1

CHAPTER - 1

INTRODUCTION

Air pollution generated from mobile sources such as automobiles contributes major

air quality problems in rural as well as urban and industrialized areas in both developed and

developing countries. About 50 million cars are produced every year and over 700 million

cars are used worldwide. Vehicle population is projected to grow close to 1300 million by the

year 2030. The pollutant emissions from automobile have been implicated in formation of

green house gases, respiratory illness, and the depletion of the earth‟s ozone layer. The three

pollutants of concern emitted from the spark ignition engines are unburned HC, CO and NOx .

Unburned HC and CO are generated due to inefficient combustion while the thermal NOx

is

formed when nitrogen reacts with excess oxygen at higher temperature (>1800K) in the

combustion process and is the predominant form produced by Zeldovich Mechanism in

combustion engines.

Two methods are being used to reduce harmful engine out exhaust emissions. One is

to improve the engine technology & composition of fuels and introduction of alternative fuels

so that better combustion occurs and consequently fewer emissions are generated. The second

method is post combustion after treatment of the engine out exhaust gases. In conventional

spark ignition engines exhaust gas temperatures may vary from 300o

C to 400o

C from idling

to around 900o

C at full load condition. However, the most common range of exhaust gas

temperature lies between 400o

C~600o

C. Oxidation of unburned HC in the exhaust requires

lower temperature than to oxidize carbon monoxide at a specified residence time. Without

using catalyst, temperatures in excess of 600o

C & residence time greater than 50ms is

required to oxidize HC and temperature in excess of 700o

C is required to oxidize CO. But,

temperature ranges between 250o

C and 300o

C are required to oxidize CO & HC in the

presence of catalysts [5].

Catalytic Converters are important post combustion after treatment devices mounted

in the exhaust system of engines to reduce engine out exhaust emissions and are classified as

Two-Way or Three-Way. Two-Way Catalytic Converter works on two gases, CO and

2

unburned HC while the NOx

is controlled though exhaust gas recirculation (EGR) and by

retarding the ignition timing.

The Three-Way Catalytic Converter works on all the three gaseous pollutants of

concern: CO, unburned HC & NOx. 3WCC typically contain active catalytic materials (Pt/Rh

or Pd/Rh) which promote oxidation of CO & unburned HC and reduction of NOx. Pt

(Platinum) and Pd (Palladium) are used as oxidation catalyst while Rh (Rhodium) is used as

reducing catalyst for NOx reduction.

Motor vehicle emissions are composed of the by-products that comes out of

the exhaust systems or other emissions such as gasoline evaporation. These emissions

contribute to air pollution and are a major ingredient in the creation of smog in some large

cities. Emission standards are set to regulate the output of air pollutants from internal

combustion engines. The first Indian emission regulations were idle emission limits which

became effective in 1989. These idle emission regulations were soon replaced by mass

emission limits for both gasoline (1991) and diesel (1992) vehicles, which were gradually

tightened during the 1990‟s. Since the year 2000, India started adopting European emission

and fuel regulations for four-wheeled light-duty and for heavy-duty vehicles. India‟s own

emission regulations still apply to two- and three-wheeled vehicles.

3

CHAPTER 2

CATALYTIC CONVERTER

The pollutants have negative impact on air quality, environment and human health

that leads in stringent norms of pollutant emission. Numbers of alternative technologies like

improvement in engine design, fuel pre-treatment, use of alternative fuels, fuel additives,

exhaust treatment or better tuning of the combustion process etc. are being considered to

reduce the emission levels of the engine. Out of various technologies available for automobile

exhaust emission control a catalytic converter is found to best option to control CO, HC and

NOx emissions from petrol driven vehicles while diesel particulate filter and oxidation

catalysts converter or diesel oxidation catalyst have so far been the most potential option to

control particulates emissions from diesel driven vehicle.

A catalytic converter (CC) is placed inside the tailpipe through which deadly exhaust

gases containing unburnt fuel, CO, NOx are emitted [17]. The function of the catalytic

convertor is to convert these gases into CO2, water, N2 and O2 and currently, it is

compulsory for all automobiles plying on roads in US and Japan to have catalytic converters

as they use unleaded petrol. In India, the government has made catalytic converters

mandatory for registration of new cars.

Fig 1 catalytic converter [4]

4

CHAPTER 3

HISTORY OF CATALYTIC CONVERTER

The catalytic converter was invented by Eugene Houdry, a French mechanical

engineer who lived in the United States. In 1950, when the results of early studies of smog in

Los Angeles were published, Houdry became concerned about the role of automobile exhaust

in air pollution and founded a special company, Oxy-Catalyst, to develop catalytic converters

for gasoline engines - an idea ahead of its time for which he attained a patent. But, until the

extremely effective anti-knock agent tetra-ethyl lead was eliminated from most gasoline over

environmental concerns, it would "poison" the converter by forming a coating on the

catalyst's surface, effectively disabling it. The catalytic converter was later on further

developed by John J. Mooney and Carl D. Keith at the Engelhard Corporation creating the

first production catalytic converter in 1973. Beginning in 1979, a mandated reduction in NOx

required the development and use of a three way catalyst for CO, HC and NOx abatement.

5

CHAPTER 4

THE CATALYST

Catalysts are needed to reduce emissions to acceptable levels without dramatically

reducing performance and fuel economy. This is true of HC, CO and NOx, but NOx is the

emission that is most dependent on the catalyst for emissions compliance. A catalyst is used

to reduce the activation energy required for the chemical reaction to initiate and it also helps

to reduce the time required for completing the reaction.

There are actually two types of catalysts. Reduction catalysts cause NOx to be

reduced into O2 and N2. Oxidation catalysts cause HC and CO to oxidize with any available

oxygen into CO2 + H2O. Unfortunately oxidation will only occur when there is enough free

oxygen, and reduction will only occur in a relative absence of free oxygen.

Rhodium is generally the most efficient reduction catalyst. Platinum and palladium

are used for oxidation. 2-way catalytic converters are oxidation catalysts. They oxidize CO

and HC but do not reduce NOx. 3-way catalysts oxidize and reduce. They oxidize CO & HC

and reduce NOx.

Proper air /fuel mixture control and exhaust oxygen content is required for proper

3-way catalyst performance. In general, oxidation and reduction cannot both occur at their

highest efficiency at the same time. Reduction efficiency is not at it's highest unless the

oxygen content is very low. This usually doesn't happen unless the air/fuel mixture is at least

a little bit rich. Oxidation only reaches it's highest efficiency when the oxygen content is

fairly high. That happens when the mixture is at least slightly lean

Fig 2 : effect of catalyst [5]

6

CHAPTER 5

TYPES OF CATALYTIC CONVERTER

1) The oxidization catalytic converter

An oxidation catalyst is a device placed on the tailpipe of a car. The oxidation catalyst is

the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon

monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst

aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas.

HC + O2 CO2 + H2O

2CO + O2 CO2

2) The reduction catalytic converter

A reduction catalyst to control NOx can be used as a separate system in addition to

the oxidation catalytic converter. The reduction catalyst is fitted upstream of the oxidation

system. The reduction catalyst is the first stage of the catalytic converter. It uses platinum and

rhodium to reduce the nitrogen oxide emissions. When such molecules come in contact with

the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing

the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are

also stuck to the catalyst forming N2

2NO N2 + O2

3) The three-way catalytic converter (TWCs)

TWCs have the advantage of performing the oxidation of carbon monoxide (CO),

hydrocarbons (HC) and the reduction of nitrogen oxides (NOx) simultaneously. Noble metals

are usually used as the active phase in TWCs. Pd catalysts are especially attractive since Pd is

by far the cheapest noble metal in the market and has better selectivity and activity for

hydrocarbons. Rhodium the other essential constituent of three-way catalysts is widely

recognized as the most efficient catalyst for promoting the reduction of NO to N2.

7

The TWCs performance in the emission control can be affected by operating the catalyst at

elevated temperatures (> 600 °C). Reactions occurring on the automotive exhaust catalysts

are very complex as listed below. The major reactions are the oxidation of CO and HC and

the reduction of NOx. Also, water gas shift and steam reforming reaction occur. Intermediate

products such as N2O and NO2 are also found. The NOx storage concept is based on

incorporation of a storage component into the three-way catalyst (TWCs) to store NOx

during lean conditions for a time period of minutes.

CO +0.5O2 CO2

CHa+ M1. O2 CO2 +0.5a. H2O

CHa + M2. O2 CO + 0.5a. H2O

H2+ 0.5 O2 H20

NH3 + (¾) O2 1.5 H20 +0.5 N2

CO + NO CO2 + 0.5 N2

2.5CO + NO + 1.5 H2O H20 + 0.5 N2

H2 +NO H20 + 0.5N2

2.5H2 + NO NH3 + H20

CHa + M1. O2 CO2 +0.5a. H20

(1/2M2) CHa + NO (1/2M2) CO + (a/4M2) H20 + 0.5 N2

CHa + M3. NO CO2 + 0.5a H20 +0.5M3 N2

(2.5/2M2) CHa + NO + ((3-a)/4M2 H20 NH3 + (2.5/2M2) CO

where “a” is hydrogen-to-carbon ratio, M1 = (1+ (a/4)) M2 = (0.5 + (a/4)) M3 = (2 + (a/2))

[1]

Oxygen Storage Mechanism

A typical closed-loop control fuel supply system causes the A/F to fluctuate rapidly

about the stoichoimetrically balanced composition with a frequency of nearly 1 Hz. The

conversion efficiency of a three-way catalytic converter can be improved by storing the extra

oxygen under fuel lean conditions and releasing it under rich conditions. The released oxygen

8

may participate in the reactions with the reducing agents, thereby increasing the conversion

of CO and HC in a rich exhaust-gas environment. Such an oxygen storage capacity OSC is

developed in the modern catalyst by coating its substrate with a wash-coat material

containing ceria. The OSC is recognized as an important mechanism affecting catalyst

behaviour during vehicle acceleration and deceleration. In addition to the pathways, which

specify the kinetics over the noble metal sites, an additional kinetic mechanism is required to

represent the OSC. In the present study, the OSC is simulated by designating two kinds of

sites that can be oxidized and reduced through a nine-step site reaction mechanism. The metal

reduction site on the surface is defined as <S> & and the oxidized site is defined as

<OS>.This oxygen storage mechanism is shown below [1]

<S> + 0.5 O2 <OS>

<OS> + CO <S> + CO2

H20 + CO H2 + CO2

<OS> + H2 <S> + H20

CHa + H20 CO + (1+0.5a)H2

(3/2) CHa + <OS> <S> + 0.5C + CO + (3a/4) H2

C + O2 CO2

<S> + NO <OS> +0.5N2

<OS> + (2/5) NH3 <S> + <2/5>N0 + (3/5) H20

9

CHAPTER 6

RESULT AND DISCUSSIONS

Response to Step Change in Air-Fuel Ratio

The response to step change in A/F is investigated by considering the catalysts

initially operating at steady state, and which are subjected to step changes in A/F. During the

step change, the other inlet conditions remain unchanged. Figure 8 shows the effect of step

change in A/F from a value of 15 ~lean condition to a value of 14 ~rich condition. The figure

shows that CO conversion efficiency, which is initially 99.7%, responds to the step change

and the efficiency drops to 39.3%. The low CO conversion performance lasts only a very

short period and the conversion efficiency increases to values over 90%. While steady-state

value of 93% is reached slowly, most major changes take place in the first second of the step

change. For the conditions studied, the step change in A/F brings about a significant change

in HC conversion performance. The efficiency drops from 92.7% to 2%. It takes a long time

~;25 seconds before the final steady state value is reached. The response of NO conversion to

step change in A/F, on the other hand, is very fast. It takes 0.3 second to attain the final

steady-state value. The NO conversion efficiency increases from 4.3% ~in the lean zone to

99.9% ~in the rich zone.

The effect of step changes in transition from rich to lean conditions is considered next. Figure

9 shows the results of this transition, in which the A/F is changed from 14 ~rich condition to

15 ~lean condition. The CO conversion is not much influenced ~from 99.2% to 99.7% by the

step change in A/F. In this case, the initial CO conversion efficiency ~99.2% is higher than

that obtained for the similar value of A/F of 14 in the previous case of step change from lean

to rich. This difference is due to a slightly higher NO conversion corresponding to A/F of 14

in the previous case than in the present case. This difference in NO conversion performance

is discussed further later in this section. There is also a small drop in the CO conversion for a

very short period as the catalyst is subjected to step change. The drop is immediately

followed by an increase in conversion. As in the previous case, the HC conversion is

significantly affected by the step change. The conversion efficiency increases from 2% to

92.7%. The step change causes the NO conversion efficiency to decrease from 99.2% to a

lower value of 42.3%. The efficiency then increases to 49.3% corresponding to A/F of 15.

Note that this efficiency is much higher than the steady-state value of 4.3% corresponding to

A/F of 15, which was obtained in the previous case. This increase in NO efficiency indicates

10

a hysteresis effect. Thus the catalyst NO conversion efficiency corresponding to a value of

A/F depends, not only on the value of the A/F, but also on the path by which that value is

reached. Higher efficiency is obtained when a particular A/F is reached from the rich zone

than the case when it is reached from the lean side. The hysteresis in NO conversion is due to

the OSC effect as this behaviour is not observed in the non-OSC case.

Conversion Efficiency Variation with A/F Ratio

Conversion efficiency of NO, CO and HC as a function of the air-fuel in a three

way catalytic converter. Fig.5 shows the conversion efficiency of NO, CO and HC as

function of the air - fuel ratio. There is a narrow range of air- fuel ratio near stoichiometry in

which high conversion efficiencies for all three pollutants are achieved. The width of this

window is narrow about 0.1 air-fuel ratio for catalyst with high mileage use and depends on

Fig 3 step change from lean to rich [1] Fig 4 step change from rich to lean [1]

11

catalyst formulation and engine operating conditions. In a multi point fuel injection system as

the air fuel ratio increases the conversion efficiency of CO and HC is increasing and at higher

A/F ratio the efficiency decreases and the conversion efficiency of NOx is maximum at the

stotichometric ratio and it goes on decreasing when goes to lean and rich zone.

Fig 5 Multi point FI [4] Fig 6 Single point FI [4]

Fig 7 Carburetor system [4]

12

CHAPTER 7

BHARATH EMISSION STANDARDS

Bharat stage emission standards are emission standards instituted by the Government of

India to regulate the output of air pollutants from internal combustion engine equipment,

including motor vehicles. The standards and the timeline for implementation are set by the

Central Pollution Control Board under the Ministry of Environment & Forests. The standards,

based on European regulations were first introduced in 2000. Progressively stringent norms

have been rolled out since then. All new vehicles manufactured after the implementation of

the norms have to be compliant with the regulations. Since October 2010, Bharat stage III

norms have been enforced across the country. In 13 major cities, Bharat stage IV emission

norms have been in place since April 2010. The phasing out of 2 stroke engine for two

wheelers, the stoppage of production of Maruti 800 & introduction of electronic controls have

been due to the regulations related to vehicular emissions.

The idling CO emissions and free acceleration smoke was first introduced in Maharashtra in

1984.The exhaust mass emission norms for gasoline vehicle below3.5t were then introduced

in 1991.The exhaust mass emission norms for diesel vehicle above 3.5t were then introduced

in 1992. Honourable Supreme Court mandated fitment of catalytic converter for gasoline

passenger cars in metropolitan cities from 1stApril 1995.India 2000 (implemented from 1st

April 2000) emission norms (Equivalent to Euro-I) norms for passenger cars in National

Capital Region (NCR-Delhi) were pre pounded for implementation from 1stJune 1999.The

Euro II equivalent emission norms for passenger cars were introduced in National Capital

Region from 1stApril 2000. In case of Mumbai they came in force from 1st January 2001 and

in case of Kolkata and Chennai from 1st July 2001.Bharat Stage II norms (equivalent to Euro

II) was applicable in entire country for all 4 wheeler vehicles from 1stApril 2005.Bharat

Stage III norms for all 4 wheeler vehicles (equivalent to Euro III) was applicable from

1stApril 2005 and Bharat Stage IV from 1stApril 2010 in 12 selected cities( Delhi/NCR,

Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Ahmadabad, Pune, Surat, Kanpur Agra,

Solapur & Luck now) ).Bharat Stage III norms for all 4 wheeler vehicles (equivalent to Euro

III) was applicable from 1st April 2010 in entire country. Bharat Stage II Norms for 2 and 3

wheeler vehicles was applicable in the entire country from 1stApril 2005.Bharat Stage III

Norms for 2 and 3 wheeler vehicles for the entire country was applicable from 1stApril 2010

13

Norms CO( g/km) HC+ NOx)(g/km)

1991Norms 14.3-27.1 2.0(Only HC)

1996 Norms 8.68-12.40 3.00-4.36

1998Norms 4.34-6.20 1.50-2.18

India stage

2000 norms

2.72 0.97

Bharat stage-II 2.2 0.5

Bharat Stage-III 2.3 0.35(combined)

Bharat Stage-IV 1.0 0.18(combined)

Table 1 Emission Norms for 4 wheelers [6]

Norms CO (g/

kwhr) HC(g/kwhr)

NOx(g/

kwhr)

PM

(g/kwhr)

1991

Norms 14 3.5 18 -

1996

Norms 11.2 2.4 14.4 -

India stage

2000 norms 4.5 1.1 8.0 0.36

Bharat stage-II 4.0 1.1 7.0 0.15

Bharat Stage-III 2.1 1.6 5.0 0.10

Bharat Stage-IV 1.5 0.96 3.5 0.02

Table 2 Emission norms for Heavy diesel vehicles [6]

14

Norms CO ( g/km) HC+NOx (g/km)

1991 norms

12-30 8-12

(only HC)

1996 norms 4.5 3.6

stage

2000 norms 2.0 2.0

Bharat stage-II 1.6 1.5

Bharat Stage-III 1.0 1.0

Table 3 Emission Norms for 2/3 Wheelers [6]

In order to establish limits beyond Bharat Stage IV, the Indian Planning Commission

established a Committee in 2013 to draft an updated Auto Fuel Policy. The panel

recommended that Bharat Stage IV fuel be required nationwide from April 2017 followed by

a further step up to the Bharat Stage V in April 2020. Draft recommendations discussed prior

to the report‟s release included a national Bharat Phase IV+ stage (40 ppm sulfur) starting in

2017 and a national Bharat Stage V fuel standard staring in 2021.

Attempts to set fuel economy standards started in 2007, but it were delayed due to inter-

ministerial conflicts and pressure from the automobile industry. In January 2014, India

notified minimum fuel efficiency norms for passenger vehicles that are sold in India. Two

sets of standards were announced: one set for fiscal years 2016-17 to 2020-21 and another for

fiscal year 2021-22 onwards

15

CHAPTER 8

CONCLUSION

Technologies exist for control of CO, HC, NOx, PM and PN, for stoichiometric and lean-

burn gasoline engines and diesel engines. They are used and proven in many different

applications. Continuous improvement in substrate and coating technologies, as part of an

integrated system comprising electronic control and fuel quality, allows meeting more and

more stringent combustion engines emissions legislations.

• CO, NOx & HC emission from automobile causes health hazards and air pollution

• A catalytic converter converts these pollutants to CO2, N2 & H2O

• Conversion efficiency of CO & HC increases with A/F ratio and NOx conversion

decreases

16

REFERENCE

[1] T. Shamim, 2003,” Dynamic Response of Automotive Catalytic Converters to Variations

in Air-Fuel Ratio”,ASME

[2] Herz, R. K., 1987, „„Dynamic Behaviour of Automotive Three-Way Emission

Control System,‟‟ Catalysis and Automotive Pollution Control, Elsevier, Amsterdam,

[3] Moore, W. R., and Mondt, J. R., 1993, „„Predicted Cold Start Emission Reductions

Resulting From Exhaust Thermal Energy Conservation to Quicken Catalytic

Converter Lightoff,‟‟ SAE Paper No. 931087.

[4] Koltsakis, G. C., and Stamatelos, A. M., 1997, „„Catalytic Automotive Exhaust

Aftertreatment,‟‟ Energy Combustion.

[5] www.howstuffworks.com

[6] https://www.araiindia.com