Combustion pollutants: predict products and evaluate controls
Introduced| English | Meaning |
|---|---|
| incomplete combustion/ɪŋkəmˈpliːt kəmˈbʌstʃn/ | Burning with insufficient oxygen for complete oxidation, often producing carbon monoxide or carbon as well as other products. |
| particulates/pəˈtɪkjʊleɪts/ | Small solid particles or liquid droplets suspended in air or another fluid. |
| global dimming/ˈɡləʊbl ˈdɪmɪŋ/ | The reduction in sunlight reaching Earth's surface caused by airborne particles and their effects on clouds. |
| acid rain/ˈæsɪd reɪn/ | Precipitation made unusually acidic mainly by atmospheric reactions involving sulfur dioxide and nitrogen oxides. |
Does sulfur-free fuel remove every engine pollutant?
- Removing sulfur targets sulfur dioxide. The air entering a hot engine still contains nitrogen and oxygen, and the fuel may still contain carbon.
- Predict products from all reactant sources and the conditions. Then match each pollutant to its effect and a control that actually targets it.
Start with fuel elements and oxygen supply
- Complete combustion of a pure hydrocarbon with sufficient oxygen produces carbon dioxide and water. Limited oxygen can cause incomplete combustion 不完全燃烧, making carbon monoxide and soot as well as some carbon dioxide/water.
- Pure hydrogen plus oxygen forms water, not carbon dioxide: no carbon atoms enter in those reactants. Fuel sulfur burns to sulfur dioxide; at high temperature, nitrogen and oxygen in air can react to form nitrogen oxides.
| Given fuel or condition | Supported product prediction |
|---|---|
| Pure hydrogen and oxygen | Water; no carbon source |
| Methane, sufficient oxygen | Carbon dioxide and water |
| Methane, limited oxygen | Carbon monoxide and/or soot possible |
| Sulfur impurity burned in air | Sulfur dioxide |
| High-temperature engine, nitrogen-free fuel | Nitrogen oxides still possible from air |
What forms when only pure hydrogen and oxygen react by complete combustion?
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Water forms in the reaction 2H₂ + O₂ → 2H₂O. No carbon atoms are supplied, so these reactants alone cannot make carbon dioxide, carbon monoxide or soot.
Separate toxic gas from particles
- Carbon monoxide is toxic, colourless and odourless. It reduces the blood's ability to transport oxygen; absence of smell cannot establish its absence.
- Particulates 颗粒物 include carbon particles and unburned hydrocarbons. They can harm health and reduce sunlight reaching the surface, causing global dimming 全球变暗. A particle filter does not necessarily remove a gas such as carbon monoxide.
Name the toxic, colourless and odourless carbon-containing gas from incomplete combustion.
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Carbon monoxide reduces blood oxygen transport and cannot be ruled out by smell. Carbon dioxide is a different gas with a different principal role in this topic.
Explain nitrogen and sulfur oxide effects
- Sulfur dioxide and nitrogen oxides cause respiratory problems and acid rain 酸雨. Acid rain can damage aquatic ecosystems, trees and some stone/buildings.
- Nitrogen oxides can form from hot air even when the fuel contains no nitrogen. Sulfur-free fuel can lower sulfur dioxide without removing that source of nitrogen oxides.
Match each pollutant or effect with the correct description.
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CO is distinct from greenhouse CO₂. Particulates reduce incoming sunlight; greenhouse gases affect outgoing surface infrared.
Check a proposed treatment by atom counts
- With the supplied reactants, $CaO+SO_2\rightarrow CaSO_3$: the product is calcium sulfite. Claiming only these reactants make $CaSO_4$ loses oxygen conservation; extra oxygen is needed for sulfate.
- A supplied converter reaction is $2CO+2NO\rightarrow2CO_2+N_2$. Both sides have two carbon, two nitrogen and four oxygen atoms. It removes carbon monoxide and nitrogen monoxide but produces carbon dioxide, so it does not eliminate greenhouse-gas impact.
Better oxygen supply can reduce incomplete-combustion products. It does not remove carbon dioxide from complete carbon-fuel combustion. Always distinguish a reduction in one pollutant from a reduction in every emission.
Balance the catalytic converter reaction
2CO + 2NO → 2CO₂ + N₂: two C, two N and four O on each side. The converter turns two pollutants into carbon dioxide and nitrogen.
In 2CO + 2NO → 2CO₂ + N₂, how many oxygen atoms are represented on each side?
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Reactant oxygen =2×1 from CO +2×1 from NO =4 atoms. Product oxygen =2×2 from CO₂ =4 atoms. N₂ contains no oxygen; the equation conserves atoms.
Evaluate controls with the right radiation model
- Particle filters and sulfur-free fuel can reduce particle and sulfur-dioxide effects. Remaining concerns include carbon dioxide from carbon fuels, carbon monoxide if combustion is incomplete and nitrogen oxides from hot air; measure each relevant emission under comparable conditions.
- Global dimming concerns particles reducing incoming sunlight. Greenhouse warming concerns gases absorbing outgoing surface infrared and emitting in all directions. These are different processes; do not assume dimming safely cancels warming.
“All climate and breathing problems are solved by a particle filter” is false. A filter targets particles; remaining gases have different sources, chemistry and effects.
Fuel elements + oxygen supply + temperature determine possible products. State the pollutant, its effect and a suitable control, and check reaction atom counts before accepting a treatment claim.
A particle filter removes all climate and breathing problems from an engine exhaust.
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It targets particles. CO₂ can remain from carbon-fuel combustion, CO can form if combustion is incomplete, and NOₓ can form from hot air. These gases have different chemistry and effects.
Which two explanations correctly limit an exhaust-control claim?
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Nitrogen can come from air, and gases can pass a particle filter. Sufficient oxygen may lower CO/soot but complete carbon-fuel combustion still makes CO₂.