Operational parameters influence on resulted noise
of multi-cylinders engine runs on dual fuels mode
Miqdam Tariq Chaichan*
Dina Saadi Muneam**
*- Assistant Prof. – Machines and Equipment Engineering Dep. University of Technology – Iraq
e. mail: miqdam_tc@uotechnology.edu.iq
**- Lecturer- Mechatronics Eng. Dept. - Al Khwarizmi Collage of Eng. Baghdad University- Baghdad- Iraq
e. mail: Deena_saadi@yahoo.com
Abstract
Noise considered as a pollutant result from the combustion
process that may have a direct influence on the surrounding
environment. In this study, noise measurements were taken for
multi cylinders, four stroke Fiat diesel engine. The engine altered to
run as dual fuel engine fueled with liquefied petroleum gas (LPG)
and natural gas (NG) gaseous fuels and diesel as a pilot fuel.
The study focused on the influence of some operating
parameters. These parameters included: engine load, pilot fuel
injection timing, pilot fuel mass, and engine speed. LPG as the
primary fuel in duel fuel mixture exhibited the higher engine noise
compared to NG or neat diesel. The results showed that advancing
injection timing from optimum ones increased engine sound
pressure levels.
Keywords: duel-engine, LPG, NG, noise, injection timing, pilot
fuel mass, engine speed.
1. Introduction
In the opposite of spark-ignition engines, the combustion of
diesel engine is known to be very stable and a regular one. The
cylinder pressure signals on an oscilloscope confirmed these
observations. However, many practical studies anglicized in detail
the diesel combustion process manifested considerable variations
from cycle to cycle resulting in combustion noise variations [1].
1
Noise is a pollutant arise from the combustion process that may
cause a direct impact on surrounding environment. Noise may
cause physiological change and immediate annoyance [2].
Combustion noise takes place in two figures, direct and indirect.
Direct noise is the noise generated in a region undergoing turbulent
combustion. The turbulent combustion caused by a transient
vibration in the total heat release of the reacting part. In spite of the
tininess of the overall fluctuation, it exists and generates pressure
waves. The indirect noise produced in the combustion region due to
interplay between different temperatures streamlines. The direct or
indirect sound may be dominant depending on the device. Noise is
results from the engine block due to vibration in a different
spectrum of frequencies can cause audible noise to the human ear
[3 & 4].
Combustion sound considered as the primary source of noise in
addition to airflow and mechanical noise. Particularly, the engines
that use high compression ratios and the combustion pressure rise
are fast results in high noise. The pressure rise rate during
combustion considered as one of the main factors that affect the
combustion noise. Different studies have shown that the maximum
pressure rise rate is directly proportional to the sound pressure level
(in decibels) observed in the diesel engine central chamber [5 & 6].
Diesel engines have been subjected to considerable efforts to
achieve smoother combustion with less noisy. Many valuable
works published in investigations on the diesel engine combustion
noise and the effects of the engine operating and design parameters
on it [7 & 8]. However, there is lacking in the data of combustion
noise for the dual-fuel engine that runs on diesel as pilot fuel and
gaseous fuel [9 & 10]. Therefore, it was considered necessary to
cover the research area on the noise resulted from the combustion
of dual fuel engine. In the recent study, the focus was on this
attempt by investigating the operating parameters for the dual fuel
engine influence on the combustion noise compared to a running
the engine with neat diesel fuel case. The engine noise levels were
measured and analyzed for variable engine loads, engine speeds,
and different pilot mass quantity. The engine resulted noise data
was compared to the sound resulted from operating the engine with
2
neat diesel fuel. This paper aims to determine the influences of dual
fuel mode operation on engine noise levels at variable engine
parameters. Conventional Iraqi produced gasses (LPG & NG) were
used in this study to provide improved knowledge of the
combustion phenomena in gas fueled internal combustion engines.
2. Experimental Setup
The engine used in the experiments was four cylinders, direct
injection (DI), water cooled and natural aspirated Fiat diesel engine.
Table 1 shows the engine major specifications. The engine is
coupled to a hydraulic dynamometer that controlled applied load by
increasing the torque. The engine’s cylinder pressure measured by
means of a piezoelectric sensor type Kistler 6125A. The output of
the pressure transducer was amplified by a Kistler charge amplifier
type 5015A (Yokogawa: GP-IB). Fig. 1 shows a schematic diagram
of the engine test rig.
Table 1, Tested engine specifications
Engine type
Engine model
Combustion type
Displacement
Valve per cylinder
Bore
Stroke
Compression ratio
Fuel injection pump
Fuel injection nozzle
4cyl., 4-stroke
TD 313 Diesel engine rig
DI, water cooled, natural aspirated
3.666 L
two
100 mm
110 mm
17
Unit pump
26 mm diameter plunger
Hole nozzle
10 nozzle holes
Nozzle hole dia. (0.48mm)
Spray angle= 160o
Nozzle opening pressure=40 Mpa
Gaseous fuel, LPG, and NG, entered the engine in the intake
manifold to run it in dual fuel mode. Gaseous fuels introduced by
3
means of a simple, low-cost air-gas mixing device, designed as
shown in Fig. 2. This gas adapter used to mix LPG or NG with inlet
air during the suction stroke. The gas introduced at a pressure
slightly higher than atmospheric pressure. Fig. 3 shows a
photographic picture of the testing rig.
In this work, the diesel fuel used was Iraqi Al-Doura refinery
production with cetane No. 49.6. The LPG fuel produced from AlTaji Gas Company; consist of ethane 0.8%, 11.47 iso-butane,
62.8% propane and 24.45% butane. The used NG produced by Iraqi
Northern Gas Company; formed from 88.23% methane, 9.21%
ethane, 2.15% propane, 0.15% iso-butane, 0.17% n. butane and
0.03% pentane.
The engine equipped for measuring the operating parameters
and combustion noise data. The diesel fuel flow rate measured by
recording the time required for 200ml of fuel consumption. The
LPG and NG fuels flow rate measured by using an orifice meter
and an electronic partial pressure transducer connected to a digital
pressure meter. Overall sound pressure measured by means of a
precision sound level meter using a microphone type 4615 as
appears in Fig. 4. The device calibrated by standard calibrator
device type pisto-phone 4220.
Fig. 1, block diagram for the test rig
4
Experiments carried out after the engine reached its steady state
and its oil temperature is at 70 oC, and cooling water temperature is
at 80oC.
Combustion pressure cyclic data presented for diesel and dual
fuel (using LPG or NG as the primary fuel) against the tested
engine operating parameters. The engine operating parameters
varied at the following levels:
Fig. 2, a cross-section sketch of the mixer
Fig. 3, Photographic picture of the testing rig
(1) The used fuel: included neat diesel fuel (used as the base
case for comparison) or dual fuel of diesel + LPG or NG.
(2) Engine load varied from 0.5 to 80 N m.
5
(3) The injection timing of the pilot diesel fuel ranged from 20 to
45 BTDC in steps of 5o.
(4) Pilot diesel fuel relative mass md from (md/md+mg)
(compared with constant mass of gaseous fuel admitted, mg) varied
from 18–42%.
(5) The engine speed varied from 1000 to 2500 rpm.
The experimental error is evaluated according to reference [11].
The experimental error divided by the average reading of the
quantity considered as the maximum uncertainty in any calculated
amount. The maximum uncertainties in engine speed, torque, diesel
proportion (md/md+mg) are 2.5, 3.35 and 2.76%, respectively. The
combustion pressure measured by means of the piezoelectric
pressure transducer and then converted to pressure from the
calibration data.
o
Fig. 4, overall sound pressure used in tests
The microphone located at an elevation equal to the engine
exhaust outlets that was 1.5 meters from the center of the
measurement line. The nominal axis of the microphone with a
maximum sensitivity directed towards and perpendicular to the
engine. It microphone supported by a cover prevented the excessive
acoustic reflection. In all cases, the microphone’s position,
direction, and mounting arrangements were recorded.
This study focused on the combustion noise resulted from the
dual fuel engine combustion mode. Notably, the phenomenon of
combustion noise variations related to the variation in engine
operation parameters. These parameters were the duel fuel type,
6
engine speed, and pilot fuel injection timing and pilot fuel mass
percentage in the fuel.
The following equations used to evaluate the engine performance
parameters:
1- Brake power
𝑏𝑝 =
2𝜋 ∗ 𝑁 ∗ 𝑇
60 ∗ 1000
𝑘𝑊
2- Brake mean effective pressure
2 ∗ 60
𝑘𝑁/𝑚2
𝑉𝑠𝑛 ∗ 𝑁
𝑏𝑚𝑒𝑝 = 𝑏𝑝 ×
3- Fuel mass flow rate
𝑣𝑓 × 10−6
𝜌𝑓 𝑘𝑔
⁄𝑠𝑒𝑐
𝑚̇𝑓 =
×
1000
𝑡𝑖𝑚𝑒
4- Air mass flow rate
𝑚̇𝑎,𝑎𝑐𝑡. =
12√ℎ𝑜 ∗ 0.85
𝑘𝑔
× 𝜌𝑎𝑖𝑟
3600
𝑠𝑒𝑐
𝑚̇𝑎𝑡ℎ𝑒𝑜. = 𝑉𝑠.𝑛 ×
𝑁
𝑘𝑔
× 𝜌𝑎𝑖𝑟
60 ∗ 2
𝑠𝑒𝑐
3. Results and Discussion
Effects of torque and fuel type
Fig. 5 illustrates the impact of fuel type on engine noise data.
The used fuels are neat diesel fuel, and dual fuel using LPG or NG
as the primary fuel. These results recorded at constant engine
parameters of 1500 rpm and optimum injection timing (OIT).
7
The figure shows the variation of noise levels with the load for
the three fuels. The load is found to increase the noise level for the
neat diesel fuel engine as well as a dual fuel mode engine using
either LPG or NG. However, it may be noticed that the noise level
is highest for LPG than that for NG, and then the pure diesel fuel
gives the lowest value. It is clear that LPG combustion produces the
highest maximum pressure followed by NG then diesel fuel.
Reference [12] has shown that the ignition delay period of
propane (the principle constituent of LPG)–diesel–air mixture is
longer than methane (the primary constituent of NG)–diesel–air
mixture. Also, the former delay period is longer than the value for
pure diesel–air mixture. When propane introduced in a dual fuel
engine, it presents a longer delay than methane and diesel. The
differences associated with the changes in temperatures during
compression and changes in pre-ignition energy release. In addition
to the loss of heat transferred to the surroundings and the
participation of residual gasses caused the elongation of delay
period.
For diesel engine running on diesel fuel the noise level
decreased with load (or increased with the mass of fuel injected).
Also, it increased with engine load for the gaseous fuels indicating
that for diesel engine, the torque increase causes the mass of fuel
injected to become bigger. Also, the flame may become bigger and
propagated smoother. However, for dual fuel combustion mode,
increasing the load means increasing the mass of gaseous fuel while
keeping the weight of diesel pilot fuel constant. The mass of
gaseous fuel increase caused a variation in the gas– air mixture
distribution especially at the start of ignition.
Effect of engine speed
Figs. 6 to 9 depict the effect of engine speed on combustion
noise for dual fuel and diesel engines running at different speeds.
As the engine speed increases, the combustion pressure raised for
most of the output loads.
Moffat [11] has concluded that increasing the engine speed
resulted in a reduction in the ignition delay period of the dual fuel
8
mixture. Therefore, the noise levels reduced due to a decrease in the
pressure rise rate. Imoto [7] has also shown that the combustion
noise decreased when the engine speed increases.
In this study, the pressure rise rate in the combustion chamber
of DI diesel engine was measured and related it to the sound
pressure level (SPL) in decibel (dB). It has shown a reduction in
noise levels as the engine speed increased. Figures 6 to 8 give the
behavior of each fuel alone, while Fig. 9 illustrates the three fuels
behaviors at 2500 rpm (High engine speed). In general, engine
noise levels increase from small to medium loads then it reduce for
high loads. Engine noise level relatively increases at small to
medium speeds, and then it decreased for high speeds. Compared to
other fuels (in Fig. 9) LPG still resulting in higher noise levels at
maximum speed.
Effect of pilot fuel injection timing
Fig. 10 illustrates the impact of injection timing of pilot diesel
fuel on the noise levels for a dual fuel engine fueled with LPG or
NG as the primary fuel at 1500 rpm and middle load.
The effect of pilot fuel injection timing advancing produced an
increment during the ignition delay period of the fuel. Therefore,
the combustion of a large diesel fuel mass or bigger flame to
propagate at higher speed achieved. This phenomenon caused the
combustion to start earlier and the maximum pressure to increase
resulting in higher noise levels.
The increment in ignition delay period of the diesel fuel that
injected earlier in lower air pressure and temperature may be the
cause. The longer delay period resulted in higher pressure rise rate.
The presence of gaseous fuel in the mixture resulted in longer
ignition delay time. Also, a higher pressure rise rate is expected to
increase with any advance in pilot injection timing.
Middle injection timing of about 30o to 37.5oBTDC caused
lowest SPL as seen in Fig. 10. Retarding injection timing caused
high-pressure rates resulted in higher SP levels.
The effects of pilot fuel mass percentage
9
Fig. 11 illustrates the effects of pilot fuel mass on the sound
pressure levels. The noise levels increased as the mass of pilot fuel
(or md/ (md+mg)) increased. A greater energy released at ignition,
improved the pilot injection characteristics. A larger size of pilot
mixture accompanied with a greater part of the gaseous fuel
resulted in higher rates of heat transfer that increased noise.
The combustion noise increased with increasing the pilot fuel
mass. An extensive pilot fuel quantity employment can lead to
successful flame propagation. Consequently, leads to increasing the
pressure rise rate that leads to the early knocking, also. It may
conclude that, using a greater pilot fuel quantity to improve the
combustion process at small loads, resulting in an increase in the
tendency to knock at high loads. However, the increment of pilot
fuel mass more (higher than md/ (md+mg) of 30%) leads to a
decrements in the pressure rise rate. The increase in the pilot diesel
fuel mass in the mixture leads to lower gaseous fuel masses. In
turn, it may result in a decrement in the ignition delay period of the
mixture. However, using more pilot fuel produces bigger initial
flame that propagates easier with less pressure rise rate.
4. Conclusions
This work presents practical measurements of the pressure sound
levels variation of a four cylinders DI Fiat engine operating in dual
fuel mode. Diesel, LPG, and NG used in the study. The following
conclusions derived from the recent investigation:
 The observed values of the combustion noise in dual fuel
combustion mode are strongly dependent on the type of the
used gaseous fuels. Also, their concentrations in the cylinder
charge have an effect.
 Dual fuel engine fueled with LPG as a primary fuel resulted
in a higher combustion noise than that fueled with NG.
 The combustion noise increased with advancing the
injection timing of pilot diesel fuel, when LPG used as a
primary fuel. Injection timing of about 30 to 37.5o BTDC
resulted in the least combustion noise.
10
 Increasing the mass of pilot diesel fuel (from 17.5 to 30%)
resulted in a rise in the combustion noise. However, more
increasing (from 30 to 45%) resulted in reducing
combustion noise.
 Engine speed increase resulted in a decrease in the
combustion noise.
5. References
[1] Michael L T, Richard J A and Christopher M A, “Neural
network-based diesel engine emissions prediction using in-cylinder
combustion pressure”, SAE No. 1999-01-1532, 1999.
[2] Harrison M, “Vehicle refinement, controlling noise and
vibration in road vehicles”, SAE International SAE ISBN
0768015057, 2004.
[3] Selim M Y E, “Effect of engine parameters and gaseous
fuel type on the cyclic variability of dual fuel engines”, Fuel, vol.
84, pp: 961–971, 2005.
[4] Bacria V and Herisanu N, “Considerations upon the noise
generated by some diesel engines used in agriculture”, Research
Journal of Agricultural Science, vol. 41, No. 2, 2009.
[5] Selim M Y E, “Pressure–time characteristics in diesel
engine fueled with natural gas”, Renewable Energy, vol. 22, pp:
473–489, 2001.
[6] Yajima Y and Nakashima K, “New measuring technique of
cylinder pressure spectrum and its application to combustion noise
reduction—time–frequency analysis of combustion excitation using
wavelet transform analysis, technical notes”, JSAE Rev 1998;
vol.19, pp: 277–282, 1998.
[7] Imoto K, Sugiyama S and Fukuzawa Y, “Reduction of
combustion induced noise in IDI diesel engine (1st report, target of
cycle and low noise combustion)”, Trans JSME, Part B vol. 63, No.
605, pp: 329–35, 1997.
[8] Reno N, “A comparison of green and conventional diesel
bus noise levels”, NOISE-CONV 2007, October 22-24, 2007.
[9] Stanislav B and Jorge M, “The development of gas (CNG,
LPG and H2) engines for buses and trucks and their emission and
11
cycle variability characteristics”, SAE paper No. 2001-01-0144,
2001.
[10] Flowers D, Aceves S M, Martinez-Frias J, Smith J R, Au
M, Girard J and Dibblem R, “Operation of four-cylinder 1.9L
propane fueled homogeneous compression ignition engine: basic
operating characteristics and cylinder-to-cylinder effects”, SAE
paper No.2001-01-1895, 2001.
[11] Moffat R J, “Describing the uncertainties in experimental
results”, Exp, Therm. Fluid Sci.; vol. 1, No. 1, pp: 3–17, 1988.
[12] Karim GA and Liu Z, “The ignition delay period of dual
fuel engines”, SAE paper No. 950466, 1995.
Notations
BMEP
bp
CR
CA
o
BTDC
dB
DI
IT
LCV
LPG
N
NG
T
Vsn
brake mean effective pressure (kN/m2)
Brake power
(kW)
compression ratio
crank angle
degree before top dead centre
Decibel
direct injection
Injection timing
(oBTDC)
Lower calorific value
(kJ/kg)
Liquefied petroleum gas
engine speed
(rpm)
Natural gas
engine torque
(kN.m)
swept volume
(m3)
12
1500 rpm, OIT
95
OIT, Diesel fuel
87
85
91
Sound pressure level (dB)
Sound pressure level (dB)
93
89
87
85
83
81
Diesel
LPG
NG
79
77
81
79
1000 rpm
1500 rpm
2000 rpm
2500 rpm
77
75
0
83
50
75
100
0
50
Torque (Nm)
Fig. 5, the effect of load on noise
levels for variable fuels at
constant engine speed and
optimum injection timing.
89
100
Torque (Nm)
Fig. 6, the effect of load on noise
levels for diesel fuel at variable
engine speed and optimum
injection timing
100
NG, OIT
LPG, OIT
Sound pressure level (dB)
Sound pressure level (dB)
87
85
83
81
79
1000 rpm
1500 rpm
2000 rpm
2500 rpm
77
95
90
85
1000 rpm
1500 rpm
2000 rpm
2500 rpm
80
75
75
0
0
20
40
60
80
100
20
40
60
80
100
Torque (Nm)
Torque (Nm)
Fig. 7, the effect of load on
noise levels for duel fuel
(diesel+NG) at variable engine
speed and optimum injection
timing
Fig. 8, the effect of load on noise
levels for duel fuel (diesel+LPG)
at variable engine speed and
optimum injection timing
13
1500 rpm
Sound pressure level (dB)
Sound pressure level (dB)
100
2500 rpm, OIT
100
95
Diesel
90
LPG
85
NG
80
75
90
85
80
Diesel
LPG
NG
75
0
20
40
60
80
100
20
Torque (Nm)
89
87
85
83
81
79
LPG
NG
77
75
20
25
30
35
40
50
Fig. 10, the effect of pilot fuel
injection timing on noise levels
for variable fuels at constant
engine speed.
1500 rpm, OIT
15
30
Injection Timing (º BTDC)
Fig. 9, the effect of load on
noise levels for variable fuels at
constant high engine speed and
optimum injection timing.
Sound pressure level (dB)
95
40
45
50
md/(md+mg) %
Fig. 11, the effect of pilot fuel
percentage on noise levels for
variable fuels at constant engine
speed.
14
‫تأثير بعض العوامل التشغيلية على الضوضاء الناتجة من محرك‬
‫متعدد األسطوانات يعمل بنظام وقود ثنائي‬
‫مقدام طارق جيجان*‬
‫دينا سعدي منعم الزبيدي**‬
‫*‪ -‬أستاذ مساعد ‪ -‬قسم هندسة المكائن والمعدات‪ -‬الجامعة التكنولوجية‪ -‬بغداد‪ -‬العراق‬
‫‪e. mail: miqdam_tc@uotechnology.edu.iq‬‬
‫**‪ -‬مدرس‪ ،‬قسم هندسة الميكاترونيك‪ ،‬كلية هندسة الخوارزمي‪ ،‬جامعة بغداد‬
‫الخالصة‬
‫يمكن للضوضاء الناتجة عن األحتراق أن تؤثر تأثيرا مباشرا على البيئة المحيطة‪،‬‬
‫وفي هذة الدراسة أخذت قياسات للضوضاء الناتجة عن استخدم محرك متعدد‬
‫حور للعمل كمحرك بوقود ثنائي‪ ،‬يعمل بوقود‬
‫االسطوانات‪ ،‬رباعي األشواط نوع فيات‪ّ ،‬‬
‫الديزل والغاز النفطي المسال‪.‬‬
‫ركزت الدراسة على تأثير بعض المتغيرات التشغيلية ‪ ،‬وتتضمن هذة المتغيرات‬
‫حمل المحرك‪ ،‬توقيت حقن الوقود الدليلي‪ ،‬كتلة الوقود الدليلي وسرعة المحرك‪ .‬بينت‬
‫النتائج أن استخدام الغاز النفطي المسال )‪ (LPG‬كوقود أساسي في خليط الوقود الثنائي‬
‫يعطي ضوضاء محرك أعلى من حالة استخدام الوقود الطبيعي )‪ (NG‬أو وقود الديزل‬
‫بمفرده‪ .‬كما أظهرت النتائج أن تقديم توقيت حقن الوقود الدليلي عن التوقيت األمثل يرفع‬
‫مستويات ضغط الصوت‪.‬‬
‫كلمات مفتاحية‪ :‬محرك وقود ثنائي‪ -‬الغاز النفطي المسال‪ -‬الغاز الطبيعي ‪ -‬توقيت‬
‫الحقن‪ -‬كتلة الوقود الدليلي‪ -‬سرعة المحرك‪.‬‬
‫‪15‬‬