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Difficulty: MediumExplicit Main Idea

In heavy-duty turbocharged diesel engines, compressing intake air significantly raises its temperature, which reduces air density and impairs combustion efficiency. Routing this compressed air through an intercooler extracts excess thermal energy before the air reaches the combustion cylinders. By lowering intake air temperature, the intercooler increases air density, delivering a greater mass of oxygen into the cylinders to directly improve combustion efficiency. Although intercoolers add physical weight and require periodic inspection for airflow blockages, their cooling function remains essential for maximizing engine power and fuel economy.

Which of the following statements best expresses the main idea of the passage?

  1. A
    Intercoolers add physical weight and require periodic inspection for airflow blockages.
  2. Intercoolers enhance turbocharged engine performance by cooling intake air to increase its density and combustion efficiency.Answer
  3. C
    Turbocharging is the sole engineering method capable of maximizing fuel economy in modern commercial vehicles.
  4. D
    Compressing intake air is performed primarily to raise operating temperatures before cylinder entry.

Answer

Intercoolers enhance turbocharged engine performance by cooling intake air to increase its density and combustion efficiency.
The correct statement captures the explicit topic sentence of the passage: the essential purpose and function of an intercooler is to cool compressed intake air, thereby increasing its density and oxygen content to boost combustion efficiency and overall performance.

Step-by-Step Solution

1
Read the passage and locate the central thesis or explicit topic sentence.
Identified the explicit statement: 'By lowering intake air temperature, the intercooler increases air density, delivering a greater mass of oxygen into the cylinders to directly improve combustion efficiency.'
An explicit main idea is directly articulated within the text and encapsulates the core function being explained.
2
Distinguish the overarching point from supporting details, secondary qualifications, and extreme scope extrapolations.
Noted that mentions of compression heating, unit weight, and maintenance are supporting context and secondary points serving the main explanation of intercooler function.
Eliminating narrow supporting details and unsupported broad statements isolates the central concept.
3
Select the option that directly matches the explicit main idea without altering scope.
The statement describing how intercoolers enhance performance by cooling air to improve density and combustion efficiency matches the passage precisely.
This captures both the mechanism and the ultimate purpose stated explicitly in the text.

Key Concept

Identifying an Explicit Main Idea in Expository Technical Prose
Estimated Time:1m 0s
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Explicit Main Idea

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