REAL AGRICULTURAL ENGINEERING EXAM WITH SOLUTIONS 2023

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PART 1 1. A dynamometer shows that the average pull required for a certain machine is 20KN. If the tractor travels at 5kph, what is the power developed? Given: F = 20KN, S = 5kph Required: power de... veloped Solution: P=(20,000 N x 5000ms)3600sec= 27.78 kW 2. A dynamometer test shows that an engine delivers an average output of 50hp at a speed of 1500rpm. What torque is exerted? Given: P = 50hp, N = 1500rpm Required: torque Solution: P = 2πTN; T =P2πN= (50hp) (76.2kg.m/s) (9.8N)2π(1500/60min) = 237.7 N-m 3. What is the piston displacement in cubic inches of a 4.5 in by 6 in cylinder engine? Given: D = 4.5 in, H = 6 in Solution: PD = πD2L4= π(4.5in)2(6in)4= 95.42 in3 4. An engine with 60mm x 60mm engine runs 1500rpm. What is the maximum piston speed inside the cylinder? Given: Engine dimension: 60mm x 60mm Solution: V = πDN=π(0.06m) (1500)60 sec=4.71 m/s 5. A tractor pulls a 2500kg of loads at a speed of 5kph on a flat ground. If the coefficient of rolling resistance is 0.25, what is the drawbar power that the tractor generates? Given: F = 2500kg, RS = 0.25, V = 5kph Solution: DHP = FV = (2500kg) (5000m)3600 sec=3472.20kg.ms76.2kg.ms=45.57hp x 0.25=11.40hp 6. A gasoline engine was tested for continuous 5hrs of operation. It consumed a total of 9 liters of fuels and developed a constant power of 3 kW. If the fuel contains 34,636MJ/m3, what is the approximate thermal efficiency? Solution: ηth = WQ= 3kW17.318kW= 17.32% Q= (9 liters/5hrs) (34636MJ/m3)(1000 lit) (3600 sec)= 17.318 KW 7. A pony brake test of an engine shows that the crankshaft rotates at 1530 rpm. The brake arm length is 0.75m and the net load on the scales is 20kgf. What if the power developed? Given: N = 1530 rpm, a = 0.75 m, F = 20kgf Solution: P = 2πFNa= 2π(20kgf)(1530rpm)(0.75m)60sec= (2403.3kgf.ms)(9.8Nkgf) =23552.52 N−ms or 23552.52Js or 23.55 kW = 23.55 kW x 1.34hp = 31.56hp 8. Determine that brake thermal efficiency of an engine if its mechanical efficiency if 87% and the indicated thermal efficiency is 45% Given: ME = 87%, ITE = 45% Solution: BTE = 0.87 x 0.45 x 100= 39% 9. What is the rim speed of a 9 in diameter flywheel turning at 1800 rpm? Given: D = 9 in, N – 1800rpm Solution: V = πDN = π(9in12in)(1800rpm)=4241.1ft/min 10. What is the speed ratio of the transmission unit to give the tractor a speed of 3.5kph? The engine speed is 2200 rpm and a rear wheel diameter of 55 cm. Given: S = 3.5kph, N = 2200 rpm, D = 55cm Solution: V = πDN = π(0.55m)(2200rpm)(60sec1000)= 228.08kph SR =228.08kph3.5kph=65.2:1 11. What is the efficiency of the transmission if the input speed is 2000 rpm, input torque of 220lb.ft and an output of torque at the final drive is 19lb-ft at 17,000rpm? Solution: Efficiency =(17,000rpm)(19lb−ft)(2000rpm)(220lb−ft)= 73.4% 12. How much power is actually received by a pump run by a 7.5hp engine running at 2800 rpm? If a 3% slip is allowed between bolt and pulley. Solution: P = 7.5hp – (7.5hp x 0.03)=7.3hp 13. Determine the brake thermal efficiency of a 5hp gasoline engine consuming 2 liters of fuel in an hour? Solution: BTE= 5 hp(2lithr)(34330MJm3)(1m31000lit)(1hr3600sec)= 5hp26hp=19% 14. A gasoline engine has a thermal efficiency of 23%. Test shows it uses 1.2 liter of premium gasoline fuel per hour. What is the approximate power it generates? Solution: P = (1.2literhr.) (34330MJm3)(1000lit) (3600sec) =11443.30Jsx 0.23= 2.632 kW [Show More]

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