Q=/\U+W energy is a closed system is always conserved, never destroyed or created
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what does a negative Q mean
heat removed from the system
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Isovolumetric
W=O therefore Q=/\U this is a constant volume
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What does a positive W mean
work is done by the system
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what is isothermal
U=O therfore there is no change in temp and the graph will follow the isotherms also W=Q
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Adiabatic?
It hapends so quickly that heat cannot flow therefore Q=O and /\U=W also the graph is steeper then the isotherms as there is an increase in temp BUT there is still a curve
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Step 1 of a petrol engine
****, piston moves down as the inlet valve opens and the exhaust valve closes. Threfore fuel and air are let in.
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Step 2 of a petrol engine
Squeeze: the gas is compressed adiabatically as the piston moves upwards causing the temperature to increase as work is done
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step 3 of a petrol engine
Bang: The gas mixture is ignited by a spark plug providing an input of heat, there is a constant volume and the pressure increases.
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step 4 of a petrol engine
Blow: the increased pressure pushes down the piston as the gas expands adiabatically, this decreases the pressure and temperature.
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step 5 of a petrol engine
the ehaust valve opens and the gas is released, removing some heat, temp and pressure dramatically decrease
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what is the indicated power of an engine
the theoretical capability of the power of the engine
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compare diesel and petrol engines
1) only air is brought in not air and fuel 2) there is no spark plug in a diesel engine there is a fuel injector therefore more comprression 3)diesel engines burn slower with a constant pressure.
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2nd law of thermodynamics
energy can never be transferred without creating some waste heat which flows into a cold sink.
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