Emission- Causes Effects And Controls full report
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Emission: Causes , Effects & Controls
Ms. Singam Swati Shankar ,
Ms. Gosavi Richa Gopal ,
Bharat-Ratna Indira Gandhi College of Engineering, Solapur
In recent times the environment has come under heavy attack due to various problem created by the internal combustion engine powered vehicle. The most serious of these problems is air pollution. Where as the main problem facing the developing countries is pollution. India is facing the same severe problem of pollution. The main pollutants present in this type of air are carbon monoxide (CO) un-burnt hydrocarbons (UBHC), oxides of nitrogen (NOx) & lead & other particulate pollutants.
The major causes of these emissions are non-stoitiometric combustion, dissociation of nitrogen, and impurities in the fuel & air. The emissions of concern are unburnt hydrocarbons (HC), oxides of carbon, oxides of nitrogen, oxides of sculpture, &solid carbon particulates.
It is the dream of engineers and scientists to develop the engines and fuels such that very few quantities of harmful emissions are generated, and these could be let into the surroundings without a major impact on the environment. However, with the present technology this is not possible, and after â€œtreatment of the exhaust gases as well as in-cylinder reduction of emissions are very important. Incase of after-treatment it consist mainly of use of thermal or catalytic converter and particulate traps .For in-cylinder reduction exhaust gas recirculation (EGR) and some fuel additives are being tried. In addition to exhaust emissions also play a part. Here air injection method and exhaust gas recirculation are also used to reduce emission from engines.
The diesel engine is similar to other kinds of automotive engine in which hydrocarbon fuels are used, but the diesel is more efficient in converting hydrocarbon fuel energy into work than other engines. In the automobile industry, the diesel engine today is used more than any other type of engine for transporting freight over the highway. The hydrocarbon fuels are highly portable, have high specific energy content and can effectively converted into work, but always waste by products-regardless of engine type.
These waste materials become air pollutants. Some are toxic while others are harmless. It should be emphasized that the exhaust pollutants from the diesel are similar to products of combustion in other typeâ„¢s engines or in other types of combustion processes. Further, the interstate road system has tended to concentrate the both public vehicles and freight vehicles on same roads. Diesel smoking is seen by many people in short period of time and is long remembered because of high level of awareness concerning air pollution.
There are two separate kinds of pollution to be considered relative to automotive diesel. First type is not the subject the judgments of general public that they do not like to see dark exhaust smokes nor do they like to neither smell the exhaust smoke nor do they like o smell the exhaust odor from some diesel-powered vehicles. It is usually granted that these effects may not be harmful to the health of general public, but excesses of smoke are long remembered. The second type of pollutants of on in the exhaust is less obvious to the general public, but may be harmful in concentrations. These must be objectively measured and accurately evaluated to determine if there are effects from them, which might endanger the public.
Air Pollution Due To IC Engines:
Until the middle of the 20th century the number of IC engines in the world so small that the pollution they caused was tolerable .During the period of environment, with the help of sunlight, stayed relatively clean. As world population grew, power plants, factories, and even increasing number of automobiles began to pollute the air to the extent that it was no longer acceptable, during the late 1940s air pollution as a problem was first recognized in the Los Angeles basin in California. Two causes of this were the large population density &natural weather conditions of the area. Smoke & other pollutants from many factories and automobiles combined with fog that was common in this ocean area, and smog resulted. During the 1950s, the smog problem increased along with the increase in population density &automobile density .At this stage it was realized that automobile was the major contributors to the problem. By the 1960s emission standards were beginning to be enforced in California.
During the next decade, emission standards were adopted in the rest of the United States and Europe and Japan. By making engines more fuel efficient, and with the use of exhaust after-treatment, emissions per vehicle of HC, CO & NOx were reduced by about 95% during the 1970s&1980s. Lead, one of the major air pollutants, was phased out as a fuel additive during 1980s.More fuel â€œefficient engines were developed, and by the 1990s the average automobile consumed less than half the fuel used in 1970.However, during this time the number of automobiles greatly increased, resulting in no overall decrease in fuel usage.
Further reduction of emissions will be much more difficult and costly. As world population grows, emission standards more stringent out of necessity. The strictest laws are generally initiated in California, with the rest of the United States and world following. Although air pollution is global problem, some regions of the world still have no emission standard or law.
What is Emission
In I.C. Engines mostly used fuel is diesel. Normally diesel is dropped into the combustion chamber at the end of compression stroke, and as the temperature is very large in the chamber at the beginning of injection, diesel is ignited spontaneously. After completion of combustion, complete or incomplete, exhaust stroke begins where gases burned and other unburned particles were expelled which is called as emission. In short, emission can be defined as: outcome result of combustion at end of exhaust stroke. Emission is in the different form like Particulate matter, Hydrogen, Carbon dioxide, carbon monoxide, Nitrogen oxide, soot particles, and smoke.
This is what most people think of when they think of vehicle air pollution; the products of burning fuel in the vehicle's engine, emitted from the vehicle's exhaust system.
Constituents of Emission
These refinements have contributed to clearing the diesel exhaust. There are many variables involved in the diesel smoke problem outside of engine cylinder such as the method measurement of smoke density, volume, and appearance. One method is to draw a measured volume of exhaust gas through a filter paper, which is blackened, to various degrees by the amount of carbon (or particulate) filtered from the gas sample. The method is quick, but does not always correlate well with visual observations of same smoke stream. A second basic type of instrument involves a photoelectric cell, which quantitatively measures the extinction of light passing through a sample stream of exhaust gas. Several instruments of this type are currently in use throughout the world Objective instruments for smoke measurements such as Hart ridge meter in England or Manual system in Japan have been developed in preference to the subjective Ringel man system in countries other than the United States.
Under some specific operating conditions, the exhaust from the diesel engines can be objectionably odors. This is especially marked during cold start-up or when operating in cold ambient conditions such that combustion is incomplete. In those cases, the odor is caused by raw fuel molecules or unburned hydrocarbons passing through the cylinder without complete combustion. Beyond a clear understanding of odor from a cold engine, there is vast field for odor studies which is not clearly defined at this time. For example, not all engines emit odors under the same operating conditions Different makes and types of engines will have different quality of odor and the odor will vary according to fuel being burned. The primary difficulty in the odor studies is that to date no instrument has been developed which will objectively measure odor.
California, the leader in setting exhaust emission standards, has established standards for unburned hydrocarbons, carbon monoxide, and oxides of nitrogen. These are shown in tables.
Air quality standards:
Unburned hydrocarbon 275ppm Hexane equivalent
Carbon monoxide 1.5% Volume
Oxides of nitrogen 350ppm Measured as NO2
The automotive diesel ready meets standards for hydrocarbons and carbon monoxide. Additional work however is being done to evaluate the unburned hydrocarbon content of diesel exhaust; particularly with regard to different types and makes of engines. The sampling and measurement techniques are critical, and those, which are suitable for spark ignition engines, are not applicable to diesel exhaust. It has been found that sampling and handling of gas for analysis must be done at high temperature prior to analysis to avoid loss of heavier hydrocarbons. Following table shows measurements of exhaust contents from four stroke diesel engines at rated speed.
Four strokes naturally aspirated diesel engine at rated speed:-
Full load Half load No load Idle
Hydrocarbon ppm 20 70 90 106
formaldehyde ppm 4.3 6.8 1.8 6.8
NOx,ppm 921 493 109 199
CO% .2 0.03 0.03 0.03
3. Oxides of nitrogen (NOx):
The entire subject of oxide of nitrogen pollution needs careful study since some research has been completed which suggests that photochemical smog production might actually increase with lesser concentrations of oxides of nitrogen. The results of oxides of nitrogen tests in our laboratories do not show good paths for significant reduction. Some of critical factors affecting this variable are compression ratio, dilution rate, injection rate, and timing of injection. These are not independent factors, and the cylinder efficiency would be adversely affected by most critical design to reduce nitrogen oxides.
4. Carbon monoxide (CO):
In addition to the hydrocarbon content and oxides of nitrogen content of exhaust, mere is factor of carbon monoxide, which does not play apart in photochemical smog production. Up to 1.5% carbon monoxide for the standard is high relative to NO or hydrocarbons as a toxic pollutant since this are equivalent to15000ppmon volume basis. It is apparent that the California air standard quantity levels have been influenced by smog potential to a greater extent than by toxicity. The diesel meets the 1-1/2%CO limit and rarely exceeds even 20% of this limit. Relative to the gasoline engine the diesel has little or no problem in this area. There are trace elements of other undesirable compounds in the diesel such as been zepyrene, olefins, and many other semi-oxidized molecules. Obviously these compounds would be harmful in high concentrations, but no standards have been written to date relative to these compounds probably due to their relatively low concentration levels in the exhaust.
5. Sulphur dioxide (SO2):
Sulphur dioxide is sometimes considered as a pollutant. It is formed in small amounts from sulphur supplied in the fuel. Currently, the sulphur dioxide content of diesel exhausts is below problem limits.
Sources of Particulate Emission:
The main sources of particulate emission are fuel and engine oil. Fig.1 shows the particulate composition and gives as impression of the sources for a typical 1988 technology turbo charged truck Diesel engine. The main portion of the soluble organic fraction originates from the engine oil consumption. The carbon (soot) and sulfate portions are mainly results of the combustion process
and may accordingly be influenced by optimizing this process. The remaining portion is mainly composed of fuel and oil derived particulates. In addition, dust particles that are not collected by the intake air filters and metals which are emitted in normal operation of engine and exhaust system may also contribute.
Fig.1 Sources of Particulate Emission
These are produced from the evaporation of fuel, and are a large contributor to urban smog, since these heavier molecules stay closer to ground level. Fuel tends to evaporate in these ways:
1. Gas tank venting:
The heating of the vehicle as the temperature rises from the night-time temperature to the hottest temperatures of the day mean that gasoline in the tank evaporates, increasing the pressure inside the tank above atmospheric pressure. This pressure must be relieved, and before emissions control it was simply vented into the atmosphere.
2. Running losses:
The escape of gasoline vapors from the hot engine.
3. Refuelling losses:
These can cause a lot of hydrocarbon vapor emission. The empty space inside a vehicle's tank is filled with hydrocarbon gases, and as the tank is filled, these gases are forced out into the atmosphere. In addition, there is loss from further evaporation and fuel spillage.
The consumption of lubricating oil must be substantially reduced to meet the 1991 and 1994 particulate emission standards. A piston / piston ring design concept for â„¢91 emission targets is derived from the analysis that is able to reach very low oil consumption standards in the important high speed / part load range diesel engine. The emission standards for heavy duty diesel engines have been substantially tightened from the last five years. The development of these legal limits along with standards is shown in table below. Major effort is necessary especially to reach the 1994 standards limits. In this effort all contributors to particulate emission have to be addressed, including combustion, engine oil consumption as well as oil and fuel composition.
Table for 91â„¢ and 94â„¢ emission standard
Constituent (g/hph) 91â„¢ emission standards 94â„¢ emission standards
Particulate matter 0.3 0.1
CO 15 15
HC 1.0 1.0
NOX 6.0 5.0
Tailpipe emissions control
Tailpipe emissions control can be categorised into three parts:
1. Increasing engine efficiency
2. Increasing vehicle efficiency
3. Cleaning up the emissions
1.Increasing engine efficiency: Engine efficiency has been gradually improved with progress in following technologies and related emissions is also reduced.
Â¢ Electronic ignition
Â¢ Fuel injection systems
Â¢ Electronic control unit
2.Increasing vehicle efficiency
Contributions to the goal of reducing fuel consumption and related emissions come from
Â¢ lightweight vehicle design
Â¢ minimized air resistance
Â¢ reduced rolling resistance
Â¢ improved powertrain efficiency
Â¢ increasing spark to the spark plug
Each of these items breaks down into a number of factors.
Increasing driving efficiency
Significant reduction of emissions come from
Â¢ driving technique (some 10-30% reduction)
Â¢ unobstructed traffic conditions
Â¢ cruising at an optimum speed for the vehicle
Â¢ reducing the number of cold starts
3.Cleaning up the emissions
Advances in engine and vehicle technology continually reduce the amount of pollutants generated, but this is generally considered insufficient to meet emissions goals. Therefore, technologies to react with and clean up the remaining emissions have long been an essential part of emissions control.
A very early emissions control system, the Air injection reactor (AIR) reduces the products of incomplete combustion (hydrocarbons and carbon monoxide) by injecting fresh air into the exhaust manifolds of the engine. In the presence of this oxygen-laden air, further combustion occurs in the manifold and exhaust pipe. Generally the air is delivered through an engine-driven 'smog pump' and air tubing to the manifolds. This technology was introduced in 1966 in California, and was in use for the next several decades. It is not generally in use any longer, having been supplanted by cleaner burning engines and better catalytic converters.
Other emission control devices:
1. Direct air injection:
If compressed air is introduced into the combustion chamber in addition to air fuel charge from the carburetor, better combustion, and hence reduced hydrocarbon and carbon monoxide emission will result. This also gives a tremendous power boost with some saving in fuel. But extra equipment in form of air compressor and air valves will raise the cost very much.
2. Ammonia injection:
As a fuel, ammonia does not hold much promise but if used as an exhaust additive, it can give excellent control for NOx emission. Ammonia and nitric oxide interact to form nitrogen and water. Ford motor Co. has been doing investigation with injecting ammonia water in the exhaust manifold, downstream from the port.
For an effective utilization of ammonia injection, the exhaust gas temperature has to kept within strict limits and injecting device has to be put sufficiently down to bring the gas temperature to165C. The present carburetors are incapable of this and it might be necessary to adopt electronic injection system to keep close control over fuel-air ratios.
3. Electronic injection:
It is possible to develop an electronic injection system with sensors for air temperature, manifold pressure and speed which will precisely regulate the fuel supply giving only such air fuel ratio as will give no hydrocarbon or monoxide emissions.
Since the injection can be affected in individual intake ports, the problem of fuel-distribution among various cylinders will automatically be avoided.
The emissions on deceleration can be completely removed by shutting off the fuel supply when the throttle is closed. But this system will still not be able to control the NOx emission. Combination of electronic injection and ammonia as an exhaust additive has an attractive future.
Large number of pollutants are continuously discharged into the environment causing air pollution.The major role in causing air pollution is played by automobiles.When discharged pollutants excceds the natural capacity it becomes hazardous to the human life.Engineering measures are adopted to artificially clean the pollutants before they are emitted in to the environment.Therefore by using follwing techniques we can reduce emission.1.Air injection,.2.Exhaust gas recirculation.
1. Internal Combustion Engine, V.Ganeshan,Tata McGraw Hill Publication Hill Ltd., second edition.
2. Internal Combustion Engine, M.L.Mathur & R.P.Sharma, Dhanpat Rai Publication rewised edition.
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EMISSION FROM AUTOMOBILES
Def : The pollutant is a substance that makes (or) damages an area, atmosphere, harmful to people.