# physical science

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Inside the cylinders of a diesel engine, the mixture of fuel and air is compressed to about 1/20 of its original volume. although diesel engines have no spark plugs to ignite this mixture, it ignites anyway because_.
a) increases in temperature decrease molecular motion
b) rapid decrease in volume raise the temperature of the mixture
c) rapid increases in volume raises the temperature of the mixture
d) change in temperature is controlled by the cooling system
e) diesel fuel and air ignite at room temperature

• physical science -

Look at b. Doing work on the system (increasing pressure and decreasing volume) raises the temperature.

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