Thermodynamics and Compression Ignition Pressure and Temp Problem?

In summary, a model diesel C.I engine has a volumetric compression ratio of 18:1 and a cut*off ratio of 1.5:1. To determine the pressure and temperature at each point in the cycle, we can use the equations p1V1/T1=p2V2/T2 and p1V1^n=p2V2^n. Using the ideal gas relation pv=RT, we can calculate the values for the different stages of the Diesel cycle. The compression ratio is equal to v1/v2 and the cut-off ratio is equal to v3/v2.
  • #1
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Homework Statement



A model diesel C.I engine has a volumetric compression ratio of 18:1 and a cut*off ratio of 1.5:1?
The engine has a volumetric compression ratio of 18:1 and a cut*off ratio of
1.5:1.

If p1 = 1 bar and T1 = 27°C, determine the pressure and temperature
at each point in the cycle.

How would I do this?

Homework Equations



p1V1/T1=p2V2/T2

p1V1^n=p2V2^n

The Attempt at a Solution



T2 = 18^(1.4-1)*300 = 954K

No idea how to work out the pressures. I know it is isentropic so p1V1^n=p2V2^n
 
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  • #2
The Diesel cycle consists of the following:
1. adiabatic (isentropic) compression from p1 v1 to p2 v2
2. isobaric expansion from p2 v2 to p2 v3
3. adiabatic expansion from p2 v3 to p4 v1
4. isochoric (constant-volume) decompression from p4 v1 to p1 v1.

Just use the ideal gas relation pv = RT to get all the above p's and v's.
Realize that compression ratio = v1/v2 and cutoff ratio = v3/v2.
 

1. What is thermodynamics and why is it important to understand in relation to compression ignition?

Thermodynamics is the study of how energy is converted between different forms, such as heat, work, and internal energy. In the context of compression ignition engines, thermodynamics is crucial as it helps us understand how the fuel-air mixture is compressed and ignited, and how this process ultimately converts chemical energy into mechanical work.

2. What factors affect compression ignition pressure and temperature?

The main factors that affect compression ignition pressure and temperature include the compression ratio of the engine, the properties of the fuel being used, and the engine speed. Additionally, factors such as the air-fuel ratio, ignition timing, and engine load can also impact the pressure and temperature during the compression ignition process.

3. How do compression ratio and engine speed affect compression ignition pressure and temperature?

The compression ratio of an engine is the ratio of the volume of the combustion chamber when the piston is at the bottom of its stroke to the volume when the piston is at the top of its stroke. A higher compression ratio results in a higher pressure and temperature during compression ignition, as the air-fuel mixture is compressed to a smaller volume. Similarly, a higher engine speed means that the piston is moving faster, resulting in a faster compression process and therefore higher pressure and temperature.

4. What is the ideal compression ratio for efficient compression ignition?

The ideal compression ratio for efficient compression ignition will depend on the specific engine design and the type of fuel being used. In general, a higher compression ratio can result in more efficient combustion and better fuel economy, but it also increases the risk of engine knocking. It is important to find the right balance for a specific engine to achieve optimal performance.

5. How can engine designers optimize compression ignition pressure and temperature?

Engine designers can optimize compression ignition pressure and temperature by carefully choosing the compression ratio and other engine parameters such as ignition timing and air-fuel ratio. They can also use advanced technologies such as direct injection and variable valve timing to improve the combustion process and achieve better compression ignition performance.

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