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    Question: Discuss whether a petrol engine is more efficient in summer than winter. (from AQA Applied Physics, 2.4 question 4b)

    Not entirely sure on this, but would it be less efficient, an increase in temperature would increase internal energy and pressure which would then make it harder for the piston to initially compress the air, and result in more input power needed to end up with the same output power.

    I was first going to write that it would be more efficient because a higher temperature would be reached quicker in hotter weather for the fuel mixture to ignite. Any help would be appreciated since AQA rarely have answers to explaining questions in every topic.
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    I am also looking for this answer, if anybody could explain it that would be great.
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    (Original post by bubbles95)
    I am also looking for this answer, if anybody could explain it that would be great.
    A petrol engine is more efficient when it is cooler. In simple terms the air behaves like an ideal gas with PV=nRT. If the temperature decreases then there are more molecules of oxygen in the same volume, so the combustion process is more efficient.
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    (Original post by bubbles95)
    I am also looking for this answer, if anybody could explain it that would be great.
    The clue is in the word 'discuss' and inevitably, assumptions must be made.

    There will not be a right or wrong answer for this type of question. It is a general discussion on the parameters of engine efficiency that are affected by air temperature. The question will look for a general understanding of the science and how efficiency is affected by them:

    Combustion efficiency (fuel octane, air pressure, density, fuel temperature, ignition temperature etc.);
    Air moisture content, altitude etc;
    Friction of the moving parts;
    Viscosity and performance of lubricants at different temperatures;
    Exhaust system pressure differential and air flow in the exhaust etc.

    How much each of these factors affects the engines overall efficiency will vary with engine design.
 
 
 
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