Recen Inno a ions in Mecha onics (RIiM) Vol. 2. (2015). No. 1-2.
DOI: 10.17667/ iim.2015.1-2/13.
1
The e ec o ai - uel equi alence a io change on
he ib a ion componen s o an in e nal-combus ion
engine
Gabo Manhe z
Depa men o Mecha onics, Op ics and Mechanical
Enginee ing In o ma ics
Budapes Uni e si y o Technology and Economics
Budapes , Hunga y
Co esponding au ho ’s e-mail: [email p o ec ed]me.hu
Akos An al
Depa men o Mecha onics, Op ics and Mechanical
Enginee ing In o ma ics
Budapes Uni e si y o Technology and Economics
Budapes , Hunga y
Abs ac — Nowadays he au omo i e indus y and he mo o
de elopmen a e one o he mos dynamically de eloping
indus ies. One solu ion o he diagnos ic sys ems p o iding
eliabili y is he acous ic and ib a ion measu emen sys em,
which can indica e and p edic a a ie y o mal unc ions a e
signal p ocessing. The pu pose o his expe imen is o analyze
he e ec o he ai - uel equi alence a io on he ib a ion
componen s o an in e nal-combus ion engine (ICE) which is a
pa o he in ques ion measu emen sys em. In he ocus o he
expe imen s a e he analysis o he ime signal, i s spec a, and
he powe con en o he signal. Wi h he inc emen o he ai - uel
a io he ampli udes o he measu ed signal and i s spec al
ampli udes showed a downwa d end as he RMS alues. In
addi ion, ce ain equency componen s disappea ed du ing he
ac ua ion o he ICE wi h an elec omo o , so he
cha ac e iza ion o he combus ion could be come o he on .
Keywo ds— ib a ion diagnos ics; in e nal-combus ion engine;
ai - uel equi alence a io, spec a, RMS
I. INTRODUCTION
The au omo i e manu ac u e s a e ying o adap mo e
om he di ec i es o he compe i ion on he ma ke . To mee
hese equi emen s he bes , hey need o ind he bes
comp omise be ween he p ice, he ope a ional sa e y, he uel
consump ion, he emission limi s and he pe o mance. The
pe o mance can be in luenced by he ai - uel equi alence
a io which can be esul ed in he examina ion o he pollu an
emission o he alida ion o ma hema ical models. Se e al
e e ences desc ibe his kind o esea ch wo ks based on ICEs
[1]-[3]. Besides o he ai - uel a io, he engine cha ac e is ics
and ope a ion can be in luenced wi h a ious ypes o uel as
well [4]. Nowadays, because o he en i onmen al awa eness,
expe imen ally iendly uels a e used also. In [5] an
expe imen al s udy can be seen on a di ec injec ion diesel
engine ope a ed wi h Kapok me hyl.
An in e nal-combus ion engine has se e al physical alues
which can be measu ed and he esul s cha ac e ize he s a e o
he engine. Vib a ion analysis is applied equen ly as he
basis o expe sys ems. Some o hese sys ems a e used o
condi ion moni o ing and aul diagnosis [6]-[8]. A e y
in e es ing esea ch can be seen in e e ence [9] whe e he
combina ion o he ib a ion and acous ic emission was
applied. F equency-based analysis is o en used in he
ib a ion diagnos ics o ICEs. Lin e . al [10] ep esen s a
ib a ion diagnos ic echnique based on he co ela ion o
disc e e spec um. In e e ence [11] he combina ion o he
ime and equency domain analysis can be seen. I can be
concluded om he li e a u e ha he ib a ion analysis o he
ICEs is qui e common and he esea ch ends a e e y di e se
o e and abo e he ela ion be ween he ib a ion and he ai -
uel a io is no a equen ly discussed opic. Howe e , he
applied diagnos ic me hods a e becoming mo e complex and
he simple ones being o go en o will be no applied
anywhe e. This esea ch wo k will go back o he basic
ib a ion diagnos ic me hods which made us also possible o
de e mine co ela ion be ween he nume ical esul s and he
ac ual ai - uel equi alence a io.
A. The Ai - uel Equi alence Ra io
The ai - uel equi alence a io gi es he a io o he in ake
ai -amoun and he heo e ically equi ed ai -amoun o he
combus ion. This a io a ec s he engines e iciency,
pe o mance and he pollu an emission. Du ing he
combus ion, because i is a chemical p ocess, he co ec a io
o he p esen uel and oxygen is a e y impo an ac o . I he
amoun o he ai and he uel is no close o equilib ium
du ing he eac ion, he combina ion o he inpu and ou pu
ma e ials will no be ully.
The ai - uel equi alence a io a he ideal – heo e ic –
ai - uel a io is 1, i.e. he mix u e is s oichiome ic. The
combus ion equi es ha he mix u e need o be be ween he
lowe and he uppe lammabili y limi . Wi hin his ange, i
he ai - uel equi alence a io is less han 1 (i.e. he mix u e is
uel- ich) he chemically bounded ene gy canno ully be
con e ed in o hea – a signi ican amoun o CO emission
occu s. I he mix u e is uel-poo , he ai - uel equi alence
Recen Inno a ions in Mecha onics (RIiM) Vol. 2. (2015). No. 1-2.
DOI: 10.17667/ iim.2015.1-2/13.
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a io will be g ea e han 1; he mix u e con ains mo e oxygen
han i is necessa y o he combus ion.
The ai - uel equi alence a io is he a io o he in ake ai -
amoun and he heo e ically equi ed ai -amoun , so i s alue
can be de e mined om oxygen concen a ion o he lue gas:
measu ed
OL
V
O
O
L
L
,20
0
2
2
09,20
9,20
21
1










 
whe e: L is he ac ual ai -amoun , L0 is he heo e ic ai -
amoun , V0 is he heo e ic lue gas-amoun .
The main ask is o analyze he e ec o change o he ai -
uel equi alence a io on he ib a ion componen s o an
in e nal-combus ion engine.
II. EXPERIMENTAL SETUP
Today’s mode n ehicle engines a e equipped wi h many
senso s and con ol uni s which de e mine he equi ed
mix u e o he ac ual ope a ing s a e. The inadequa e ai - uel
equi alence a io can a ec o he pa ame e s analyzed by he
ECM so he con inuous moni o ing o hese pa ame e s is he
base o he diagnos ics.
The ib a ion measu emen s based on a gas-powe ed ICE.
The main pa o he uni is a BAG-20 ype de ice
manu ac u ed by Ganz-Se L d. which consis s o he
ollowing componen s
 Wiscon To al TM27 ype gas-engine
 Ma elli CX IM B3 180M ype asynch onous gene a o
Fo he measu emen s a single-axis knock senso used in
au omo i e indus y manu ac u ed by Siemens was applied. I s
signal was eco ded by a USB-6008 DAQ de ice p oduced by
Na ional Ins umen s. The da a acquisi ion de ice had 12bi
esolu ion and 10000samples/sec maximum sampling
equency. Wi h hese de ices he lowe equency ib a ion
o he engine we e measu ed well bu o u he esea ches i
is essen ial o examine he highe equency anges. The uel-
ai mix u e o he engine was con olled wi h a al e and i
was de e mined om he oxygen concen a ion o he exhaus
gas. To measu e he O2 concen a ion du ing he es a
Se omex 570A ype pa amagne ic de ice was used.
In o de o moun he knock senso wo moun ing place
we e possible. The i s was a he join o he c ank-case and
he cylinde -head, he second was on he c ack-case (Fig. 1).
F om he measu emen s o he i s moun ing place, a numbe
o ac o s seemed o a ec nega i ely he esul s.
Fig. 1. The moun ing o he accele ome e on he i s (le ) and on he
second ( igh ) moun ing place
One o he p oblems was he moun ing place i sel , since
he c ank-case and he cylinde -head was no lush so he
senso could no abu on comple ely on he su ace. A space
was needed o be equipped which wo ked as a sp ing and
caused up o 100 m/s2 (hence o wa d [g]) accele a ion alues
in he ime signal (Fig. 2). Ano he p oblem was he hickness
o he space because he base o he accele ome e could no
s ill abu comple ely on he cas o he c ank-case. The hi d
p oblem was he bad ib a ion ansmission o he pain ing o
he engine o he senso . On he housing was app ox. a 0,3mm
hink laye o pain which was no conduci e o he
measu emen as well. These ac o s men ioned abo e b ough
majo noise in o he sys em, as well as hey occu ed non- eal
equencies in he spec um and he eal ones ha e been
blu ed.
A he second moun ing place, aking in o accoun he
expe ienced de ec s p e iously, he pain has been emo ed
om he engine and he accele ome e could be able o be
moun ed comple ely on he su ace wi hou a space .
The esul s ob ained wi h his se -up ca ied much mo e
p ocessable in o ma ion. The maximum accele a ion alue o
he measu emen s pe o med a he second moun ing place
nea ly wi h he same ai - uel equi alence a io was less han
hal o he p e ious.
Fig. 2. The eco ded ime signals o senso a he i s (abo e) and he second
(bo om) moun ing place – he ime [s] unc ion o he accele a ion [g]
Recen Inno a ions in Mecha onics (RIiM) Vol. 2. (2015). No. 1-2.
DOI: 10.17667/ iim.2015.1-2/13.
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Du ing he measu emen he engine’s speed was 1500
RPM ( o a ion pe minu e) which was equal o 25Hz. Due o
he p ope ies o he da a acquisi ion ca d, he maximum
compu able 5000 Hz was su ice o he analysis o he lowe
equencies. The ca d ecei ed ol age signal wi h mV
magni udes he e o e o de e mine he accele a ion alues a
con e sion had o be applied. The sensi i i y o he senso was
30mV/g which needed o be co ec ed by -8,1mV/g p o me e .
The a ached cable leng h was 0,74m which dec eased he
o iginal sensi i i y wi h 6mV so he esul ing sensi i i y o he
senso was 24mV/g.
Du ing he esea ch h ee ime signals we e measu ed a
wa m engine unde di e en ai - uel equi alence a ios
(Table I.) as well as ano he signal which was eco ded when
he e was no combus ion in he engine only he asynch onous
machine ac ua ed i .
TABLE I. THE THREE PRESET AIR-FUEL EQUIVALENCE RATIO VALUES
DURING THE MEASUREMENTS
O2 con en o
he exhaus gas
[%]
Ai - uel
equi alence
a io [-]
1,3
1,063
3,9
1,214
7,6
1,515
III. THE EVALUATION OF THE MEASUREMENT RESULTS
The measu emen s we e ca ied ou on cons an pm, so as
a consequence he equency componen s o he signal should
ha e changed only a li le. This can be e i ied i he ime
signal was subjec o he STFT1 ans o ma ion [12] wi h
which he ime- equency-ampli ude unc ion, he so-called
Wa e all-diag am could be plo ed.
The STFT p inciples a e he same as he as Fou ie
ans o m bu in his case he ans o m is execu ed a speci ic
ime s eps and i s equency esolu ion is much less. I du ing
he measu emen he spec a would ha e changed, i would be
clea ly isible on he diag am.
On he signal measu ed a he lowes ai - uel equi alence
a io such ans o ma ion has been execu ed on which i is
clea ly isible ha he spec um does no change in ime
signi ican ly as i was expec ed. On he h ee-dimensional
1 Sho -Time Fou ie T ans o m
diag am he spec a can be seen be ween 20 and 32,6 seconds
wi h a s ep size o 0,7seconds. The illus a ed equency ange
is he 0-700Hz in e al.
To e alua e he measu emen s a he gi en ai - uel
equi alence a ios he ampli udes o he ime signals, he
spec al ampli udes and componen s, and he powe con en
(RMS2 alue) o he signal should be analyzed.
Fig. 3. STFT ans o m pe o med a he lowes ai - uel equi alence a io
( he ime [s] unc ion o he ampli ude [g] and he equency [Hz])
A. The Analysis O The Time Signals
In he able below he maximum and minimum ampli ude
alues o he en i e ime signals a e shown.
TABLE II. THE MAXIMUM AND MINIMUM AMPLITUDE VALUES OF THE FOUR
MEASUREMENT SETUP AS A FUNCTION OF THE AIR-FUEL EQUIVALENCE RATIO
Ai - uel
equi alence
a io [-]
Maximum
accele a ion [s]
Minimum
accele a ion [s]
1,063
46,57
-54,645
1,214
36,81
-38,306
1,515
31,51
-32,491

29,38
-28,97
The able shows ha he maximum and minimum
ampli udes o he ime signals ha e a dec easing as unc ion o
he ai - uel equi alence a io. This means ha he deg ada ion
o he ai - uel mix u e, i.e. he s ep-by-s ep ga bling o he
pe ec ion o he combus ion, he ib a ion componen s we e
dec easing. In he case o no combus ion (ac ua ion wi h he
asynch onous machine) we e he ib a ion componen s he
lowes . This led o he conclusion ha he combus ion i sel
could a ec he ib a ion o he engine.
B. The Analysis O The Spec a
Based on he esul s o he STFT analysis, he Fou ie
ans o ma ion could be used o de e mine he spec al
componen s. Figu e 4 shows he spec a o a ime signal
2 Roo Mean Squa e
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belongs o =1,063 ai - uel equi alence a io. Fo he
aceabili y o he la e analysis ha equency componen was
ma ked which belongs o he e o he engine (25Hz). In
addi ion, his equencies mul iplies could be ound which
could be a esul o he ope a ion o he a ious engine
componen s.
Se e al componen s o he engine depend on he e o he
c anksha hus ha could be iden i ied which componen
belongs o which ha monic o spec al componen . The e o
he camsha is he hal o he e o he c anksha so he
ela ed equency componen is 12,5Hz. The 50Hz componen
may be in connec ion wi h he combus ion p ocess bu he
elec ical 50Hz was also p esen ing signi ican . Due o he
ou cylinde s he combus ion occu ed in wo cylinde s p o a
o a ion and he equency o he asynch onous machine
changed his componen as well.
On he spec a o he measu emen s a h ee di e en ai -
uel equi alence a ios i could be seen ha he ampli udes o
he componen s we e p og essi ely dec easing (Fig. 8) o e en
disappea ed in he backg ound noise. As ega ds o he
analysis o he ha monic componen s, ha signal eco ded a
ac ua ion o he engine wi h asynch onous machine was also
analyzed (Fig. 7). On his i could be seen ha he 48,5Hz
componen is much highe han he 25Hz componen . A his
case wo p ominen equencies should be highligh ed. The
i s one is he 48,5Hz componen which de i ed om he
50Hz o he gene a o as well as om i s cha ac e is ic 3%
slip. The o o o he gene a o has ou poles so i s o h
ha monic equency is 194Hz (4x48,5=194Hz).
Compa ing he spec a wi h each o he , i can be concluded
ha in he case o he disappea ance o he equency
componen s a asynch onous machine ac ua ion, and he
dec easing o he ampli udes ( he combus ion equencies
we e no supe pona ed on o he o he componen s) we e
esul ed om he cha ac e (o he exis ence) o he
combus ion. The equencies which comple ely disappea ed a
he low- equency ange: 75Hz, 100Hz, 112,5Hz, 125Hz,
150Hz.
Fig. 4. Spec a a =1,063 ai - uel equi alence a io ( he equency [Hz]
unc ion o he accele a ion [g])
Fig. 5. Spec a a =1,214 ai - uel equi alence a io ( he equency [Hz]
unc ion o he accele a ion [g])
Fig. 6. Spec a a =1,515 ai - uel equi alence a io ( he equency [Hz]
unc ion o he accele a ion [g])
Fig. 7. Spec a a he ac ua ion wi h he asynch onous machine ( he
equency [Hz] unc ion o he accele a ion [g])
Recen Inno a ions in Mecha onics (RIiM) Vol. 2. (2015). No. 1-2.
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Fig. 8. The changes o he ampli udes o some equency componen as a
unc ion o he ai - uel equi alence a io
Powe Con en
In ib a ion diagnos ics and analysis, a gene ally accep ed
measu e is he RMS alue o he signal which ep esen s he
powe con en o he s udied signal sec ion in a nume ical
o m. This powe con en is de i ed om he selec ed a iable
in eg al o he analyzed sec ion. Du ing he pos -p ocessing,
he ime signal and he spec a RMS alue was calcula ed wi h
he ollowing o mulas [12]:
In case o ime signal:
  
In case o spec a:
 
As he e he powe con en was he main poin o he
analysis ha cases was needed o be s udied when he e was
combus ion in he engine, i.e. he asynch onous machine
ac ua ion was i ele an in his case.
Be o e p ocessing he measu emen esul s he dec easing
o he RMS alues we e expec ed as he unc ion o he ai -
uel equi alence a io. The heo e ical explana ion o his is
(as be o e) because o he deg ada ion o he mix u e he
combus ion will be shi ed om he =1 alue equi ed o he
pe ec combus ion, so he e ec i e medium p essu e and
he eby he o que will be educed.
The esul s (Table III.) we e as expec ed. This means ha
all o he RMS alues o he ime signals and he spec um
showed a dec easing end do o he inc ease o he ai - uel
equi alence a io.
TABLE III. THE RMS VALUES OF THE TIME SIGNAL AND THE SPECTRA AS
FUNCTION OF THE AIR-FUEL EQUIVALENCE RATIO
Ai - uel
equi alence
a io [-]
Time signal
RMS
[g RMS]
FFT ampli ude
RMS [g RMS]
(0-300Hz)
1,063
2,57438
0,01080030
1,214
2,11306
0,00814465
1,515
2,06645
0,00659716
C. Fu he esea ch oppo uni ies
To imp o e and suppo he esea ch esul s u he
measu emen s a e necessa y e.g. wi h less han one ai - uel
equi alence a io, a iable e and load, adial ib a ion
measu emen s and wi h he use o a da a acquisi ion ca d
ha ing highe esolu ion and sampling equency. Wi h hese
esul s a complex engine cha ac e is ic will be able o
ob ained.
IV. CONCLUSION
The expe imen al esul s showed ha wi h he inc ease o
he ai - uel equi alence a io o a gas engine ope a ing a a
cons an speed, he ampli udes o he measu ed signals and
spec um dec eased as well as hei RMS alues – he powe
con en .
This means ha nume ical esul s o he basis ib a ion
diagnos ic me hods a e able o show co ela ions and ends
be ween he ai uel a ion and he ib a ion o a gas engine.
Du ing he measu emen s he engine was ac ua ed wi h an
asynch onous machine as well – he e was no combus ion in
he combus ion chambe . As a esul , compa ed o he cases
wi h combus ion, he ampli ude alues we e he leas and
spec al componen s disappea ed.
The eason could be ha he e was no combus ion, so i s
spec al componen s we e no p esen and we e no added o
he ib a ions o igina ed om he mechanical sys em. Based
on his obse a ion i can be concluded ha he high equency
ib a ions caused by he combus ion may be de ec able wi h
p ope algo i hms.
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