KAROL KWIATKOWSKI BOGDAN ĩÓŁTOWSKI
University of Technology and Life Sciences
Summary
This paper present the most annoying sources of noise and vibration for envi-ronment – road vehicles (lorries, buses, cars and bikes), their influence on the hu-man body and procedures of engine noise reduction, tyres and road surfaces. Keywords: noise, vibrations, engine, vehicle
1. Introduction
In the second half of the seventies a durable tendency to limit the harmful influence of vehi-cles on the environment was shaped. This tendency caused the intensification of works connected with lowering noise level that contributes to human natural environment degradation.
Acoustics vibration band that human can hear contains the frequency from 16Hz to 20000 Hz. Vibrations below 16 Hz frequency are called infrasonic; vibration above 20000Hz – supersonic.
Vibrations of springy environment particles in relation to balance position are called acoustics vibrations. Acoustics vibrations spread in environment with a constant velocity. The wavelength is the smallest distance between vibrating particles with the same phase and is shown below [3]:
k
T
C
f
C
π
λ
=
=
⋅
=
2
⋅
(1) where: λ – wavelength [m], f – frequency of vibration [Hz], T – vibration period, k – wave number,c
k
=
1
ω = 2πf – angular velocity.The difference between the pressure of vibrations and static pressure in a given point of envi-ronment is called sound pressure. The space where we notice acoustic vibrations is called a sound field. One of the basic parameters that describe an acoustics state in a given point of the sound field is sound pressure level:
0
log
20
p
p
L
N=
[dB] (2)where:
p – effective sound pressure of a sound [Nm-2],
p0 – reference value
2
⋅
10
−5[Nm-2]Sound power level for a given source can be described as follows:
0
log
10
N
N
L
N=
[dB] (3) where: N – sound power [W], N0 – reference level 10– 12 [W].A sound has loudness equal to 1 sone if it is estimated as simple sound loudness (with sinu-soidal course) with 1000 Hz frequency and i 40 dB sound pressure level. A sound with a frequency of 1000 Hz and intensity of 10-7 W/m2 creates an impression of quite high volume, although
a sound with the same intensity but with the frequency of 40 Hz is almost audible [3].
The threat on the human health is connected with the influence of audible vibrations in the frequency range from 16 Hz to 16 kHz. When these vibrations are burdensome or harmful, they are defined as noise. However, to estimate acoustic vibration harmfulness, vibrations from beyond this range should also be considered. Acoustic vibrations, spreading in the air, come across every day also in the infrasonic range – below 16 Hz – and also in the supersonic range – from 16 kHz to 107 kHz.
Noise is a result of various overlapping sounds which mix without any order in the surround-ing environment. We also call every disturbsurround-ing sound noise. The influence of noise on the human body is different, but noise has a big influence on the nervous system. Noise is more dangerous because its consequences come out suddenly – often accumulate in the time. In critical cases noise could be a reason of immediate death. Noise in natural conditions is practically unavoidable. It accompanies humans at home, work, during the walk and comes with all civilization achieve-ments. The quantity of noise sources is huge, but the most special sources are: industry (noisily working machine engines and devices), transportation (lifts, ventilators, pumps, and others).
Considering harmful influence of noise on man, we can affirm that noises of A level (this is a standard level of volume from 0 to 50 phon) do not cross 35 dB and are not dangerous for human health, but sometimes irritating. Noises of A level in the range of 35–70 dB have a negative influence on the human, causing the fatigue of the nervous system, lowering of sight tenderness, obstructing the understanding of speech and communicating, exerting a negative influence on the rest and dreams. A continuous exposure to the noise of A level in the range of 70–90 the dB has a negative influence on job efficiency and human health. It causes of hearing weakness, headache, nervous disorders. Noises of A level in the range of 90–130 dB could develop vibrations of inter-nal human organs, causing their ailment and even their destruction. Exposure to this noise level causes balance disorders, nausea, also changes of human blood component proportion, calling out certain mental changes.
2. Vehicle noise sources
For so many years engine has been the main source of noise in vehicles, although induction system and exhaust system has also had a notable part in noise generation.
Nowadays in countries with the highest technical culture, not engine, but tyres and road sur-face should be the aim of future works and investigations connected with lowering noise in vehi-cles.
Fig. 1. Comparison of noise sources in typical German cars in the years 1979 and 1995 Source: [3].
Noise and vibrations of vehicles could be divided with consideration of their sources as be-low:
• combustion engine work as a process that makes noise and vibrations in the range of 20– 180 Hz (fume frequency) and 1000–5000 Hz – natural vibrations of cylinder head (im-pulse initiation),
• power transmission system and engine timing systems making noise and vibration, as a results of rotary motions and cooperation with tooth gear. This arrangement is charac-terized by a big quantity of harmonic components,
• tyres and road surface making vibrations with short impulses in the range of 10–200 Hz, especially in the car body. Slick tyres cooperating with road surface make noise in the range of frequency from 500 to 5000 Hz,
• vibrations and noise emission from other arrangements of vehicle, characterized by a big quantity of harmonic components of vibration can be considered similar to the main transmission.
Car noise is a sum of every noise component from different sources which are all car ar-rangements and parts. Noise connected with car movement could be divided into [2]:
• mechanical, • aerodynamic.
Mechanical noise is a sum of engine vibrations and its arrangements. It is a result of emission of energy accumulated in the engine into the environment.
Aerodynamic noise is connected with liquid flow in engine arrangements (gases and liquids). In vehicles we could mark the following sources of aerodynamic noise:
• noise as an acoustic effect connected with air rotation around the car body, engine and ventilator with maximal values in the range of frequency from 2000 – 5000 Hz,
• thermodynamic process in combustion engine cylinders,
• period opening and closing of fumes arrangements into atmosphere (noise in induction system end exhaust system ),
• cooling system noise,
• hydrodynamic disturbances in pumps and through system.
The most important sources of noise in combustion engines is piston – cylinder arrangement. This vibration depends on piston construction and its weight, velocity of piston movement and also surface between piston and piston rings.
An example drawing of noise spectrum with the specification of sound sources from individ-ual aggregates of a lorry is presented as figure 2.
Fig. 2. The spectrum analysis of lorry noise Source: [3].
Fuel arrangement noises are a part of noise emitted by combustion engines. The source of noises and vibrations in this arrangement are hydraulic impacts, which rise as a result of
pressure violent change of pumped fuel during raising and leaving nozzle needle of injector and closing the pump valve.
The opening and closing of diesel engine valves proceed in a percussive way. This percussive work developing violent duties of timing gears system cylinder head of the engine as an acoustic wave and vibration propagation to the environment in a form of noise.
3. Vehicle noise and vibration decreasing procedures
The basic ways of vehicle noise and vibration processes intensity reduction is the limitation of vibration form by [1]:
• decreasing engine unbalanced parts,
• decreasing percussive duties by limiting the necessity of applying large free – plays by controlled stiffness of co-operating engine units, improvement of the quality of engine parts of units, applying the materials and technology that enable the decrease of waste and durability improvement of engine parts and units,
• reducing percussive duties, generated in the engine cylinder by limiting the speed of pres-sure growth of the working medium – the maximum value of medium prespres-sure derivative in the cylinder pg in relation to time or the crank angle
α
:
(
dp
g/
dt
)
max ormax
)
/
(
dp
gd
α
,• decreasing percussive duties connected with the co-operation of tyres with road surface by the material, construction and technology change of tyres and road surface,
• decreasing surface vibrations by their flexibility control (local stiffening) and applying materials with large internal suppression,
• decreasing vibration process intensity connected with the liquid flow by the limitation of flow turbulence through the suitable construction of channels that enable the decrease in violent changes of the sections and reduction of the speed of liquid flow.
The other way of vibroacoustic process propagation minimization is the utilization of dissipa-tion energy phenomena, as it happens in the exhaust silencer. This is the main way of exhaust gases noise lowering, but we also could:
• cover the exhaust system with materials that dump the acoustics waves, • apply the stratified sides of exhaust system,
• use susceptible mount of exhaust system to engine. Exhaust silencer classification:
• an absorptive silencer, which changes the energy of acoustic waves into heat; the usage of these silencers is lower because of their effectiveness;
• the reactionary (aerodynamic interference), which uses wave reduction phenomenon as a result of interference; we could distinguish expansive silencers with chambers of expan-sion arranged in rows and resonance silencers with parallel resonance chambers;
• reflective silencers, with dissipation of acoustic wave energy as a result of dynamic phe-nomena connected with the changes of shapes and sizes of exhaust gases sections; • dispersal silencers, which dissipation of acoustic wave energy as a result of exhaust gas
flow by perforated conductor sections.
A suitable selection of the exhaust system silencer enables the reduction of sound intensity level of about (12–16) dBA.
4. Conclusion
The most essential problems connected with the formation and reduction of noise and vibra-tion in combusvibra-tion engines were presented in this paper. It was showed that the range of system operation had to be wider, from the engine and its arrangements constructional changes, including building constructional and architectural changes and the changes of road movement organization. The ways of the vibroacoustic process propagation minimization were introduced by proper utilization of energy dissipation phenomena by proper usage of exhaust gas silencers. It was showed that the noise emitted by cars is connected with lower parts of vehicles, which suggests the necessity to use well-chosen casings.
Bibliography
1. Chłopek Z.: Ochrona Ğrodowiska naturalnego. WKiŁ. Warszawa 2002.
2. Gronowicz J.: Ochrona Ğrodowiska w transporcie lądowym. Wydawnictwo Instytutu Tech-nologii Eksploatacji. Radom 2004.
3. Gronowicz J.: Gospodarka energetyczna w transporcie lądowym, Wyd. Politechniki PoznaĔskiej, 2006.
4. Kwiatkowski K., ĩółtowski B.: Silniki spalinowe Ĩródłem szkodliwych składników spalin. PAN, DIAGNOSTYKA, vol. 32, Wyd. PTDT, Olsztyn 2004.
5. Merkisz J.: Ekologiczne problemy silników spalinowych. Wydaw. Politechniki PoznaĔskiej, 1998r.
6. NiziĔski S., Michalski R.: Diagnostyka obiektów technicznych, 2002.
7. ĩółtowski B.: Podstawy diagnostyki maszyn, Wydawnictwo uczelniane ATR, 1996. 8. ĩółtowski B., Kwiatkowski K.: Pomiary składu spalin silników spalinowych. ZN Akademii
Morskiej, Nr 5 (77), Szczecin 2005 s. 361–370.
9. ĩółtowski B., Jaime L. B. Perez, Leonel F. Castañeda Heredia: Study of the technical state of a Francis turbine by rotor dynamic simulations. CIMAC, Vol.4, Nr 3, 2009 pp. 191–210. 10. ĩółtowski B., Leonel F. Castañeda Heredia: Multidimensional condition monitoring of
critical machines. CIMAC, Vol.4, Nr 1, 2009 pp. 191–210.
11. ĩółtowski B.: Diagnostic system of machine exploitation. CIMAC, Vol.4, 2009 pp. 191– 210.
12. ĩółtowski B., Castaneda Heredia L.F., Betancur Giraldo G.R.: Multidimensional monitor-ing of condition – MMC – based on the smonitor-ingle value decomposition – SVD – Case study: railway system. CIMAC, Vol.4, Nr 1, 2009 pp. 191–210.
13. ĩółtowski B.: Procedure of constructing and evaluating linear diagnostic models of com-plex objects. CIMAC, Vol.4, Nr 2, 2009 pp. 191–210.
14. ĩółtowski B., Castaneda Heredia L.F.: Estudio de explotación de vehículos ferroviarios. EAFIT University, Colombia, 2009 s. 298.
15. ĩółtowski B., Castaneda Heredia L.F.: Badania pojazdów szynowych. Transport. Wy-dawnictwo UTP, Bydgoszcz, 2009 s. 220.
16. ĩółtowski B.: System diagnostic for the metro train. Konfer. UTP, Bydgoszcz 2009. 17. ĩółtowski B.(red. wyd.): Elementy diagnostyki maszyn roboczych i pojazdów. Zbiór
mate-riałów, Radom–Bydgoszcz–Borówno, 2009, s. 391.
18. ĩółtowski B.: Diagnostyczny system utrzymania ruchu w transporcie kolejowym. TRANSCOMP – International Conference. Zakopane 2009.
19. ĩółtowski B.: Monitoring of condition the railway system. Engineering Mechanics, vol.17, no.1, Praga 2010 pp. 15–27.
OCHRONA ĝRODOWISKA PRZED ZAGROĩENIAMI DRGANIOWYMI I HAŁASEM Streszczenie
W pracy przedstawiono wpływ drgaĔ i hałasu na Ğrodowisko naturalne – ze strony pojazdów. Wskazano na opis degradacji Ğrodowiska, maszyn oraz ich wpływ na człowieka. Analizując normy przeanalizowano zasady redukcji hałasu drogowe-go, drgaĔ maszyn oraz zapylenia przemysłowego.
Słowa kluczowe: hałas, drgania, maszyny, samochody, Ğrodowisko, zagroĪenia
This paper is a part of WND-POIG.01.03.01-00-212/09 project.
Karol Kwiatkowski Bogdan ĩółtowski
University of Technology and Life Sciences Faculty of Mechanical Engineering
