Discussion
Arrange the emission control measures in the order they were historically adopted:
1. Positive crankcase ventilation
2. Evaporative canisters and exhaust gas recirculation
3. Oxidation and then three-way catalytic converters with unleaded fuel
4. Diesel particulate filters and urea reduction systems
Select the correct sequence.
Answer: B
Correct answer: 1, 2, 3, 4
The order runs from the simplest measure to the most demanding. Positive crankcase ventilation came first in the early 1960s, routing blow-by back to the intake - cheap and requiring nothing of the fuel.
Evaporative canisters and exhaust gas recirculation followed. Catalytic converters came next and required unleaded fuel to survive. Diesel particulate filters and urea reduction came last, and required sulphur to be removed. Each step needed a fuel change the previous one did not.
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