Exhaust gas or flue gas is emitted as a result of the combustion
of fuels such as natural gas, gasoline/petrol, diesel fuel,
fuel oil
or coal.
According to the type of engine, it is discharged into the atmosphere through
an exhaust pipe, flue gas stack
or propelling nozzle. It often disperses downwind in a pattern called an exhaust
plume.
It is a major component of motor
vehicle emissions (and from stationary internal combustion engines), which
can also include:
- Crankcase by-blow
- Evaporation of unused gasoline
Motor vehicle emissions contribute
to air pollution and are a major ingredient in the creation of smog in some large cities.
A 2013 study by MIT
indicates that 53,000 early deaths occur per year in the United States alone
because of vehicle emissions.
According to another study from the same university, traffic fumes alone cause
the death of 5000 people every year just in the United Kingdom.
Composition
The largest part of most combustion
gas is nitrogen
(N2), water vapor (H2O) (except with pure-carbon fuels),
and carbon dioxide (CO2) (except for fuels without carbon); these
are not toxic or noxious (although carbon dioxide is generally recognized as a greenhouse gas
that contributes to global warming). A relatively small part of combustion gas is undesirable
noxious or toxic substances, such as carbon monoxide
(CO) from incomplete combustion, hydrocarbons
(properly indicated as CxHy, but typically shown simply
as "HC" on emissions-test slips) from unburnt fuel, nitrogen oxides
(NOx) from excessive combustion temperatures, ozone (O3), and particulate matter
(mostly soot).
Exhaust
gas temperature
Exhaust gas temperature (EGT) is
important to the functioning of the catalytic converter of an internal
combustion engine. It may be measured by an exhaust
gas temperature gauge. EGT is also a measure of engine
health in gas-turbine engines (see below).
Cold
engines
During the first two minutes after
starting the engine of a car that has not been operated for several hours, the
amount of emissions can be very high. This occurs for two main reasons:
- Rich air-fuel ratio requirement in cold engines: When a cold engine is started, the fuel does not vaporise completely, creating higher emissions of hydrocarbons, nitrogen oxides and carbon monoxide, which diminishes only as the engine reaches operating temperature. The duration of this start-up phase has been reduced by advances in materials and technology, including computer-controlled fuel injection, shorter intake lengths, and pre-heating of fuel and/or inducted air.
- Inefficient catalytic converter under cold conditions: Catalytic converters are very inefficient until up to their operating temperature. This time has been much reduced by moving the converter closer to the exhaust manifold and even moreso placing a small yet quick-to-heat-up converter directly at the exhaust manifold. The small converter handles the start-up emissions, which allows enough time for the larger main converter to heat up. Further improvements can be realised in many ways, including electric heating, thermal battery, chemical reaction preheating, flame heating and superinsulation.
Passenger
car emissions summary
U.S.
Environmental Protection Agency estimates of average passenger car emissions
in the United States for July 2000
|
||
Component
|
Emission
Rate
|
Annual
pollution emitted
|
Hydrocarbons
|
2.80 grams/mile (1.75 g/Km)
|
77.1 pounds (35.0 kg)
|
Carbon monoxide
|
20.9 grams/mile (13.06 g/Km)
|
575 pounds (261 kg)
|
NOx
|
1.39 grams/mile (0.87 g/Km)
|
38.2 pounds (17.3 kg)
|
Carbon dioxide - greenhouse gas
|
0.916 pounds per mile
(258 g/km)
|
11,450 pounds (5,190 kg)
|
In 2000, the United States
Environmental Protection Agency began to implement more stringent emissions
standards for light duty vehicles. The requirements were phased in beginning
with 2004 vehicles and all new cars and light trucks were required to meet the
updated standards by the end of 2007.
United
States Light-Duty Vehicle, Light-Duty Truck, and Medium-Duty Passenger
Vehicle—Tier 2 Exhaust Emission Standards (for Bin 5)
|
||
Component
|
Emission
Rate
|
Annual
pollution emitted
|
0.075 grams/mile (0.046
g/Km)
|
2.1 pounds (0.95 kg)
|
|
Carbon Monoxide
|
3.4 grams/mile (2.1 g/Km)
|
94 pounds (43 kg)
|
NOX
|
0.05 grams/mile (0.0305 g/Km)
|
1.4 pounds (0.64 kg)
|
0.015 grams/mile (0.0092
g/Km)
|
0.41 pounds (0.19 kg)
|
|
Types
Internal-combustion
engines
Spark-ignition
engines
In spark-ignition engines the gases resulting from combustion of the fuel and air mix
are called exhaust gases. The composition varies from petrol to diesel engines,
but is around these levels:
This table DOES NOT correctly
reflect graph presented on page 6 of referenced document!
The 10% oxygen for
"diesel" is likely if the engine was idling, e.g. in a test rig. It
is much less if the engine is running under load.
Combustion-engine exhaust gases
All figures are approximate |
%
of total
|
|
Compound
|
Petrol
|
Diesel
|
71
|
67
|
|
14
|
12
|
|
12
|
11
|
|
10
|
||
< 0.5
|
~ 0.3
|
|
< 0.25
|
< 0.15
|
|
1 - 2
|
< 0.045
|
|
< 0.045
|
||
< 0.25
|
< 0.03
|
|
possible traces
|
< 0.03
|
|
Nitromethane
additive
Exhaust gas from an internal
combustion engine whose fuel includes nitromethane
will contain nitric acid vapour, which is corrosive, and when inhaled causes a
muscular reaction making it impossible to breathe. People exposed to it should
wear a gas mask.
Diesel
engines
Gas-turbine
engines
- In aircraft gas turbine engines, "exhaust gas temperature" (EGT) is a primary measure of engine health. Typically the EGT is compared with a primary engine power indication called "engine pressure ratio" (EPR). For example: at full power EPR there will be a maximum permitted EGT limit. Once an engine reaches a stage in its life where it reaches this EGT limit, the engine will require specific maintenance in order to rectify the problem. The amount the EGT is below the EGT limit is called EGT margin. The EGT margin of an engine will be greatest when the engine is new, or has been overhauled. For most airlines, this information is also monitored remotely by the airline maintenance department by means of ACARS.
Jet
engines and rocket engines
What looks like exhaust from jet
engines, is actually contrail. (Jet flying over the United States Air Force Academy
in Colorado
Springs, Colorado).
In jet engines
and rocket engines, exhaust from propelling nozzles which in some applications shows shock diamonds.
Other
types
From
burning coal
Steam
engines
In steam engine
terminology the exhaust is steam that is now so low in pressure that it can no
longer do useful work.
Main
motor vehicle emissions
Smog in New York City
as viewed from the World Trade Center in 1988. A 2009 report indicates that, despite the City's
air being close to the EPA's short-term ozone standard, that New Yorkers still
face a 25 per-cent increased risk of dying from lung disease.
Mono-nitrogen oxides NO and NO2
react with ammonia,
moisture, and other compounds to form nitric acid
vapor and related particles. Small particles can penetrate deeply into
sensitive lung tissue and damage it, causing premature death in extreme cases.
Inhalation of such particles may cause or worsen respiratory diseases such as emphysema
and bronchitis.
It may also aggravate existing heart disease.
In a 2005 U.S. EPA study the largest emissions of NOx
came from on road motor vehicles, with the second largest contributor being non-road equipment which is mostly gasoline and diesel stations.
Volatile
organic compounds
Non road equipment is mostly gasoline
and diesel stations.
When oxides of nitrogen (NOx) and volatile
organic compounds (VOCs) react in the presence of
sunlight, ground level ozone is formed, a primary ingredient in smog. A 2005 U.S. EPA report gives road
vehicles as the second largest source of VOCs in the U.S. at 26% and 19% are
from non road equipment which is mostly gasoline and diesel stations.
27% of VOC emissions are from solvents which are used in the manufacturer of
paints and paint thinners and other uses.
Ozone
Ozone is beneficial in the upper
atmosphere, but at ground level, ozone irritates
the respiratory system, causing coughing, choking, and reduced lung capacity.
and has many bad effects throughout the ecosystem.
Carbon
monoxide (CO)
MOPITT
satellite computer image of carbon monoxide March 2010.
Carbon
monoxide poisoning is the most common type of fatal
air poisoning in many countries.
Carbon monoxide is colorless, odorless and tasteless, but highly toxic. It
combines with hemoglobin to produce carboxyhemoglobin, which is ineffective for delivering oxygen to bodily
tissues. In the U.S. 60% of carbon monoxide is caused by on road vehicles.
Hazardous
air pollutants (toxics)
Chronic (long-term) exposure to benzene
(C6H6) damages bone marrow.
It can also cause excessive bleeding and depress the immune system,
increasing the chance of infection. Benzene causes leukemia and is associated with other blood
cancers and pre-cancers of the blood.
Particulate
matter (PM10 and PM2.5)
The health effects of inhaling airborne particulate matter
have been widely studied in humans and animals and include asthma, lung cancer,
cardiovascular issues, and premature death. Because of the size of the
particles, they can penetrate the deepest part of the lungs.
A 2011 UK study estimates 90 deaths per year due to passenger vehicle PM.
In a 2006 publication, the U.S. Federal Highway Administration (FHWA) state that in 2002 about 1 per-cent of all PM10
and 2 per-cent of all PM2.5 emissions came from the exhaust of
on-road motor vehicles (mostly from diesel engines).
Carbon
dioxide (CO2)
Carbon dioxide is a greenhouse gas.
Motor vehicle CO2 emissions are part of the anthropogenic
contribution to the growth of CO2 concentrations in the atmosphere
which is believed by a majority of scientists to play a significant part in climate change. Motor vehicles are calculated to generate about 20% of the
European Union's man-made CO2 emissions, with passenger cars
contributing about 12%.
European
emission standards limit the CO2 emissions
of new passenger cars and light vehicles. The European Union average new car CO2
emissions figure dropped by 5.4% in the year to the first quarter of 2010, down
to 145.6 g/km.
Pollution
reduction
Emission standards focus on reducing pollutants
contained in the exhaust gases from vehicles as well as from industrial flue
gas stacks and other air pollution exhaust sources in various large-scale industrial
facilities such as petroleum refineries, natural gas processing plants, petrochemical
plants and chemical production plants.
However, these are often referred to as flue gases.
Catalytic converters in cars intend to break down the pollution of exhaust gases
using a catalyst. Scrubbers in ships intend to remove the sulfur dioxide (SO2)
of marine exhaust gases. The regulations on marine sulfur dioxide emissions are
tightening, however only a small number of special areas worldwide have been
designated for low sulfur diesel fuel use only.
One of the advantages claimed for advanced
steam technology engines is that that they produce
smaller quantities of toxic pollutants (e.g. oxides of nitrogen) than petrol
and diesel engines of the same power. They produce larger quantities of carbon dioxide but less
carbon monoxide due to more efficient combustion.
Health
studies
Researchers from the University of
California, Los Angeles School of Public Health say preliminary results of
their statistical study of children listed in the California Cancer Registry
born between 1998 and 2007 found that traffic pollution may be associated with
a 5% to 15% increase in the likelihood of some cancers.
A World
Health Organization study found that diesel fumes cause
an increase in lung cancer.
Localised
effects
The California Air Resources Board
(C.A.R.B.) found in studies that 50% or more of the air pollution
(smog)
in Southern California is due to car emissions.
SUBSCRIBERS - ( LINKS) :FOLLOW / REF / 2 /
findleverage.blogspot.com
Krkz77@yahoo.com
+234-81-83195664
No comments:
Post a Comment