What is it exactly about an explosion that pushes the piston in an engine?

In summary: Caused by the molecular expansion due to the exothermic reaction?Where is the pressure coming from?In summary, the pressure in a combustion engine is caused by the increase in temperature and number of gas molecules due to the exothermic reaction of gasoline. This increase in pressure is what pushes the piston and creates motion in the engine. The increase in gas molecules is a result of the liquid gasoline changing into gas during the reaction. Overall, the pressure is a result of the electro-magnetic force between the atoms and the repelling force caused by the atoms being too close together.
  • #1
Qaiphyx
92
0
What are all the given aspects of this?

I understand how the reaction happens, but what about it pushes the piston.
 
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  • #2
It's the pressure.
 
  • #3
Qaiphyx said:
... what about it pushes the piston.

An increase of pressure.
 
  • #4
russ_watters said:
It's the pressure.

Caused by the molecular expansion due to the exothermic reaction?

Where is the pressure coming from?
 
  • #5
If you need an equation, the ideal gas law should be a first crude approximation : PV = nRT. The temperature in the cylinder clearly increases as the fuel/air mixture burns, and whatever gas is present has to increase either P, V or both to satisfy the gas law. Since the cylinder is made of solid steel, the only way V is going to increase is by having the piston head move away, bringing along a crankshaft rotation.
 
  • #6
Qaiphyx said:
Caused by the molecular expansion due to the exothermic reaction?

Where is the pressure coming from?

A mole of an ideal gas occupies 22.4 liters at standard temperature and pressure. Gasoline combustion gasses are not ideal but you get the idea.
 
  • #7
oh ok I get it ha, wow, dumb question looking at it now. So basically it has to do with liquid changing into gas. the hydrocarbon gasoline reacts to create carbon dioxide and hydrogen?
 
  • #9
Qaiphyx said:
What are all the given aspects of this?

I understand how the reaction happens, but what about it pushes the piston.

Actually, in my opinion there is the electrical force (or electro-magnetical force) which pushes the piston. The fact that in the explosion the atoms are generating smaller molecules and reorganize, make increase drastically the volume.
 
  • #10
The force is a repelling force caused by the atoms that were too close each other.
 
  • #11
Dr Lots-o'watts said:
If you need an equation, the ideal gas law should be a first crude approximation : PV = nRT. The temperature in the cylinder clearly increases as the fuel/air mixture burns, and whatever gas is present has to increase either P, V or both to satisfy the gas law. Since the cylinder is made of solid steel, the only way V is going to increase is by having the piston head move away, bringing along a crankshaft rotation.
Besides the Temperature increase, there is a very high increase in the 'n' of the equation -number of moles-. The gasoline enters as liquid and changes into gas.
 
  • #12
Sakha said:
Besides the Temperature increase, there is a very high increase in the 'n' of the equation -number of moles-. The gasoline enters as liquid and changes into gas.

The increase is very modest. you get something like

C5H12 + 8 O2 -> 5 CO2 + 8 H20

only 13/8 as much molecules. But air contains only ~20% O2 so the
reaction should be

40 N2 + C5H12 + 8 O2 -> 40 N2 + 5 CO2 + 8 H20

so you get only 53/48 as much molecules, so only an 10% volume increase from the
increased number of gas molecules
 

1. How does an explosion push the piston in an engine?

When fuel and air are ignited in the combustion chamber, a controlled explosion occurs. This explosion creates a rapid expansion of gases, which produce a high amount of pressure. This pressure pushes against the piston, forcing it to move downwards.

2. What causes the explosion in an engine?

The explosion is caused by a controlled ignition of fuel and air in the combustion chamber. This ignition is usually initiated by a spark plug, which ignites the fuel and air mixture, resulting in the explosion.

3. Does the size of the explosion affect the movement of the piston?

Yes, the size of the explosion directly affects the amount of pressure produced and therefore, the force pushing against the piston. A larger explosion will create more pressure, resulting in a stronger push on the piston.

4. Is there a specific timing for the explosion to push the piston?

Yes, the explosion must occur at the right time in order to push the piston effectively. This timing is controlled by the engine's timing mechanism and is crucial for the engine to function properly. If the timing is off, it can result in engine knocking or loss of power.

5. Can an explosion push the piston in two directions?

No, an explosion can only push the piston in one direction. In a four-stroke engine, the explosion occurs on the top of the piston, pushing it downwards. The upward movement of the piston is achieved through other mechanisms such as the crankshaft and connecting rods.

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