możliwości obniżenia strat tarcia silnika ozi w zalezności od rodzaju

możliwości obniżenia strat tarcia silnika ozi w zalezności od rodzaju

Journal of KONES Internal Combustion Engines 2003, vol. 10, No 3-4
SELECTION OF LUBRICATING OIL AIMED AT REDUCTION OF
IC – ENGINE FRICTION LOSSES
Anna Krzymień, Piotr Krzymień
Institute of Combustion Engines and Fundamentals of Machinery Design
Poznań University of Technology
ul. Piotrowo 3, 60-965 Poznań
Phone: +48(61) 665 22 39, Fax: +48(61) 6652204
e-mail: [email protected]
e-mail: [email protected]
Abstract
Rheological properties of lubricating oil decisively affect the engine internal power loss. An increase in
engine mechanical efficiency can be achieved through the reduction in engine’s power loss caused by friction.
The paper will present some results of an experiment carried out on a SI engine lubricated with three types of
lubricating oil. The achieved results allow to formulate conclusions relating to the reduction of friction loss
thanks to the use of proper oil.
MOŻLIWOŚCI OBNIŻENIA STRAT TARCIA SILNIKA O ZAPŁONIE
ISKROWYM W ZALEZNOŚCI OD RODZAJU
ZASTOSOWANEGO OLEJU
Streszczenie
Właściwości reologiczne oleju smarującego w zasadniczy sposób wpływają na wartość oporów
wewnętrznych silnika. Zwiększenie sprawności mechanicznej można uzyskać m. in. przez zmniejszenie strat
tarcia potrzebnych na pokonanie oporów własnych silnika spalinowego.
W pracy zostaną przedstawione wyniki badań mocy tarcia silnika o zapłonie iskrowym do smarowania
którego zastosowano trzy rodzaje oleju. Uzyskane wyniki pozwalają na sformułowanie wniosków odnośnie
zmniejszenia oporów tarcia w wyniku zastosowania odpowiedniego oleju smarującego.
1. Introduction
Following kinds of efficiency serve as indicators of engine run: theoretical (ηt), indicated
(ηi), thermal (ηc), mechanical (ηm) and total efficiency (ηo). Hence, the last is the product of
all efficiencies:
η o = η c ⋅η m = η t ⋅η i ⋅η m
In spite of constant efforts on engine modernization and development, the IC engine total
efficiency is still quite low and equals η = 0.25-0.32 [7]. Therefore the constructors’ attention
is focused on each of constituent efficiencies. The mechanical efficiency constitutes the
measure of engine parts’ production and lubrication quality as well as the volume of energy
consumed as a result of auxiliaries operation. Energy loss result from:
•
friction,
•
gas exchange,
•
auxiliaries drive,
•
ventilation,
•
blower or mechanical supercharger drive.
The engine mechanical efficiency can be increased thanks to modern manufacturing of
cooperating parts, e.g. journals and shells or elements of the crank mechanism as well as
improvement of lubricating media like lubricating oil. The analysis of mechanical loss proved
that the decisive role play friction losses in crank mechanism, which constitute as much as
65% of the total mechanical loss. Other losses result from the drive of such mechanisms as
cooling water pump, lubricating oil pump, fan, alternator, compressor or hydraulic pumps.
The rheological properties of lubricating oil affect the engine inner resistance, which
eventually manifest in increased fuel consumption and toxic emissions [3]. This makes that
lubricating oil should reduce the wear of rubbing surfaces when engine runs. As to achieve
this, the oil should be viscous in order to build up a continuous oil film between cooperating
surfaces and at the same time should be liquid for quick distribution over the lubricated area.
Because of those requirements the most wanted oils are those which possess low viscosity,
but a high viscosity index, i.e. those of viscosity relatively stable with changes in temperature.
2. Test bed investigations
Tests have been carried out in order to prove a relation between the type of lubricating oil
and friction loss in an IC engine. They were performed on a typical test bed furnished with a
4-stroke gasoline engine ((Ne = 55.2 kW at 5200 rpm, Mo = 114.7 Nm at 3200 rpm). LOTOS
lubricating oils (synthetic, semi-synthetic and mineral one) have been used for lubrication.
The properties of each lubricating oil have been presented in Table 1.
Table 1. List of LOTOS lubricating oils’ properties
No
1
2
3
4
5
6
7
8
9
oil type
Parameter
Density at 20OC [g/ml]1
Kinematic Viscosity at
100 OC [mm2/s]2
Viscosity Index
Dynamic Viscosity at 15
O
C [mPa⋅s]
Dynamic Viscosity at
100 OC [mPa⋅s]
HT/HS Viscosity [mPa⋅s]
Flash Point
Contents of volatile parts,
Noack method [%}
Water [%]
Syntetic
API
Quality
Standard
SJ/CF/EC
Viscosity Grade
SAE 5W/40
0.847
15.2
Semisyntetic
API Quality
Standard
SG/CD
Viscosity Grade
SAE 10W/40
0.871
14.6
Mineral
API Quality
Standard
SG/CD
Viscosity Grade
SAE 15W/40
0.884
13.9
165 (155, min.)
2900
(3500, max.))
12.0
150 (140, min.)
3400
(3500, max.))
11.9
135 (130, min.)
3000
(3500, max.)
11.5
3.8
231
8.5
(10, max.)
no
3.7
226
10.6
(13, max.)
no
3.8
233
8.5
(155, max.)
no
The research methodology consisted in application of two methods of engine friction
power determination:
•
method of external drive – the IC engine is driven by an electric motor with swinging
stator, which allowed reading the value of torque necessary for maintain the engine run
at applied speed, and
1
2
measured at the IC Engine Laboratory of PUT
as above
•
method of subsequent cylinder exclusion where reading of the torque value is carried out
after exclusion of ignition in consecutive cylinders.
Details of both methods can be found in [6].
Measurements of friction power performed according to the first method have been carried
out for three values of rotational speed at engine run temperature (75±5oC, measured in oil
sump). The results are presented in Table 2.
Table 2. Results of test-bed investigation – friction power determined according to the external drive method for
LOTOS oils
Oil type
Mineral oil
Semisynthetic
oil
Synthetic oil
Oil temperature
to [oC]
75.6
77.5
80.0
74.9
77.8
77.3
75.8
78.7
79.0
Rotational
speed n [rpm]
1500
2500
3500
1500
2500
3500
1500
2500
3500
Torque Mo
[Nm]
23.50
26.83
31.77
22.17
25.18
30.68
19.87
24.23
30.25
Friction power
Nt [kW]
3.69
7.02
11.64
3.48
6.59
11.24
3.12
6.34
11.08
The measurements of engine mechanical efficiency followed the introductory tests of
mechanical loss of the external drive, i.e. electrical motor with an articulated shaft and gear
box. Relation between external drive unit mechanical loss and rotational speed were presented
in Fig. 1.
5,00
Nt [kW]
4,00
3,00
2,00
1,00
0,00
1500
2000
2500
3000
3500
n [rpm]
Fig. 1. Mechanical loss of external drive vs. rotational speed
0,80
η m 0,78
0,76
0,74
1
0,72
0,70
2
0,68
3
0,66
0,64
0,62
0,60
1500
2000
2500
3000
3500
n [rpm]
Fig. 2. Mechanical efficiency vs. speed determined according to the successive cylinders switch – off method for
three types of lubricating oil: synthetic (1), semisynthetic (2) and mineral one (3) at the temperature of
engine run (oil sump temperature 75±5 oC).
The next figure presents the comparison of mechanical loss determined according to the
external drive method for three types of lubricating oil and different speeds at the temperature
of engine run (oil sump temperature 75±5 oC).
3. Result analysis
Figs. 3 and 4 present the comparison of mechanical loss determined according to the
external drive method and the successive cylinders switch-off method, respectively, for three
types of lubricating oil: mineral (1), semisynthetic (2) and synthetic one (3) at the temperature
of engine run (oil sump temperature 75±5 oC).
14
12
Nt [kW]
10
1
8
2
6
3
4
2
0
1500
2000
2500
3000
3500
n [rpm]
Fig. 3. Comparison of mechanical loss determined according to the external drive method for three types of
lubricating oil: mineral (1), semisynthetic (2) and synthetic one (3) at the temperature of engine run (oil
sump temperature 75±5 oC).
8,00
7,00
Nt [kW]
6,00
1
5,00
3
4,00
2
3,00
2,00
1,00
0,00
1500
2000
2500
3000
3500
n [rpm]
Fig. 4. Comparison of mechanical loss determined according to the successive cylinders switch-off method for
three types of lubricating oil: mineral (1), semisynthetic (2) and synthetic one (3) at the temperature of
engine run (oil sump temperature 75±5 oC).
Comparing the values of friction loss determined according to both methods mentioned
one should notice that the method of external drive gives results higher than those obtained
using the other method. The difference results from the mechanical power loss generated by
the drive unit (see Fig. 1). Taking it into account the results achieved are almost identical,
what proves the accuracy of measurements.
Friction loss increase with speed almost linearly for all types of lubricating oil used in the
tested engine. In the case of mineral oil they are the highest for the entire range of rotational
speed. For semisynthetic and syntetic oil the friction losses are about the same in the speed
range 2000 to 3000 rpm (see Fig. 4).
4. Conclusions
The tests carried out on a test bed allow to formulate the following observations:
in running engine the lowest friction power loss has been encountered for synthetic oil, a
little bit higher for the semisynthetic oil,
•
the same values of friction losses achieved using both methods prove the accuracy of
measurements (at the same test conditions),
•
in order to verify the obtained results it seems to be useful to carry out similar
examination, but for a modern engine lubricated with synthetic oil of new generation.
•
References
[1] Krzymień A.: „Wyznaczenie strat tarcia w węzłach ciernych silnika spalinowego”.
Zagadnienia Eksploatacji Maszyn.. Z.2 (106), Vol.31/1996. PWN Warszawa 1996,
[2] Krzymień A., Krzymień P.: „Wpływ rodzaju oleju na straty tarcia pierścieni tłokowych
w czterosuwowym silniku samochodowym w warunkach rozruchu”. Eksploatacja
silników spalinowych, Zeszyt Nr 6 – Problemy Rozruchu silników spalinowych,
Szczecin 2002.
[3] Krzymień A., Krzymień P.: „Badania stanowiskowe wpływu rodzaju oleju smarującego
na straty tarcia w czterosuwowym silniku spalinowym o zapłonie iskrowym”. Nr pracy
52-819/2001/DS (praca niepublikowana).
[4] Merkisz J.: „Ekologiczne problemy silników spalinowych” Tom 2., Wydawnictwo
Politechniki Poznańskiej, Poznań 1999.
[5] Serdecki W.: „Wpływ wybranych parametrów pracy silnika na straty tarcia w układzie
tłokowo-cylindrowym”. KONMOT’1996
[6] Serdecki W.: „Badania silników spalinowych. Laboratorium”. Wydawnictwo
Politechniki Poznańskiej, Poznań 2001.