Argon

Energy Conversion and Management 50 (2009) 2699–2708

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Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman

NO x emission control in SI engine by adding argon inert gas to intake mixture Hany A. Moneib a,b, Mohsen Abdelaal c, Mohamed Y.E. Selim d, , Osama A. Abdallah e *

a

Industrial Education College, Helwan University, Cairo, Egypt Mech. Power Engg., Mattaria College of Eng., Cairo, Egypt c Mechanical Eng., Faculty of Engineering, Al-Azhar University, Cairo, Egypt d Mech. Eng. Dept., College of Eng. UAE University, P.O. Box 17555, Al-Jimi, Al-Ain, Abu Dhabi, United Arab Emirates e Sharjah Institute of Technology, Sharjah, United Arab Emirates

b

a r t i c l e

i n f o

Article history: Received 21 March 2008 Received in revised form 27 October 2008 Accepted 30 May 2009 Available online 26 July 2009 Keywords: Petrol engines Inert gas Argon-exhaust emissions Artificial air

a b s t r a c t

The Argon inert gas is used to dilute the intake air of a spark ignition engine to decrease nitrogen oxides and and improv improve e the perfor performan mance ce of the engine engine.. A resear research ch engine engine Ricard Ricardo o E6 with with variab variable le compre compressi ssion on was used in the present work. A special test rig has been designed and built to admit the gas to the intake air of the engine for up to 15% of the intake air. The system could admit the inert gas, oxygen and nitrogen gases at preset amounts. The variables studied included the engine speed, Argon to inlet air ratio, and air to fuel ratio. The results presented here included the combustion pressure, temperature, burned mass fraction, heat release rate, brake power, thermal efficiency, volumetric efficiency, exhaust temperature, brake specific fuel consumption and emissions of CO, CO 2, NO and O2. It was found that the addition of Argon gas to the intake air of the gasoline engine causes the nitrogen oxide to reduce effectively and also it caused the brake power and thermal efficiency of the engine to increase. Mathematical program has been used to obtain the mixture properties and the heat release when the Argon gas is used. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Due to increasi increasing ng mobilit mobility y especiall especially y in large large cities, cities, environ environ-mental protection has advanced to become a topic of central concern. cern. Emissio Emission n control control regulatio regulations ns have have been been introdu introduced ced in all industrialized countries in order to reduce the emissions of vehicles powered by internal combustion engines. There have been a number of methods to reduce the exhaust emissio emissions ns from spark spark ignition ignition engines engines as well well as diesel diesel engines. engines. Some of these methods deal with the exhaust gases directly and try to reduce reduce the concent concentrati rations ons of the dangero dangerous us gases. gases. These These are called after treatment devices e.g. catalytic converters. Some of the the metho ethods ds used used are are cutt cuttin ing g down down the the leve levell of thos those e gase gasess from from forming in the first place. These methods include the use of exhaust gas recycle (EGR), the use of water in combustion chamber or admittin admitting g inert inert gases gases inside inside the combustion combustion chamber chamber of the engine. For spark ignition engines, engines, the most dangerous dangerous pollutants emitted are the nitrogen nitrogen oxides oxides NO x which which cause cause fatal diseases. diseases. For these these gases (NO and and NO2), the followi following ng convert converters ers are being being developed and improved: three way catalyst system, NO x storage catalysts, selective catalytic reduction systems. They require the Correspondin Corresponding g author. author. On leave from Helwan University, University, Egypt. Egypt. Tel.: +971 504494723; fax: +971 37623158. E-mail address: [email protected] (M.Y.E. Selim). *

0196-8904/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2009.05.032

use of noble material and other gases or liquids. They also require oxygen to be available in the exhaust gases i.e. to run the engine always lean. Using EGR in spark ignition engines always required the addition of pipin piping g and valve valve systems systems to recircu recirculate late some some of the the exhaust exhaust gases back into the intake air. The power output and/or thermal efficiency have to be sacrificed. Similar scarify has to be given for water addition into the combustion chamber. The promising approach for reducing the NO x gases is to add small amount of an inert gas. There have been many references in the use of intak intake e air dilutio dilution n of diese diesell engin engine e to redu reduce ce the NO x emission e.g. using enriched enriched oxygen [1] and carbon dioxide [2].. [2] To compensate for the smaller specific heat ratio value of CO 2, an inert gas with higher specific heat ratio can be added to the intake take gas, gas, and and argo argon n whic which h has has a spec specifi ific c heat heat rati ratio o valu value e of 1.66 1.667 7 at room temperature can be used [3,4] [3,4].. The compre compressio ssion n temper temperatur ature e for the case of oxygen oxygen–ar –argon gon–he –he-lium mixtu mixture re has been found found to be 300 K higher than that that of the case when air is used [5–7] [5–7].. Also the gas temperature during combustion period period is 300–400 K higher for the case of oxygen–argon– oxygen–argon– helium mixture. Argon has been also used in a diesel engine to dilute the intake mixture and has been varied up to 10% [8,9] [8,9].. At the argon concentration 0f 10% the mixed gas takes a specific heat ratio value of 1.405 1.405 which which is the the same same as that that of air. air. As speci specific fic heat heat ratio ratio

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H.A. Moneib et al. / Energy Conversion and Management 50 (2009) 2699–2708

increased, the peak cylinder pressure increased and it occurred at earlier crank angle. Diluents are found to be effective way in reducing NO x emissions. Although dilution of intake air especially with argon gas has been used before, it appears that it was used only in diesel engine. The objective was always to decrease the exhaust emission of NO x and slightly improve the engine power and thermal efficiency. However, it has not been used before for dilution in spark ignition engines to reduce the exhaust emission of NO x. The effects of adding argon gas to the intake air of spark ignition engines performance are also lacking. Therefore, it is the main objective of the present work to investigate in details the effects of diluting the intake air with argon gas as an inert gas on the performance and emissions of a single cylinder spark ignition engine. The present study was carried out on a Ricardo E6 variable compression spark ignition (SI) engine. The scope of the present work included the investigation of the thermodynamics properties of the intake gas mixture when argon is added, the effects of adding argon on the performance of the engine and the exhaust emissions, and finally the heat release rate analyses.

Air Filter

Atmospheric Air

Ar + O2 MV i e s t e c r o u s F l o w

(0-15)% AR

2

Mixer

21% O2

Rotameter

Rotameter

Pressure Pressure regulating Valveregulating Valve

Carburetor

r A

Mixture Ricardo E6 Engine

2

O

2. Experimental set-up The intake of the engine has been modified to allow the admission of controlled amount of the argon, oxygen and nitrogen gases. This section will present the experimental apparatus and the experimental procedure. 2.1. Engine experimental apparatus

The present study has been conducted on a Ricardo E6 research engine at Al-Azhar University, Egypt. The technical specifications of the 507 cc engine are given in Table 1. Fig. 1 shows a schematic diagram of the argon and air admissions system. Argon has been selected as mentioned above due to its chemical and physical properties. It has been decided to dilute the intake air with the following percentages: from 0% up to 15% by volume. Since the atmospheric air comprises 79% nitrogen and 21% oxygen by volume, both the nitrogenand oxygen concentration will be reduced by adding more argon to the intake air. However, the oxygen concentration will be kept constant throughout the experimental program at 21%. The added argon will replace the nitrogen gas concentration i.e. if the intake air contains 2% argon, then the intake mixture will be 21% oxygen, 2% argon, 77% nitrogen and carbon dioxide. Oxygen and argon have been admitted through the intake mixer shown in the figure to allow good mixing between the two gases. The air flow rate is measured through an Alcock viscous flow meter, while the fuel flow rate is measured by using a calibrated rotameter. A variable area rotameter has been used to measure the volume flow rate of the argon gas admitted to the engine. The following parameters have been kept fixed during the work:

ignition timing constant at 20° BTDC, carburetor position at full throttle opening, fuel used is gasoline with octane number 90 and compression ratio is 8 (constant). A Piezotronics engine combustion sensor has been used to measure the combustion pressure inside the engine cylinder. A dual mode charge amplifier was used to amplify the signal from the engine combustion sensor. The degree marker shaper amplifier measured and displayed angular crank shaft location. A Tectonics American two channels high-speed digital storage oscilloscope has been used to measure, store and analyze the pressure and crank angle signals. The output signals from the pressure sensor and degree marker were fed into the amplifier then the output signals have been fed into the oscilloscope. The oscilloscope was provided with a highspeed analog to digital (Analogue/Digital) converter for each channel to allow the measurement, storing and analysis of high-speed phenomena. The input signal could be stored at the rate of up to 1000 MHz. Up to two sets of the stored waveform could be saved. The saved waveform was retained then transferred to a PC for further computation. An infrared gas analyzers were used for measuring NO x, CO2, and CO and O 2 paramagnetic analyzer was also used for the exhaust gas analyses. The temperatures of inlet cooling water, outlet cooling water, air inlet, exhaust and oil sump were measured using Type K thermocouples. 2.2. Experimental program and test procedures

The present work aims at studying the effect of diluting inlet air with argon gas in gasoline engine. For this purpose, the experimental program was designed and may be divided into two categories.

Table 1

Research engine Ricardo E6 technical details. Number of cylinders Bore, mm Stroke, mm Capacity, cc Maximum speed, rpm Max. cylinder pressure, bar Compression ratio Ignition timing, deg. BTDC Throttle opening

Fig. 1. Schematic drawing for argon, oxygen and air mixture.

1 76.2 111.125 507 3000 150 8 20 WOT

(a) Experiments on gasoline engine running on diluted intake air with argon at constant engine speed. (b) Experiments on gasoline engine running on diluted intake air with argon At different engine speeds. In the first set of tests, the engine has been running on mixture of oxygen, argon and nitrogen on preset ratios. These ratios have

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been selected to be from 0% to 15% argon to mixture with oxygen always at 21%. The engine speed has been kept constant at 35 rev/s and at constant engine conditions (throttle valve/ignition timing and compression ratio). The argon amount is then increased at 2% step. The performance and exhaust emissions have been measured and recorded. In the second set of tests, the engine runs at the same conditions above but tests are repeated at different engine speeds and the same performance and exhaust emissions measurements are carried out. The engine speeds selected are 24, 30, 35 and 39 rev/s. The engine performance and emissions variables included the volumetric efficiency of the engine, motoring and firing cylinder pressures, brake mean effective pressure, brake power, specific fuel consumption, thermal efficiency and emission of nitrogen oxide, oxygen, carbon monoxide, carbon dioxide and molecular nitrogen.

1.4

Gamma ( γ )

) 1.39

γ ( o i t a r t a e 1.38 h c i f i c e p S 1.37

2.3. Experimental error analysis

The maximum error in the flow rate of air measured by the rotameter was 1.58 Â 10 4 m3/s and a relative error of 1% while the maximum error of measuring the fuel flow rate was 1 cm 3 and 10 ms in measuring the time of flow and this gives a relative error of about 0.7% in the mass flow rate. The relative error in measuring the argon gas flow rate was 5% . The maximum error in measuring the engine speed was 0.1 rev/ s which gives a relative error of about 0.4% in the speed measurement. The engine torque was measured with an error of 0.1 Nm that gives a relative error of 4% in the brake power and 3% in the brake specific fuel consumption. The maximum error in exhaust gas temperature measurement was 0.1 °C which gives 0.1% relative error. The exhaust gas concentration was measured with an absolute error of 1 ppm for NO and N 2 and 0.1 for CO, CO 2 and O2.

1.36

0

2

4

6

8

10

À

Argon(%) Fig. 2. Calculated mixture specific heat ratio (c) variationwith argon percentages at and of compression.

1.26

K 0 0 1.24 3 = e

Mixture density at 300 K

k a t n i

T t a 1.22 ) 3

3. Results and discussions An experimental study has been performed in the present work on a single cylinder constant compression ratio spark ignition engine (Ricardo E6) fuelled with gasoline. A preliminary study is presented first for the thermodynamic effects of adding the argon to the intake air of the engine. The amount of oxygen gas has been kept constant at 21% by volume. The engine parameters have been kept at the values mentioned above. The experimental results shown next are specific heats and their ratio, mole fraction of nitrogen, oxygen, mixture density, gas constant and air to fuel ratio as a function of the argon percentage added to the engine intake. Following these thermodynamic effects, other engine effects of the volumetric efficiency, combustion pressures and temperatures, heat release rate, burnt mass fraction, brake mean effective pressure ; bmep, brake power, specific fuel consumption, exhaust gas temperature and emissions of NO, CO and CO 2 are presented. The effects of varying the engine speed on the performance and exhaust emission are then presented. 3.1. Effect of argon concentration on the thermodynamic properties

Argon gas has a lower than air specific heat capacity of 0.528 kJ/ kg K (at constant pressure) but a higher specific heat ratio of 1.667 and has been chosen for this purpose to replace some intake air volume. The mixture properties have been calculated by a FORTRAN program prepared at different ratios of argon gas. The mixture properties at the end of the compression stroke has been obtained using thermodynamic relations and ideal gas equations and may be seen in Figs. 2–4.

m / g k ( y t i 1.2 s n e d e r 1.18 u t x i M 1.16

0

4

8

12

Argon (%) Fig. 3. Mixture density variation at intake temperature = 300K with argon percentages.

Fig. 2 shows the specific heat ratio increases with increasing argon dilution percentages to reverse the trend for normal air mixture in which its specific heat ratio decreases. Fig. 3 shows the mixture density as calculated at room temperature of 300 K as a function of the argon added percentage. It can be seen from the figure that adding more argon gas to intake air is increasing the mixture density as it has a density of 1.783 kg/ m3. This is higher than that for air and it causes the mixture density to increase. Another reason for the mixture density to increase is the gas constant which decreases as the argon addition is increased; Fig. 4. Adding more argon gas reduces the gas constant as shown as it has higher molecular weight than air (40 compared to 29 kg/kmol for air). This increases the density of the mixture if it is assumed to be an ideal gas. This increase in the density of

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1600

0.288

Mororing pressure (kPa) 2 % Ar

Gas constant (KJ/Kg.K)

4 % Ar 6 % Ar

) 1200 a P k ( e r u s s e r 800 p g n i r o t o M

) 0.284 K . g k / J k ( r n 0.28 a t s n o c s a G 0.276

8 % Ar 10 % Ar 12 % Ar 14 % Ar

400

0.272

0

4

8

12

0 100

Argon (%)

200

300

400

500

Crank angle (Degrees)

Fig. 4. Mixture gas constant variation of intake air at intake temperature = 300 K with argon percentages.

Fig. 6. Motoring pressure variation with crank angle for different argon percentages.

mixture increases the mass flow rate of the intake air and hence the air/fuel ratio increases.

Fig. 6 as a function of the crank angle. It may be seen from this figure that increasing the argon addition has increased the motoring pressures at all crank angles and particularly at near the end of the compression stroke. The increase in the pressure is a result of the increase in the specific heat ratio of the mixture. It has been shown above that the specific heat ratio increases with adding more argon to the intake, and this will increase the pressures during the compression stroke. It may be seen that the maximum motoring pressure increased from about 1180 kPa at 0% argon to about 1450 kPa at 14% argon.

3.2. Effect of argon concentration on the engine performance 3.2.1. Volumetric efficiency The increase in the mixture density and mass flow rate caused by the argon density and molecular weight increases the volumetric efficiency as may be shown in Fig. 5. The volumetric efficiency has increased from approximately 81% at 0% argon, to about 90% at argon ratio of 16%. The engine appears to be supercharged by about 12.5% which may reflect later on the power output and specific fuel consumption. 3.2.2. Motoring pressure The motoring pressure of the engine (cylinder pressure without combustion) at different ratios of argon gas added may be seen in

3.2.3. Firing pressure Fig. 7 shows the combustion pressure–crank angle variation for different ratios of argon gas added to the intake air of the engine. It can be seen from this figure that the combustion pressure increased with adding more argon. For argon addition ratio of 2%

4000

92

Firing pressure (kPa) 2 % Ar

) % (

Volumetric effeciency

90

4 % Ar

) 3000 a P k ( e r u s s e r 2000 p g n i r o t o M

v

η

y 88 c n e i c e f f 86 e c i r t e 84 m u l o V

6 % Ar 8 % Ar 10 % Ar 12 % Ar 14 % Ar

1000

82

80 0

4

8

12

16

Argon (%) Fig. 5. Volumetric efficiency (gv) variation with argon percentages O2 = 21%, N = 35rps.

0 100

200

300

400

500

Crank angle (Degrees) Fig. 7. Combustion pressure variation with crank angle for different argon percentages.

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the maximum combustion pressure was about 2000 kPa, while it increased to about 3800 kPa at argon of 14%. It may be also seen that as the argon ratio increased the maximum pressure occurs earlier in the cycle. For argon of 2% the maximum pressure occurred at about 380° ATDC while it occurred at about 365 ° ATDC for argon of 14%. The increase in the maximum combustion pressure is due to the fact that the motoring pressure increased as a result of increasing the specific heat ratio mentioned above. The maximum combustion pressure at higher values of argon ratio occurs earlier in the cycle due to the reduction in the ignition delay. The ignition delay appears to have reduced as a result of the addition of more argon. This has been also shown by [5] for similar conditions of a diesel engine. The reduction in the ignition delay is due to increase in the pre-combustion temperature and pressure associated with the use of argon gas. This increase in the pressure and temperature is due to the increase in the specific heat ratio of the argon–oxygen–nitrogen mixture [5]. The reduction of the delay period causes the combustion to occur earlier and earlier in the cycle, however, the maximum pressure occurs after the top dead centre i.e. at beginning of expansion stroke which may reflect later with slight increase in the net work produced by the engine cycle. 3.2.4. Combustion temperature Fig. 8 depicts the variation of the combustion temperature with crank angle for different ratios of argon gas. It can be seen fromthis figure that increasing the amount of argon gas has resulted in an increase in the combustion temperature. The combustion temperature has been calculated from thermodynamic relations from other properties e.g. the measured pressure. The combustion temperature was about 1400 K for 2% argon while it increased to 1950 K at 14% argon. The increase in the combustion temperature is due to increase in the combustion pressure mentioned above which produces higher temperatures. It may be also worthy to mention that using more argon reduces the specific heats (both at constant pressure and volume) of the intake mixture. The reduction in the specific heats may have caused the temperature to increase for the same amount of heat added per cycle. 3.2.5. Rate of heat release Fig. 9 shows the heat release rate (HRR) at different ratios of the argon addition. It may be seen that the heat release rate generally

2000 Combustion Temperature ( K) °

2 % Ar

) K1600 ( e r u t a r e 1200 p m e T n o i t 800 s u b m o C °

4 % Ar 6 % Ar 8 % Ar 10 % Ar

Total heat release (J/C.A)

) a . C / J ( e t a r e s a e l e r t a e h l a t o T

2 % Ar 4 % Ar 6 % Ar 8 % Ar 10 % Ar 12 % Ar 14 % Ar

30

20

10

0

-10 320

360

400

440

Crank angle (Degrees) Fig. 9. Rate of heat release variation with crank angle for different argon percentages.

increases with increasing the argon as well as its slope of increase with crank angle i.e. the maximum HRR occurs earlier with adding more argon. It may be also seen that the heat release reduces faster with adding more argon gas. The maximum HRR was about 20 J/CA at 2% argon, while it is about 35 J/CA for 14% argon. The maximum HRR occurred at 380°ATDC for 2% argon while it moved earlier to about 352° ATDC for 14% argon. The heat release rate increase with adding more argon may have occurred as a result of the thermodynamic properties change e.g. pressure and temperature. The increase in the motoring pressure, combustion pressure and temperature may have increased the rate of heat release as shown in the figure. The maximum HRR also occurs earlier with adding more argon as a result of the thermodynamic properties improvement mentioned above. 3.2.6. Burnt mass fraction Fig. 10 illustrates the variation of the burnt mass fraction ( bmf ) as a function of the crank angle for different ratios of the argon to intake air. It may be seen from this figure that increasing the argon gas has resulted in a faster combustion as the bmf reaches unity at 14% argon faster than for 2% argon. This implies the increase in the combustion speed as shown above with the HRR data. For example, at 2% the bmf reached unity at about 400 ° ATDC while for 14% argon it was about 365° ATDC.

12 % Ar 14 % Ar

400

0 100

40

200

300

400

500

Crank angle (Degrees) Fig. 8. Temperature variation with crank angle for different argon percentages.

3.2.7. Brake mean effective pressure It has been shown before that combustion pressure increases with adding more argon with some advance in the maximum pressure occurrence. It has been found that the bmep increases slightly with adding more argon. It increased from 7.7 bar at 2% argon to 8.2 bar at 14% argon. The increase in the bmep may have been postulated to the fact the maximumpressure increases and occurs earlier with increasing the argon which increases the net work produced by each cycle. This increases the bmep as the engine is running at the same speed and friction losses. The increase in the bmep with adding more argon increases the brake power output of the engine as the engine speed was kept constant. Fig. 11 shows the slight increase of the brake power with adding more argon. It increased from 6.8 kW to 7.2 kW (5% increase) with increasing the argon gas from 2% to 14%, respectively.

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H.A. Moneib et al. / Energy Conversion and Management 50 (2009) 2699–2708 1

288

) h . W k / 284 g ( n o i t p m280 u s n o c l e u 276 f c i f i c e p s 272 e k a r B

Burnt mass fraction 2% Ar 4 % Ar 6 % Ar 8 % Ar 10% Ar 12% Ar 14% Ar

0.8

n o i t c0.6 a r f s a m t 0.4 n r u B 0.2

0 320

bsfc (g/kW.h)

268 360

400

440

480

0

520

4

Crank angle (Degrees) Fig. 10. Burnt mass fraction variation with crank angle for different argon percentages.

8

12

16

Argon (%) Fig. 12. Brake specific fuel consumption variation with argon percentages, N = 35rps.

710 10

) C700 ° ( e r u t a r e p 690 m e t t s u a h x E680

9

Brake power (kW)

) W k ( r 8 e w o p e k 7 a r B

T exh ( C) °

6

670

0

5

0

4

8

12

16

4

8

12

16

Argon (%)

Argon (%) Fig. 13. Exhaust temperature variation with argon percentages, N = 35rps. Fig. 11. Brake power variation with argon percentages, N = 35rps.

3.2.8. Brake specific fuel consumption Fig. 12 gives the brake specific fuel consumption ( bsfc ) at different argon ratios. It can be seen from the figure that increasing the argon addition ratio from 0% to 15% has resulted in a drop in the bsfc from 285 g/kWh to 268 g/kWh, respectively. This drop in the bsfc is a result of the slight increase in the power output produced by the engine as mentioned above. It may be worth telling here that utilizing the argon as a diluent to reduce the dangerous exhaust gases will not harm the engine performance but actually it will keep it the same if not improved. 3.2.9. Exhaust temperature The exhaust gas temperature variation with the argon addition ratio may be seen in Fig. 13. It may be seen that increasing the argon ratio decreases the exhaust gas temperature. It decreased from 706 °C to about 670 °C when the argon increased from 0% to 15%, respectively. The drop in the exhaust gas temperature may be pos-

tulated to the drop in the temperatures by the end of the expansion stroke. This has been shown with the combustion temperature in Fig. 8. The combustion temperature has been shown to increase more when more argon is added; however, it also decreased faster in the expansion stroke. The combustion temperature reduced faster when more argon is added which leads to a reduction in the exhaust gas temperature. This is considered as an advantage to the addition of argon to the intake of the engine. 3.3. Effect of argon concentration on the engine exhaust emissions 3.3.1. Nitrogen oxide emissions The main objective of the work is to reduce the nitrogen oxides from the spark ignition engines. The effect of adding argon gas diluent to the intake air of the engine on the nitrogen oxide emission index may be seen in Fig. 14. The argon was successfully selected for this purpose as the emission index of NO is apparently decreasing with the increase of argon gas.

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) f g k / g ( O N I E e d i x O n e g o r t i N r o f x e d n I n o i s s i m E

7

0.2

) f g k / g ( 2 O I 0.19 E n e g y x O r 0.18 o f x e d n I n o 0.17 i s s i m E

EINO(g/kgf ) Measured Calculated

6

5

4

EIO2 Measured Calculated

0.16

3

0

2

4

6

8

0

10

2

Argon (%) Fig. 14. Emission index of nitrogen oxide variation with argon percentages, N = 35rps.

Fig. 14 depicts both the measured nitrogen oxide and the calculated values as obtained from the FORTRAN equilibrium program. It can be seen from this figure that introducing argon gas in the intake has resulted in the drop of NO from 6.7 to 3 g/kg when argon is increased from 0% to 10%, respectively (55% drop). It may be mentioned here that the NO is generally formed and affected by the following: (1) the existence of nitrogen and oxygen from the atmospheric air, (2) the air/fuel ratio, (3) high temperature and (4) the existence of a diluent. Here the addition of argon reduced the molecular nitrogen in the intake air. The addition of argon reduced the N2 mole fraction by about 19% while the O 2 has been kept constant. Reducing the N2 mole fraction by 19% reduced the emission of NO in the exhaust gases by 55% means there are other factors that play an important role in the process. The other reason for the reduction of NO in the exhaust gases is increasing the air/ fuel ratio as it plays important role in this reduction as has been shown before [10]. The combustion temperature has been shown above to increase with adding more argon as may be seen in Fig. 8. Although the combustion temperature has increased but it seems that it has been overwhelmed by the other factors. The remaining factor that plays an important role in reducing the NO in the exhaust is the existence of an inert gas which is the argon here. The increase of inert argon in the combustion chamber leads to the reduction of the NO as has been shown before for many other inert gases e.g. CO 2, H2O and exhaust gases. 3.3.2. Exhaust oxygen emissions The measured and calculated oxygen concentration in the exhaust gases may be seen in Fig. 15. It may be seen from the figure that increasing the argon from 0% to 10% has resulted in the reduction of the emission index of O 2 in the exhaust gases. It has been also mentioned above that the concentration of O 2 in the intake air was kept constant at 21% as the argon was increased. 3.3.3. Exhaust carbon monoxide The variation of the carbon monoxide (CO) against the argon added ratio may be seen in Fig. 16. It can be seen that the CO emission index slightly increases as the argon increases. This increase may be postulated to the fact that the available oxygen decreases with adding more argon; Fig. 15.

4

6

8

10

Argon (%) Fig. 15. Emission index of oxygen variation with argon percentages, N = 35rps.

) f 92 g k / g ( O C I E e 90 d i x o n o M n o 88 b r a C f o x e d 86 n I n o i s s i m E 84

EICO Measured Calculated

0

2

4

6

8

10

Argon (%) Fig. 16. Calculated emission Index of carbon monoxide variation with argon percentages, N = 35rps.

3.3.4. Exhaust carbon dioxide Fig. 17 shows the variation of carbon dioxide (CO 2) against the argon added percentage. It may be seen that the CO 2 slightly increases from 0.177 to 0.195 g/kg up to 4% argon then it decreases to 0.16 g/kg with adding more argon up to 10%. Adding argon in the first range slightly increases the air–fuel ratio and this increases the CO2 as the fuel molecules can easily find the oxygen atoms. As the argon increases more the air/fuel increases and the exhaust oxygen reduces and CO increases then the CO 2 decreases. 3.3.5. Exhaust nitrogen molecule The variation of the emission index of molecular nitrogen against the argon added percentage may be shown in Fig. 18. It may be seen that increasing the argon in the intake leads to the reduction of the molecular nitrogen in the exhaust gases. This is in accordance with the reduction of the molecular nitrogen added with the intake air. The added argon caused slight reduction in the

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) f g 0.21 k / g ( 2 O C I 0.2 E e d i x o i d 0.19 n o b r a C 0.18 f o x e d n I n 0.17 o i s s i m E 0.16

100 Volumetric effeciency N=24 rps N=30 rps N=35 rps N=39 rps

EICO2 Measured

) 90 %

Calculated

( v

η

y c n 80 e i c e f f e c 70 i r t e m u l o V 60

0

2

4

6

8

10

50

0

Argon (%)

2

4

6

8

10

Argon (%)

Fig. 17. Calculated emission index of carbon dioxide variation with argon percentages, N = 35rps.

Fig. 19. Volumetric efficiency variation with argon percentages and engine speeds.

124 12

) f g k / g 120 ( )

Brake power (KW) N=24 rps N=30 rps N=35 rps N=39 rps

EIN 2

2

N I E ( n 116 e g o r t i N112 f o x e d 108 n I n o i s s 104 i m E

10

) W k ( r 8 e w o p e k 6 a r B 4

100

0

2

4

6

8

10

Argon (%)

2

0

2

4

6

8

10

Argon (%) Fig. 18. Calculated exhaust emission index of nitrogen molecule variation with argon percentages, N = 35rps.

intake nitrogen which reduced the exhaust nitrogen. It has been shown above too the NO emission has also reduced as the argon increased.

Fig. 20. Brake power variation with argon percentages and engine speed.

The effects of increasing the engine speed from 24 to 39 rev/s will be presented in the following sub-sections. The effects of speed on the volumetric efficiency, brake mean effective pressure, brake power, brake specific fuel consumption, brake thermal efficiency and exhaust temperature will be shown next.

ing the argon has been already explained above. It may be seen from the figure that increasing the engine speed from 24 to 39 rps has resulted in the increase in the volumetric efficiency. This is expected trend as the volumetric efficiency is low at low engine speed due to the charge heating and backflow possibilities [10]. Increasing the engine speed would then improve this trend and reduce the charge heating and backflow as the engine cycle occurs in a less time. If the engine speed has been increased more than 39 rps, the volumetric efficiency may have been reduced. If the volumetric efficiency increases, the mass flow rate of the intake air will increase and more power can be produced from the engine.

3.4.1. Volumetric efficiency The effects of the engine speed and argon added ratio on the volumetric efficiency may be seen in Fig. 19. The effect of the add-

3.4.2. Brake power Fig. 20 depicts the variation of the brake power against the engine speed. It may be seen from these figures that increasing the

3.4. Effect of engine speed


) h . 320 W k / g ( ) c 300 f s b ( n o i t p 280 m u s n o c l 260 e u f c i f i c 240 e p s e k a r b 220

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it seems that the increase in the fuel overwhelms the increase in engine power which caused this deterioration in the performance.

Specific fuel consumption N=24 rps N=30 rps N=35 rps N=39 rps

3.4.4. Exhaust temperature The exhaust gas temperature against the engine speed and argon added ratio may be seen in Fig. 22. The effect of the argon added ratio on the exhaust gas temperature has already been explained above. The engine speed increase led to the increase in the exhaust gas temperature as seen in the figure. The increase in the engine speed increases the fuel flow rate and heat released from the fuel which could increases the combustion temperature and hence the exhaust gas temperature.

4. Conclusions From this study, the following conclusions may be drawn: 0

2

4

6

8

10

4.1. Effect of argon concentration on the thermodynamic properties

Argon (%) Fig. 21. Brake specific fuel consumption variation with argon percentages and engine speeds.

(1) The specific heat ratio of the intake air increases, and the specific heat capacities (at constant pressure and constant volume) decrease. (2) The intake air gas constant decreases and hence the intake air density and the air/fuel ratio increase.

760

Exhaust temperature ( C) N=24 rps N=30 rps N=35 rps N=39 rps °

)

720

C ° (

Adding argon with different concentrations to the intake air had the following effects:

4.2. Effect of argon concentration on the engine performance

e r u t a r e p 680 m e t t s u a h x E 640

600

0

2

4

6

8

10

Argon (%) Fig. 22. Exhaust temperature variation with argon percentages and engine speed.

engine speed led to the increase of the engine torque and brake power. This increase in the brake torque and power may be postulated to the increase in the volumetric efficiency and mass flow rate of the intake air. The engine could use more fuel when the air is increased then the power output should increase. 3.4.3. Brake specific fuel consumption and thermal efficiency The variation of the brake specific fuel consumption ( bsfc ) against the engine speed and argon added ratio may be seen in Fig. 21. It may be seen from this figure that increasing the engine speed led to the increase in the bsfc or drop in the thermal efficiency. Although the increase in the engine speed leads to the increase in the engine output power, it is apparently increasing the fuel flow rate greatly. The increase in the engine speed already leads to the increase in the volumetric efficiency or mass flow rate of air; hence the mass flow rate of fuel should also increase. As the bsfc is the mass flow rate of fuel divided by the power output, then

(1) Adding more argon increased the engine volumetric efficiency. (2) The peak value of motoring pressure increases as the dilution percentage of argon increases. (3) The peak value of firing pressure increases as the dilution percentage of argon increases and occurs at earlier crank angles. (4) The peak value of combustion temperature increases as the dilution percentage of argon increases and occurs at earlier crank angles. (5) The heat release rate generally increases with increasing the argon as well as its slope of increase with crank angle i.e. the maximum value occurs earlier with adding more argon. (6) Increasing the argon gas has resulted in a faster combustion. (7) The brake mean effective pressure and brake power slightly increase as the argon dilution percentage increases. (8) Adding more argon decreased the brake specific fuel consumption and increased the brake thermal efficiency. (9) The exhaust temperature decreases as the argon dilution percentage increases. (10) Increasing the argon concentration resulted in the decrease of the emission index of nitrogen oxide (NO), oxygen (O 2), nitrogen (N2) and carbon dioxide (CO 2). (11) The emission index of carbon monoxide (CO) increases as the argon dilution percentage increases.

4.3. Effect of engine speed

(1) For the same amount of argon concentration, increasing the engine speed decreased the air/fuel ratio, increased the volumetric efficiency, increased the brake specific fuel consumption, increased the brake mean effective pressure and the brake power.

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(2) For the same amount of argon concentration, increasing the engine speed decreased the brake thermal efficiency and increased the exhaust temperature.

References [1] Watson H, Milkins E, Rigby G. A new look at oxygen enrichment of the diesel engine. SAE paper no. 900344; 1990. [2] Asada T, Nagai M. Investigations on recycle and closed-cycle diesel engines. SAE paper no. 800964; 1980. [3] Pin Zeng, Dennis N. Assanis. Cylinder pressure reconstruction and its application to heat transfer analysis. SAE paper no. 2004-01-0922. Automotive Research Center, University of Michigan. [4] ladommatos N, Abdelhalim SM, Zhao H, Hu Z. The dilution, chemical, and thermal effects of exhaust gas recirculation on diesel engine emissions – Part 2: effects of carbon dioxide. SAE paper no. 961167. Brunel university; 1996.

[5] No SH, Kobori S, Kamimoto T, Enomoto Y. High temperature diesel combustion in a rapid compression–expansion machine. SAE paper no. 911845; 1991. [6] Volponi Joanne V, Branch Melvyn C. Flame structure of C2H2–O2–argon and C2H2–NO2–argon laminar premixed flames. In: 24th Symposium (int.) on combustion. The Combustion Institute; 1992. p. 823–31. [7] Ohigashi S, kuroda H, Hayashi Y, Sugihara K. Heat capacity changes predict nitrogen oxides reduction by exhaust gas recirculation. SAE paper no. 710010; 1971. [8] Assanis SDN, Heywood JB. Simulation studies of the effects of low-heatrejection on turbo-compound diesel engine performance. Int J Vehicle Design 1987;8(3):282–99. [9] Li Jian Wen, Chae Jae Ou, Park SB, Paik HJ, Park K, Jeong YS, Lee SM, Choi YJ. Effect of intake composition on combustion and emission characteristics of DI diesel engine at high intake pressure. SAE paper no. 970322. [10] Heywood John B. Internal combustion engine fundamentals. McGraw Hill Publisher; 1988.

Argon

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