Environmental Engineering Reference
In-Depth Information
and water, the exhaust of diesel engines produces particle matter, carbon monoxide, nitrogen
oxides, sulfur dioxide, hydrocarbons, aldehydes, volatile organic compounds, and a long list
of hazardous pollutants. The theoretical amount of carbon dioxide produced by a diesel engine
is proportional to the amount of fuel burned and is approximately 2.6 kg/liter (21.7 lb/gallon),
but in real life, the amount of carbon dioxide and other compounds produced by a diesel
engine depends on the type of engine (normally aspired or turbo), the type of fuel used, state
of calibration of the injection pump, engine temperature, load, and maintenance (e.g., condi-
tion of air filters).
Tail pipe fumes from diesel engines have a high local impact because of their negative
effect on human health; therefore, emissions are regulated in many countries. Diesel exhaust
has a two-phase composition: a gas and a solid phase constituted by particle matter. The gas
phase is mostly carbon dioxide and water but it also contains hydrocarbons, carbon monoxide,
and hazardous chemicals such as acetaldehyde, acrolein, benzene, 1,3-butadiene, formalde-
hyde, toluene, and polycyclic aromatic hydrocarbons (Environmental Protection Agency
[EPA], n.d.). Particle matter has a variable composition, but it is composed basically of “fine
particles” of elemental carbon with diameters ranging from 0.01 and 0.08 microns, as indi-
vidual particles, and between 0.08 and 1 microns when agglomerated (Nett Technologies,
n.d.). Particles can be emitted dry or with hazardous organic compounds, sulfates, nitrates,
and metals adsorbed to their surface (EPA, n.d.; Nett Technologies, n.d.). A third type of par-
ticles is hydrated sulfuric acid particles, which contain around 8000 molecules of water and
3000 molecules of sulfuric acid (Nett Technologies, n.d.). Acute exposure to diesel exhausts
my result in eyes, nose, and lungs irritation, lightheadedness, nausea, cough, and aggravated
asthma. Epidemiological studies show a correlation between chronic exposure to diesel
exhaust and increased cases of lung cancer (EPA, n.d.).
The emission of nitrogen oxides and sulfur dioxide by diesel engines produces an impact
at the regional level that is manifested mainly as acid rain (after combination with water and
transformation into nitric acid, HNO
3
) and formation of smog. Nitrogen oxides are generated
by combination of atmospheric nitrogen with oxygen when the fuel is burned at high pressures
and temperatures in engine cylinders. Sulfur dioxide is formed from sulfur compound present
in the diesel fuel. By oxidation sulfur dioxide turns into sulfur trioxide, which then turns into
sulfuric acid in the form of particles or as acid rain (see Chapter 8).
Air transport
With exception of transportation of goods by plane in remote areas, which is done with small
propeller planes generally known as bush planes, air transportation is performed with planes
powered by jet engines. All jet engines are fueled with different types of jet fuel that is basi-
cally a mixture of kerosene (a mix of hydrocarbons with boiling points between 145 and
300°C) and additives, of which the composition varies depending on the application and
region in the world.
Estimating emission from planes can be challenging because planes operate at different
power setting depending on the flight mode. During take off, a jet engine is set at 100-percent
power, during climb out mode at 85-percent power, during approach at 30-percent power, and
in taxi/idle mode at approximately 7-percent power (Wayson et al., 2009). Therefore, air trans-
port emissions of carbon, in the form of carbon dioxide, and pollutants depend on the length
of the haul. Also, emissions depend on plane fuel consumption, which is contingent on the age
of the engines. Specific fuel consumption has decreased 70 percent from 1969 to 2000 (Penner
et al., 1999), so the age of the fleet will definitely have an impact on fuel consumption and
emissions.
