Adiabatic compression in a diesel engine

In summary, this conversation discusses the process of compressing atmospheric air in a diesel engine and its resulting temperature. It is estimated that the temperature of the compressed air is 300*exp(1.2) K, and it is explained that diesel engines do not require spark plugs due to the high compression causing the air to ignite on its own without the need for external heat production.
  • #1
pentazoid
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Homework Statement



In a diesel engine, atmospheric air is quickly compressed to about 1/20 of its original volume. Estimate the temperature of the air after compression , and explain why a Diesel engine does not require spark plugs.

Homework Equations



f/2*ln(T_f/T_i)=-ln(V_f/V_i)

The Attempt at a Solution



I will assume the temperature inside a diesel engine is room temperature or 300 K.

f=5 since air is a diatomic gas.
T_i=300 K
T_f=?
V_i=V_i
V_f=.05*V_i

2.5*ln(T_f/(300K)=-ln(.05)

ln(T_f/300 K)=3/2.5

In(T_f/300)=1.2

T_f/300=exp(1.2)

T_f=300*exp(1.2)

since this is an adiabatic compression , no heat escapes. I guess spark plugs are not required because they produced heat and heat production isn't required to compress air inside a diesel engine. OR . The compression must be so high that heat is produced and the engine ignites by itself that there is no need for spark plugs.
 
Last edited:
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  • #2
Anybody not understand my question?
 
  • #3
Your answer is a touch off (<1%) due to rounding errors, but the approach is fine.
 

1. What is adiabatic compression in a diesel engine?

Adiabatic compression is the process in which the air-fuel mixture inside a diesel engine's combustion chamber is compressed rapidly and without any heat transfer to or from the surroundings. This results in an increase in temperature and pressure within the chamber, leading to a more efficient combustion process.

2. How does adiabatic compression impact the efficiency of a diesel engine?

The adiabatic compression process is essential for the efficient functioning of a diesel engine. It ensures that the air-fuel mixture is compressed to a high enough pressure and temperature for a strong and efficient combustion reaction to occur.

3. What factors affect the adiabatic compression in a diesel engine?

The main factors that affect adiabatic compression in a diesel engine are the compression ratio, engine speed, and air-fuel ratio. A higher compression ratio, lower engine speed, and proper air-fuel mixture can result in a more efficient adiabatic compression process.

4. What are the potential drawbacks of adiabatic compression in a diesel engine?

One potential drawback of adiabatic compression is the increase in temperature, which can lead to overheating of the engine. This can be managed by using proper cooling systems and materials that can withstand high temperatures.

Another drawback is the possibility of pre-ignition or detonation due to the high pressure and temperature inside the combustion chamber. This can be prevented by using higher octane fuel and optimizing the engine design.

5. How is adiabatic compression different from isothermal compression in a diesel engine?

In adiabatic compression, there is no heat transfer during the compression process, whereas in isothermal compression, the temperature remains constant. Adiabatic compression results in a higher temperature and pressure, leading to a more efficient combustion process compared to isothermal compression. However, isothermal compression is more difficult to achieve in a real-world engine due to heat transfer and friction losses.

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