I.C. Engine Question. Solve for: Mean Effective Pressure & Volumetric Efficiency

In summary, we have discussed the homework statement given, which includes information about the engine's specifications and performance. The student has already solved for the mechanical and brake thermal efficiencies but is having trouble with calculating the mean effective pressure and volumetric efficiency. Tips have been provided for these calculations, including using the displacement volume and number of power strokes for MEP, and using the actual and theoretical mass of air/fuel mixture for volumetric efficiency.
  • #1
Jr.
1
0
Hello all. I am new to the forums. I am having trouble solving a couple of questions. Maybe some of you can help me out. Thanks in advance!

Homework Statement



Number of cylinders 4
Stroke cycle 4
running at 4400 rpm
Volume compression ratio 7.6:1
Cylinder diameter 78 mm
Stroke 105 mm
Brake Power 38 KW
Indicated Power 47.5 KW
Air consumption 21 kg/kg fuel
Fuel consumption 13.6 kg/l
Each kg of fuel releases 41800 kg of energy
Given R = 0.287 kJ/kgK

Find:
a. Mechanical efficiency
b. The mean effective pressure
c. The volumetric efficiency (refer to 101.3 kpa and 0 C)
d. Brake thermal efficiency


The Attempt at a Solution



I think I solved for both parts a and d. I'll show them below.
I am however having a very hard time with parts b and c. Any help would be great.

a. Mechanical efficiency = (Brake Power / Indicated Power) x 100
= (38000 w / 47500 w) x 100
= 80 %

d. Brake thermal efficiency
Brake Thermal Efficiency = 3600 x Brake Power / Fuel consumption x calorific value
= 3600 x 38 KW / 13.6 kg/l x 41800 kg of energy
= 136800 / 568480
= 0.24 or 24%
 
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  • #2


Hello and welcome to the forums! It looks like you're making good progress on your calculations. Here are some tips to help you with parts b and c:

b. The mean effective pressure (MEP) is a measure of the average pressure that acts on the piston during the power stroke. It is calculated by dividing the indicated power by the displacement volume (volume of the cylinder swept by the piston during one stroke) and the number of power strokes per minute (N/2). In this case, the displacement volume can be calculated by using the cylinder diameter and stroke length. So your equation would look like this:

MEP = (Indicated Power / (Displacement Volume x N/2))

c. Volumetric efficiency is a measure of how well the engine is able to fill the cylinder with air/fuel mixture. It is calculated by dividing the actual mass of air/fuel mixture entering the cylinder by the theoretical mass of air/fuel mixture that would fill the cylinder at atmospheric pressure and temperature. In this case, you will need to use the air consumption and fuel consumption values to calculate the actual mass of air/fuel mixture entering the cylinder. The theoretical mass can be calculated using the ideal gas law (PV = mRT) and the given values for pressure (101.3 kPa) and temperature (0°C). Your equation would look like this:

Volumetric efficiency = (Actual mass of air/fuel mixture / Theoretical mass of air/fuel mixture) x 100

I hope this helps! Let me know if you have any other questions. Good luck with your calculations!
 

Related to I.C. Engine Question. Solve for: Mean Effective Pressure & Volumetric Efficiency

1. What is mean effective pressure (MEP)?

MEP is a measure of the average pressure that acts on the piston during the power stroke of an engine. It is calculated by dividing the total work done during the power stroke by the displacement volume of the engine.

2. How is mean effective pressure related to engine performance?

MEP is directly related to engine performance, as it indicates the efficiency with which the fuel is converted into mechanical work. Higher MEP values indicate better engine performance and efficiency.

3. How is volumetric efficiency (VE) defined?

VE is a measure of the amount of air-fuel mixture that is actually taken into the engine compared to the amount that could potentially enter the engine. It is expressed as a percentage and is affected by factors such as valve timing and air intake restrictions.

4. Why is it important to calculate MEP and VE?

Calculating MEP and VE allows engineers to evaluate the performance of an engine and identify areas for improvement. By optimizing these values, they can improve the efficiency, power, and overall performance of the engine.

5. How can MEP and VE be improved?

MEP and VE can be improved through various methods such as optimizing valve timing, increasing air intake, and reducing friction in the engine. Regular maintenance and tuning also play a crucial role in maintaining and improving these values.

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