investigations on reduction of carbon monoxide from

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11

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INVESTIGATIONS ON REDUCTION OF CARBON MONOXIDE FROM CATALYTIC COATED SPARK IGNITION ENGINE· WITH CATALYTIC CONVERTER M. V.S. Murali Krishna 1, T. Ratna Reddy2, & CM. Vara Prasad 3 1,2 Asst. Professor, Department of Mechanical Engineering, Chaitanya Bharathi Institute of Technology, Hyderabad-500075, Andhra Pradesh. 3 Principal, S. V. Engineering College, Suryapet-508213, Nalgonda Dt, Andhra Pradesh

ABSTRACT

This paper reports the investigations that are carried out on control of carbon monoxide (CO) content in the exhaust of catalytic coated, variable compression ratio spark ignition (SI) engine with catalytic converter. Copper is coated over the crown of the piston and inside cylinder head of combustion chamber of conventional SI engine. Sponge is used as catalyst in the converter. The influence of the parameters/conditions such as void ratio, air-fuel ratio, injection of air,

temperature of air, mass of catalyst, speed and load of the engine on control of CO emission from the exhaust of catalytic coated SI engine are studied and compared with those of conventional SI engine. In both versions of the engine, the air-fuel ratio, speed and load of engine have shown greater influence in the emission of CO, whereas; the void ratio, mass of the catalyst, temperature of injected air has shown significant control of CO in the exhaust. Catalytic coated engine reduces the CO emissions considerably at different operating conditions when compare with those of conventional engine. Key words : Pollution levels, CO emissions, Spark ignition engine, Catalytic coating, .. Catalytic converter.

INTRODUCTION: The rapid industrialization, faster urbanization and drastic increase in automobile population are considered as major factors responsible for air pollution. (De, 1994: Sharma,1996). CO is major pollutant contributed by the automobile exhaust, particularly SI engine, breathing of which causes asphyxia due to formation of carboxy hemoglobin in the blood of human beings. The other health disorders caused by CO intoxication are headache, weariness, retarded mental activity etc., (Khopkar, 1993; Fulekar, 1999). It also causes detrimental effects on other animal and plant life besides, environmental disorders (Sharma, 1996). The use of catalysts to promote combustion is an old concept. Commercially, the catalysts (Pfefferle William, 1978) are employed in the form of catalytic igniters and low temperature catalytic burners for weak non flammable mixtures in the gas turbine field Platinum mesh (Thring, 1980) is tested in a pre-chamber of Ricardo Comet diesel engine with reduced compression ratio and it is concluded that the engine with platinum catalyst can run with (a) higher fuel economy (b) lower Nox emission (c) lower hydrocarbon emission (d) multi fuel capability. Copper coils are used (Rychter et al, 1981) inside a pre-chamber of an SI engine and is found that, the catalyst shortens ignition delay and reduces the flame kernel in its initial development phase. More recently (Hu Zhengyun, 1996), platinum catalyst is employed in ~he piston crown top and ring crevices for reducing hydrocarbon emission. Copper is coated over piston crown and inside of cylinder head wall (Dhandapani, 1991; Nedunchezhian et al, 2000).) ana it is reported that the catalyst improves the fuel economy and increased combustion stabilization. The CO is formed in the combustion process in the engine due to incomplete combustion of fuel. Increasing the air-fuel ratio in the combustion process can decrease the engine levels of CO emission, but it increases other pollutants like NO, abnormally (Khopkar, 1993; Sharma, 1996). However, the use of catalytic converter is found to be more effective in control of CO emission (Vara Prasad et al.,l997; Luo et al, 1999; Murali Krishna et al, 2000). The present paper reports the study made by using sponge, which is easily available and cheaper in cost, as catalyst, in controlling CO levels in the exhaust of SI engine and comparison is made in reduction of CO at different conditions for conventional engine and catalytic coated engine.

MATERIALS AND METHODS In the present investigations, in reducing CO emissions, the piston crown and inside surface of the cylinder head are coated with copper by plasma spraying. The basic principle and the schematic arrangement of the plasma coating equipment are given in reference (Nedunchezhian eta!, 2000). A bond coating ofNICoCr alloy is applied for a thickness of about 200 microns using a 100 k W METCO plasma spray gun. Over the bond coating copper 89.5%, Aluminum 9.5% and iron 1.0% are coated for 400 microns thickness. The coating has very high bond strength and does not wear off even after 100 hours of operation.

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Investigations on reduction of carbon monoxide from catalytic coated ...

185

The experimental set-up employed in the present investigation (Fig 11.1) consists of four stroke, single cylinder, petrol engine of 1.85 kW brake power coupled to an eddy current dynamometer for measuring brake power (BP) of the engine. The compression ratio can be varied from 5 to 9 at varying speeds in the range of 2200 to 2800 rpm. A catalytic converter which is of 8.9 em diameter and length 21 em (Fig 11.2) is connected to the exhaust pipe of the engine. Provision is made to inject a definite quantity of air into the converter. The converter is filled with catalyst of varying void ratios ranging from 0.1 to 1.0 such that back pressure on the engine is not · increased. A microprocessor based CO analyzer is employed to measure the percentage of CO in the exhaust of engine. The following versions of the engine are used in the study of controlling

co, (A)

Conventional, variable compression ratio, spark ignition engine (CE),

(B)

Catalytic coated, variable compression ratio, spark ignition engine (CC), at following operating conditions of the catalyst,

1.

Set A - Sponge iron as catalyst,

2.

Set B - Sponge iron as catalyst with air injection at room temperature.

The exhaust gases are drawn, at three different locations for measuring the % of CO, (i) immediately after the exhaust valve of different versions of the engine, when no catalyst is used, (ii) at the outlet of the catalytic cor.verter (when catalyst is used, Set-A) for both version of the engine (iii) at the outlet of the converter after air injection into the converter (catalyst along with , air injection, Set-B) for both versions of the engine. The quantity of air drawn from compressor and injected into the converter is kept constantly by taking care to see that the back pressure does not increase and reverse flow is not created in the converter.

RESULTS AND DISCUSSION The percentage variation of CO in the exhaust of the engine at peak load, at a speed of 2800 rpm, with a compression ratio of 9:1, at an air-fuel ratio of 13:1 with varying void ratio of catalyst, for different versions of the engine and at different operating conditions of the catalyst is shown in Fig.ll.3. The void ratio is given by volume occupied by the catalyst to volume of catalytic chamber. It can be observed from the figure that the CO emission decreases considerably with increasing void ratio in all cases, for different versions of the engine. In addition, the air injection has further decreased the CO content (Sets B) in the exhaust, but using catalyst this may be reduced further as shown in Figure.l1.3. Peak catalytic efficiencies of reduction of CO are observed, at a void ratio of 0.75, for both versions 0f the engine, at different operating conditions of the catalyst, and beyond which no significant variations are noticed. This is because, increase of back pressure is observed if void ratio is more than 0.75, which deteriorates the performance of the both versions of the engine. The injection of air further promotes oxidation process for both versions of the engine. Combustion in CC engine is improved due to increase of flame speed, with the provision of copper coating on cylinder and piston, leading to reduction in the percentage of CO. Figure 11.4 shows, the variation of the percentage of CO in the exhaust of the engine, at peak load operation, for different versions of the engine, at a speed of 2800 rpm and at air-fuel ratio of 13: 1 with mass of the catalyst in the converter. From the figure it can be observed that CO content decreases with increasing mass of the catalyst, and a mass of 2 kg of catalyst in the converter is found to be optimum for better results, for different versions of the engine. Back pressure is observed, with Increase of mass of catalyst beyond this quantity, for both versions of the engine and at different operating conditions of the catalyst.

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The data pertaining to the percentage of CO emission in different operating conditions of catalyst \vith different versions of the engine is shown in Table 11.1. The data shows a substantial reduction of CO levels in the exhaust of the engine with the use of catalytic converter, for different versions of the engine. Drastic reduction of CO (54%) is observed, with CC engine with catalytic converter, with different conditions of the operation of the catalyst, over CE engi1ie, without catalytic converter. A further decrease in CO levels by 15% is observed with air injection for catalytic coated engine, at the same operating conditions of the catalyst, over conve11tional engine with out catalytic converter. The percentage variation of CO in the exhaust of the engine, at peak load, with a compression ration of 9:1, void ratio of 0.75 and air fuel ratio of 13: with speed of the both versions of the engine is shown in Fig 11.5. The figure shows a declination in CO content with increase in speed of the engine and the effect is more pronounced with the air injection into the converter:This is because, as speed increases, turbulence increases leading to better combustion, causing reduction in CO emissions from the exhaust of the engine. With CC engine, due to increase of flame velocity with catalytic effect, more turbulence of charge occurs, leading to further reduction in CO emissions. Figure 11.6 shows the percentage variation of CO in the exhaust of the engine at a speed of 2800 rpm,· void ratio of 0.75 and airfuel ratio 13:1 with brake power (BP)of both versions of the engine. CO emissions are more at part bad and at peak load for both versions of the engine. As BP of the engine increases, the CO content in the exhaust decreases for both versions of the engine, upto 80% of the bad and again increases. During part loads, the combustion temperatures are low, leading to incomplete combustion causing more amount of CO in the exhaust of the both versions of the engine. When the !oad/BP (up to 80%) on the engine is increased, the combustion chamber temperature and air movement increases leading to reduction in CO content in the exhaust of the both version of the engine. In other words, CO emissions are less at the load (usually at 80% of the peak load), where maximum thermal efficiency is obtained. At peak load operation of the engine, due to incomplete combustion of the charge because of the presence of residuals and deposits and complete utilization of air at peak loads In combustion chamber, lead to more amount of CO in the exhaust of both versions of the engine. The conventional engine with set-A operation, reduce the amount of CO during entire load operation and further reduction of CO is observed with Set-B. This reduction of CO is less at part load and is more at peak load of operation of the engine. This is due to, oxidation reaction of CO, at higher combustion temperatures generated at peak load operation of the engine. At part load the magnitude of temperature is less causing less reduction of CO at part load. The injection of air promotes further oxidation leading to more reduction of CO with Set-B operation for conventional engine. The catalytic coated engine reduces more amount of CO for entire load operation of the engine, when compare with that of conventional engine. As load increases, temperature increases with which surface catalytic activity increases, leading good combustion causing lower amount of CO, when compare with that of conventional engine: With Set-A and Set-B operations, further reduction of CO is observed with this version of the engine compare with conventional engine. Similar to conventional engine, the emission reduction is more at higher loads and less at part bad operation of the catalytic coated engine. The data given by the Nedunchezhian (Nedunchezhian et al, 2000) agrees with these trends observed by the authors. The percentage variation of CO in the exhaust of the engine at peak load with a compression ratio 9:1, void ratio 0.75 and at a speed of 2800 rpm with the air-fuel ratio of the both versions of the engine is shown in Fig. 11.7. As expected on theoretical grounds (Mathur and Sharma, 1999), a decrease in CO levels is observed, for both versions of the engine, with increase of air-fuel ratio. As air content increase, effective combustion of fuel takes place leading to generate high combustion temperatures with which CO content reduce in the exhaust of engine. With employing catalytic converter, further reduction of CO is observed with conventional engine, at both operating conditions

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187

of the catalyst. Drastic reduction of CO emissions are observed with catalytic coated engine with catalytic converter, at higher air fuel ratio of the engine. This is due to increased surface activity at higher combustion temperature at higher air fuel ratio. With air injection in to the catalytic converter of catalytic coated engine, drastic reduction of CO is observed at higher air fuel ratio of the engine. Fig. 11.8 represents the variation of percentage of CO, at peak load operation of both versions of the engine, at void ratio of 0.75, at a speed of 2800 rpm and at air-fuel ratio of 13:1 with temperature of injected air. When the temperature of the injected air is raised, a significant decrease in CO levels is observed (Sets B) up to a temperature of 350 o C. The increase in temperature of the air facilitates the faster oxidation of CO into CO, which is less toxic The CO emissions from the catalytic coated engine are less, due to better combustion of charge because of increase of flame speeds. The reduction of CO is further less with CC engine, with the increase of air temperature of injected air. Maximum reduction of CO occurs nearly, when injected air temperature is 350 o C with CC engine also. Surprisingly CO emissions increase beyond this temperature, for both versions of the engine. This is due to the fact that, catalytic activity of converting CO into C0 2 ceases at higher temperatures, as C02 dissociates into CO and oxygen.

CONCLUSIONS During these studies a void ratio of 0.75 is found to be optimum for both versions of the engine. Increase of mass of catalyst leads to decrease the amount of CO emissions from the exhaust of the both versions of the engine. A mass of 2 kg is found optimum for reducing CO emissions for both versions of the engine. CO emissions decrease with Increase of speed of the both versions of the engine. A speed of 2800 rpm of the both versions of the engine gives better results in reducing CO emissions. CO emissions are more at peak load ar.d at part bad operations of both versions of the engine. Increase of air fuel ratio leads to decrease the amount of CO for both versions of the engine. An air-fuel ratio of 13: I is found suitable in reducing CO emissions, for both versions of the engine. With increase of air quanity in all cases, the CO is oxidized to C02 in the presence of catalysts. When air is injected, the reduction of CO levels is more pronounced for both versions of the engine. CO emissions further reduce with the increase of temperature of air for both versions of the engine. Drastic reduction of CO is observed with catalytic coated S.I engine provided with catalytic converter with preheated air injection

ACKNOWLEDGEMENTS The authors are thankful to the authorities of Chaitanya Bharathi Institute of Technology, Hyderabad, for the facilities provided.

REFERENCES De, A.K., 1994, Environmental Chemistry, New Age International (P) Ltd Publishers, New Delhi. Danddapani, S., 1991,Theoretical and experimental investigation of catalytically activated lean bum combustion', Ph.D Thesis , liT, Madras. Fulekar, M.H., 1999, 'Chemical pollution - a threat to human life', Indian Journal of Environmental

Protection, pp 353-359. Hu Zhengym, 1996, 'A mathematical model for .in cylinder catalytic oxidation of hydrocarbons in SI engines', SAE Paper No 961196. Khopkar, S.M., 1993, Environmental Pollution Analysis, New Age International (P) Ltd, Publishers, New Delhi.

Environment & its Challenges Luo, M.F. and Zheng, X.M., 1999, 'CO oxidation activity and TPR characterization of Ce02- supported manganese oxide catalysts', Indian Journal of Chemistly, 38,A, pp 703-707. Mathur, M.L. and Sharma, R.P., 1999, IC Engines, Dhanpath Rai Publications (P) Ltd., New Delhi, pp. 734736.

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Murali Krishna, M.V.S., Varaprasad, C.M. and Venkata Ramana Reddy, Ch., 'Studies on control of carbon monoxide emission in spatk ignition engine using catalytic converter, Indian Journal of Ecology, Environment and Conservation, September, 2000, pp 377-380. Nedunchezhian,N and Dhandapani.S., 2000 'Experimental investigations of cyclic variation of combustion chamber', Indian journal of Engineering Today, Vol-2, September ,2000. Pfeferie William, C., 1978, The catalytic combustor an approach to cleaner combustion', Journal of Energy, Vol-2, May-June ,/978,pp /42-146. Rychter ,T.J., Saragih, R., Lezanski, T. and Wjcicki .~ .• 1981, 'Activation of a charge in a prechamber of a SI lean-bum engine', Eighteenth International Symposium on Combustion, The combustion Institute, 1981, pp 1815-1824. Sharma, B.K., 1996, Engineering Chemistry, Krishna Prakash an Media (P) Ltd, Meerut. Thring, R.H., 1980, The catalytic engine -Platinum improves economy and reduces pollutants fro111 a range of fuels', Pl~tinum Metal Review, Vol24,No 4, 1980, ppl26-133. Vara Prasad, C.M., Murali Krishna, M.V.S. and Prabhakar Reddy, C.,1997, 'Reduction of carbon monoxide in high speed petrol engines with catalytic converter', Proceedings of XV national Conference of IC engines and CQmbustion, Chennai, pp. 372-377.

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Table 11.1. Data of CO emissions in the exhaust of conventional SI engine and catalytic coated SI engine at a compression ratio of 9; 1 and speed 2800 rpm under different conditions. Operation

No catalyst

Condition

Parameter

At void ratio 0.75 At mass of Catalyst 2 Kg

At a void ratio, 0.75

Engine CE

cc

%CO

3.58

2.58

%CO

3.5

2.5

%CO

2.02

1.6

% decrease wrt CE

43.6

55.3

% decrease wrt CC

21.7

37.98

%CO

SetA At mass of the catalyst, 2 Kg

SetB

40.2

53.35

% decrease wrt CC

14.4

33.2

1.3

1.01

% decrease wrt CE

63.7

71.8

% decrease wrt CC

49.6

60~85

%CO At mass of the catalyst, 2 Kg

1.67

% decrease wrt CE

%CO At a void ratio, 0.75

2.14

1.41

1.24

% decrease wrt CE

60.6

65.36

% decrease wrt CC

43.6

50.4

CE- Conventional Engine, CC- Catalytic Coated Engine., Set A- Sponge iron aJ catalyst, Set B - Sponge iron as catalyst with air injection.

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(1) Engine (2) Dynamometer (3) Fuel tank (4) Burette (5 and 6) Three way valve (7) Rotameter (8) Catalytic Converter (9) CO analyzer (10) Air comp~or

Fig. 11.1 : Experimental Set-up

Fig. 11.2 : Details of catalytic Converter

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CONDITION I :ENGINE CE l C C o.--o 1 o---o

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~

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A-A I A---A A---.6. I •--·•

L.

3

- -o----- -- -o---0 u

2 ......,. ...._---A-- ...

-- -... __ _

~ 0

0

0·75

0·25 0·50 VOID RATIO

Fig. 11.3 : Percentage variation of CO with void ratio

CONDITION I ENGINE CE cc No Catalyst SC!t-A 4L I Set-8

G--O

0---0

·-· ·---· A----A 6.---A

3

-o--

---~-

2 0

u

__..,..,., -:-tr--

.......

~ 0

0

1 2 3 MASS OF CATALYST (Kg)

Fig. 11.4 : Percentage variation of CO with mass (kg) of catalyst

191

- ------

CONDITION No Cata_!yst Set-A Set-8

--·n-~

ENGINE CE cc 0 - 0 0---0

.. __. 6~

6---6

·---.&

4

0

u ~

0

-416...._ --._. ... -

0 2200

2400

. 2800

2600

SPGED {RPM)

Fig. 11.5 : Percentage variation of CO with speed (rpm) of the engine CONDITION

cc

CE

0

u

I

ENGINE

No Catalyst

o-a-

Set-A Set- 8

·-· A-A

'

0----0

6----A

A.- --6

2

~ 0

~-,

0

0·5

....

1·0

- _, .,. ......

1·5

2·0

BRAKE POWER(kW)

Fig. 11.6 : Percentage variation of CO with Brake Power(k W) of the engine

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CONDITION

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ENGINE

cc

CE

~

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No Catalyit Set-A Set-8

193

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·-· A--A

..

A--~

... __

G

0

u ~ 3·

2

... ....

;. o~----~----~----~7 9 11 13

AIR-FUEL RATIO

Fig. H.7 :Percentage variation of CO with air-fuel ratio

CONDITION

I

ENGINE

CE

4r

No Co tal st I Set -8·

o-·o

..,_....

cc 0---0

·--··

02 c._, ~

.......

__ --- -.......... ,.

75 225 375 L.'SO AIR TEMPERATURE ( 0c)

.Fig. 11.8 : Percentage variation of CO with temperature CC) of air