Question 7.1: Two possible overhead valve combustion chambers are being considered - the first has two valves; the second has four valves per cylinder. The diameter of the inlet valve is 23 mm for the first design and 18.5 mm for the second design. If the second design is adopted, show that the total valve perimeter is increased by 60.8%. If the valve lift is restricted to the same fraction of valve diameter, calculate the increase in flow area. What are the additional benefits in using 4 valves per cylinder?

1) The adoption of the second design we can see that the total valve perimeter is increased by 60.8%

2) Increase in flow are : 29%

3) Additional benefits in using 4 valves per cylinder:

a) For the purpose of controlling the combustion process, the inlet valves will give more flexibility

b) There is a larger valve throat areas for the flow of gas

Explanation:

1) Perimeter of the first possible overhead valve combustion chamber with two valves:

P₂ = πd = π * 23 = 72.26mm

Perimeter of the second possible overhead valve combustion chamber with four valves:

P₄ = π2d = π * 18.5 * 2 = 116.24 mm

If second design is adopted, percentage increase = ((P₄ - P₂) / P₂) * 100

= ((116.24 - 72.26) / 72.26) * 100 = 0.6086 * 100 = 60.86%

Therefore, the total valve perimeter is shown to have increased by 60.8%

2) Formula for flow Area (A) = P * L = πkd²

Area of the first possible overhead valve combustion chamber with two valves: A₂ = πkd² = πk (23) ² = 1662k mm²

Area of the first possible overhead valve combustion chamber with four valves: A₄ = πkd² = 2πk (18.5) ² = 2150k mm²

The percentage increase in flow area: ((A₄ - A₂) / A₄) * 100 = ((2150 - 1662) / 2150) * 100 = 29%

3) The additional benefits of using are:

a) For the purpose of controlling the combustion process, the inlet valves will give more flexibility

b) There is a larger valve throat areas for the flow of gas