The Problem of Fire Ironed Out
A. It has been quite a while since man discovered fire. But it is only recently that he has learnt enough chemistry to think of improving it. Take fossil fuels, such as coal and oil, for example. They give off plenty of heat when they burn; unfortunately, they give off plenty of other things as well, including the particles that make up smog and soot, the carbon dioxide responsible for the greenhouse effect and the oxides of nitrogen and sulphur that help to make acid rain. A new fuel additive called Carbonex seems drastically to reduce emissions of particles and of nitrogen oxides. It may thus help to solve half the problems.
B. To understand the solution, take a closer look at the problem. Fossil fuels are mostly made of carbon, which reacts with oxygen to produce carbon dioxide (in the case of coal) or carbon dioxide and water (in the case of petrol, diesel fuel and other refined oils). The combustion of fossil fuels is never quite complete. Small, unbumt particles of fuel always escape, often as black smoke. These particles contain cancer-causing chemicals and are ever more unpopular.
C. There is a standard fix for this. To reduce the problem of incomplete burning, combustion chambers are routinely flooded with about 25% more air than they need to burn their fuel. The idea is to give the flame more oxygen and hence, increase the efficiency of burning. But there is a snag. Dry air is 21% oxygen and 78% nitrogen. Nitrogen, like carbon, reacts with oxygen at high temperature — in this case producing the nitrogen oxides (NOX) that help cause acid rain. When extra air is added to a combustion chamber, emissions of soot and smog go down but NOX emissions go up.
D. Carbonex, invented by an academic chemist, Dr. David Farrar, at the University of Toronto, and developed by Velino Ventures of Toronto, tries to alleviate this. The active ingredient is a hydrocarbon molecule to which an iron atom is bound. The molecule acts as a carrier for the iron, letting it dissolve in organic liquids like oil and petrol. When sprayed into a flame at the same time as a carbon-based fuel, Carbonex makes it bum more efficiently. The result is fewer particles and less need for extra air.
E. It seems to work at two points during burning. If Carbonex is sprayed into a stream of fuel entering a flame in a combustion chamber, it coats the fuel and deposits iron atoms on the surface of the fuel particles. As the particles enter the outer part of the flame, which is cooler than the core, the more volatile components in the fuel vaporize. The faster these vapours leave the fuel, the sooner oxygen can get to the surface of the fuel particle and react with the carbon. Carbonex appears to speed up the exodus. Fuel particles that survive the hot core of the flame contain several large and unhealthy molecules that do not bum well without a fuel additive. Carbonex also seems to lower the temperature at which these compounds bum, allowing them to disintegrate even while the fuel particle is cooling.
F. Iron is not the only substance that can manage this trick; any metal should do. Barium, magnesium, manganese, cobalt, nickel and lead have all been tried as fuel additives, but all are toxic and so in disfavour. Iron was picked for Carbonex because it is non-toxic and very effective even in small doses.
G. Over the past two years, Carbonex has been tested by an independent research group at the Battelle Memorial Institute in Columbus, Ohio. The researchers found that it reduced emissions of particles from diesel engines by 43% and increased the yield of energy from combustion by 1.5-3%. When tested in a light-fuel-oil industrial burner in Geneva, it cut emissions of particles by 67%; added to a coarsely ground bituminous coal it reduced NOX emissions by 25%. In addition to reducing NOX and virtually eliminating black smoke, Carbonex cut the amount of soot left behind in combustion chambers, and so made maintenance cheaper. The fuel additive paid for itself in increased energy efficiency.
H. Although Carbonex could be used in petrol for cars, Dr. Farrar thinks petrol is already refined enough to make it unnecessary. The real need for his invention, he thinks, is in plants that bum coal and less refined oils such as furnace and bunker oil. Farewell to those dark satanic mills.
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Question Focus: List match - the summary lists three harms. The passage lists the same three: smog and soot, the greenhouse effect, and acid rain.
Why this is correct: The passage lists three harms from burning coal and oil. Smog and soot pollute the air, and carbon dioxide adds to the greenhouse effect. The last harm is the oxides of nitrogen and sulphur that help to make acid rain. So the answer is acid rain.
Passage Reference: They give off plenty of heat when they burn; unfortunately, they give off plenty of other things as well, including the particles that make up smog and soot, the carbon dioxide responsible for the greenhouse effect and the oxides of nitrogen and sulphur that help to make acid rain.
Tips: When the summary gives a list, match each item to the list in the text. The gap is the item that is left over.
Why the other options are wrong:
- NOX: Students may pick this because nitrogen oxides are in the same sentence. But the oxides are the cause, and the summary asks for the harm they cause. This is a Causation trap.
- black smoke: Students may pick this because black smoke is pollution too. But the summary has already covered air pollution, and smoke is named in a later paragraph. This is a Wrong section trap.
Key Vocabulary:
- fossil fuels = fuels such as coal and oil
- emissions = gases and particles sent into the air
- oxide = a chemical made with oxygen
Question Focus: Synonym match - 'combustion of fossil fuels is never quite complete' and 'the problem of incomplete burning' = 'the problem of incomplete combustion'.
Passage Reference: There is a standard fix for this. To reduce the problem of incomplete burning, combustion chambers are routinely flooded with about 25% more air than they need to burn their fuel.
Why this is correct: Paragraph B says burning fossil fuels is never quite complete. Paragraph C then talks about how to reduce the problem of incomplete burning. Burning and combustion mean the same thing. So the answer is incomplete.
Tips: Find the part of the text about the problem the scientist wanted to solve. Then choose the box word that describes the same kind of burning.
Why the other options are wrong:
- small: Students may pick this because the text talks about small particles of fuel that do not burn. But 'small' describes the particles, not the burning. This is a Context shift trap.
Key Vocabulary:
- combustion = burning
- alleviate = make a problem less bad
- complete = full, finished
Question Focus: Detail match - Carbonex cuts two kinds of pollution: particles and nitrogen oxides, which the passage shortens to NOX.
Passage Reference: A new fuel additive called Carbonex seems drastically to reduce emissions of particles and of nitrogen oxides.
Why this is correct: Paragraph A says Carbonex seems drastically to reduce emissions of particles and of nitrogen oxides. Paragraph C gives the short name for nitrogen oxides: NOX. The summary pairs particles with the second pollutant. So the answer is NOX.
Tips: Read the words before and after the gap. Decide what kind of word fits, then find the part of the text that says the same thing.
Why the other options are wrong:
- black smoke: Students may pick this because black smoke comes from burning. But black smoke is made of the unburnt particles, so it is the same as the first item. It is not a second pollutant. This is a Partial truth trap.
- acid rain: Students may pick this because NOX helps cause acid rain. But acid rain is a result in the air, not something the fire gives off. This is a Causation trap.
Key Vocabulary:
- additive = something added to a product to change it
- drastically = by a very large amount
- nitrogen oxides = gases that help cause acid rain
Question Focus: Time order - Carbonex is sprayed into the fuel as it enters the flame, so it is mixed in before the fuel burns.
Passage Reference: If Carbonex is sprayed into a stream of fuel entering a flame in a combustion chamber, it coats the fuel and deposits iron atoms on the surface of the fuel particles.
Why this is correct: The passage says Carbonex is sprayed into a stream of fuel entering a flame. Then it coats the fuel. The fuel is still on its way into the flame, so it has not burned yet. Carbonex is mixed in before the fuel burns.
Tips: Read the whole summary sentence. Then find the same step in the text and check that your word matches what the text says happens.
Why the other options are wrong:
- after: Students may pick this because paragraph E also talks about what happens later in the flame. But Carbonex must coat the fuel first, or it cannot help it burn. This is a Sequence trap.
- inside: Students may pick this because the fuel goes inside a chamber. But 'inside it burns' does not make sense here, and the summary needs a time word. This is a Context shift trap.
Key Vocabulary:
- blend = mix together
- coat = cover the outside of something
- deposit = leave something on a surface
Question Focus: Synonym match - 'carried by ___ molecules' = 'a hydrocarbon molecule ... acts as a carrier for the iron'.
Passage Reference: The active ingredient is a hydrocarbon molecule to which an iron atom is bound. The molecule acts as a carrier for the iron, letting it dissolve in organic liquids like oil and petrol.
Why this is correct: The passage says the active ingredient is a hydrocarbon molecule to which an iron atom is bound. Then it says the molecule acts as a carrier for the iron. A carrier carries something. So the iron is carried by hydrocarbon molecules.
Tips: Find the part of the text about the iron atoms. Then check which box word describes the molecules in that part.
Why the other options are wrong:
- small: Students may pick this because atoms and molecules are very small. But the text never calls these molecules small, and 'small' does not name the carrier. This is a Not Given trap.
Key Vocabulary:
- molecule = a very small group of atoms joined together
- carrier = something that carries or moves something else
- dissolve = mix into a liquid and disappear
Question Focus: Number comparison - particles fell by 67% in the industrial burner but only by 43% in diesel engines.
Passage Reference: When tested in a light-fuel-oil industrial burner in Geneva, it cut emissions of particles by 67%; added to a coarsely ground bituminous coal it reduced NOX emissions by 25%.
Why this is correct: The passage gives two results for particles. Diesel engines had 43% fewer particles. But in a light-fuel-oil industrial burner in Geneva, it cut emissions of particles by 67%. 67% is better than 43%, so it works better with industrial burners.
Tips: When the summary says 'better than', find the two numbers in the text and compare them. The bigger cut goes with 'better'.
Why the other options are wrong:
- vehicle: Students may pick this because both gaps are in the same sentence. But the diesel engine result was the weaker one, so it goes in the second gap. This is a Reverse meaning trap.
Key Vocabulary:
- burner = a machine that burns fuel to make heat
- industrial = used in factories and big plants
- yield = the amount produced
Question Focus: Paraphrase - 'diesel engines' are the engines used in vehicles such as trucks and buses.
Passage Reference: The researchers found that it reduced emissions of particles from diesel engines by 43% and increased the yield of energy from combustion by 1.5-3%.
Why this is correct: The passage says it reduced emissions of particles from diesel engines by 43%. Diesel engines are the engines in many vehicles. 43% is a smaller cut than 67%. So Carbonex works less well here. The answer is vehicle.
Tips: Read the words around the gap. Then find the same idea in the text and choose the box word with the same meaning.
Why the other options are wrong:
- industrial: Students may pick this because industrial burners are named in the same set of tests. But that word already fits the first gap, which has the better result. This is a Reverse meaning trap.
Key Vocabulary:
- diesel = a heavy fuel used in many trucks, buses and cars
- vehicle = a car, bus or truck
- independent = not controlled by the company
Question Focus: Collocation - the passage uses 'emissions of particles' and 'NOX emissions'.
Passage Reference: When tested in a light-fuel-oil industrial burner in Geneva, it cut emissions of particles by 67%; added to a coarsely ground bituminous coal it reduced NOX emissions by 25%.
Why this is correct: The test results say Carbonex cut emissions of particles by 67%. With coal it reduced NOX emissions by 25%. Both results use the same word. So the answer is emissions.
Tips: Read the gap with the words before it. Decide what kind of noun you need, then find the same idea in the test results.
Why the other options are wrong:
- input: Students may pick this because the next part of the summary is about energy output. But 'input' means what goes in, and the cuts are in what comes out. This is a Reverse meaning trap.
Key Vocabulary:
- emissions = gases and particles that come out of an engine
- reduce = make smaller
- output = what comes out
Question Focus: Paraphrase - 'cut the amount of soot left behind in combustion chambers' = 'make the inside of engines cleaner'.
Passage Reference: In addition to reducing NOX and virtually eliminating black smoke, Carbonex cut the amount of soot left behind in combustion chambers, and so made maintenance cheaper.
Why this is correct: The passage says Carbonex cut the amount of soot left behind in combustion chambers, and so made maintenance cheaper. The combustion chamber is the part inside the engine where fuel burns. Less soot there makes the inside of engines cleaner.
Tips: Find the part of the text about cleaner engines and lower costs. Then choose the box word that fits the meaning and the grammar.
Why the other options are wrong:
- outside: Students may pick this because black smoke goes outside into the air. But the soot in this sentence stays in the chambers, inside the engine. This is a Reverse meaning trap.
Key Vocabulary:
- soot = black powder left after burning
- combustion chamber = the part of an engine where fuel burns
- maintenance = work to keep a machine in good condition
General Tips:
- Read the whole summary first. Then decide what kind of word each gap needs: a noun, an adjective or a time word.
- There are more words in the box than gaps, so some words are not used.
- The summary usually follows the order of the text, but not always. If you cannot find an answer, look a little earlier in the text too.
- The text may not use the word in the box. Match the meaning, not the spelling.
- When a gap is about 'better' or 'worse', compare the numbers in the text.
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