Problem 2: A gas spring is often used in car trunks to make it easier to lift th

Question

Problem 2: A gas spring is often used in car trunks to make it easier to lift the heavy trunk. It is simply a piston cylinder device that is filled with pressurized gas which exerts an outward force and the magnitude of the force depends on how much the gas spring is compressecd. The fluid is free to move between the top and bottom compartments of the cylinder. Your boss thinks using a liquid instead of a gas will mean a much smaller piston/cylinder. Is this person correct? Try to design one of these using a liquid.

Explanation / Answer

Given that the gas is used in piston to exert some force. But as the boss says, yes the usage of the liquid will give more force on the heavy trunks.
The force due to liquids will be depend on the density.
For example the density of vegetable oil is 0.93gm/cm3 but the density of the argon gas is 0.001449 gm/cm3 which is very very less than that of the liquids.
Hence the boss had the correct opinion.
To design the piston we can consider the hold spring force of 1000N.
Consider the four stroke deisel engine as we are having liquid inside the piston to improve the force. Hence for a 4-stroke engine the diameter of a piston must be 50-90mm for a perfect design.
The liquid we can choose in the piston is a vegetable oil, because of its high density of 0.9gm/cm3 .
The crown thickness is given by T = 0.9 D k (P/f). Usually the thickness of the crown is 10mm for perfect design.
k=1.0 for bowl top liquid pistons.
f = vapour pressure of vegetable oil = 0.0485 bar
Hence T = 0.9 D k (P/f) ,
10*10-3 = 0.9 * 50*10-3*(1.0)* (P/0.0485)
hence the pressure P = 0.0097 bar

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.