Stroke and Bore of a Piston
Date: 05/11/2000 at 01:21:40 From: Frank Walsh Subject: Stroke and bore of a piston A double-acting diesel engine for a ship has eight cylinders with bore 1 m and stroke 1.3 m. The piston-rod diameter is 150 mm. Determine: a) The capacity of the engine. b) The distance between the top face of the piston and the top of the cylinder head in the Top Dead Center (TDC) position, and the distance between the bottom face of the piston and the bottom of the cylinder in the Bottom Dead Center (BDC) position for a compression ratio of 18:1 on both sides of the piston. Assume the compression starts at the extreme stroke positions and that the piston and cylinder heads are flat. Answers: a) 16.15 m^3 b) 76.5 mm, 74.8 mm These are the answers in the book but it doesn't show how to work them out. I'm really stuck! Thanks a million.
Date: 05/11/2000 at 05:45:06 From: Doctor Mitteldorf Subject: Re: Stroke and bore of a piston a) The capacity is the displaced volume, pi*R^2 times the stroke. Multiply by 8 for 8 cylinders. But the "double-acting diesel" gets power from both sides of the piston, so you get to almost double this, but not quite because the piston-rod takes up some volume. The effective area on one side is really pi*R^2, but on the other side it's pi*(R^2-r^2), where r is the piston rod radius = .075 m. b) The minimum distance to the top and the maximum distance to the top must be in the ratio 18 to 1, and their difference must be the stroke, which is 1.3 m. A little algebra gives you the min and max. This gives the 76.5 mm answer. For the other side of the cylinder, where the effective bore area is reduced by the area of the piston-rod, they've reduced this by the ratio (bore-rod)/(total bore area). I can't imagine why they've done this. - Doctor Mitteldorf, The Math Forum http://mathforum.org/dr.math/
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