INFLUENCE OF THE EXHAUST GAS RECIRCULATION ON THE OXYGEN CONTENTS AND ITS EXCESS RATIO IN THE ENGINE COMBUSTION CHAMBER

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1 Journal of KONES Powertrain and Tranport Vol. 0 No INFLUENCE OF THE EXHAUST GAS ECICULATION ON THE OXYGEN CONTENTS AND ITS EXCESS ATIO IN THE ENGINE COMBUSTION CHAMBE Stan Potrzednik Zbigniew mudka Grzegorz Przybya Sileian Univerity of Technology Intitute of Thermal Technology Konarkiego Street Gliwice Poland tel.: fax.: pot@poll.pl Abtract Exhaut ga recirculation (EG) can be realized on the external or internal way. The main goal of EG i to decreae the combution temperature of the combutible mixture by increaing the relative heat capacity of the working medium. An additional fect i to reduce the oxygen content in the ga mixture flowing into the combution chamber. To quantify the exhaut ga recirculation ome decriptive parameter are dined including: exhaut ga recirculation rate multiple of exhaut ga recirculation K relative exhaut ga recirculation W. The analyi concern the fective oxygen exce ratio in the combutible mixture and the o-called internal oxygen exce ratio w which additionally take into account the upplied oxygen with the recirculation tream. It wa found that with increaing of the exhaut ga recirculation degree ytematically decreae the content of the oxygen [O ] d in the combutible mixture while increae the oxygen exce ratio oberved in the exhaut gae. Change of thi all parameter influence the combution codition in the engine cylinder and next the achieved pecifaic work energy ficiency and emiion of the combution engine. An advanced ytem with independent early exhaut valve cloing enable realization of an internal EG. Effectivene of internal recirculation i lower than the external recirculation. Keyword: exhaut ga recirculation oxygen content toichiometric condition oxygen exce 1. Introduction ISSN: e-issn: DOI: / Exhaut ga recirculation (EG) mean the recycling of the flu gae generated in the device into the combution chamber of the ame unit. The main goal of EG i to decreae the combution temperature of the combutible mixture by increaing the relative heat capacity of the working medium. An additional fect i to reduce the oxygen content [O]d in the ga mixture flowing into the combution chamber. Both of thee fect contribute fectively to a ignificant reduction of nitrogen oxide [NOx] emiion produced during fuel-mixture combution. In thi repect exhaut ga recirculation i a fundamental element of the o-called low-emiion fuel combution. Exhaut ga recirculation can be realized on the external (bypa of exhaut gae) or internal way. Uing the external EG the ma tream and parameter (e.g. temperature T) of recycled flu gae can be more precie programmed and conditioned. An advanced new ytem with e.g. independent early exhaut valve cloing enable realization of an internal EG. Therore fectivene of internal recirculation i ignificantly lower than the external recirculation. The analyi concern the fective oxygen exce ratio in the combutible mixture and the o-called internal oxygen exce ratio w which additionally take into account the upplied oxygen with the recirculated tream. On thi way fective change of the exhaut ga recirculation influence the content of the oxygen [O]d in the combutible mixture too. Thi both parameter influence the combution condition in the engine cylinder and next the achieved pecific work energy ficiency and emiion of the combution engine.

2 . Quantitative parameter of the EG S. Potrzednik Z. mudka G. Przybya Exhaut ga recirculation (EG) i an important element of low-emiion fuel combution. To quantify the exhaut ga recirculation ome decriptive parameter are dined including: exhaut ga recirculation rate: multiple of exhaut ga recirculation: relative exhaut ga recirculation: K W df n df df n r c r r a 0 0 K 0 W 1 (1) () (3) where: kmol/ tream of recirculated exhaut ga (recirculation) within the ytem r c kmol/ the total flue ga tream flowing from the combution chamber kmol/ exhaut ga tream (net) flowing out from the ytem to the environment. The above lited dinition of EG parameter illutrate a model ytem hown in the Fig. 1. recirculated exhaut ga tream r kmol / mixture oxygen O d d COMBUSTION CHAMBE r kmol / exhaut ga tream kmol / freh air tream a kmol / fuel tream m p kg / total exhaut ga tream c kmol / df df r r exhaut ga recirculation ratio: 0 1 relative recirculation: W 0 W c a df r multiplicity of exhaut ga recirculation: K 0 K whereby: K W K. 1 a Fig. 1. Typical ytem with the external exhaut ga recirculation The ubtance balance of the exhaut ga node (at the outlet fig. 1) follow the relationhip: c (4) from which having regard to the dinition (1) () (3) the relationhip are obtained: r K 1 W K a. (5) 316

3 Influence of the Exhaut Ga ecirculation on the Oxygen Content and It Exce atio in the Engine Exhaut ga tream kmol/ flowing out from the ytem to the environment i cloely aociated with a tream of freh air a kmol/ flowing into the ytem and therore uually hold the following inequality > a from where reult relation: W > K. Likewie with regard to the dry flue gae can be enter the appropriate quantitative parameter of the flu ga recirculation which include: dry exhaut ga recirculation rate: df r 0 1 (6) n c multiple of dry exhaut ga recirculation: df n r K 0 K n (7) relative dry exhaut ga recirculation: df r W 0 W (8) a where: kmol/ ubtance tream of the recirculated dry exhaut ga within the ytem r c kmol/ dry flue ga tream flowing from the combution chamber kmol/ dry exhaut ga tream (net) flowing out from the ytem to the environment. The tream kmol/ of dry exhaut ga flowing out from the ytem into the environment i cloely linked with the dry air tream a kmol/ flowing into the ytem and therore uually the following inequality hold: < a from where reult relation: W < K. The quotient of thee mentioned tream i a follow: 1 min ( 1) a a min where: fective air (oxygen) exce ratio and toichiometric quantitie: a min n min depend only from the compoition (element) of the combuted fuel e.g. for the tandard compoition (for given ma content: c = 0.84 h = 0.14; o = 0.01 min n = = 0.005) of engine fuel can be taken: amin For the global ytem (fig. 1 when recirculation located inide the control urface) it may be written an fective air (oxygen) exce ratio at auming that the combution i complete and total then: min ( 1) amin (10) and uing (7) the ubtance tream of the recirculated dry exhaut ga reult:. (11) r K nmin ( 1) namin The oxygen content [O] in combution product leaving the ytem can be calculated uing relation: df [ O ] O amin 01 ( 1) (1) min ( 1) 317

4 S. Potrzednik Z. mudka G. Przybya and principally i independent from the recirculation ratio occurring in the ytem. Taking into account that the combuted fuel i a tandard engine fuel: (ma content: c = 0.84 h = 0.14 o = 0.01 n = = 0.005) then on bae of eq. (1) can be written: [ O ] 0.1 ( 1). (13) ( 1) With the increae of the fective oxygen exce ratio the oxygen content [O] in dry flue ga leaving the ytem increae approaching to the value of oxygen tandard content (0.1) in the air upplied from the environment into the ytem. By meauring the oxygen content [O] in the flue ga and next uing the achieved eq. (13) the value of actual fective air exce ratio can be determined. It can be proved on the bai of the given dinition that at the end occur ome benicial identitie: 0 1 (14) furthermore alo: wherea: K K K 0 K (15) W K (16) 1 K 1 X z W (17) 1 X z a where: Xza Xz molar humidity degree (repectively of the air and exhaut ga) and a uually: Xz > Xza o therore: W > W. 3. Effective and internal oxygen exce ratio and it content The combution of fuel inide the ytem with realized exhaut ga recirculation doe not occur in an atmophere of pure air but in a mixture of air and exhaut ga. The eential i the preence of oxygen in the real combutible mixture. Oxygen flow into the combution chamber with both freh air tream in an amount of [0.1 a ] a well a a component of the recirculating exhaut ga tream in an amount n O r. An illutration of thi i the diagram hown in the Fig.. The total oxygen tream O which flow into the combution chamber i: O O a O r n O 0.1 a [ O r and then: ]. (18) It i expedient to dine the o-called. internal oxygen exce ratio w which i: df O O w (19) 0.1 O a a m 0. 1 min p and determine the fuel burn condition in the combution chamber. After taking into account formula (9) (18) and uing the recirculation rate form. (1) the equation (19) take next the finally form: w ( 1) (0) 1 318

5 Influence of the Exhaut Ga ecirculation on the Oxygen Content and It Exce atio in the Engine recirculating exhaut ga tream r kmol / ga mixture oxygen O d inlet air tream a kmol / d fuel tream m p kg / fective air exce ratio: COMBUSTION CHAMBE total exhaut ga tream c kmol / internal air exce ratio: w ( 1 w 1 ) r kmol / exhaut ga tream kmol / fective air exce ratio: df r 0 1 c exhaut ga ratio and next: Fig.. Air (oxygen) exce ratio in the ytem with external exhaut ga recirculation K ( 1). (1) w From eq. (0) and (1) it how clearly that the oxygen exce ratio: w >. Further an increae of the exhaut ga recirculation rate while keeping contant value of the fective air (oxygen) exce ratio = idem the value of the internal oxygen exce ratio w gradually increae a illutrated in the Fig. 3. Fig. 3. Influence of the exhaut ga recirculation rate on the internal oxygen exce ratio w Uually with an increae of the exhaut ga recirculation tream i reduced flow a of freh combution air and thu the tream m of the fuel conumed (while maintaining the unchanged p value of the fective air (oxygen) exce ratio = idem). Thi i omewhat connected with a decreae of the fective engine torque Me and next it power Ne which i proportional to the tream m of the fuel conumed. p 319

6 S. Potrzednik Z. mudka G. Przybya Exhaut ga recirculation caue that the combution chamber i fed with the tream of gaeou mixture d kmol/ which i formed after mixing the two tream: freh air a and exhaut ga recirculating r that i: d r a d r a () whereby the econd equation relate to the dry ga occurring in the ytem. Intereting i the oxygen content [O]d in the ga tream at the inlet to the chamber which i: df O d 0.1 a [ O] r [ O ] d (3) d r a where equation (1) () hould be taken into account. In order to ue the degree (rate) of recirculation then uing the formula (3) can be written: ( 1) (1 ) [ O ] (4) d n min 1 ( 1) (1 ) namin and then for the tandard engine fuel (at ma content: c = 0.84 h = 0.14 o = 0.01 n = min = and ) the relationhip can be written: amin ( 1) (1 ) [ O ] 1 (1 ) d. (5) ( ) Equation (5) how that an increae of the recirculation relation rate the oxygen content [O]d at the inlet to the combution chamber teadily decreae and approache the value of oxygen [O] - commonly found in the flue gae leaving the ytem. Uing equation (5) in the Fig. 4 i hown the oxygen content [O]d in the mixture of gae at the flow into the combution chamber (ee Fig. ) a a function of the exhaut ga recirculation rate while retaining the value of the fective air (oxygen) exce ratio. Fig. 4. Influence of the exhaut ga recirculation rate on the internal oxygen content [O ] d By meauring the oxygen content [O]d in the ga mixture at the inlet channel and next uing the achieved eq. (5) the value of actual exhaut ga recirculation rate can be fective determined. 30

7 Influence of the Exhaut Ga ecirculation on the Oxygen Content and It Exce atio in the Engine The obtained relationhip inform that the increae of the exhaut ga recirculation rate caue ytematically increaing (Fig. 3) of the internal oxygen exce ratio w while at the ame time decreaing the oxygen content [O]d of combutible mixture (Fig. 4) all for the fective air (oxygen) exce ratio. In cae of internal recirculation the flue ga temperature equal (or i higher) the temperature of flue ga leaving the combution chamber o the fectivene of the internal recirculation i not o high than the external recirculation. In the cae of an external recirculation temperature of Tr i cloe to the temperature of exhaut gae leaving the engine or may be lower if cooling of recirculating ga i performed. 4. Cloing remark The fuel combution proce in the ytem with implemented within the exhaut ga recirculation take place in a mixture of air and exhaut gae; for the combution proce i important the fective content (concentration) of oxygen [O]d in the combutible mixture. Oxygen flow into the combution chamber with both freh air tream a well a a component of the recirculating exhaut ga tream. The analyi alo concern the fective exce oxygen ratio in the combutible mixture which i oberved directly in the exhaut manifold. The increae of the exhaut ga recirculation rate caue ytematically decreaing the oxygen content [O]d in combutible mixture for all value of the fective air (oxygen) exce ratio 1. For a full evaluation of toichiometric condition it wa adviable to dine the internal oxygen exce ratio w too in which account i alo the oxygen upplied with the recirculating exhaut ga tream. It wa found that an increae of the exhaut ga recirculation rate reduce the content of oxygen in the combutible mixture and imultaneouly increae the internal oxygen exce ratio w. Acknowledgement The work wa upported and performed by uing of tatutory funding for reearch on faculty ISiE of STU. erence [1] Hribernik A. Samec N. Effect of Exhaut Ga ecirculation on Dieel Combution Journal of KONES IC Engine No [] Kowalewicz A. Sytemy palania zybkoobrotowych tokowych ilników palinowych WKi Warzawa [3] Merkiz J. J. Pielecha I. Alternatywne paliwa i ukady napdowe pojazdów Wydawnictwa Politechniki Poznakiej 004. [4] Müller M. Olin P. Schreur B. Dynamic EG Etimation for Production Engine Control SAE Paper [5] Pietra D. Sobiezczaki M. Problemy regulacji ilnika o zaponie ikrowym z recyrkulacj palin Silniki palinowe Nr (119) 004. [6] Potrzednik S. mudka Z. Termodynamiczne oraz ekologiczne uwarunkowania ekploatacji tokowych ilników palinowych Wydawnictwo Politechniki lkiej Gliwice 007. [7] oth D. Sauertein. Becker M. Meiling. Application of hybrid EG ytem to turbo charged GDI engine MTZ

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