UNIT-3 EMISSION FORMATION AND CONTROL.pptx

Emission formation and control Techniques

1. UNIT-III EMISSION FORMATION AND CONTROL

2. FORMATION OF NO X MECHANISM Oxygen and nitrogen molecules are formed due to the peak combustion temperature and persists during expansion and exhaust in non-equilibrium amounts within the combustion chamber. The concentration of NOx will fall with pressure and temperature during expansion stroke to negligible level at equilibrium condition during the exhaust valve opening. Concentration of NOx in exhaust gases is well above equilibrium values.

3. Nitric oxide is the major source of pollutants in industries. Here, NOx , is produced in various ways like: (a) Thermal NOx (b) Fuel NOx (c) Prompt Nox Thermal NOx Due to heat generation, large amount of thermal NOx is produced, when natural gas undergoes combustion process. But in coal fuel it contains nitrogen.

4. When the combustion takes place in coal, minimum amount of NOx is produced. Thermal NOx occurs when the temperature is in the process of more than 1600°C. This is due to the disassociation of nitrogen and oxygen molecules. Fuel NOx Fuel NOx is produced when the fuel which contains nitrogen undergoes high combustion temperature. For example, coal fuel and oil fuels undergo this type of NOx formation. During combustion, the nitrogen bound in the fuel is released as a free radical and forms free nitrogen and nitrogen oxides

5. In the combustion stage, the volatile nitrogen is first oxidized, then it reacts with the inter mediants and nitric oxide is formed. (c) Prompt Nox Reaction of nitrogen with the atmosphere gives out prompt NOx . This is then reacts with C, CH and CH which is delivered from fuel. This type of NOx occurs in the earlier stage of the combustion processes. This type of NOx formed when the oxygenated fuels such as biodiesel is combusted under low temperature

6. The formation of NOx concentration in the exhaust gas from S.I engine is reduced by Decreasing the oxygen available by decreasing the air fuel ratio and homogeneity of the mixture. (b) Decreasing the combustion temperature. ( i ) Increasing valve overlap (ii) By adding exhaust gas to the fresh charges (iii) Avoiding knocking combustion (iv) Reducing the spark timing (v) Decreasing the compression ratio, charge temperature, speed and mixture pressure.

7. Carbon monoxide is emitted with the exhaust gas due to the incomplete combustion of carbon. This incomplete combustion occurs due to the dissociation process. The measured concentration of CO is greater than the equilibrium concentrations. CO concentration does not drop to zero when the mixture is chemically correct and leaner. FORMATION OF CARBON MONOXIDE MECHANISM

8. FORMATION OF HYDROCARBON MECHANISM Hydrocarbon level in the exhaust gas is in the range of 1000-3000 ppm . HC emission rises rapidly as the mixture becomes substantially richer than the stoichiometric . In lean mixture, HC emission can rise rapidly due incomplete combustion of misfire in a fraction of the engine’s operating cycle. HC emission formation mechanisms are dealt as follows; Leaving a layer of unburned air fuel mixture to adjacent wall is known as flame quenching. Crevice volume plays a vital role in HC emission.

9. Carbon particles suspended in the exhaust gas is known as smoke. It is generated when the engine is accelerated (or) decelerated. The smoke colour determines the problem of the engine. Different colours of smoke are produced while using a diesel engine. White smoke will arise when the fuel is not fully burnt (or) due to the cold engine (or) leakage in the coolant. Black smoke is caused due to extremely rich air fuel mixture White smoke is caused due to cool engine and cool leakage. SMOKE EMISSION

10. . SMOKE FORMATION MECHANISM Fuel droplet is made up of several layers. After ignition, the process first starts at the outer layer of the fuel droplet. As soon as the outer droplet of the ignition heat is generated t it passes to core of the fuel droplet. At the core, the oxygen content is little (or) no oxygen. The hydrocarbons get cracked into hydrogens and carbons. Hydrogen has more affinity towards oxygen when compared with carbon.

11. . FACTORS INFLUENCING SMOKE PRODUCTION Engine details Fuel Factors Engine Maintenance Engine details Engine design Quantity of fuel introduced Mixing ratio of the fuel Heat due to uncontrollable combustion process Inlet port design Movement of air Time intensity for premixing, and burning soot. Heat loss on the walls

12. Fuel Factors Ignition delay and fuel mixing completely depends on the cetane number. Ignition of fuel depends on the fuel injection quality Fuel should be ignited slowly. Viscosity of fuel affects the penetration of the heat to its core. Engine Maintenance Injection System Blocks at the nozzle holes should be reduced. Checking the piston rings, cylinder chambers, pump plungers, fuel injector needle, fuel filters, etc. Loss of compression due to worn out piston rings, seating valves, fuel intake system, etc.

13. Small, solid particles and liquid droplets are collectively termed as particulates. These are present in the atmospheric fairly large numbers and sometimes pose a serious air pollution. The size of the particulate is the major factor Particulate range in diameter of 0.0002 mm with life time varies for a few seconds to several months. Its life time depends on the settling rate, size, density and turbulence of air. Sources of Particulates Natural sources Man-made factors PARTICULATE EMISSION

14. GREEN HOUSE EFFECT Carbon dioxide, although a relatively insignificant non- pollutant species in the atmosphere, is of serious environmental concern. Among the constituents of the atmosphere, only carbon dioxide and water vapour strongly absorb infrared radiation and effectively block a large fraction of the earth's emitted radiation. The radiation thus absorbed by CO2 and H₂O vapour is partly re-emitted to the earth's surface. The net result is that the earth's surface gets heated up by a phenomenon called Green house effect.

15. An overview of the global warming problem

16. EMISSION CONTROL SYSTEMS Fuel system optimization. Control of ignition timing. Exhaust gas recirculation. Engine design modification. Exhaust gas after treatment using catalysts. Fuel modification.

17. Fuel system optimization Fuel system may be optimized by using electronic fuel injection. Equal distribution of mixture to all the cylinders. Atomization of fuel for better mixing. Avoiding variance in the idling speed. Exhaust gas recirculation system (EGR) System In this method, a little amount of exhaust gas is sent into the engine cylinder. This reduces the combustion temperature and thereby prevents NOx pollution.

18. Evaporative emission control system Evaporative emission control system is achieved by adsorption. Positive Crankcase Ventilation (PCV) system keeps the engine crankcase fumes out of atmosphere. Catalytic converter Thermal reactor for burning and chemically changing the harmful exhaust by products into harmless substances. These harmful toxic substances in the S.I engine exhaust gases are mostly made harmless by means of catalytic converters. The catalytic converter is installed between the exhaust manifold and muffler in the exhaust system.

19. THREE WAY CATALYTIC CONVERTER The catalytic converter consists of a catalytic unit contained in a metal canister which surrounds the ceramic catalyst unit with a steel sheet. To avoid corrosion, the converter shell is made up of a special stainless steel. In between the steel shell and the exterior of the catalytic unit, there is a compliant layer which exerts sufficient force to prevent movement within the canister and it compensates for the differences in thermal expansion between the catalyst and the metal shell.

20. Three way catalytic converter

21. PARTICULATE TRAPS An exhaust treatment technology that substantially reduces diesel engine particulate emissions is the trap oxidiser . A temperature-tolerant filter or trap removes the particulate material from the exhaust gas, the filter is then "cleaned off" by oxidizing the accumulated particulates. This has great disadvantage for practical use because The filter, even when clean, increases the pressure in the exhaust system

22. An exhaust treatment technology that substantially reduces diesel engine particulate emissions is the trap oxidiser . A temperature-tolerant filter or trap removes the particulate material from the exhaust gas, the filter is then "cleaned off" by oxidizing the accumulated particulates. This has great disadvantage for practical use because The filter, even when clean, increases the pressure in the exhaust system. Types of particulate filters include the following: Ceramic monolith Alumine - coated wire mesh Ceramic foam Ceramic fiber mat Woven silica-fiber rope wound on a porous tube

23. EXHAUST GAS RECIRCULATION (EGR) NO x emission can be easily reduced by keeping the combustion chamber temperature down. This reduces the engine's thermal efficiency. The simplest practical method of reducing maximum flame temperature is to dilute the air-fuel mixture with a non- reacting parasite gas. This gas absorbs energy during combustion without contributing any energy input. This leads to the lower flame temperature.

24. EXhaust gas recirculation EGR

25. INDIAN DRIVING CYCLE The driving cycle of any country is the probable plot of the vehicle speed right from the start of the engine through its journey over a prescribed time

26. EMISSIONS From the point of view of pollution control, measurement of emissions from engines is very important Emissions may be divided into two groups, viz., invisible and visible emissions. The exhaust of an engine may contain more of the following carbon dioxide water vapour oxides of nitrogen unburnt hydrocarbons

27. NOX Detector

28. The chemiluminescence method offers the best results whenever the difficult analysis of the tiny molecule NO in gases is required. Chemiluminescence method allows to detect extremely low concentrations of NO, being not only fast but also very sensitive and not specified. mech cabin 2 23-05-30 10:42:38 -------------------------------------------- NO2 * The reaction scheme of NO and O3 by chemiluminescence is as follows: NO +O3 → NO₂+O2 (1) NO + O3 → NO2* +O2 (2) NO2* →NO2 + hv (3) NO 2 +M→NO 2 + M (4)

29. Components of a nitrogen oxide analyser

30. The radiation emission is in the wavelength 600nm and 3000nm with an intensity maximum at approximately 1200nm. This chemiluminescence signals is detected photoelectrically . When O3 is present in excess; the signal is proportional to the NO concentration of the sample gas. The length portion of the NO2 * returns to ground state without radiation emission, due to collisions with other molecules (M) i.e., in order to enhance the light yield, the pressure in the reaction chamber is reduced.

31. Quenching is an unwanted phenomenon, the extent to which it occurs depends on the character of the colloiding molecule M. For instance with (H2O) and carbon dioxide (CO2) quench NO chemiluminescence more effectively than nitrogen (N2) and oxygen (O2). In order to measure NO₂ in the sample gas, it has to be converted into NO. To accomplish this chemical reduction, the sample gas is passed through a converter which is heated to more than 300°C.

32. EXHAUST GAS ANALYSERS For measuring the gaseous pollutants two analysers are used. They are: Non-Dispersive Infrared Gas Analyser (NDIR) (to measure CO) Flame Ionization Detector (FID) (to measure HC)

33. Non-Dispersive Inafrared Gas Analyser (NDIR)

34. Non-Dispersive Inafrared Gas Analyser (NDIR)

35. Flame Ionization Detector (FID)

36. Flame Ionization Detector (FID)

37. SMOKE MEASUREMENT Exhaust gas, i.e. smoke, is measured by two methods. Light extinction. Continuous and spot filtering

38. Light Extinction Smoke Meter Here photoelectric cell is used to measure the smoke. An extinction of light is passed through the sample stream of exhaust gas. Here the photoelectric cell is lightened by a tungsten filament bulb after traversing a 45 cm column of exhaust gas. Zero reading on the scale of the output meter occurs with clean air tube and a reading of 100 on the scale corresponding to complete observation of the light. 1% of light absorbed is represented as an hartidge smoke unit.

39. Measuring of BOSC smoke meter

40. Continuous & Spot Filtering Smoke Meter In continuous filtering smoke meter, the smoke is continuously passed through a moving strip of filter paper and collecting particles. Calibration is facilitated by adjusting the sample rate, tape speed, and working, etc. In spot filtering smoke meter, photoelectric device is used to measure the smoke rate. Smoke is continuously passed through a fixed filter paper

41. PARTICULATE MEASUREMENTS

42. The exhaust of CI engines contains solid carbon soot particles that are generated in the fuel-rich zones within the cylinder during combustion. These are seen as exhaust smoke and cause an undesirable odorous pollution. Maxi- mum density of particulate emissions occurs when the engine is under load at WOT. At this condition maximum fuel is injected to supply maximum power, resulting in a rich mixture and poor fuel economy. This can be seen in the heavy exhaust smoke emitted when a truck or railroad locomotive accelerates up a hill or from a stop.

43. Emission norms for automobiles are the standards set by the authority of differes countries focusing on controlling the amount of pollutants released into the environment from automobiles. Each stage of emission standards specifically describes the amount of pollutants from vehicles such as carbon monoxide (CO), nitrogen oxides (NO), sulphur dioxide, con dioxide (CO), hydrocarbons (HC) and particulates which can be emitted from an automobile into the environment. These regulatory standards differ from nation to nation. But the aim is common to control the environmental pollution. EMISSION NORMS (EURO AND BS)

44. Parameters determining emission from vehicles While each one of the following four factors have direct environmental implications, the vehicle and fuel systems have to be addressed as a whole and jointly optimized in order to achieve significant reduction in emission. • Vehicular technology • Fuel quality • Inspection& maintenance of in-use vehicles • Road and traffic management.

45. Setting Emission Norms The focus here is on simulation of actual driving versus assumed driving pattern in a cycle based on long observation and trials on road. In simulation, the vehicle is "exercised" on "tread mill" called chassis dynamometer replicating the assumed driving- pattern of the country. This is called the driving cycle of the country. The emissions are measured over the cycle and the results computed to give mass emissions .

46. Euro Norms Euro norms refer to the permissible emission levels for both petrol and diesel vehicles, which have been implemented in Europe. In European Union member countries , some automobile manufacturing countries in Asia and Africa and several non- manufacturing countries imports vehicles which have adopted European emission standard as their standards. European standards are set on the classification of vehicles based on their weight and engine capacity

47. BS Norms Bharat Stage (BS) 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 set by the Central Pollution Control Board under the Ministry of Environment & Forests India is using European emission norms with a time lag of five years with BS-IV norm currently applicable in 50 cities where the required grade of fuel is available while the rest of the country follows BS-III standards. But many vehicles are BS-1 and BS-11 compliant and more polluting.

48. Overview of the Emission Norms in India: 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 1) 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:

49. 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. 2017 – Bharat Stage IV norms for all vehicles. 2018 - Bharat Stage VI fuel norms from 1 April 2018 in Delhi instead of 2020. 2020 – Bharat Stage VI fuel norms from 1 April 2020 nationwide switching India to world's cleanest diesel and petrol. 2023 - Bharat Stage VI Second Phase Fuel norms from 1 April 2023 have only Petrol also called RDE norms with e20 fuels.

50. NATIONAL AND INTERNATIONAL EMISSION STANDARDS Euro emission limits for gasoline cars (values in g/Km)

51. Euro emission limits for diesel cars (values in g/Km)

52. BS emission standards for gasoline vehicles (values in g/km)

53. BS emission standards for diesel vehicles (values in g/km)

54. Thank you