# How Do You Calculate Volumetric Efficiency in a Twin Cylinder Air Compressor?

• budak-budak
In summary, the task is to design a single acting twin cylinder air compressor that can deliver 17.2kg/min of compressed air at 7.2 bar. The intake pressure is 1 bar and the temperature is 15oC, with a compressor speed of 300 rpm. The clearance volume is 5% of the swept volume, and the stroke to bore ratio is 1.2 with an assumed value of n=1.3. To find the bore and stroke of the cylinder, the density of air inside the compression chamber must first be calculated using the ideal gas law. The polytropic formula can then be applied to determine the final conditions of the air, including the discharge temperature. By calculating the percentage
budak-budak

## Homework Statement

It is required to design a single acting twin cylinder air compressor to deliver 17.2kg/min of compressed air at 7.2 bar. The intake pressure and temperature are 1 bar and 15oC respectively. Compressor speed is to be 300 rpm. Take clearance volume as 5% of the swept volume. The stroke to bore ratio is 1.2 and assume n=1.3. Find the bore and stroke of the cylinder.

## Homework Equations

Vc/Vs = 0.005

PV=mRT

volumetric efficiency = Va/Vs = (V1 - V4)/(V1 - V3)

## The Attempt at a Solution

Firstly i try to find volumetric efficiency. However, V1, V3 and V4 still did not know.. so how...

Last edited:
Hi budak - welcome to the board. Just a suggestion, but a better title to your thread would help.
1. Calculate the density of air inside the compression chamber just prior to the start of compression using the ideal gas law. Note that the total mass of air in the cylinder is simply density times volume.
rho = ?

2. Do you know how to apply the polytropic formula? Note the exponent, n is given, so you should be able to find the final conditions (ie: final state) of the air given the inlet pressure, inlet temperature and discharge pressure. Can you find the discharge temperature? If so, you have the final state.
T(final) = ?

3. If you have the final state, you can apply ideal gas law to find density for the final state. Since you've been given the clearance volume as a percentage of total volume, you should also be able to calculate the percentage of air in the clearance volume that stays inside the chamber after compression. This percentage of mass does not exit the compressor. The rest of the air leaves the compressor, so this is the percentage of air which is displaced by each stroke. Now you have (% displaced).
% displaced = ?

4. On the intake stroke, just assume this small mass of air re-expands back to the inlet conditions, so you can neglect this small mass of air after you do the compression stroke calculation in 3 above.

5. Calculate the mass of air that must be displaced with each stroke in order to get the total throughput.
Mass per stroke needed = ?

6. Find total displacement of cylinder from % displaced and mass per stroke as found above.
Volume of cyl = ?

7. Find bore and stroke from stroke to bore ratio and volume calculated in 6.
Bore = ?
Stroke = ?

hope that helps.

## What is volumetric efficiency?

Volumetric efficiency is a measure of the amount of air or fuel-air mixture that is actually drawn into an engine's cylinders during the intake stroke compared to the theoretical maximum amount that could be drawn in. It is expressed as a percentage.

## Why is volumetric efficiency important?

Volumetric efficiency is important because it directly affects an engine's power and performance. The higher the volumetric efficiency, the more air and fuel can be burned, resulting in increased power and torque.

## How is volumetric efficiency calculated?

Volumetric efficiency is calculated by dividing the actual air or fuel-air mixture mass that is drawn into the cylinder by the theoretical maximum mass that could be drawn in. This value is then multiplied by 100 to get a percentage.

## What factors affect volumetric efficiency?

There are several factors that can affect an engine's volumetric efficiency, including the engine's design and size, the efficiency of the intake and exhaust systems, the quality of the fuel and air filters, and the condition and tuning of the engine.

## How can volumetric efficiency be improved?

Volumetric efficiency can be improved by optimizing the engine's design and size, upgrading the intake and exhaust systems, using high-quality fuel and air filters, and properly tuning the engine. Regular maintenance, such as cleaning the air filter and replacing worn spark plugs, can also help improve volumetric efficiency.

• Engineering and Comp Sci Homework Help
Replies
7
Views
5K
• Engineering and Comp Sci Homework Help
Replies
1
Views
2K
• Mechanical Engineering
Replies
5
Views
3K
• Engineering and Comp Sci Homework Help
Replies
21
Views
7K