Saheed Wasiu and Rashid Abdul Aziz.

Transcription

1 Effects of Hydroge gas as a Dual fuel o a Cylider Pressure of the Directiectio Compressed Natural Gas Egie Employig Exhaust Gas Recirculatio at various excess air ratios Saheed Wasiu ad Rashid Abdul Aziz. Mechaical Egieerig Sectio, Uiversity of Kuala Lumpur, Malaysia Frace Istitute Sectio 14, Jala Teras Jerag, 43650, Badar Baru Bagi, Selagor, Malaysia. Correspodig author Orcid id: Abstract A experimetal study has bee coducted to study the effects of hydroge as a dual fuel o the cylider pressure of the direct iectio compressed atural gas egie employig EGR (i.e. DI-CNG-EGR) at various excess air ratios ( λ = 1.0, 1.2, 1.3 ad 1.4 ) which represet stoichiometric, moderately lea, lea ad very lea mixtures respectively. The results showed that for a specified EGR rate, icrease i hydroge fractio will icrease the cylider pressure. This is simply due to the fact that hydroge additio will icrease the burig velocity ad combustio maximum temperature; cosequetly; the cylider pressure will icreases. More so, at 0% EGR rate; the maximum cylider pressure for all the mixtures (i.e. stoichiometric, moderately lea, lea ad leaer mixtures) respectively are bar, bar, bar ad bar; while at 17% EGR rate; the maximum cylider pressures for various mixtures uder cosideratio are 74.6 bar, bar, bar ad bar respectively. From the foregoig, it is obvious that the maximum cylider peaks at stoichiometric mixture i compariso with other mixtures. This is largely due to the efficiet combustio which occurs at stoichiometric mixture. Furthermore, maximum cylider pressure decreases ust as EGR rates icreases. This is largely due to the reductio i combustio maximum temperature ad burig velocity due to the dilutio effects of EGR. Thus, it ca be cocluded that EGR dilutio is capable of reducig icylider stresses ad cosequet upo this; it ca be used to suppress abormal combustio occurrece such as surface igitio ad kock. Keywords: Hydroge, Direct iectio compressed atural gas egie (DI-CNG), Exhaust gas recirculatio (EGR), Excess air ratios, Cylider pressure. INTRODUCTION Research o improvig egie s fuel ecoomy ad reducig exhaust emissios has become imperative i combustio ad egie developmet due to icrease i eergy price ad coupled with icreased cocer o eergy shortage ad evirometal protectio [1]. The developmet of alterative fuels for egies has bee a maor cocer of the egie developers sice they are cleaer as compare to diesel ad gasolie i egie combustio process. The itroductio of the alterative fuel is expected to alleviate problems of fuel shortage ad reduces the exhaust emissio from the egies [2]. Natural gas is regarded as oe the most promisig alteratives fuels ad probably oe of the cleaest fuel i combustio. The use of atural gas has bee realized i both spark igitio ad compressio igitio egie. Natural gas comprises of mixture of differet gases where methae is its maor compoet. The combustio of atural gas produces lesser emissio whe compared to that of gasolie ad diesel egie due to its simple chemical structure ad absece of fuel evaporatio. The egie possess high ati-kockig capability due to its high octae umber ad this allows it to operate at eve high compressio ratio; leadig to further improvemet of both power output ad thermal efficiecy. However, atural gas as a egie fuel suffers two maor setbacks viz: slow burig velocity ad poor lea bur capability which ofte leads to icomplete combustio, high misfire ratio, ad large cycle-by-cycle variatio at lea mixture combustio which decreases the egie power output ad icreases the fuel cosumptio [1, 2]. A viable approach to overcome these challege of slow burig velocity ad poor lea bur capability of atural gas fuel is to mix atural gas with the fuel that possess fast burig velocity. Hydroge is regarded as the best gaseous cadidate for atural gas due to its very fast burig velocity; much better lea capability ad small quechig distace. This combiatio is expected to improve the lea-bur characteristics ad reduces the egie emissio [3-5]. 1109

2 Ufortuately, this method always icreases the combustio temperature ad heat loss to the cylider wall as well as high NOX emissio [3]. To solve the problem of high NOX; Exhaust gas recirculatio (EGR) is itroduced ito the itake system with the aid of regulatig valve. EGR is the pricipal techique used to cotrol SI egie NOX emissios [5-12]. There are may published literatures regardig the experimetal researches o the combustio characteristics of the spark igitio egie fuelled with atural gas hydroge mixtures combied with EGR [5, 11-12]. The results of these studies geerally cetered o mass fractio bured ad cylider pressure at stoichiometric mixtures. Till date, o literature has ever examied the impact of hydroge as a dual fuel o the cylider pressure at various excess air ratios (λ = 1.0, 1.2, 1.3 ad 1.4 which represet stoichiometric, moderately lea, lea ad leaer mixtures respectively) of the direct iectio compressed atural gas egie(di-cng) employig EGR rates uder part-throttled coditio. Thus, the obective of this paper is to study the effects of hydroge as a dual fuel o the cylider pressure at various excess air ratios of the direct iectio compressed atural gas egie (DI- CNG) employig EGR. The study is expected to clarify the combustio behaviours of the egie fuelled with differet fractios of the atural gas-hydroge bleds ad at differet EGR rates ad to provide a practical guide to the egie applicatio. METHODS The specificatios of the test egie are listed i Table 1 below. A four-stroke sigle cylider research egie was used to ivestigate the effect of hydroge gas o the cylider pressure of the direct-iectio compressed atural gas egie employig EGR at various excess air ratios. Figure 1.0 below shows the schematic diagram of the experimetal set up. Table 1. Egie specificatios ad test bed Figure 1.0: Schematic diagram of the experimetal set up. The supplyig system of the egie cosists of a atural gashydroge bled (mixed together usig i- situ strategy), gas valve, gas flow meter, a pressure regulator. A electroic cotrol uit was used to adust the amout of CNG-H2 gas ad the excess air ratio ito the system, also cotrolled by the electroic system was also iectio timig. Experimets was coducted after ruig the egie util it reached steady state, with oil temperature at 60 C ad coolig water temperature 70 C. The experimetal work was started by directly iectig a mixture of CNG-H2 ito the egie cylider while simultaeously recyclig the exhaust gas from a hole located o the exhaust pipe with the aid of coectig pipe. A regulatig valve was istalled: i order to regulate the exhaust gas flow. Percetage icrease of EGR i the ilet mixture was doe by icreasig the amout of the exhaust gas flowig back to the egie itake system. Air ad exhaust gas were mixed i the egie itake, while CNG-H 2 was directly iected ito the egie. A 5mm square orifice meter was used to measure the flow rate of the exhaust gases recycled back ito the egie itake. The pressure differece across the orifice meter was measured usig U tube maometer. The percetage of the exhaust gases recycled back to the egie itake was calculated as a percetage of the total ilet mass flow rate as follows: megr % EGR 100 m m a EGR (1) The equatio for determiig the mass flow rate of EGR is give below: Where: (2) 1110

3 m EGR = mass flow rate of EGR (kg / s) A 2 = Area of the orifice plate (m 2 ) Desity of the combustible products (kg / m 3 ) Pressure differece from the orifice plate (N / m2) C = Coefficiet of flow A pressure gauge was used to measure the ilet pressure. Fig. 2.0 below shows the schematic diagram of the EGR cotrol system. I this method for ay crak agle iterval the actual pressure chage pp p is assumed to be made up of a pressure rise due to combustio p c ad a pressure chage due to volume chage p V pp cp v (4) The pressure ad volume at the start ad ed of the iterval i the absece of combustio are related: P 1V 1 = P 1V 1 V p v p 1, v p p 1 (5) V 1 Figure 2.0 Schematic diagram of the EGR cotrol system. The research was carried out at part-throttled, with spark timig set at 26.0 o CA, iectio timig of 300 o CA (which represet early iectio timig), ad four (4) excess air ratio comprises of = 1.0,1.2, גּ) 1.3 ad 1.4) which represet stoichiometric, moderately lea; lea ad leaer mixtures respectively ad costat egie speed of 2000r/mis, were beig utilized. The system for the acquisitio of i-cylider pressure is composed of: (1) Piezo electric cylider pressure sesor- AVL QH32D, gai pc/bar rage bar (2) Charge amplifier- AVL3066AO (3) Shaft positio ecoder-avl364c (4) Piezos resistive pressure sesor fixed iside the ilet maifold The Rassweiler-Withrow model also kow as polytropic model was origially preseted i 1938 ad is still beig used for determiig mass fractio bured, reaso beig its simplicity ad less computatioal complexity. As this model is also amed as polytropic model, so it assumes that the pressure volume relatio ca be modeled as polytropic relatio. PV = costat (3) Where the costat expoet value rages from 1.25 to These values of gives a good fit to experimetal data for both compressio ad expasio process. This expoet is termed as polytropic idex. Applyig, equatios (3-38) ad (3-39) yields to the pressure chage due to combustio as p c RESULTS p V 1 p (6) V 1 Figure 3.0 shows the relatioship of the cylider pressure agaist crak agle for differet percetage by volume of hydroge gas at various EGR rates ad excess air ratios. Followig the spark discharge; there is a period durig which the eergy release from the developig flame is too small for the pressure rise due to combustio to be discered. As the flame cotiues to grow ad propagate across the combustio chamber; the pressure the steadily rise above the value it would have i the absece of combustio. The pressure reaches a maximum after TDC; but before the cylider charge is fully bured ad the decreases as the cylider volume cotiue to icrease durig the remaider of the expasio stroke. More so, for specified percetage of EGR rates; icrease i hydroge fractios will icrease the cylider pressure. This is simply due to the fact that hydroge additio will icrease the burig velocity ad combustio maximum temperature; cosequetly; the cylider pressure will icreases. This is the more reaso why maximum cylider pressure peaks at 46% H2 as compared to 28% ad 0% H2 for all the cases. Figure 3.0 (a) (p) support this claim. Furthermore, maximum cylider pressure decreases ust as EGR rates icreases. This is largely due to the reductio i 1111

4 combustio maximum temperature ad burig velocity due to the dilutio effects of EGR. This cofirms that EGR dilutio is capable of reducig i-cylider stresses ad cosequet upo this; it ca be used to suppress abormal combustio occurrece such as surface igitio ad kock. Figure 3.0 (a), (e), (i), (m) at stoichiometric mixture (i.e. whe % EGR rate is icreased from 0% to 17, 20 ad 24% respectively); also, figure 3.0 (b), (f) at moderately lea mixture whe percetage EGR rate is icreased from 0 to 17% ; also figure 3.0 (c), (g), (k) ad (o) at lea mixture; whe percetage EGR rate is icreased from 0% to 17, 20 ad 24% respectively; while figure 3.0 (h) ad (l) at leaer mixture; whe the percetage EGR rate is icreased from 17% to 20% support this claim. Exceptio to this i.e. where icrease i percetage EGR rate leads to icrease i cylider pressure. This might be due to cycle-by-cycle combustio variatio caused by variatio i mixture compositio or gas motio. Moreover, cosider figure 3.0 (a)-(d) i.e. 0% EGR rate; the maximum cylider pressure for all the mixtures (i.e. stoichiometric, moderately lea, lea ad very lea mixtures) respectively are bar, bar, bar ad bar. This idicates that the maximum cylider pressure peaks at stoichiometric mixture. This is largely due to the efficiet combustio which occurs at stoichiometric mixture. But at 17% EGR rate i.e. figure 3.0 (e) (h). The maximum cylider pressures for various mixtures uder cosideratio are 74.6 bar, bar, bar ad bar respectively. Agai maximum pressure peaks at stoichiometric mixture due to efficiet combustio. From the foregoig; it is plausible to say that for part-throttle operatio ad early iectio timig ad at 0% EGR rate i.e direct iectio hydroge eriched compressed atural gas egie (DI-HCNG egie) attai its highest efficiecy at stoichiometric mixture whe maximum cylider pressure is almost 78.29bar at 4.5 o CA ATDC. While direct-iectio hydroge eriched compressed atural gas egie employig EGR (DI-HCNG-EGR egie) attai its ow highest efficiecy also at stoichiometric mixture whe the maximum cylider pressure approximately equal to 74.6bar at 6.0 o CA ATDC at the same operatig coditio. These experimet measuremets gave results coheret with [5, 11]. (a) (b) (c) 1112

5 (d) (h) Figure 3.0: Relatioship of the cylider pressure agaist crak agle for differet percetage by volume of hydroge gas at various EGR rates ad excess air ratios. CONCLUSION (e) (f) A experimetal study of the effects of hydroge as a dual fuel o the cylider pressure i a direct iectio compressed atural gas egie (DI-CNG) employig EGR at various excess air ratios (λ = 1.0, 1.2, 1.3 ad 1.4 which represet stoichiometric, moderately lea, lea ad leaer mixtures respectively) uder part-throttle coditio was coducted. The mai results are summarized as follows: For specified percetage of EGR rates; icrease i hydroge fractio will icrease the cylider pressure. This is simply due to the fact that hydroge additio will icrease the burig velocity ad combustio maximum temperature. Maximum cylider pressure decreases ust as EGR rates icreases. This is largely due to the reductio i combustio maximum temperature ad burig velocity due to the dilutio effects of EGR. This cofirms that EGR dilutio is capable of reducig icylider stresses ad cosequet upo this; it ca be used to suppress abormal combustio occurrece such as surface igitio ad kock. The maximum cylider peaks at stoichiometric mixture i compariso with other mixtures. This is largely due to the efficiet combustio which occurs at stoichiometric mixture. l eviromet makes it difficult for the maagers of the road trasport eterprises to make competet strategic maagemet decisios, able to esure the developmet of the iovative busiess structures. (g) 1113

6 NOMENCLATURE P dq ch dq ht du s dw h i dm i T T w C v C p R m EGR m AIR cylider gas pressure (kpa) chemical eergy released by combustio, J heat trasfer to chamber wall, J chage i sesible eergy, J pisto work, J ethalpy of flux i eterig or leavig the system, J/kg mass flow rate ito the system across the system at locatio i, kg/s mea gas temperature, K mea wall temperature, K specific heat at costat volume, J/kgk specific heat at costat pressure, J/kgk specific heat ratio specific gas costat, J/kgk Mass flow rate of EGR, kg/s Mass flow rate of the Air, kg/s ACKNOWLEDGEMENTS This research has bee fiacially supported by Short Term Research Grat (STRG) provided by Uiversity of Kuala Lumpur. (Grat No. UikL / CoRI / strl 7086). REFERENCES [1] Rousseau,S., Lemoult, B & Tazerout,M Combustio characteristics of atural gas i a lea bur spark-igitio egie. Proc Ist Mech Eg Part D J Automobile Egieerig, 213(D5), pp [6] Amr,I., Saiful,B A experimetal ivestigatio o the use of EGR i a supercharged atural gas (SI) egie. SAE, paper o , [7] Mig,Z., Graham,Z & Gary,J Diesel egie exhaust gas recirculatio- a review o advaced ad ovel cocepts; 45(6): [8] Haiyog,P., Yi, C & Kagyao, D Effect of exhaust gas recirculatio (EGR) o combustio ad emissios durig cold start of direct iectio (DI) diesel egie; 33(3) : [9] Saaum I., Bysvee M., Tuestal P., Johasso B Lea bur versus stoichiometric operatio with EGR ad 3-way catalyst of a egie fueled with atural gas ad hydroge eriched atural gas. SAE paper o [10] Eriag, H., Zuohua,H., Big,Liu, Jiau,Z & Xiaolei,G A experimetal ivestigatio o performace ad emissios of spark-igitio egie fueled with atural gas-hydroge bleds combiig with EGR. It J Hydroge Eergy; 34: [11] Eriag, H., Zuohua,H., Big,Liu, Jiau,Z & Xiaolei,G A experimetal study o combustio characteristics of a spark igitio egie fueled with aturalgas-hydroge bleds combiig with EGR. It J Hydroge Eergy 34: [12] Jie,W., Zuohua,H., Big,Liu & Xibi,W Simulatio of combustio i spark igitio egie fueled with atural gas-hydroge bleds combied with EGR ; 3(2) : [2] Be,L., Dacros, NR., Truquet, R & Charay,G Ifluece of air/fuel ratio o cyclic variatio ad exhaust emissio i atural gas (SI) egie,sae, paper o [3] Akasu,S.,Dulger, Z, Kahrama, N & Veziroglu,T Iteral Combustio Egies fueled by atural gas-hydroge mixtures; 29(14),pp [4] Das,A., Watso, HC Developmet of a atural gas spark igitio egie for optimum performace. Proc Ist Mech Eg Part D J Automobile Egieerig,. 211(D5), pp [5] Heywood,J Iteral Combustio fudametals. New York: McGraw-Hill Book Compay; ,