The effect of air-fuel equivalence ratio change on the vibration components of an internal-combustion engine

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. 2 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. 3 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 Recen Inno a ions in Mecha onics (RIiM) Vol. 2. (2015). No. 1-2. DOI: 10.17667/ iim.2015.1-2/13. 4 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. DOI: 10.17667/ iim.2015.1-2/13. 5 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 . 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