
mm from the ground
75
74
72
M2
Mass ≤ 2 500 kg
72
70
69
M2
2500 kg < Mass ≤ 3 500 kg
74
72
71
M2
3500 kg < Mass ≤ 5 000 kg;
Rated engine power ≤ 135 kW
75
73
72
M2
3500 kg < Mass ≤ 5 000 kg;
Rated engine power > 135 kW
75
74
72
M3
Rated engine power ≤ 150 kW
76
74
73
M3
150 kW < Rated engine power
≤ 250 kW
78
77
76
M3
Rated engine power > 250 kW
80
78
77

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IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
Table 4. European sound level limits of motor vehicles for carriage of goods [8].
Vehicle
Category
Description of vehicle category
Limit values expressed in dB (A)
Phase 1
applicable for
new
vehicle types
from 1 July
2016
Phase 2 applicable
for new
vehicle type from
1 July
2020 and for first
registration from 1
July
2022
Phase 3 applicable
for new
vehicle type from
1 July
2024 and for first
registration from 1
July
2026
N - Vehicles used for the carriage of goods
N1
Mass ≤ 2 500 kg
72
71
69
N1
2 500 kg < Mass ≤ 3 500 kg
74
73
71
N2
Rated engine power ≤ 135 kW
77
75
74
N2
Rated engine power > 135 kW
78
76
75
N3
Rated engine power ≤ 150 kW
79
77
76
N3
150 kW < Rated engine power
≤ 250 kW
81
79
77
N3
Rated engine power > 250 kW
82
81
79
The studies revealed that people who are regularly exposed to consistent high sound levels they are
more prone to hearing disorders, hypertension, ischemic heart disease, discomfort and sleep
disturbances.
3. Design differences between servo-controlled electrohydraulic (solenoid) and direct acting
(piezoelectric) injectors
The design and working principle of servo-controlled electrohydraulic (solenoid) and direct acting
(piezoelectric) injectors are totally different.
For the solenoid injector, the operating principle consists of using a servo-hydraulic concept to
control the needle movement, such as the actuation of the Solenoid 1 and opening of the Control Valve
2 (figure 2). Then, the pressure is released from the control chamber through an orifice which creates a
hydraulic imbalance and leads to needle lifting from the nozzle seat.
Also, consideration should be given to the opening time of the injector, where servo-controlled
electrohydraulic injector (solenoid) depends on the rail pressure and the negative pressure on the
return circuit created by the high-pressure pump on the fuel return circuit to the tank. Due to a
multitude of factors that influence the opening and closing time of the injector, a ramp shape of
injection under all system pressure conditions is generated and this shape tends to approach a square
shape as the system pressure increases.
On the other hand, the opening and closing of the direct acting (piezoelectric) injector is controlled
by actuating the Piezoelectric Stack 1 and the Needle Movement Amplifier 3 which acts directly on
the injector Needle 4 and lifts up the needle from the nozzle seat (figure 3).

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The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
1-Solenoid; 2-Control Valve;
3-Helicoidal Spring; 4-Needle;
5-Capnut;
1-Piezoelectric Stack; 2-Injector Body;
3-Needle Motion Amplifier; 4-Needle;
5-Capnut;
Figure 2. Servo-controlled electrohydraulic
injector (Solenoid) [9].
Figure 3. Direct acting injector
(Piezoelectric) [10].
Compared to the servo-controlled electrohydraulic (solenoid) injector, the direct acting
(piezoelectric) doesn’t have a return circuit and the opening and closing times do not depend on the
rail pressure, which is a significant advantage, as the rail pressure is not constant during engine
operation and varies depending on the engine load.

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The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
The visible difference can be seen in figure 5 where the direct acting (piezoelectric) has a square
shape injection at all system pressure conditions compared to the servo-controlled electrohydraulic
(solenoid) injector of figure 4 which has a ramp shape injection under all system pressure conditions.
Figure 4. Injection rate diagram at different
rail pressures for the servo-controlled
electrohydraulic injector (Solenoid) [10].
Figure 5. Injection rate diagram at different
rail pressures for the direct acting injector
(Piezoelectric) [10].
Figure 6 describes the injection pattern of the servo-controlled electrohydraulic injector (solenoid)
and figure 7 presents the injection pattern for the direct acting injector (piezoelectric) at 220 μs after
the start of the injection.
Figure 6. Injection pattern for servo-controlled
electrohydraulic injector at 220 µs after the
start of injection (Solenoid) [10].
Figure 7. Injection pattern for direct acting
injector at 220 µs after the start of injection
(Piezoelectric) [10].
From a visual point of view, it can be seen that the direct acting (piezoelectric) injector introduces
much more fuel into the cylinder, which means that it better controls the total amount of fuel injected

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The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
and further conducts to a better control of the air-fuel mixture and resulting in reduced pollutant
emissions released to the atmosphere.
4. Divided injection
The split injection has emerged as a necessity for the development of direct injection systems due to
the combustion noise produced and the emissions generated by single main fuel injection. Figure 8
shows an example of divided injection from a diesel engine with five injections per cycle.
1-Pre-Pilot Injection; 2-Pilot Injection; 3-Main Injection; 4-Post Injection;
5-Post-Late Injection
Figure 8. Example of divided injection for diesel engines.
Below are summarised the characteristics and advantages of each split injection sequence:
 Pre-Pilot:
o Is carried out with an advance of 120÷90º to TDC;
o The amount of fuel injected is around 1÷4 mm3;
o Controls the pressure variation in the cylinder;
o Reduces combustion noise;
o Improves the cold start of the engine;
o Increases engine torque at reduced speeds.
 Pilot:
o Controls combustion noise;
o Reduces particle formation, NOx and HC.
 Main:
o Makes the requested engine torque.
 Post:
o Reduces particulate emissions by extending the combustion process.
 Post-Late:
o Regenerates the particulate filter.
5. Conclusions
In the future, to meet the new regulations, the diesel engines will certainly be equipped with a
common-rail system with direct acting (piezoelectric) injectors.
As an advantage of the direct acting (piezoelectric) injectors in addition to those servo-controlled
electrohydraulic (solenoid) ones, it can be mentioned a three times faster opening and closing of the
nozzle needle independent of rail pressure at a speed of 3 m/s which leads to a square injection shape
at any rail pressure [10]. Considering that the fuel spraying is improved and the control of the total
amount of fuel injected into engine’s cylinders is more accurate than the servo-controlled
electrohydraulic (solenoid) injectors, the pollutant emissions such as nitrogen oxides and particulate

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The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 042020 doi:10.1088/1757-899X/444/4/042020
are reduced by 30%. In the same time, the torque and the engine power are increased by 10%, as well
the noise level and the fuel consumption are improved due to precise multiple injections per cycle.
The performances of the direct acting (piezoelectric) injectors compared to the servo-controlled
electrohydraulic (solenoid) injectors were presented in this paper, and it is clear that the piezoelectric
has the key characteristics to create a clean combustion process inside the combustion chamber.
6. References
[1] Worldwide emissions standards 2018 Passenger cars and light duty vehicles 2018-2019
http://www.delphi.com/emissions-pc
[2] European Environment Agency 2017 Air quality in Europe report
http://www.eea.europa.eu/publications/air-quality-in-europe-2017
[3] Dober G, Tullis S, Greeves G, Milovanovic N, Hardy M and Zuelch S 2008 The Impact of
Injection Strategies on Emissions Reduction and Power Output of Future Diesel Engines,
SAE World Congress Detroit 2008-01-0941
[4] Directive 2007/46/EC of the European Parliament and of the Council of 5 September 2007
establishing a framework for the approval of motor vehicles and their trailers, and of
systems, components and separate technical units intended for such vehicles, https://eur-
lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32007L0046&from=EN
[5] Commission Regulation (EC) No 692/2008 of 18 July 2008 implementing and amending
Regulation (EC) No 715/2007 of the European Parliament and of the Council on type-
approval of motor vehicles with respect to emissions from light passenger and commercial
vehicles (Euro 5 and Euro 6) and on access to vehicle repair and maintenance information,
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32008R0692&from=EN
[6] Licitra G, d'Amore G and Magnoni M 2018 Physical Agents in the Environment and
Workplace: Noise and Vibrations, Electromagnetic Fields and Ionizing Radiation (Taylor
and Francis Group: CRC Press)
[7] Pignier N 2015 The impact of traffic noise on economy and environment: a short literature
study, ECO2 project Noise propagation from sustainable vehicle concepts, KTH
Aeronautical and Vehicle Engineering Stockholm Sweden
[8] Regulation (EU) No 540/2014 of the European Parliament and of the Council of 16 April 2014
on the sound level of motor vehicles and of replacement silencing systems, and amending
Directive 2007/46/EC and repealing Directive 70/157/EEC https://eur-lex.europa.eu/legal-
content/EN/TXT/PDF/?uri=CELEX:32014R0540&from=EN
[9] Mercedes Forum 2012 Présentation du moteur OM651 http://www.forum-mercedes.com/topic-
10-presentation-du-moteur-om651.html
[10] Delphi TVS Diesel Systems Limited 2008 DFI 1&3 Direct Acting Injector - Tomorrow’s
Technology Today Delphi Corporation http://www.delphitvs.com/images/dfi_1&_3.pdf