Vehicular Internal Combustion Engines MECH 454 / MECH 6761 Department of Mechanical and Industrial Engineering Concordia University
Assignment #3 Due: Monday, March 28, 2011 Instructions: Answer all questions; ensure your homework assignment is completed properly. Please clearly write down your name and student ID. List all necessary assumptions and the models you used. 1. An SI engine operating at WOT on a four-stroke ideal Otto cycle has cylinder condition at the start of compression of 38°C and 101.3kPa. Compression ratio is r = 10, and the heat added during combustion is qin = 2.0 MJ/kg. During compression the temperature range is such that a value for the ratio of specific heats γ = 1.4 would be correct. During the combustion and the power stroke the temperature range is such that a value of γ = 1.3 would be correct. Use these values for compression, heat addition and expansion, respectively, when analyzing the cycle. Use a value for specific gas constant of R = 0.287 kJ/kg-°K. Calculate: a. Temperature at all states in cycle b. Pressure at all states in cycle c. Average value of γ which would give the same indicated thermal efficiency value as the analysis in parts (a) and (b). 2. A CI engine operating on the air-standard Diesel cycle has cylinder conditions at the start of compression of 65°C and 130 kPa. Light diesel fuel is used at an equivalence ratio of φ = 0.8 with a combustion efficiency ηc = 0.98 and QHV = 42,500kJ/kg fuel. Compression ratio is r = 19. Assume γ = 1.35 and R = 0.287 kJ/kg-°K, when analyzing the cycle. Calculate: a. Temperature at each state of the cycle b. Pressure at each state of the cycle c. Cutoff ratio d. Indicated thermal efficiency e. Heat lost in exhaust 3. An in-line six-cylinder, 3.3 liter CI engine using light diesel fuel with QHV = 42,500kJ/kg at an air-fuel ratio of AF = 20 operates on an air-standard Dual cycle. Half the fuel can be considered burned at constant volume, and half at constant pressure with combustion efficiency ηc = 100%. Cylinder conditions at the start of compression are 60°C and 101kPa. Compression ratio r = 14:1. Assume γ = 1.35 and R = 0.287 kJ/kg-°K for the analysis, a) calculate: - Temperature and pressure at each state of the cycle - Cutoff and pressure ratios - Indicated thermal efficiency - Heat added during combustion - Net indicated work 1
b) This engine produces 57kW of brake power at 2000RPM. Calculate: - Torque - Mechanical efficiency - Brake mean effective pressure and brake specific fuel consumption 4. Develop a 4-stroke Diesel cycle with the following data: r = 20, γ = 1.3, Ti = 300K, Pi = 101kPa, Pi/Pex = 0.98, M = 29 g/mol and qin = 2090kJ/kgcombustible, i.e. per (mair + mfuel). 5. An SI engine operates on an air-standard four-stroke Otto cycle with turbocharging. Airfuel enters the cylinders at 70 °C and 140 kPa, and heat in by combustion equals qin = 1800 kJ/kg. Compression ratio rc = 8 and exhaust pressure Pex = 100kPa. Calculate: a. Temperature and pressure at each state of the cycle b. Work produced during expansion stroke c. Work of compression stroke d. Net pumping work e. Indicated thermal efficiency 6. A two-stroke cycle SI automobile engine operates on the air-standard cycle, with a compression ratio of 10.5:1. When the intake valve opens at 52° bBDC a supercharger supplies air-fuel to the cylinders at a pressure of Pintake = 128kPa. The exhaust port opens at 70° bBDC. Maximum temperature and pressure in the cycle are Tmax = 2589K and Pmax = 7840kPa. Connecting rod length is l = 24.1cm and crank radius is a = 6.35cm. Calculate: a. Cylinder temperature when exhaust port opens b. Effective compression ratio c. Temperature and pressure at the end of the compression stroke 7. As an engine operates at 3200 RPM, 0.0012 kg of air-fuel-exhaust residual experience tumble in each cylinder. The radius of tumble rotation is 0.90 cm, and tumble ratio is 1.78. Calculate: a. Tangential velocity at edge of tumble rotation [m/sec] b. Rotational kinetic energy of tumble in one cylinder [J] 8. A 150 in3, four-cylinder, four-stroke cycle, high-swirl CI engine is running at 3600RPM. Bore and stroke are related by L = 0.95B. During the compression stroke, the cylinder air has a swirl ratio (SR)2 of 8. Calculate: a. Swirl tangential speed b. Angular velocity of cylinder air c. Swirl ratio (SR)1
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