The pollutants present in auto exhaust gas are

Sulphur dioxide, SO2 (primary pollutant) Nitrogen oxides NOx (primary or secondary

pollutants) Particulate matter PM (primary and secondary

pollutants) Carbon monoxide, CO, (primary pollutant) (volatile) organic compounds, HC (or VOCs)

(primary and secondary pollutants), and photochemical oxidants,

PAN -peroxyacetyl nitrate(secondary pollutants).

DE is a complex mixture of hundreds of constituents in either a gas or particle form.

Gaseous components of DE include carbon dioxide, oxygen, nitrogen, water vapor, carbon monoxide, nitrogen compounds, sulfur compounds, and numerous low-molecular-weight hydrocarbons.

Among the gaseous hydrocarbon components of DE that are individually known to be of toxicological relevance are the aldehydes (e.g., formaldehyde, acetaldehyde, acrolein), benzene, 1, 3-butadiene, and polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs.

DPM consists of fine particles (fine particles have a diameter

<2.5µm), including a subgroup with a large number of

ultrafine particles (ultrafine particles have a diameter

<0.1µm). Collectively, these particles have a large surface

area which makes them an excellent medium for adsorbing

organics. Their small size makes them highly respirable and able to

reach the deep lung. A number of potentially 1-1

toxicologically relevant organic compounds are on the

particles.The particles present in DE (i.e., diesel particulate matter

[DPM]) are composed of a center core of elemental carbon

and adsorbed organic compounds, as well as small amounts

of sulfate, nitrate, metals, and other trace elements.

The hazards include acute exposure-related symptoms, chronic exposure related non-cancer respiratory effects, and lung cancer.

The health hazard conclusions are based on exhaust emissions from diesel engines built prior to the mid-1990s. With current engine use including some new and many older engines (engines typically stay in service for a long time)

The health hazard conclusions, in general, are applicable to engines currently in use. As new and cleaner diesel engines, together with different diesel fuels, replace a substantial number of existing engines, the general applicability of the health hazard conclusions will need to be reevaluated.

According to the pollutants exposure the effects are classified as

Acute (Short-Term Exposure) Effects Chronic (Long-Term Exposure) Non-

cancer Respiratory EffectsAnd Chronic (Long-Term Exposure)

Carcinogenic Effects.

Standard Reference Date Region

India 2000 Euro 1 2000 Nationwide

Bharat Stage II Euro 2 2001 NCR*,Mumbai, Kolkata, Chennai

2003.04 NCR*,10 Cities

2005.04 Nationwide

Bharat Stage III Euro 3 2005.04 NCR*,10 Cities

2010.04 Nationwide

Bharat Stage IV Euro 4 2010.04 NCR*,10 Cities

*National capital Region()10 cities- Mumbai, Kolkata, Chennai, Bengaluru, , Ahmedabad, Pune, , and Agra.(Ref: wiki)

The Globally automotive pollution is controlled by various emission performance standards set by countries according to their population and economic considerations.

The Emission Performance standard is the requirements that set specific limits to the amount of pollutants that can be released into the environment.

Many emissions standards focus on regulating pollutants released by automobiles (motor cars) and other powered vehicles but they can also regulate emissions from industry, power plants, small equipment such as lawn mowers and diesel generators.

*Did you notice the Tamil nadu pollution control notice board in velachery gate-IITM*

1991 - Idle CO Limits for Gasoline Vehicles and Free Acceleration Smoke for Diesel Vehicles, Mass Emission Norms for Gasoline Vehicles.

1992 - Mass Emission Norms for Diesel Vehicles. 1996 - Revision of Mass Emission Norms for Gasoline and Diesel

Vehicles, mandatory fitment of Catalytic Converter for Cars in Metros on Unleaded Gasoline.

1998 - Cold Start Norms Introduced. 2000 - India 2000 (Eq. to Euro I) Norms, Modified IDC (Indian

Driving Cycle), Bharat Stage II Norms for Delhi. 2001 - Bharat Stage II (Eq. to Euro II) Norms for All Metros,

Emission Norms for CNG & LPG Vehicles. 2003 - Bharat Stage II (Eq. to Euro II) Norms for 11 major cities. 2005 - From 1 April Bharat Stage III (Eq. to Euro III) Norms for

11 major cities. 2010 - Bharat Stage III Emission Norms for 4-wheelers for entire

country whereas Bharat Stage - IV (Eq. to Euro IV) for 11 major cities. Bharat Stage IV also has norms on OBD (similar to Euro III but diluted)

The European Union standards for emission limits of automotive exhaust gases (values in g km-1) are given in the Table previous slide.

The typical concentration of the various pollutants are listed out and when our (Bharat stage –IV) compared to the European standards we lag behind nearly 5 years.

Modification of engine design (e.g., the fuel management system) and the engine calibration (e.g., the ignition timing) to decrease the engine output (also called raw emission)

Aftertreatment of the engine exhaust by solid catalysts, to convert the engine raw emission

A combination of engine exhaust after treatment by solid catalysts with engine design modification and/or controlled engine operation, to allow optimal functioning of the aftertreatment device.

Retrofit: Diesel retrofit involves the addition of an emission

control device to remove emissions from the engine exhaust.

Retrofits can be very effective at reducing emissions, eliminating up to 90 percent of pollutants in some cases.

Some examples - Diesel oxidation catalysts, diesel particulate filters, NOx catalysts, selective catalytic reduction, and exhaust gas recirculation. Devices to control crankcase emissions also exist.

Repower: Repowering involves replacing an existing engine with a

new engine. This strategy is most effective for use in diesel-powered equipment with a useful life longer than that of the engine.

Rebuild: All diesel equipment requires periodic maintenance.

Routine maintenance and repairs help to ensure that engines operate at maximum performance and emission rates do not exceed the designed standard.

Refuel: A variety of alternative fuels can be used in diesel engines.

Some require little or no modification to the engine while others require engine conversion or replacement.

Some of the alternative fuels include emulsified diesel, biodiesel, natural gas, propane and ethanol. In addition to these fuels, use of diesel fuel with lower sulfur content can help to reduce emissions.

Replace: Replacement involves retiring higher polluting equipment

from service before it would otherwise be retired. Newer equipment that meets more stringent emission standards is purchased to replace the retire equipment.

Reducing the base emissions from the engine by improvements to the combustion process and fuel management, addition of air injection or exhaust gas recycle or by changes to the type of fuel or its composition.

Decreasing the time taken for the catalytic converter to reach its full operating efficiency.

Increasing the conversion efficiency of catalysts at their working temperature.

Store pollutants during the cold start for the release when the catalyst is working.

Device catalysts or strategies to destroy nitrogen oxides under lean (oxygen rich) operation.

Devise reliable ways to regenerate particulate filters.

Increase the operating lifetime during which autocatalysts and their supporting systems efficiently convert pollution.

Typical automotive exhaust converters. The one on the left has been cut open to reveal the monolith. The insert shows a blow up of the upper part of the monolith where a part has been chipped off

Five basic catalytic concepts have been used in the development of catalytic emission control they are

Closed loop control catalystOpen loop catalystDual bed catalystOxidation catalystLean oxidation catalyst

In the closed-loop-controlled three-way catalyst, one type of catalyst, which is placed in the exhaust gas stream, is able to promote all the main reactions that lead to the simultaneous removal of CO, HCs and NOx.

To balance the extent of the oxidation and the reduction reactions, the composition of the engine-out exhaust gas is maintained at or around stoichiometry.

This is achieved by a closed-loop engine operation control, in which the oxygen content of the engine-out exhaust gas is measured upstream of the catalyst with an electrochemical oxygen sensor, also called the lambda sensor.

This component is used by the engine management system to regulate the amount of fuel fed into the engine, and so to regulate the engine operation around the stoichiometric A/F ratio.

The extent of the secondary reactions is minimal under these conditions. The feedback control of the engine causes a small cyclic variation of the engine exhaust gas composition.

This variation occurs in a second, which means a frequency of 1 Hz, and with amplitude of 5–10% of the A/F set point. This transient operation of the catalyst, however, has a significant effect upon its performance, as will be described below.

There exists a multitude of engine management systems with various degrees of complexity and refinement, affecting the speed and the amplitude range of control of the engine A/F ratio at each of the engine load and speed operation conditions.

The refinement of the engine management system affects both the performance and the durability of the emission control catalyst.

This concept is a simplification of the first, as again a multifunctional catalyst is used, that is able to promote all of the reactions that lead to the removal of CO, HCs and NOx.

The composition of the exhaust gas is not controlled and therefore varies over a wide range. This wider operation range results in an overall lower simultaneous conversion of the three exhaust gas constituents

This concept is used if the legislative limits can be reached with a conversion of about 50%, or for the retrofitting of engines that were not designed to be equipped with catalytic emission control devices.

Two different types of catalyst are used. The first catalyst is either multifunctional, or is at least of capable of promoting NOx reduction reactions.

The engine is calibrated so as to guarantee a net reducing exhaust gas composition. Under these conditions, the first catalyst will lead to an elimination of the nitrogen oxides. The second catalyst is an oxidation catalyst.

Extra air is injected in front of the second catalyst to assist the removal of CO and HCs. The secondary air can be added either by mechanically or by electrically driven air pumps.

The dual-bed concept allows for a wider engine A/F range and also maintains high conversion efficiency for the three exhaust gas constituents under these conditions. Therefore, a less-sophisticated engine management system can be used.

In this emission control concept, secondary air is added to the exhaust gas to ensure a lean composition, independent of the engine operation condition. The catalyst is designed to promote reactions between oxygen and both CO and HCs, which can be removed to a great extent, but NOx cannot be removed in this manner.

The fifth concept is also an oxidation catalyst, but it is applied to engines that operate under lean conditions, the so-called lean-burn engines. The A/F ratio of these engines reaches values up to 26, corresponding to a lambda value of about 1.8.

The function of the catalyst could be limited to converting CO and HCs. Because of the dilution effect in lean combustion, the exhaust gas is colder than for closed-loop controlled engines, and therefore special catalysts with good low-temperature activity for the oxidation reactions are needed.To date, however, this concept has not achieved widespread application.

The latest generation of lean-burn gasoline engines applies the direct fuel injection principle, which enables different catalytic exhaust gas after treatment concepts to be used, such as the NOx-adsorber systems

The three-way catalyst, consisting of Pt and Rh particles supported on a ceramic monolith, represents a remarkably successful piece of catalytic technology. It enables the removal of the three pollutants CO, NO and hydrocarbons

Additionally, NO is reduced by H2 and by hydrocarbons. To enable the three reactions to proceed simultaneously – notice that the two first are oxidation reactions while the last is a reduction – the composition of the exhaust gas needs to be properly adjusted to an air-to-fuel ratio of 14.7

At higher oxygen content, the CO oxidation reaction consumes too much CO and hence NO conversion fails.

If, however, the oxygen content is too low, the entire NO is converted, but hydrocarbons and CO are not completely oxidized.

An oxygen sensor (λ-probe) is mounted in front of the catalyst to ensure the proper balance of fuel and air via a microprocessor-controlled injection system.

It is a simple oxygen sensor made in a similar manner to the solid oxide fuel cell. An oxide that allows oxygen ions to be transported is resistively heated to ensure sufficiently high mobility and a short response time (~1 s.).

The oxygen content in the exhaust is measured against a suitable reference, in this case atmospheric air.

The response is given by the Nernst equation:

The λ-probe relies on the diffusion of atomic oxygen through a solid electrolyte and, therefore, it will have a certain response time.

Reducing the thickness of the oxide membrane and increasing the temperature both shorten the response time, but a certain delay cannot be avoided.

For example, if the driver suddenly steps on the gas pedal the exhaust becomes reducing. Consequently, sulfur deposited in the catalyst becomes hydrogenated to H2S, causing the characteristic “rotten eggs” smell (this smell sometimes arises during the startup of a cold engine).

New types of sensors with faster response are therefore being explored to avoid these effects. Ideally these should be placed immediately after each cylinder and therefore they should be capable of withstanding high temperatures.

The Performance of the catalyst depends upon the various factors such as

the chemistry of the catalyst (e.g., the wash coat, precious metals, age and preparation),

the physics of the catalyst (e.g., support and converter design) and

the chemical engineering aspects of the catalyst (e.g., reaction temperature, residence time, gas composition and dynamic conditions)

The catalytic converters have three important layers. First is a wash coat, which increases the surface area that the catalysts are on: a large surface area is essential for high-efficiency exhaust emission reductions.

Next, a layer of noble metals like platinum and palladium are vaporized on to the wash coat; these encourage carbon monoxide and hydrocarbons to react into water vapor and carbon dioxide.

Then there is a third layer of platinum and rhodium that reduces nitrogen oxides (the third layer is what makes the converter 'three-way').

These reactions seem contradictory: the oxidation process is more efficient when large amounts of oxygen are present, but reduction happens more efficiently in a low oxygen environment. But there is a small window of exhaust stoichiometry, called the lambda window, which creates favorable conditions for both reactions to take place. Maintaining the air/fuel ratio to keep exhaust gasses in this window is extremely important, hence the requirement of oxygen sensor monitoring.

Ceria is well known for his Oxygen storage capacity and redox properties and these properties are the key for the three-way catalyst development.

The major problem for the catalyst to stay active is that to have adequate contact points between the pollutant soot and the catalyst.

When these catalysts are used through fuel borne then this increases the contact points between the soot and the catalyst and in turn decreases the temperature of oxidation from 600 C to 400 C.

CeO2 is one of the extensively used catalytic components in many of the above described after-treatment technologies due to its high activity in the redox reactions

. CeO2 is used in a well- known three-way catalyst for CO, HC, and NOx abatement, as a fuel-borne catalyst, and in the catalysed soot filters in elimination of the soot particulates.

The fuel-borne ceria catalyst leads to the formation of the CeO2 nano-particles trapped within the soot particle.

Improving the cold-start performance HC adsorbers into the aftertreatment system-like

activated carbon, zeolites etc., usage of precious metals should be limited to

achieve cost reduction future development will be the exchange of a

substantial portion of the platinum by palladium in high performance oxidation catalyst

In order to cope with the changing boundary conditions, and especially the further reduction in exhaust gas temperature, it is highly probable that at least a portion of the catalyst volume will be moved closer to the engine outlet.

Thanks