First midterm exam for Internal Combustion Engines in the Mechanical Engineering degree programme at Politecnico di Milano. The document covers: Internal Combustion Engines, Part B (7 pts, 25 min) Name: ..……………….........……….. A spark ignition, 4-stroke, naturally aspirated engine has the following design values: • 12 cylinders • bore B = 87 mm • stroke S = 82.6 mm At WOT operating condition regime of maximum power,
First midterm exam for Internal Combustion Engines in the Mechanical Engineering degree programme at Politecnico di Milano. The document covers: Internal Combustion Engines, Part B (7 pts, 25 min) Name: ..……………….........……….. A spark ignition, 4-stroke, naturally aspirated engine has the following design values: • 12 cylinders • bore B = 87 mm • stroke S = 82.6 mm At WOT operating condition regime of maximum power,
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Internal Combustion Engines, Part B (7 pts, 25 min) Name: ..……………….........……….. A spark ignition, 4-stroke, naturally aspirated engine has the following design values: • 12 cylinders • bore B = 87 mm • stroke S = 82.6 mm At WOT operating condition regime of maximum power, knowing the following parameters: • engine rotational speed = 6700 rpm • BMEP =1.2 Mpa • LHV = 44 MJ/kg • engine overall efficiency = 32% • ambient conditions: o pair = 101.3 kPa o Tair = 293 K o Rair = 287 J/ kg K • volumetric efficiency = 0.95 • air-fuel stoichiometric ratio = 14.6 • maximum Gulp factor for chocking: Zmax = 0.6 computing: 1. the effective power and effective torque performed by engine 2. the BSFC, fuel and air mass flow rates 3. the air-fuel ratio and equivalence ratio 4. the inlet valve diameter (div) and its maximum lift (hv,max), knowing that div/B = 0.32 and hv,max/div = 0.3 5. the length of the primary intake duct to have the maximum ram effect at open valves 6. the effective area of the two inlet valves at maximum lift and the corresponding Gulp f actor, knowing that the discharge coefficient, at maximum lift, is equal to 0.52 7. the maximum air mass flow rate which can be achieved at 8500 rpm Internal Combustion Engines, Part C (15 pts) Name: ..……………….........……….. 6 cfu exam (45 min): 1) Compare constant pressure and impulse turbocharging systems: working principle, turbine work in the T-s plane, exhaust manifold configurations, advantages and disadvantages of both solutions (7.5 points) 2) Give a definition for the flow coefficient and the swirl number of a cylinder head. Describe how these values are experimentally meas ured, show some pos sible trends as function of the h/dv ratio commenting the relation between the two numbers. (7.5) 10 cfu exam (65 min): A) Compare…
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