Emission Control Methods

Nitin Joshi B Tech Mechanical

VARIOUS METHODS USED TO CONTROL ENGINE EMISSION

SUBMITTED BY:NITIN JOSHI

CONTENTS [email protected]


1. Abstract………………………………………………………………………1 2. Introduction…………………………………………………………………..1 3. Thermal Converters…………………………………………………………..2 4. Catalytic Converters………………………………………………………….2-3 5. CI Engine……………………………………………………………………..3 6. Particulate Traps……………………………………………………………....4-5 7. Reducing emissions by chemical methods…………………………………...5 8. Exhaust Gas Recirculation (EGR)……………………………………….......5-6 9. Air Injection………………………………………………………………..…6 10. Evaporative Emissions Control……………………………………………….6 11. Ceramic Engine Coatings……………………………………………………..6 12. Evaporation Loss Control Device…………………………………………….6-7 13. Other Methods………………………………………………………………...7 14. List of tables ……………………………………………………………….…8 14.1 Table 1: IC Engine Typical Emission Level 14.2 Table 2: Cost of Catalytic Control Technologies 15. Conclusion…………………………………………………………………….9 16. References…………………………………………………………………….9

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Abstract:The topic of term paper is methods used to control the engine emissions. In this we will discuss about the emission type and the methods to control the emission. In this we will discuss the thermal converters, Catalytic Converters, Particulate Traps, Exhaust Gas Recirculation (EGR), Air Injection, Evaporative Emissions Control, Ceramic Engine Coatings, and Other Methods. At last we will conclude that at what level we reach to control the emissions and which method is the best one among the others and why.

Introduction:Our topic of term paper is to tell about the methods to control the engine emissions. In this firstly I would like to discuss about the emissions & its types. To control the pollution it is necessary to measure the emissions coming out from the engine. Emissions are of two types i.e. invisible & visible emissions. These emissions are very harmful to the environment & human beings, so it is necessary to control these emissions. The methods used to control the emissions are discussed here in this term paper. First method is thermal converter in this the temperature play the important role to control the emission. Catalytic converter is the method in which by using the catalyst we reduce the temperature requirement for the different reactions to occur efficiently it reduce the temperature required. In particulate traps method we use the trap system to control the amount of particulates released to the atmosphere. We also use chemicals to control the emission in this chemical react with the emission and reduce its harmful effect. Exhaust gas recirculation is also one of the methods to control the emission in this we recirculate the exhaust gas and reburn it. There are also many other methods used to control the emissions discussed in this term paper but the main methods are those discussed above. In other methods there is air injection method, ceramic engine coating, and evaporative emissions control method.

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Thermal Converters:As we know that the secondary reactions occur completely & readily if the temperature is high. That’s the reason behind using the thermal converters it lowers the emissions. Thermal converters are the high temperature chambers through which the exhaust gas flows. It oxidizes the CO & HC remain in the exhaust. Consider the following reaction. CO + ½ O2

→ CO2

For this reaction to occur at a useful rate the temperature must be held above 700°c.now consider another reaction. Cx Hy + zO2 → xCO2 + y H2 O Where z = x + 0.25y. This reaction needs a temperature of range 600°c for at least 50 milliseconds to reduce the HC. It is therefore necessary for a thermal converter to be effective; it should be operate at high temperature. It should also provide the sufficient time for exhaust gases for occurring these reactions. Most of thermal converters are having an enlarged exhaust manifold connected to the engine outside the exhaust port. It is used to reduce the heat losses and keeps the exhaust gases from cooling to nonreacting temperatures. It creates a serious problem for the engine because in modern engine the compartment space is very low. Some thermal converters consist of the air intake which provides additional oxygen to react with the CO & HC. It increases the cost and, size of the system. We can reduce the HC & CO emissions by the oxidation but we can’t reduce NOx emissions by using a thermal converter.

Catalytic Converters:The other most used method to control the engine emission is catalytic converter used in most automobiles and other modern engines of medium or large engines. These are also called as the three way converters because they are used to reduce the concentration of CO, HC, and NOx. It is usually a stainless steel container mounted somewhere along the exhaust pipe of the engine. Inside the converter there is a porous ceramic structure through which the exhaust gas flows. There are some small embedded particles of catalytic material in the ceramic passage which promotes the oxidation reactions in the

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Nitin Joshi B Tech Mechanical exhaust gas as it passes. We can oxidize CO & HC into CO2 & H2O in exhaust system & thermal converter if the temperature is held at 600-700°C. If there is certain catalyst is present the temperature needed to sustain these oxidation processes can be reduced to 250-300°C. Catalyst is a substance that accelerates a chemical reaction by lowering the energy needed for it to proceed. The catalyst is not consumed in the reaction. These are chamber mounted in the flow system through which the exhaust gas passes. It converts hydrocarbons, carbon monoxide and, NOx into less harmful gases by using the combination of platinum, palladium and, rhodium as catalysts. The efficiency of the catalytic converter is depending upon the temperature. When a converter is in good working condition it is working on a temperature of 400°C or above. At this position it will remove 98-99% of CO, 95% of NOx, and more than 95% of HC from exhaust flow emissions. Effective control of HC & CO occurs with stoichiometric or lean mixtures while control of NOx requires near stoichiometric conditions. Very poor NOx control occurs with lean mixture. So it is necessary to operate converter hot to be effective but not hotter. It is desirable that catalytic converter have an effective life time equal to that of the automobile or at least 200, 000km. converters loss their age due to thermal degradation and poisoning of the active catalyst material. When we use leaded gasoline it would completely poison a converter and make it totally useless. Also catalytic converters are not very effective when they are cold. It is estimated that about 70-90% of all HC emissions are because of cold start up.

CI Engine:Catalytic converters are being tried with CI engines but are not efficient at reducing NOx due to their overall lean operation. Platinum & palladium are two main catalyst materials used for converters on CI engines. They remove 30-80% of the gaseous HC & 40-90% of the CO in the exhaust. It has a little effect on carbon soot but can remove 30-60% of the total particulate mass by oxidizing a large percent of the HC absorbed on the carbon particles.

Particulate Traps:[email protected]

Nitin Joshi B Tech Mechanical Particulate trap is an emission control device in the exhaust system of a diesel engine that captures particulates before they can enter the atmosphere. As we know that in gas engine fuel is injected during the intake stroke whereas in diesel engine fuel is injected during the compression stroke. As a result of this the gas engine have the advantage of having more time to mix the air and fuel before ignition occurs, this reduces the amount of unburned fuel. The consequence of this is that the diesel engine exhaust contains incompletely burned fuel known as particulate matter. In order to minimize this amount of unburned fuel, we use particulate filters. The key to the successful application of particulate filters on diesel engine was the ability to reliably regenerate the filter , or in other words, burn the pm that the particulate filter “traps” or collects. To understand how this filter regenerates, we must understand how the pm burns. Combustion of soot is done in an oxygen atmosphere. In air, soot will burn at about 450 degree to 500 degree. As a result in order to burn soot in air, an active system, one that increase the temperature of the exhaust using some external heat source is required. But if this active system is not controlled careful, it would experience uncontrolled burn where the temperature increases to 60 degree or more. This will damage the filter element and also pose some potential risk to the vehicle. The particulate filter is a passive filter using only the heat in the exhaust to combust the soot. It is a dual brick system containing a highly loaded platinum catalyst upstream of a filter element. The pt catalyst serves two functions: 1. First to convert a portion of the nitrous oxide in the exhaust to no2, which allows the soot to be burned as this much lower temperature 2. Secondly to burn or reduce both carbon monoxide and hydrocarbon by over 90 percent. The requirements for particulate filter technology to operate are simple. They are : 1. Use of USLD 2. An exhaust temperature of 250 degree for 40% of operating cycle 3. A NOx/PM ratio or more for the proper amount of NO2 for combustion

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Nitin Joshi B Tech Mechanical When these conditions are met the CRT filter will operate reliably and will reduce PM, CO and HC by more than 90 % for many years and hundreds of thousands of miles. These filters have around 1,000,000 miles of reliable service reducing diesel emissions every day.

Reducing Emissions By Chemical Methods:Work has been done on large stationary engines using cyanuric acid to reduce the NOx emissions. This acid is a low cost solid material that sublimes in the exhaust flow. The operating temperature is about 500°C. Upto 95% of NOx reduction can be achieved without any loss in engine performance. Some large marine engines are using NH3 spray system to reduce the NOx emissions. In the presence of catalyst following reaction occurs 4 NH3 + 4 NO + O2 → 4 N2 + 6 H2O 6 NO2 + 8 NH3 → 7 N2 + 12 H2O Ammonia injection system is not practical in automobiles or on other smaller engines because of the need of NH3 storage and fairly complex injection and control system.

Exhaust Gas Recirculation (EGR):The most effective way to control the emissions of NOx is to hold the combustion chamber temperatures down. It also reduces the thermal efficiency of engine. To reduce the flame temperature we dilute the air fuel mixture with a non reacting parasite gas. This gas absorbs energy during the combustion process. Also adding of any non reacting neutral gas to the inlet air fuel mixture reduces the flame temperature and NOx generation. In this method a valve is inserted between the exhaust and intake manifold. This valve opens under some conditions to admit exhaust into the intake tract. Exhaust neither burn nor support the combustion it just dilutes the air fuel ratio to reduce the peak combustion chamber temperatures and thus help to reduce the formation of NOx. EGR not only reduce the maximum temperature in the combustion chamber but also lower the overall efficiency. Increase in EGR results in the some cycle partial burns and in the extreme total misfire. Then by using EGR NOx can be controlled but it increased the HC emissions and lower thermal efficiency. The amount of the EGR is controlled by the

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Nitin Joshi B Tech Mechanical engine management system. By sensing the inlet and exhaust conditions the flow controlled ranging from 0 upto 15-30%. No EGR is used during WOT when maximum power is desired. No EGR is used at ideal and very little at low speeds. There is a problem with CI engines when using EGR is the solid carbon soot in the exhaust. The soot acts as an abrasive and breaks down the lubricant. Greater wear on the piston rings and valve train occurs.

Air Injection:Air injection is one of the methods used to control the emissions. This method provides the oxygen to burn the unburned hydrocarbons inside the combustion chamber. It is used to reduce the startup emissions.

Evaporative Emissions Control:Evaporative emissions are the result of gasoline vapors escaping from the vehicle fuel system. In this system the vapors from the fuel tank and carburetor bowl vent are ducted to canisters containing activated carbon. Canister absorbed the vapors, and during engine operational modes fresh air is drawn through the canister, pulling the vapor into engine, where it is burned.

Ceramic Engine Coatings:This technology is used in mobile and stationary diesel engines from many years. The function of this is to reduce the carbon soot or visible smoke. It reduces the NOx emission by 40% with decrease in NMHC and CO.

Evaporation Loss Control Device:The aim of this device is to control the evaporative emissions by capturing the vapours & recirculating them at the appropriate time. It consists of an absorbent chamber, the pressure balance valve and the purge control valve. The absorbent chamber holds the hydrocarbons vapour before they can escape to atmosphere. The carburettor bowl & the fuel tank main sources of HC emissions are directly connected to the absorbent chamber when engine is turned off i.e. under hot soak. Hot soak is a condition when a warmed up [email protected]

Nitin Joshi B Tech Mechanical car is stopped & its engine turned off. The absorbent when saturate is relieved of the vapours by a stripping action allowing the air from the air cleaner to draw them to the intake manifold through the purge valve. The internal seat of the pressure valve at that time is so located that there is a direct pressure communication between the internal vent and top of the carburettor bowl maintaining designed carburettor metering forces. The operation of the purge valve is to take care of the exhaust bake pressure. Under normal conditions the fuel supply is cut off so that the level of HC can be reduced. The ELCD completely controls all types of the evaporative losses. It requires very accurate metering control.

Other Methods:We can also control the emissions by improving the engine design, more precise ignition timing, more precise fuel metering, proper mixing of fuel and air. When the mixing of the air fuel will be proper then the combustion will be completely and the emission will be less. Carbon soot can be reduced in modern CI engines by advanced design technology in fuel injection system and combustion chamber geometry. With greatly increased mixing efficiency and speeds, large regions of fuel rich mixtures can be avoided when combustion starts. These are the regions where carbon soot is generated, and by reducing there volume far less soot is generated. Indirect injection into a secondary chamber that promotes high turbulence and swirl greatly speeds the air fuel mixing process. Better nozzle design and higher injection pressures creates finer fuel droplets which evaporate and mix quicker. Injection against a hot surface speeds evaporation, as do air assisted injectors. Some modern top of the line CI automobiles engines have reduced particulates generation enough that they meet stringent standards without the need for particulate traps. All methods listed above helps to reduce the engine emissions and hence help to prevent the environment and human beings. Proper running conditions also help to reduce the emissions. Using these standard methods one can control the emissions from the engine

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Table 1: IC Engine Typical Emission Level Engine Type Natural Gas

Diesel Dual Fuel

Lambda*(ë) 0.98 0.99 1.06 1.74 1.6-3.2 1.6-1.9

Mode Rich Rich Lean Lean Lean Lean

NMHC 0.3 0.2 1.0 1.0 0.3 0.5

Emission (g/bhp-hr) CO NOx 13.9 8.3 8.0 11.0 1.0 18.0 3.0 0.7 1.0 11.6 2.5 4.1

PM Low Low Low Low 0.25-0.8 NA

* ë is the ratio of the actual air to fuel ratio to the stoichiometric air to fuel ratio.

Table 2: Cost of Catalytic Control Technologies Catalyst Type NSCR SCR Oxidation Lean NOx Engine Coating

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$/bhp 10-12 50-125 9-10 10-20 5-12


Conclusion: From the above methods we can conclude that it is possible to control the emissions from the engine by applying these methods. These methods are widely used. Some of these methods are not easy to use, some are costly and, some methods are complicated. No methods can be used to control the all type of emissions. For each type of emission there is a different method. So while choosing the emission control method one should take care and should select the most effective method according to conditions in which the engine has to be run. Effectiveness of the engine also depend upon the emissions, if the emissions are high then the efficiency will be low. So to save the environment and make the engine more effective it is necessary to control the emissions.

References:I have taken the references from the following websites and books. 1. www.google.co.in 2. www.wikipedia.com 3. IC engines by V Ganesan 3rd edition tata mcgraw hill 4. IC Engine Fundamentals by John B. Heywood

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Nitin Joshi B Tech Mechanical 5. Emission Control Technology for Stationary Internal Combustion Engines (Status Report) by Manufacturers of Emission Controls Association.

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Emission Control Methods

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