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, biodiesel blends,[1] 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 blow-by
- 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.[2] According to another study from the same university, traffic fumes alone cause the death of 5,000 people every year just in the United Kingdom.[3]
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 water vapor and carbon dioxide are greenhouse gases that contribute to motor vehicle emissions (and from stationary internal combustion engines), which can also include:
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.[2] According to another study from the same university, traffic fumes alone cause the death of 5,000 people every year just in the United Kingdom.[3]
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 vaporize completely, creating higher emissions of hydrocarbons 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 warmed up to their operating temperature. This time has been much reduced by moving the converter closer to the exhaust manifold and even more so 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,[4] including electric heating, thermal battery, chemical reaction preheating, flame heating and superinsulation.
Passenger car emissions summary
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, although diesel engines always operate with an excess of air over fuel.[citation needed] The CO content for petrol engines varies from ~ 15ppm for well tuned engine with fuel injection and a catalytic converter up to 100,000 ppm (10%) for a richly tuned carburetor engine, such as typically found on small generators and garden equipment.[8]
Nitromethane additive
Exhaust gas from an internal combustion engine whose fuel includes 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, although diesel engines always operate with an excess of air over fuel.[citation needed] The CO content for petrol engines varies from ~ 15ppm for well tuned engine with fuel injection and a catalytic converter up to 100,000 ppm (10%) for a richly tuned carburetor engine, such as typically found on small generators and garden equipment.[8]
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 who are likely to be exposed to it should wear a gas mask.[9]
Diesel engines
Gas-turbine engines
- In aircraft gas turbine engines, "exhaust gas temperature" (EGT) is a primary measure of engine health. Typicall
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 who are likely to be exposed to it should wear a gas mask.[9]
Diesel engines
- jet engines and rocket engines, exhaust from propelling nozzles which in some applications shows shock diamonds.[citation needed]
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
NOx
Mono-nitrogen oxides NO and NO2 (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
NOx
Mono-nitrogen oxides NO and NO2 (NOx)(whether produced this way or naturally by lightning) 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 NO species increases the risk of lung cancer[10] and colorectal cancer.[11] and inhalation of such particles may cause or worsen respiratory diseases such as emphysema and bronchitis and heart disease.[12][13][14]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.[14]
The resulting nitric acid may be washed into soil, where it becomes nitrate, which is useful to growing plants.
Volatile organic compounds
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.[14]
The resulting nitric acid may be washed into soil, where it becomes nitrate, which is useful to growing plants.
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.[15] 27% of VOC emissions are from solvents which are used in the manufacturer of paints and paint thinners and other uses.[16]
Ozone
Ozone is beneficial in the upper atmosphere,[17] but at ground level ozone irritates the respiratory system, causing coughing, choking, and reduced lung capacity.[18] It also has many negative effects throughout the ecosystem.[19]
Carbon monoxide (CO)
[17] but at ground level ozone irritates the respiratory system, causing coughing, choking, and reduced lung capacity.[18] It also has many negative effects throughout the ecosystem.[19]
Carbon monoxide (CO)
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.[22][23]
Particulate matter (PM10 and PM2.5)
Carbon dioxide
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 according to the vast majority of the scientific community is causing climate change.[30] Motor vehicles are calculated to generate about 20% of the European Union's man-made CO2 emissions, with passenger cars contributing about 12%.[31] 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.[32]
Water vapour
Vehicle exhaust contains much water vapour.
Water recovery
There has been research into ways that troops in deserts can recover drinkable water from their vehicles' exhaust gases.[33]
Pollution reductionThe California Air Resources Board found in studies that 50% or more of the air pollution (smog) in Southern California is due to car emissions.[citation needed] Concentrations of pollutants emitted from combustion engines may be particularly high around signalized intersections because of idling and accelerations. Computer models often miss this kind of detail.[38]
See also
U.S. EPA