© Strojni{ki vestnik 50(2004)1,44-54 © Journal of Mechanical Engineering 50(2004)1,44-54 ISSN 0039-2480 ISSN 0039-2480 UDK 621.43.038:665.75 UDC 621.43.038:665.75 Kratki znanstveni prispevek (1.03) Short scientific paper (1.03) Obravnavanje curka plinskega olja in nadomestnih goriv A Spray Analysis of Petrol and Alternative Fuels Martin Volmajer - Breda Kegl V prispevku je obravnavana numerična analiza curkov plinskega olja in nekaterih nadomestnih goriv. Z uporabo paketa računske dinamike tekočin FIRE so bile določene karakteristike curkov (velikost kapljic in domet) plinskega olja, biodizla in odpadnega rastlinskega olja. Nekatere vrednosti karakterističnih veličin curka so bile primerjane tudi z vrednostmi, izračunanimi z uporabo znanih empiričnih modelov za določitev karakteristik curka. Analize so bile izvedene za dva tipa vbrizgalnih sob oz. vbrizgalnih sistemov (neposredni in posredni). V primeru slednjega so rezultati numerične analize primerjani se s fotografijami curka. © 2004 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: vbrizgavanje goriva, olje plinsko olje, biodizel, olja odpadna, olja rastlinska) This paper presents numerical analyses of sprays of diesel and some alternative fuels. The fuel spray characteristics (the droplet size and the penetration length) of diesel fuel, biodiesel and waste cooking oil were calculated using the computational fluid dynamics program FIRE. Some of the characteristics were calculated using existing empirical models. The analyses were made for two different injection systems: direct and indirect injection. In the case of indirect injection, the results were also compared with fuel-spray photographs. © 2004 Journal of Mechanical Engineering. All rights reserved. (Keywords: fuel injection, diesel fuels, biodiesel, waste cooking oils) 0 UVOD Z uporabo nadomestnih goriv rastlinskega porekla lahko klasičen dizelski motor z notranjim zgorevanjem obratuje brez prirastka emisij ogljikovega dioksida (CO2). To pomeni, da se z uporabo teh goriv ne povečuje količina CO2 v atmosferi. Kot gorivo rastlinskega porekla se običajno uporabljajo estri maščobnih kislin rastlin, to so: oljna repica, sončnično olje, sojino olje ipd. Ti estri se imenujejo biodizel. Lahko pa nadomestna goriva izdelujemo tudi iz odpadnega rastlinskega olja. Znano je, da lastnosti goriva, kakor tudi njegova sestava, odločilno vplivajo na postopek vbrizgavanja ter s tem neposredno na postopek zgorevanja in nastanek nezaželenih ostankov. Ob upoštevanju dejstva, da se sestava goriv rastlinskega porekla razlikuje od sestave mineralnih goriv, je za prilagoditev delovanja dizelskega motorja z nadomestnimi gorivi potrebno dobro poznavanje omenjenih postopkov. Z uporabo paketov računske dinamike tekočin (CFD) računalniška oprema dandanes dopušča razmeroma hitre analize postopka 0 INTRODUCTION A conventional compression ignition engine is capable of running with a zero net emission of a carbon dioxide (CO2) when alternative fuels based on vegetable oil are used. In this way the concentra-tion of CO2 in the atmosphere stays the same. For the plant source it is common to use esters from rapeseed, sunflower, soya, etc. These esters are commonly re-ferred to as biodiesel. Alternative fuels can also be made of waste cooking oils. It is well known that the fuel characteristics and the fuel composition significantly affect the in-jection process, which in turn has a direct affect on the combustion and emission-formation processes. Since the composition of vegetable-source fuels dif-fers from that of petroleum-based fuels, the conven-tional compression-ignition engine needs to be adapted to run on alternative fuels. This step requires a good understanding of the injection and combus-tion processes of alternative fuels. Today we are able to run relatively fast analy-ses of the injection and spray-formation processes, as well as the combustion and emission-formation grin^SfcflMISDSD VBgfFMK stran 44 Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol vbrizgavanja, nastanka curka, kakor tudi zgorevanja processes, by using computational fluid dynamics in nastanka emisij, s čimer lahko že pred prvimi (CFD) programs. By using these tools we are able to praktičnimi preizkušnjami do neke mere prilagodimo partly adjust the engine to the new conditions, even motor novim delovnim razmeram. before the first experimental tests. Z namenom spoznavanja vplivov The objective of this paper is to learn how nadomestnih goriv na postopek vbrizgavanja in the alternative fuels affect the injection and spray- nastanek curka ter možnostjo predelave sedanjih formation processes and to get some information sistemov za obratovanje z nadomestnimi gorivi so about how the existing injection systems should be bile izvedene tudi analize v tem prispevku. adapted to run with these fuels. 1 TEORETIČNE OSNOVE 1 THEORETICAL BACKGROUND 1.1 Lastnosti goriva 1.1 Fuel characteristics Rastlinska olja so zgrajena v obliki Vegetable oils exist in the form of trigliceridov, ki jih sestavljajo tri verige ogljikovodikov triglycerides, which consist of three hydrocarbon povezane med seboj z glicerolom. Kot takšna sicer chains connected together by glycerol. Vegetable gorijo, a jih v takšni obliki v praksi zelo redko oils are combustible, but they are rarely used in this uporabljamo. Njihova največja pomanjkljivost je zelo form. The problem with vegetable oils is their very velika viskoznost, ki povzroča težave z dovodom high viscosity, which causes problems with fuel flow goriva. Tem težavam se lahko izognemo z gretjem from the tank to the engine. Those problems can, goriva, večjim prerezom cevi ali s kemičnim however, be reduced by preheating the oil and us- postopkom esterifikacije, to je s proizvodnjo biodizla. ing larger fuel lines or by chemical modification, i.e. To je postopek, pri katerem esterske vezi v trigliceridih producing biodiesel. In this process the ester bonds hidroliziramo, s čimer nastanejo proste maščobne in the triglycerides are hydrolysed. The result is kisline, ki po reakciji z metanolom ali etanolom delajo free fatty acids, which form methyl or ethyl esters metil- ali etilestre. Njihove lastnosti se lahko razlikujejo after a reaction with methanol or ethanol. The prop- v odvisnosti od osnovne rastline. erties of these esters are mainly dependent on the Kot druga nadomestila se lahko uporabi tudi source plant. odpadno rastlinsko olje. To ima podobne lastnosti An alternative is to use waste cooking oil. kakor čisto rastlinsko olje, zato neesterificirano ni But since it has similar properties to pure vegetable najprimernejše za uporabo. Lastnosti biodizla (BIO), oil, in its unesterified form it is not suitable to be used plinskega olja (D2) in odpadnega rastlinskega olja as a fuel. The characteristics of diesel fuel (D2), (ORO-WCO) so predstavljene v preglednici 1. V biodiesel (BIO) and waste cooking oil (WCO) are pre- predstavljenih analizah je bilo, ne glede na nekatere sented in Tab. 1. The WCO used in the presented predhodne negativne izkušnje, uporabljeno rastlinsko analyses was, in spite of past negative experiences, olje, pri katerem ni bil izveden postopek esterifikacije. unesterified. 1.2 Numerična analiza 1.2 Numerical analyses Numerična analiza je narejena z uporabo The numerical analyses were made using programskih paketov RDT FIRE v7.2b in FIRE v.8.1 the CFD programs FIRE v7.2b and FIRE v.8.1 (AVL) (AVL) na delovnih postajah HP 9000/782 in 9000/785 on two workstations (HP 9000/782 and HP 9000/785) oz. osebnem računalniku P3 450 MHz. and a P3 personal computer (450 MHz), respectively. Preglednica 1. Lastnosti goriv [1] in [2] Table 1. Fuel characteristics [1] and [2] D2 BIO ORO / WCO r (kg/m3) 820 do/to 845 875 do/to 900 915 n (mm2/s) 2 do/to 4,5 3,5 do/to 5,0 36,7 H (MJ/kg) 42,6 37,3 - cetanskošt/cetane no. 46 >49 - | lgfinHi(s)bJ][M]lfi[j;?n 04-1_____ stran 45 I^BSSIfTMlGC Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol 1.3 Empirični modeli Kot hiter kazalnik razvoja sprememb oblike curka in kakovosti razpršitve lahko uporabimo tudi nekatere empirične modele, s katerimi lahko ocenimo srednji Sauterjev premer (d 32) in domet curka (LP). V predstavljenem delu sta bila uporabljena naslednja modela: Filipovič [3] (1) za srednji Sauterjev premer kapljic ter Yule-Filipovič [4] (2) za domet curka: d32 vmm = 324,6 L v mm = 2,65-10 -dh V enačbah (1) in (2) sta gostota zraka, rf gostota goriva, sf pomeni povr ra insko napetost goriva, mf dinamično viskoznost goriva, ma pa dinamično viskoznost zraka. Iztočna hitrost je označena z u0, tlačna razlika z Dp, medtem ko dh pomeni premer odprtine šobe. Vse enote so v skladu s sistemom SI. 1.4 Vbrizgalni sistemi V predloženem delu je bil analiziran postopek vbrizgavanja in nastanka curka za dva vbrizgalna sistema: (i) VBRIZGALNI SISTEM 1 (VS1) - klasičen vbrizgalni sistem z linijsko tlačilko in vbrizgalno šobo s štirimi izvrtinami premera 0,375 mm, pri katerem imata odprtini št. 1 in št. 4 nagibni kot kanala odprtine 95°, odprtini št. 2 in št. 3 pa kot 49°, (ii) VBRIZGALNI SISTEM 2 (VS2) - vbrizgalni sistem z rotacijsko tlačilko in šobo s čepom, s premerom odprtine 1,1 mm. 2ŠTEVILCNI PRIMERI Analize so bile izvedene pri dveh različnih obratovalnih režimih (največji vrtilni moment (VS1_A) in največja moč (VS1_B) pri VS1 in največji vrtilni moment (VS2_C) ter 80% vrtilne frekvence največje moči (VS2_D) pri VS2 za tri različna goriva: biodizel (BIO), odpadno rastlinsko olje (ORO) in plinsko olje (D2). Vrtilni frekvenci tlačilke v primeru VS1 sta 600 min1 in 1000 min1, medtem ko vrtilni frekvenci pri VS2 znašata 1000 min1 in 2000 min-1. Analiza z uporabo RDT je za VS1 potekala v diskretiziranem modelu v obliki kocke s stranico 300 mm, za VS2 pa v modelu oblike kvadra izmer 50x50x500 mm. Obe geometrijski obliki predstavljata vbrizgalno komoro. Izmere so bile izbrane v skladu s pričakovanimi dometi in obliko curkov. Za izračun karakteristik vbrizgavanja, potrebnih za določitev začetnih in robnih pogojev 1.3 Empirical models The empirical model for calculating the Sauter mean diameter (d32) and the spray penetration length (L ) can be used as a tool for fast analyses, showing the tendency of the spray changes and the quality of the atomisation. In this paper, two empirical models were used: Filipovič [3] (Eq.1) for the Sauter mean diameter of the droplets, and Yule - Filipovič [4] (Eq.2) for the spray penetration length: ra-u02-dh 3 |rau0'dh s rf-dh-sf -0,1 rf m2f ¦u • d mf (1) (2). In Eq.1 and 2, ra is the air density, rf is the fuel density, sf represents the surface tension, mf is the viscosity of the fuel, and ma is the air viscosity. The outflow velocity is denoted by u0, Dp is the pressure difference, and dh is the nozzle hole diameter. The units of all the input values are according to the SI system. 1.4 Injection system The injection characteristics and the spray formation process were analysed for two injection systems: (i) INJECTION SYSTEM 1 (VS1) - a conventional fuel-injection system with an in-line pump and a four-hole injection nozzle (hole diameter 0.375 mm, holes #1 and #4 have an inclination angle of 95°, whereas holes #2 and #3 have an inclination angle of 49°), (ii) INJECTION SYSTEM 2 (VS2) - an injection system with a rotational pump and a pintle nozzle (hole diameter 1.1mm). 2 NUMERICAL EXAMPLES The analyses were made for two different operating conditions: maximum torque (VS1_A) and rated (VS1_B) for injection system 1 (VS1), and maximum torque (VS2_C) and 80% of the rotational speed at maximum power (VS2_D) for injection system 2 (VS2)). Three different fuels were used: biodiesel (BIO), waste cooking oil (WCO) and diesel fuel (D2). The pump rotational speeds for VS1 were 600 min1 and 1000 min1, and for VS2 the rotational speeds were 1000 and 2000 min1. The CFD analyses were made on the cube model with a side of 300 mm for VS1 and on the block model with sides 50x50x500 mm for VS2. Both geometries represent the injection chamber. The dimensions were set according to the expected spray shapes and the penetration lengths. The injection characteristics needed for the setting of the initial and boundary conditions were grin^SfcflMISDSD VBgfFMK stran 46 Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol numeričnih analiz, je bil uporabljen enorazsežni obtained by using the one-dimensional mathemati- matematični model [6] oz. meritve. V primeru VS1 so cal model [6] and the experimental results, respec- karakteristike vbrizgavanja za posamezno gorivo tively. In the case of VS1 the injection characteristics dobljene iz rezultatov analize, predstavljene v [7], for all three fuels were obtained from the results pre- medtem ko so bile pri VS2 le-te dobljene na podlagi sented in [7], whereas the characteristics in the case meritev. Tlak v komori je 1 bar, temperatura 313 K. of VS2 were measured. The pressure in the chamber Začetna velikost kapljic in verjetnostna porazdelitev was 1 bar, while the temperature was 313 K. The ini- (začetni pogoji) sta določeni v skladu z ugotovitvami tial size of the bubble and the probability distribu- predhodne analize [8]. Pri verjetnostnih porazdelitvah tions were defined according to the findings of pre- v primeru analize nadomestnih goriv je določena vious analyses [8]. The bubble-size distribution in velikost kapljic z največjo verjetnostjo za okrog 15% the case of the alternative fuels was set 15% higher večja od tiste pri plinskem olju. than in the case of diesel fuel. 3 REZULTATI 3 RESULTS V nadaljevanju so predstavljeni rezultati The results of the numerical and empirical analy- numeričnih in empiričnih analiz za vbrizgalni sistem 1 ses for the injection system 1 (VS1) and 2 (VS2) and the (VS1) in 2 (VS2) ter fotografije curka VS2. fuel-spray photographs for VS2 are presented below. 3.1 Vbrizgalni sistem 1 3.1 Injection system 1 3.1.1 Numerična analiza 3.1.1 Numerical analysis Na slikah 1 do 4 so prikazane oblike curka in Fig. 1-4 show the spray shapes and the positions lega kapljic ob koncu vbrizgavanja, izračunane srednje of the droplets at the end of the injection process, the calcu- vrednosti srednjega Sauterovega premera v komori lated mean values of the Sauter mean diameter in the cham- ter največji domet curka pri posameznem gorivu. Na ber, and the maximum spray penetation length for all three slikah 1 do 3 je velikost kapljic predstavljena z fuels. In Fig. 1-3 the size of the droplets is represented by the velikostjo krožcev S slik je razvidno, da je domet curka size of the circles. From the figures presented below it is clear odpadnega rastlinskega olja večji od dometov that the penetration length when using the waste cooking biodizla in plinskega olja. Prav tako je jasno vidna oil is larger than in the case of the biodiesel and the diesel razlika med dometi curka v posameznem obratovalnem fuel. An obvious difference in the penetration lengths under režimu. different operating conditions can also be seen. Zanimivo je, da so v primerjavi It is interesting that the differences between izračunanih največjih dometov (sl.4) razlike the calculated values of the penetration length are smaller nekoliko manjše, kakor bi lahko sklepali iz than the differences between the penetration lengths grafičnega prikaza curkov. Razlike med grafičnim shown in the figures. These differences are probably the prikazom in absolutnimi vrednostmi so verjetno result of the definition of the maximum penetration length posledica tega, da največji domet pomeni pot which is equal to the path of the droplet that travelled the Sl. 1. Curek plinskega olja (levo: največji vrtilni moment (VS1_A), desno: največja moč (VS1_B)) Fig. 1. Diesel fuel spray (left: maximum torque (VS1_A), right: rated (VS1_B)) | lgfinHi(s)bJ][M]lfi[j;?n 04-1_____ stran 47 I^BSSIfTMlGC Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol ¦ 1 - -1 - II II . & .: d ¦¦: & _^H -. I' r p ¦'/:: ..¦ : ')¦ WjS? ¦ML; H rfej-: . ^ <— ^ i- ::-_ 3 0 mm version 7Jib Sl. 2. Curek biodizla (levo: največji vrtilni moment (VS1_A), desno: največja moč (VS1_B)) Fig. 2. Biodiesel spray (left: maximum torque (VS1_A), right: rated (VS1_B)) J J r ^ ¦:^^9B^%4SPa— ... 30 30 mm Sl. 6. Curek plinskega olja pri največjem vrtilnem momentu (VS2_C) Fig. 6. Diesel fuel spray at maximum torque (VS2_C) ^ ^^sasko M9»,nis*i at?<>«z-yi **rjv^-j: Vn^iraä,J«N03!K33LCM!eVIHBaEb3HI Sl. 7. Curek plinskega olja pri 80% vrtilne frekvence največje moči (VS2_D) Fig. 7. Diesel fuel spray at the 80 % of maximum power rotational speed (VS2_D) 200 160 120 80 40 0 D32_VS2_C Lp_VS2_C D32_VS2_D Lp_VS2_D ¦ D2 D BIO DORO/WCO Sl. 8. EMPIRIČNA ANALIZA - primerjava karakteristik curka obravnavanih goriv pri najv. vrt. momentu (D32_VS2_C, LP_VS2_C) in 80% vrt. frekvenci najv. moč (D32_VS2_D, Lp_VS2_D) , D32 je Sauterjev srednji premer , Lp je domet curka Fig. 8. EMPIRICAL ANALYSIS - Comparison of spray characteristics at the max. torque (VS2_C) and at the 80% of rotational speed of the maximum power (VS2_D): D32 is the Sauter mean diameter, Lp is the penetration length 3.2.2 Empirična analiza Rezultati empirične analize za VS2 so prikazani na sliki 8. Na prvi pogled je razvidno, da uporabljena modela napovesta razmeroma kratke curke z velikimi vrednostmi srednjih Sauterjevih premerov, kar ni v skladu s predhodnimi numeričnimi ugotovitvami (sl. 7 in 8) ter v nadaljevanju predstavljenimi fotografijami curka (sl. 9 in 10). 3.2.3 Fotografiranje curka Za primer VS2 je bilo v okviru Laboratorija za motorje z notranjim zgorevanjem Fakultete za strojništvo Maribor izvedeno fotografiranje curka (sl. 9 in 10). Zaradi razmeroma preprostega postopka in izvedbe je kakovost slik sorazmerno slaba, vidni pa 3.2.2 Empirical analysis The empirical analysis results for VS2 are presented in Fig. 8. It can be clearly seen that the empirical models gave rather short sprays with rela-tively high values of the Sauter mean diameter, which is not in accordance with the numerical results (Fig. 7 and 8) and the photographs (Fig. 9 and 10) for this case. 3.2.3 Spray photography For VS2 the spray photographs were taken at the Engine Research Laboratory of the Faculty of Mechanical Engineering, Maribor (Fig. 9 and 10). The quality of presented photographs is relatively low, due to the low resolution and the back grin^SfcflMISDSD VBgfFMK stran 50 « Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol Sl. 9. Fotografije curkov pri VC2_C (od leve: plinsko olje, biodizel, odpadno rastlinsko olje) Fig. 9. Spray photographs for VS2_C (from left: diesel fuel, biodiesel, waste cooking oil) Sl. 10. Fotografije curkov pri VC2_D (od leve: plinsko olje, biodizel, odpadno rastlinsko olje) Fig. 10. Spray photographs for VS2_D (from left: diesel fuel, biodiesel, waste cooking oil) Preglednica 2. Domet curka, dobljen s fotografij Table 2. Spray penetration length acquired from the spray photographs VC2 C VC2 D D2 150 mm 120 mm BIO 230 mm 185 mm WCO 280 mm 215 mm so tudi številni odsevi. Kljub temu je bilo mogoče do neke mere določiti največji domet pri posameznem obratovalnem režimu. S fotografij je razvidno, da je domet v obeh primerih najkrajši v primeru uporabe plinskega olja, najdaljši pa v primeru odpadnega rastlinskega olja. Izmerjene vrednosti so predstavljene v pregl. 2. Vidno je tudi, da je kot curka v bližini odprtine največji pri plinskem olju, kar kaže na boljši razpad goriva. Pri nadomestnih gorivih, posebej pri odpadnem rastlinskem olju, je vidna nit goriva na izstopu iz odprtine, ki se začne trgati komaj na razdalji okrog 70 mm v primeru VS2_C (sl. 9) oz. 50 mm v primeru VS2_D (sl.10). Šele od tukaj dalje lahko govorimo o razpadu curka. 3.3 Razprava Kljub temu, da se rezultati numerične in empirične analize, kakor tudi vrednosti določene s scattering of the stroboscope lamp. Both are the re-sult of a relatively simple procedure. Nevertheless, we were able to measure the spray penetration length under certain operating conditions. From the photographs it is clear that the penetration length is always the shortest when using diesel fuel, and the longest when using waste cooking oil. The measured values are presented in Tab. 2. The spray-cone angle is the largest for the diesel fuel, which also indicates better atomisation of the spray. For the alternative fuels, especially the waste cooking oil, a filament of the fuel at the nozzle outlet can be observed. This starts to decay at a distance of about 70 mm from the nozzle outlet, for VC2_C (Fig. 9), and at about 50 mm for VC2_D (Fig. 10). From this point on we can talk about the spray atomisation. 3.3 Discussion Even though the results of the numerical and empirical analyses as well as the results obtained gfin^OtJJIMISCSD stran 51 Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol fotografijami, medsebojno v celoti ne ujemajo, lahko ugotovimo, da je v vseh analizah zaznan podoben trend spreminjanja karakterističnih veličin curka. Na podlagi podobnih gibanj lahko analiziramo ter do neke mere določimo, kakšen vpliv ima posamezno gorivo na postopek vbrizgavanja, zgorevanja in tvorbe nezaželenih produktov zgorevanja. Tako je v vseh primerih, pri vseh analizah, najslabši razpad curka zaznan pri uporabi odpadnega rastlinskega olja, najboljši pa v primeru plinskega olja. Vrednosti za biodizel so v skoraj vseh primerih med obema omenjenima gorivoma. V odvisnosti od uporabljene analize so te enkrat bližje vrednostim plinskega olja, drugič pa bližje tistim pri odpadnem rastlinskem olju. Glede na to, da je biodizel danes praktično že v uporabi; dovoljenje za uporabo le-tega pa je tudi na svojih najsodobnejših dizelskih motorjih odobrilo precejšnje število proizvajalcev [9], je na vprašanje smiselnosti in ustreznosti uporabe tega goriva že bolj ali manj odgovorjeno. Vsekakor pa velja pri starejših vbrizgalnih sistemih, ki so bili razviti zlasti za klasično gorivo in dosegajo manjše tlake vbrizgavanja, pred uporabo nadomestnih goriv razmisliti o morebitni predelavi vbrizgalnega sistema in zgorevalnega prostora. Na tem mestu se vprašanje ustreznosti oz. vpliva na postopke vbrizgavanja, zgorevanja in tvorbe nezaželenih produktov zgorevanja postavlja bolj za odpadno rastlinsko olje, ki bi lahko ob predstavljenih rezultatih povzročalo nepopolno zgorevanje ter s tem povezan nastanek nezaželenih ostankov zgorevanja. Težave se lahko pričakujejo predvsem s predolgim dometom in s tem povezanim zadevanjem goriva ob steno zgorevalne komore, zato je pametno poiskati možnost spremembe geometrijske oblike zgorevalne komore v primeru delovanja motorja z odpadnim rastlinskim oljem. Na podlagi tega lahko po predstavljenih analizah do neke mere že zanesljivo trdimo, da nepredelano odpadno rastlinsko olje ni primerno gorivo za dizelske motorje. Če na temelju dobljenih karakteristik curka odpadnega rastlinskega olja vseeno do neke mere poskusimo določiti, kako je z emisijami, lahko zapišemo naslednje. V splošnem pri dizelskem motorju, ki obratuje s plinskim oljem, velja, da v primeru slabšega razpada curka prihaja do povečanja emisij saj oz. trdnih delcev. Ne glede na to, da rezultati pri odpadnem rastlinskem olju kažejo najslabši rezultat, teh sklepov zaradi drugačne sestave goriva ne moremo neposredno prenesti na odpadno rastlinsko olje. Rastlinska olja imajo namreč v molekulah vezanega več kisika, kar bi lahko ugodno vplivalo na postopek zgorevanja tudi v primeru slabšega razpada oz. v primeru, ko ni velikega presežka zraka. Težava je tudi v tem, da so trdni delci, ki nastajajo pri postopku zgorevanja nadomestnih goriv, svetlejše barve od tistih pri plinskem olju, zato jih z optičnimi merilnim tehnikami ne moremo zaznati. Glede drugih emisij lahko do neke mere sklepamo, da bi lahko bile emisije NO , zaradi slabšega ^BSfiTTMlliC | stran 52 from the photographs differ significantly, we were able to determine that the trend in the changes of the characteristic values is the same for all the analyses. On this basis we are able to discuss the results and to define how a specific fuel is affecting the injection, combustion and emission-formation processes, at least to some extent. The worst spray atomisation was always obtained when waste cooking oil was used as a fuel; the best results were obtained for the diesel fuel. The values for the biodiesel were always in between. De-pending on the analyses used, the results for the biodiesel were closer to one or other fuel. As biodiesel is already available on sev-eral markets and since many engine producers al-low it to be used in their diesel engines [9], the ques-tions concerning its suitability are more or less an-swered. However, conventional injection systems, which were primarily designed for use with diesel fuel and for which injection pressures are lower, need to be redesigned before using alternative fuels. In particular, the combustion chamber should be rede-signed. The suitability and the influence on the processes of injection, combustion and emission formation, should be discussed for the waste cooking oil, since these factors could cause incomplete com-bustion followed by emission formation. The problems could occur due to a high penetration length and possible collision with the combustion-chamber walls. For this reason possible ways of changing the combustion-chamber geometries when waste cook-ing oil is used as a fuel should be discussed. Accord-ing to these discussions we can already confirm the statement that unmodified waste cooking oil is not suitable for use as a fuel in compression-ignition engines. Based on the presented waste cooking-oil spray characteristics we can try to predict the emis-sions, to some extent. In general, the soot emis-sions of a compression-ignition engine operating on diesel fuel are bigger when the fuel atomisation is worse. However, despite the fact that the spray atomisation in the case of waste cooking oil was the worst, we cannot directly transfer these statements to the case of waste cooking oil, since the structure of the fuel is different. Vegetable oils have more oxygen bonded in the molecule, which positively affects the combustion process, even if the spray atomisation is bad and there is no large excess of air. The other problem is that the particulate matter during the alternative-fuel combustion process is brighter than in case of diesel fuel. This means it cannot be measured with conventional optical meth-ods. Regarding the other emissions, the emission of NOx could be smaller since the combustion tem-peratures could be lower due to worse atomisation. Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol razpada curka, nekoliko manjše, česar pa zaradi razlik v sestavi goriva ponovno ne moremo zanesljivo trditi. 4 SKLEP Na podlagi predstavljenih rezultatov so mogoči naslednji sklepi v zvezi z uporabo plinskega olja, biodizla in odpadnega rastlinskega olja v dizelskem motorju: Vse analize kažejo podobne usmeritve vplivov goriva na značilnosti curka. Biodizel in odpadno rastlinsko olje pri postopku vbrizgavanja obeh vbrizgalnih sistemov dajeta večje kapljice in imata daljši domet, kar je posebej očitno v primeru odpadnega rastlinskega olja. Prve analize kažejo, da bi lahko uporaba nadomestnih goriv na klasičnih vbrizgalnih sistemih oz. motorjih, zasnovanih za uporabo plinskega olja, povzročala težave z zadevanjem curka goriva ob stene zgorevalnega prostora oz. vdolbine na batu. Predstavljeni rezultati kažejo, da bodo za boljše poznavanje vpliva nadomestnih goriv na postopek vbrizgavanja potrebne še podrobnejše analize. Tako bo treba opravitišeštevilne meritve obratovalnih značilnosti motorja ter pred tem po možnosti tudi curka vbrizganega goriva. Prav tako je smiselno izboljšati sistem za vidno opazovanje curka (fotografiranje), kakor tudi vpeljati sodobnejše tehnike merjenja značilnosti curka. Nenazadnje pa bo treba razmišljati tudi o modelih vbrizgavanja (RDT), ki bodo dovolj natančno popisali pogoje pri nadomestnih gorivih. 5 ZAHVALA Za rezultate meritev karakteristik vbrizgavanja VS2 in sodelovanje pri fotografiranju curka se avtorja najlepše zahvaljujeta sodelavcem Fakultete za strojništvo Maribor, mag. Gorazdu Bombeku, Avgustu Polaniču in Andreju Pagonu ter študentu Borutu Peklarju. But there is again the question how the fuel structure influences these processes. 4 CONCLUSION The following conclusions can be made regarding the use of diesel, Biodiesel and waste cooking oil in a compression-ignition engine: All the analyses gave similar trends concerning how the fuel affects the spray characteristics. The penetration length is higher and the droplets are bigger when the Biodiesel and the waste cooking oil are used. The results vary, particularly in the case of waste cooking oil. The first analyses show that the use of alternative fuels in conventional injection systems, i.e. engines designed for diesel fuel, could cause problems related to the collision of the spray with the chamber wall or the piston. The presented results show that for a better understanding of the alternative fuel’s influence on the injection process some further analyses need to be made. In future, many additional measurements of the engine characteristics should be made. The system for optical spray observation should be modified. And last, but not least, the CFD models should be modified in order to run the analyses with alternative fuels more accurately. 5 ACKNOWLEDGMENT The authors’ special thanks go to their coworkers at the Faculty of Mechanical Engineering, Maribor (mag.Gorazd Bombek, Andrej Pagon, Avgust Polanič), and to student Borut Peklar for providing the experimental results of the injection characteristics for VS2 and for helping with the spray photography. 6 LITERATURA 6 REFERENCES [1] DIN V 51606, Ausgabe:1994-06 Flüssige Kraftstoffe; Dieselkraftstoff aus Pflanzenölmethylester [2] Koerbitz, W. (1999) Biodiesel production in Europe and North America, an Encouraging Prospect, Renewable Energy 16, 1078-1083 [3] Filipovič I. (1983) Analiza motornih parametra ubrizgavanja alternativnih goriva, PhD Thesis, Masinski fakultet Univerze u Sarajevu, Sarajevo. [4] Yule, A.J., I. Filipovič (1992) On the break-up times and lengths of diesel sprays, Int. J. Heat and Fluid Flow, 13, 197-206. [5] Hiruyasu, H. et al. (1980) Fuel spray characterization in diesel engines, combustion modelling in reciprocating engines, 369-408, Plenum Press. [6] Kegl, B., An improved mathematical model of conventional FIE processes, SAE 950079. [7] Volmajer, M., B.Kegl, PPogorevc (2002) Injection characteristics of an in-line fuel injection system using the nadomeste fuels, Journal of KONES, vol.9, no.1-2, 259-267. [8] Volmajer, M., B. Kegl (2001) Obravnavanje curka plinskega olja, Diesel-spray analysis. Strojniški vestnik., letnik 47, št. 10, 627-636. [9] BIODIESEL: Aussagen der Fahrzeughersteller, UFOP, Berlin, 2002 (http://www.ufop.de/Freigaben.pdf) gfin^OtJJIMISCSD stran 53 Volmajer M., Kegl B.: Obravnavanje curka plinskega olja - A Spray Analysis of Petrol Naslov avtorjev: mag. Martin Volmajer doc.dr. Breda Kegl Univerza v Mariboru Fakulteta za strojništvo Smetanova ulica 17 2000 Maribor martinvolmajer@uni-mb.si breda.kegl@uni-mb.si Authors’ Address: Mag. Martin Volmajer Doc.Dr. Breda Kegl University of Maribor Faculty of mechanical eng. Smetanova ulica 17 2000 Maribor, Slovenia martin.volmajer@uni-mb.si breda.kegl@uni-mb.si Prejeto: Received: 13.10.2003 Sprejeto: Accepted: 12.2.2004 Odprto za diskusijo: 1 leto Open for discussion: 1 year grin^SfcflMISDSD VBgfFMK stran 54