# Automotive Engine Components Design Questions and Answers – IC Engine – Thickness of Piston Head

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This set of Automotive Engine Components Design Objective Questions & Answers focuses on “IC Engine – Thickness of Piston Head”.

1. Which are the two types of piston head?
a) Cup and flat type
b) Cup and cone type
c) Cone and bowl type
d) Flat and bowl type

Explanation: There are two types of piston heads- Flat and Cup type, Cup type is concave in cross-section and flat type has a straight surface in cross-section.

2. Piston thickness depends on what criteria?
a) Volume for combustion
b) Gas pressure
c) Aesthetic
d) Products of combustion

Explanation: The selection of the type of piston head depends on two criteria Volume of combustion and the arrangement of valves. Therefore, Volume for combustion is the right answer.

3. Which are the two criteria for calculating the thickness of the piston head?
a) Heat and Strain
b) Strain and stress
c) Fracture and Strength
d) Strength and Heat dissipation

Explanation: A lot of stresses are induced during combustion and it should be able to withstand the heat. Hence, Piston thickness can be calculated based on Strength and Heat dissipation.
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4. Which of the mentioned below is the Grashoff’s formula?
a) th=D$$\sqrt{\frac{3}{16}\frac{P_{max}}{T}}$$
b) th=D$$\sqrt{\frac{3}{16}\frac{P_{max}}{\sigma_b}}$$
c) th=D$$\sqrt{\frac{3}{16}\frac{P_{max}}{BP}}$$
d) th=D$$\sqrt{\frac{3}{16}\frac{P_{max}}{IP}}$$

Explanation: According to Grashoff’s law formula, the thickness of the piston head is given by, th=D$$\sqrt{\frac{3}{16}\frac{P_{max}}{\sigma_b}}$$ Where D is the bore diameter, Pmax is maximum gas pressure and σb is the stress on the cylinder head.

5. Which of the mentioned below is the Held and favary for the thickness of the piston head?
a) th=0.032D+1.5
b) th=0.032D+1.5d
c) th=0.032D+1.5h
d) th=0.032V+1.5D

Explanation: Held and Favary suggested an empirical formula for finding the thickness of the piston head and it is given by th=0.032D+1.5, where D is bore diameter.
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6. Which of the mentioned below is used to calculate the thickness of the piston head based on heat dissipation?
a) th=$$\frac{T}{12.56K(T_c-T_e)}$$ × 103
b) H=$$\frac{H}{12.56K(T_c-T_e)}$$ × 103
c) th=$$\frac{H}{12.56K(T_c-T_e)}$$ × 103
d) th=$$\frac{m}{12.56K(T_c-T_e)}$$ × 103

Explanation: th is the thickness of the piston head, H is the Heat conducted, K is thermal conductivity factor, Tc-Te is the temperature from the center to edge of the piston. When all these are summed, we get th=$$\frac{H}{12.56K(T_c-T_e)}\times 10^3$$.

7. Bore diameter is 150mm, calculate the thickness based on Held and favary formula?
a) 6.3mm
b) 5.7mm
c) 6.3mm2
d) 5.7mm2

Explanation: th=0.032D+1.5
=0.032(150)+1.5
=6.3mm

8. Calculate the amount of heat conducted through piston head, when C=0.05, HCV=47×103 KJ/Kg, m=0.25 Kg/Kw/s, BP=8W?
a) 4500KJ
b) 450KJ
c) 470KJ
d) 4700KJ

Explanation: H=[C×HCV×m×BP] ×103
=[0.05×47×103×0.25×8] ×103
= 4700KJ

9. Calculate the thickness of the piston head based on head dissipation, given H=5398.82, k=46.8, (Tc-Te)=200?
a) 45.92mm
b) 30.85mm
c) 43.3mm
d) 35.98mm

Explanation: th=$$\frac{H}{12.56K(T_c-T_e)}$$ × 103
=$$\frac{5398.82}{12.56×46.8(200)}$$ × 103
= 45.92mm

10. Calculate the thickness of the piston head by strength criteria, given D=250mm, Pmax=3MPa, σb= 43N/mm2.
a) 23.92mm
b) 32.85mm
c) 43.3mm
d) 28.593mm

Explanation: th=D$$\sqrt{\frac{3}{16}\frac{P_{max}}{\sigma_b}}$$
=250$$\sqrt{\frac{3}{16}\frac{3}{43}}$$
= 28.593mm

11. In the formula th=D$$\sqrt{\frac{3}{16}\frac{P_{max}}{\sigma_b}}$$, what is the unit σb?
a) N/mm3
b) KN/mm2
c) N/mm2
d) N/m2

Explanation: Here D is the bore diameter, Pmax is the maximum gas pressure and σb is the stress on the piston. Stress is always forced upon unit area hence N/mm2.

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