iss report gaurav

7/27/2019 Iss Report Gaurav

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VARIABLE COMPRESSION RATIO (VCR)

ENGINES

SUBMITTED BY :

AMULYA SAINI (10-MEU-010)

SUBMITTED TO :

Mr. MANOJ KUMAR GOPALIYA

Mrs. AMRITA JHAWAR

HUDA Sector 23-A Gurgaon - 122017.

Tel : + 91 124 2365811 to 13 Fax : + 91 124 2367488

Email :[email protected]

2013-2014


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ACKNOWLEDGEMENT

Apart from the efforts by me, the success of the report largely depends on the encouragement

and the guidelines by many others. I take this opportunity to express my gratitude to people

who have been instrumental in the success completion of the report. I would like to show my

greatest appreciation to Mr. Manoj kumar gopaliya. I felt motivated and encouraged every

time I met him. Without his encouragement and guideline, this project report would not have

been completed. The guidelines and support received from my friends who contributed to this

report was vital for the success of the report. I am grateful for their constant support and help.

SUPERVISIOR SIGNATURE SUPERVISIOR SIGNATURE


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ABSTRACT

The aim of this report is to discuss about the CATALYTIC CONVERTERS which are

installed in the exhaust pipe of almost all the cars and other automobiles. The main purpose

of their installation is to reduce the emissions of HC, CO, AND NO X . A brief description

including their history, uses , types of catalytic converters, advantages, structure and their

working is discussed in this report. The damage to the catalytic converters, their

environmental effects are also discussed in this report.


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LIST OF ABBREVIATIONS

TEL- Tetraethyl lead

DOC- Diesel Oxidation Catalyst

HC- Hydrocarbon

DEF- Diesel Emission Fluid

DPF- Diesel Particulate Filter

CI- Compression Ignition


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LIST OF GRAPHS PAGE No.

Efficiency vs. temperature ratio plot 12

Efficiency vs. equivalence ratio plot 13

Efficiency vs. lead contamination 13


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Leaded gasoline contains about 0.15gm/litre of lead in the fuel. 10 to 50% of this gets

exhausted out with the other combustion products. The remaining lead gets deposited on the

walls of the engine and the exhaust system. The hardened combustion chamber surfaces

which resulted from the burning of the leaded gasoline were quite impervious to the

absorption of gases such as fuel vapour. HC emissions were also, therefore, slightly reduced

in these engines.

1.2 NEED FOR REDUCING EMMISIONS

Due to increased vehicular emissions, there has been a detrimental effect of these gases and

the pollutants as these emissions pollute our environment. The gases like nitrogen oxides

produce photochemical smog, acid rain, and nitrate particulates. They also result in the

destruction of the stratospheric ozone. The gases like sulphur dioxide results in acid rain and

it has also serious impact on the human health. The gases like carbon monoxide also has

serious impacts on the human health. So, there is a need to reduce these vehicular emissions.

Efforts are being put into this field to reduce the emissions and keep their level to the

minimum extent.

1.3 EMMISION CONTROL TECHNIQUES

There are many techniques of reducing the vehicular emissions such as

1) By the use of thermal converters

2) By the use of catalytic converters

3) By particulate trap methods

4) By exhaust gas recirculation

4) By positive crankcase ventilation techniques

There are also many other techniques which are used to control the vehicular emissions but

here the attention is focussed on the structure, types, working of the CATALYTIC

CONVERTERS which is a very good technique for reducing these emissions and is mainly

used in every automobile.


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catalytic converters are equipped with a computerized closed loop feedback fuel injection

system system using one or more oxygen sensors, though early in the deployment of three-

way converters, carburettors equipped for feedback mixture control were used. Three-way

catalysts are effective when the engine is operated within a narrow band of air-fuel ratios near

stoichiometry, such that the exhaust gas oscillates between rich (excess fuel) and lean (excess

oxygen) conditions. However, conversion efficiency falls very rapidly when the engine is

operated outside of that band of air-fuel ratios. Under lean engine operation, there is excess

oxygen and the reduction of NOx is not favoured. Under rich conditions, the excess fuel

consumes all of the available oxygen prior to the catalyst, thus only stored oxygen is

available for the oxidation function. Closed-loop control systems are necessary because of the

conflicting requirements for effective NOx reduction and HC oxidation. The control system

must prevent the NOx reduction catalyst from becoming fully oxidized, yet replenish the

oxygen storage material to maintain its function as an oxidation catalyst. Three way catalytic

converters can store oxygen from the exhaust gas stream usually when the air fuel ratio goes

lean. When sufficient oxygen is not available from the exhaust stream, the stored oxygen is

released and consumed. A lack of sufficient oxygen occurs either when oxygen derived from

nitrogen oxides reduction is unavailable or when certain maneuvers such as hard acceleration

enrich the mixture beyond the ability of the converter to supply oxygen. Unwanted reactions

can occur in the three-way catalyst, such as the formation of odoriferous hydrogen

sulphide and ammonia. Formation of each can be limited by modifications to the wash coat

and precious metals used. It is difficult to eliminate these by-products entirely. Sulphur-free

or low-sulphur fuels eliminate or reduce hydrogen sulphide. For example, when control of

hydrogen-sulphide emissions is desired, nickel or manganese is added to the wash coat. Both

substances act to block the absorption of sulphur by the wash coat. Hydrogen sulphide is

formed when the wash coat has absorbed sulphur during a low-temperature part of the

operating cycle, which is then released during the high-temperature part of the cycle and the

sulphur combines with HC.

Figure 4: 3-Way catalytic converter [5]


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3) THREE WAY+AIR CATALYTIC CONVERTER-The three-way + air converter

performs the same functions as the three-way converter but has secondary air pumped into

the middle of the converter between two separate catalyst coated ceramic substrates. The

addition of air improves the oxidation capabilities of the converter.

4) DIESEL OXIDATION CATALYST- For compression-ignition (i.e.,diesel engines), the

most commonly used catalytic converter is the Diesel Oxidation Catalyst (DOC). This

catalyst uses O2 (oxygen) in the exhaust gas stream to convert CO (carbon monoxide) to

CO2 (carbon dioxide) and HC (hydrocarbons) to H2O (water) and CO2. These converters

often operate at 90 percent efficiency, virtually eliminating diesel odour and helping to

reduce visible particulates (soots). These catalysts are not active for NOx reduction because

any reductant present would react first with the high concentration of O2 in diesel exhaust

gas. Reduction in NOx emissions from compression-ignition engines has previously been

addressed by the addition of exhaust gas to incoming air charge, known as exhaust gas

recirculation (EGR) . In 2010, most light-duty diesel manufacturers in the U.S. added

catalytic systems to their vehicles to meet new federal emissions requirements. There are two

techniques that have been developed for the catalytic reduction of NOx emissions under lean

exhaust conditions selective catalytic reduction (SCR) and the lean NOx trap or nitrogenoxides absorber. Instead of precious metal-containing NOx adsorbers, most manufacturers

selected base-metal SCR systems that use a reagent such as ammonia to reduce the NOx into

nitrogen. Ammonia is supplied to the catalyst system by the injection of urea into the exhaust,

which then undergoes thermal decomposition and hydrolysis into ammonia. One trademark

product of urea solution, also referred to as Diesel Emission Fluid (DEF), is adblue. Diesel

exhaust contains relatively high levels of particulate matter (soot), consisting in large part of

elemental carbon. Catalytic converters cannot clean up elemental carbon, though they do

remove up to 90 percent of the soluble organic fraction, so particulates are cleaned up by a

soot trap diesel particulate filter (DPF). Historically, a DPF consists of a Cordierite or Silicon

Carbide substrate with a geometry that forces the exhaust flow through the substrate walls,

leaving behind trapped soot particles. Contemporary DPFs can be manufactured from a

variety of rare metals that provide superior performance ( at a greater expense). As the

amount of soot trapped on the DPF increases, so does the back pressure in the exhaust

system. Periodic regenerations (high temperature excursions) are required to initiate

combustion of the trapped soot and thereby reducing the exhaust back pressure. The amount


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CHAPTER-3

WORKING OF CATALYTIC CONVERTER

3.1 WORKING OF CATALYTIC CONVERTER

There are millions of cars on the road in the United States, and each one is a source of air

pollution. Especially in large cities, the amount of pollution that all the cars produce together

can create big problems. To solve those problems, cities, states and the federal government

create clean-air laws that restrict the amount of pollution that cars can produce. Over the

years, automakers have made many refinements to car engines and fuel systems to keep up

with these laws. One of these changes came about in 1975 with an interesting device calleda CATALYTIC CONVERTER. The job of the catalytic converter is to convert harmful

pollutants into less harmful emissions before they ever leave the car's exhaust system. In

order to reduce emissions, modern car engines carefully control the amount of fuel they burn.

They try to keep the air-to-fuel ratio very close to the stoitiometric point, which is the ideal

ratio of air to fuel. Theoretically, at this ratio, all of the fuel will be burned using all of the

oxygen in the air. For gasoline, the stoichiometric ratio is about 14.7:1, meaning that for each

pound of gasoline, 14.7 pounds of air will be burned. The fuel mixture actually varies from

the ideal ratio quite a bit during driving. Sometimes the mixture can be lean (an air-to-fuel

ratio higher than 14.7), and other times the mixture can be rich (an air-to-fuel ratio lower

than 14.7). The main emissions of a car engine are nitrogen, carbon-dioxide and water

vapour. These emissions are mostly begin, although carbon dioxide emissions are believed to

contribute to global warming. Because of the combustion process is never perfect, some

smaller amounts of more harmful emissions are also produced in car engines. Catalytic

converters are designed to reduce carbon monoxide, hydrocarbons or volatile organic

compounds and nitrogen oxides. In chemistry, a catalyst is a substance that causes or

accelerates a chemical reaction without itself being affected. Catalysts participate in the

reactions, but are neither reactants nor products of the reaction they catalyze. In the human

body, enzymes are naturally occurring catalysts responsible for many essential biochemical

reactions. In the catalytic converter, there are two different types of catalyst at work,

a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure

coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to

create a structure that exposes the maximum surface area of catalyst to the exhaust stream,


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while also minimizing the amount of catalyst required, as the materials are extremely

expensive. Some of the newest converters have even started to use gold mixed with the more

traditional catalysts. Gold is cheaper than the other materials and could increase oxidation,

the chemical reaction that reduces pollutants, by up to 40 percent. Most modern cars are

equipped with three way catalytic converter. This refers to the three regulated emissions it

helps to reduce.

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

rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts 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 or 2NO2 => N2 + 2O2

2NO => N2 + O2 or 2NO2 => N2 + 2O2

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. For example:

2CO + O2 => 2CO2

There are two main types of structures used in catalytic converters --

honeycomb and ceramic beads. Most cars today use a honeycomb structure.

Figure 6: Ceramic honeycomb catalyst structure [7]


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CHAPTER-4

PROBLEMS FACED BY CATALYTIC CONVERTERS

4.1 COLD START UPS

As seen from Fig-7 that catalytic converters are not very efficient when they are cold. When

the engine is started after not being operated for several hours, actually it takes a several

minutes for the converter to reach an efficient temperature and the temperature at which the

catalytic converter becomes 50% efficient is known as light off temperature, which is in the

range of 250-300C and the large amount of the car travel is for shorter distances where the

catalytic converter never reaches the efficient operating temperature and which results in

higher emissions. A major reduction in these emissions is possible if the catalytic converters

could be preheated, at least to the light off temperature, before engine start up. Methods of

catalytic converter preheating include the following-

1) By locating the converter close to the engine.

2) By providing super insulation.

3) By employing electric preheating.4) By using flame heating.

5) Incorporating thermal batteries.

4.2 PROBLEMS FACED WITH CI ENGINES

Catalytic converters are being tried with CI engines but are not efficient in reducing NOX due

to their overall lean operation. HC and CO can be adequately reduced, although there is

greater difficulty because of the cooler exhaust gases of a CI engine because of the larger

expansion ratio. This is counterbalanced by the fact that less HC and CO are generated in the

lean burn of the CI engine. NOX is reduced in the CI engine by the use of EGR, which keeps

the maximum temperature down. The EGR technology is becoming really common in case of

CI engines as it plays a significant role in reducing the nitrogen oxides emissions. This EGR

also keeps the maximum temperature down. However, it has been found out that the increase

in the use of EGR and thereby lower combustion temperatures contribute toward the increase

in the solid soot. Also, diesel fuel contains sulphur impurities which leads to the poisoning of


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the catalytic material. This problem is getting minimized to a great extent as the legal levels

of the sulphur in diesel fuels continue to be lowered.


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Figure 11: Catalytic converter installed in car [15]

5.3 DAMAGE TO CATALYTIC CONVERTERS

Catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing

substances that coat the working surfaces, encapsulating the catalyst so that it cannot contact

and treat the exhaust. The most notable contaminant is lead. Any condition that causes

abnormally high levels of unburnt hydrocarbons whether it is raw or partially burnt fuel to

reach the converter will tend to significantly elevate its temperature, bringing the risk of a

meltdown of the substrate and resultant catalytic deactivation and severe exhaust restriction.

5.4 NEGATIVE ASPECTS OF CATALYTIC CONVERTERS

Some early converter designs created a great deal of restriction to the flow of exhaust which

negatively affected vehicle performance, drivability and fuel economy. It has been stated that

catalytic converters are known in a lot of cases to have an excessively long warm up time

period, in a great deal of cases ranging upto 30 minutes. [16]

5.5 ENVIRONMENTAL IMPACT OF CATALYTIC CONVERTERS

It Reduces fuel economy of cars resulting in greater use of the fossil fuels. Although

catalytic converters are effective at removing hydrocarbons and other harmful emissions,

most of the exhaust gas leaving the engine through the catalytic converter is mainly carbon

dioxide which is responsible for the greenhouse effect.


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REFERENCES

[1]- catalytic converters used in automobiles (westerman.com)

[2]- history of catalytic converters (wikipedia.com)

[3]- honeycomb structure inside the catalytic converter (bikechatforums.com)

[4]- James D Halderman. (2010); automotive engine performance; 2-way catalytic

converter

[5]- 3-way catalytic converter (performanceexhaustplus.com)

[6]- diesel oxidation catalyst (catalystproducts.com)

[7]- ceramic honeycomb catalyst structure (howstuffworks.com)

[8]- K Nice, C. W. Bryant. how catalytic converters work (howstuffworks.com)

[9]- V. Ganesan; catalytic converters; engine emissions and their control.

[10]- V. Ganesan; conversion efficiency of catalytic converters as a function of

converter temperature; engine emissions and their control.

[11]- V. Ganesan; conversion efficiency of catalytic converters as a function of fuel

equivalence ratio; engine emissions and their control

[12]- V. Ganesan; catalytic converters; engine emissions and their control.

[13]- V. Ganesan; reduction of catalytic converter efficiency due to contamination

by lead; engine emissions and their control.

[14]- location of catalytic convertor (davisconverters.com)

[15]- catalytic converter installed in car (autorepairschaumburgil.com)

[16]- Donga Ravi. negative aspects of catalytic converters; presentation on

catalytic converters.

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