Diesel exhaust
[1][6] While the distribution of the individual components of raw (untreated) diesel exhaust varies depending on factors like load, engine type, etc., the table below shows a typical composition.
[8][9][10] However, the lean-burning nature of diesel engines and the high temperatures and pressures of the combustion process result in significant production of NOx (gaseous nitrogen oxides), an air pollutant that constitutes a unique challenge with regard to their reduction.
[not verified in body] Even so, diesel exhausts continue to contain an array of inorganic and organic pollutants, in various classes, and in varying concentrations (see below), depending on fuel composition and engine running conditions.
To rapidly reduce particulate matter from heavy-duty diesel engines in California, the California Air Resources Board created the Carl Moyer Memorial Air Quality Standards Attainment Program to provide funding for upgrading engines ahead of emissions regulations.
[40][41][42] Diesel combustion exhaust is a source of atmospheric soot and fine particles, which is a component of the air pollution implicated in human cancer,[43][44] heart and lung damage,[45] and mental functioning.
[56] In 2013, the Environmental Protection Agency (EPA) established the Clean School Bus USA initiative in an effort to unite private and public organizations in curbing student exposures.
[1] The polycyclic aromatic hydrocarbons (PAHs) in the exhaust stimulate nerves in the lungs, causing reflex coughing, wheezing and shortness of breath.
[14][verification needed][1] A study of particulate matter (PM) emissions from transit buses running on ULSD and a mixture of biodiesel and conventional diesel (B20) was reported by Omidvarborna and coworkers, where they concluded that PM emissions appeared lower in cases of mixed diesel/biodiesel use, where they were dependent on the engine model, cold and hot idle modes, and fuel type, and that heavy metals in PM emitted during hot idling were greater than those from cold idling; reasons for PM reduction in biodiesel emissions were suggested to result from the oxygenated structure of biodiesel fuel, as well as arising from changes in technology (including the use of a catalytic converter in this test system).
[60] Exposures have been linked with acute short-term symptoms such as headache, dizziness, light-headedness, nausea, coughing, difficult or labored breathing, tightness of chest, and irritation of the eyes, nose, and throat.
Although one study found no significant evidence that short-term exposure to diesel exhaust results in adverse extrapulmonary effects, effects that are correlated with an increase in cardiovascular disease,[64] a 2011 study in The Lancet concluded that traffic exposure is the single most serious preventable trigger of heart attack in the general public, as the cause of 7.4% of all attacks.
The black smoke consists of carbon compounds that have not burned because of local low temperatures where the fuel is not fully atomized.
Older engines with mechanical injection can have mechanical and hydraulic governor control to alter the timing, and multi-phase electrically controlled glow plugs, that stay on for a period after start-up to ensure clean combustion; the plugs are automatically switched to a lower power to prevent their burning out.
[citation needed] Wärtsilä states that there are two ways of forming smoke, on large diesel engines, one being fuel hitting metal and not having time to burn off.
[68] Experiments in 2013 showed that diesel exhaust impaired bees' ability to detect the scent of oilseed rape flowers.
[69] Emissions from diesel engines contribute to the production of ground-level ozone, which can damage crops, trees, and other vegetation.
Diesel exhaust also contributes to the formation of acid rain, which affects soil, lakes, and streams, and can enter the human food chain via water, produce, meat, and fish.
Mixing in bio ether (or other fuels such as hydrogen)[74][75] into conventional diesel also tends to have a beneficial effect on the pollutants that are emitted.
[citation needed] Selective catalytic reduction (SCR) injects a reductant such as ammonia or urea — the latter aqueous, where it is known as diesel exhaust fluid (DEF) — into the exhaust of a diesel engine to convert nitrogen oxides (NOx) into gaseous nitrogen and water.
[71] Exhaust gas recirculation (EGR), on diesel engines, can be used to achieve a richer fuel to air mixture and a lower peak combustion temperature.
The richer mix is achieved by displacing some of the intake air, but is still lean compared to petrol engines, which approach the stoichiometric ideal.
[citation needed][78] John Deere, the farm equipment manufacturer, is implementing a combined SCR-EGR design, in a 9-liter "inline 6" diesel engine that involves both system types, a PM filter and additional oxidation catalyst technologies.
Recirculated exhaust gas and the compressed air from the turbochargers have separate coolers, and air merges before entering the intake manifold, and all subsystems are controlled by a central engine control unit that optimizes minimization of pollutants released in the exhaust gas.
