PROBLEMS 11. What is the tractive power of a locomotive having 19 in. dia. cylinders and 12 in. cranks with 68 in. drive wheels and gauge pressure 160 lbs.? 12. What is the tractive power of a locomotive having 16 in. dia. cylinders with 12 in. cranks, 72 in. drive wheels at 180 lbs. gauge pressure of which 50% is M. E. P.? Also what H. P. can be applied at the draw bar if only 45% of the indicated H. P. of the piston is effective? GASOLENE ENGINES The difficulty of computing the horse power of the gaso lene engine with the formula H. P.= PLAN is to establish the M. E. P. and to keep the piston speed at a uniform rate. The A. L. A. M. (Association of Licensed Automobile Manufacturers) have adopted the following standard formula: Let D= diameter of cylinder in inches. Example. Find the H. P. of a 6 cylinder gasolene engine when the cylinders are 4 in. diameter. The following formulas are used by the mechanical engineers in some of the leading automobile factories as giving close results under certain conditions. This formula is based on 20 cubic inches piston displacement and 600 R. P. M.=1 H. P. P=M. E. P. taken as 87 pounds per square inch. D= diameter of cylinder in inches. N= number of cylinders. All of the formulas given are based on the effective work that a certain size of engine should accomplish and have been found correct in actual practice. PROBLEMS 13. Find the M. E. P. of a gas engine from formula when the dia. of cylinder is 73 in., length of stroke 15 in., making 200 R. P. M., when a brake test of the engine shows 8 H. P. 14. A gas engine does 25 horse power in a test with a 6 in. dia. cylinder, 12 in. stroke, at 600 R. P. M. What is the M. E. P.? 15. A single cylinder motorcycle 2 length of stroke makes 2,500 R. P. M. when M. E. P. is 10 lbs.? in. dia. and 3 in. What is the H. P. 16. If the engine in problem 15 has two cylinders, and dimensions the same, what is the H. P.? cylinder gasolene engine, 5 in. stroke, 4 in. dia., 1,000 R. P. M. 18. Find the H. P. by formula, H. P.= cylinder automobile engine making 750 R. and stroke 4 in. long with M. E. P. 87 lbs. P. M., 4 in. dia. 19. What is the H. P. of a six cylinder automobile gasolene motor if D=43 in. and L= 4 inches. 20. Find the H. P. of a four cylinder gasolene engine 3 in. diameter. 21. What is the H. P. of a six cylinder automobile engine with cylinder 4 in. dia. and length of stroke 44 inches? 22. What is the H. P. of a single cylinder gasolene motor 37 in. dia., 5 in. length of stroke? ENGINE CYLINDERS The size of the cylinder can be found by transposing the 23. Find the H. P. of an engine when the cylinder is 18 in. dia., 26 in. stroke, R. P. M. 200, and M. E. P. of 48 lbs. 24. What is the H. P. of an engine per lb. M. E. P. when piston is 20 in. dia., 36 in. stroke, 175 R. P. M.? 25. A locomotive's cylinders are 16 in. dia., 26 in. stroke, drivers 6 ft. dia. What is the tractive power when boiler pressure is 200 lbs., M. E. P. taken at 50% of boiler pressure, as shown by the steam gauge? 26. The same as problem 25 except boiler pressure is 175 lbs. and M. E. P. taken at 60%. 27. What size cylinder will be required for an engine to develop 250 H. P. when the boiler pressure is 100 lbs., and M. E. P. taken at 50%, 24 in. crank, at 74 R. P. M.? 28. What is the H. P. of an engine per lb. M. E. P. when the piston is 18 in. dia., 30 in. stroke, crank making 112 R. P. M.? 29. Find the size of a cylinder to develop 75 H. P. with 18 in. crank at 115 R. P. M., boiler pressure of 85 lbs. and M. E. P. taken at 45% of the boiler pressure. 30. What dia. of cylinder will be required for a 150 H. P. engine with 24 in. crank, at 85 R. P. M., 80 lbs. boiler pressure if M. E. P. is taken at 40%? 31. Find the size of a cylinder required for a 75 H. P. engine with 16 in. crank at 150 R. P. M. and M. E. P. 37 1⁄2 lbs. 32. Find the length of an engine crank when R. P. M. is 85, dia. of cylinder 16 in., M. E. P. 371⁄2 lbs. when the engine is to develop 62 H. P. 33. What is the length and R. P. M. of a crank for a 50 H. P. engine, when the piston is 12 in. dia., and the length of crank is of the dia. of piston and the M. E. P. is 30 lbs.? 34. Find the H. P. of an engine with a 20 in. crank at 140 R. P. M. with cylinder 20 in. dia. and M. E. P. 49 lbs. 35. Find the H. P. per lb. M. E. P. with an 18 in. crank at 130 R. P. M. and dia. of cylinder 16 inches. INDICATOR DIAGRAM The M. E. P. on the piston of an engine can be found accurately with an indicator. By the mechanism of the instrument the exact pressure on the piston during the entire length of the stroke is obtained in diagram on a A card. A sketch of an indicator Fig 59 B card diagram from one end of cylinder is shown at Fig. 59. To find the M. E. P. from the diagram, the line AB, which is the atmospheric line, is drawn by the pencil of the indicator when the connections with the engine are closed and each side of the piston is open to the atmosphere. Divide the length of a base line as AB into any even number of equal parts, say 10, setting off half a part from ends A and B with 9 parts between and from these points of division erect perpendiculars to the base line AB crossing the diagram at top and bottom; add together the lengths of these lines cut off by the diagram and divide by the number of lines. This will give the mean height, which multiplied by the scale of the spring used to get the diagram will give the M. E. P. The area can also be found by Simpsons' rule, or more accurately by using a planimeter. STEAM BOILER The unit of H. P. for the steam boiler is derived from the number of pounds of water evaporated or converted into steam in one hour. The American Society of Mechanical |