ps5 - Massachusetts Institute of Technology DEPARTMENT OF...

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Massachusetts Institute of Technology DEPARTMENT OF OCEAN ENGINEERING 2.611 SHIP POWER and PROPULSION Problem Set #5, Diesel Engine Problems, Due: November 14, 2006 1. A diesel engine designer is interested to know the effect of turbo-charging on mean effective pressure and power. The engine he is considering is a 14 cylinder, 4 stroke diesel engine. The rotational speed is 1200 rpm, mean piston speed of 12 m/s, and stroke to bore ratio of 1.25. The following data is estimated: Note: Review chapter 7 in the text before attempting this problem. Thermodynamic efficiency = 58.5% Mechanical losses = 8 % Heat losses = 9 % Charge pressure = 3.5 bar over pressure in inlet receiver Charging is reasonably effective (93%) Inlet receiver temp 60 Celsius Air excess ratio 1.8 Lower heating value of fuel 42,000 kJ/kg Stoichiometric fuel air ratio = 13:1 Gas constant air/exhaust gas R = .287 kJ/kg a. Calculate engine efficiency, mean effective pressure, and power output. (Note: you can assume that the combustion efficiency is 100%). b. If an engine of the same size was not turbocharged, what would be the efficiency, mean effective pressure and power (keep assumptions unchanged).

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2. The air standard dual-cycle is used to represent the thermodynamic characteristics of a large two-stroke diesel engine. The cylinder volume V 1 =1.0 m 3 ; the compression ratio ; the value of 12 /1 3 . v rVV == 0 0 32 . 8 p rT T = = ; and the cut-off ratio ; the temperature of the air entering the cylinder ; and the pressure 43 . 4 c rTT 0 1 300 TK = ( ) 2 1 1.0 bar 100 / p kN m = . Determine: a. the temperatures , , and in K 2 T 3 T 4 T 5 T b. the mass of the gas, m , in the cylinder in kg c. the heat transfers, 1 H Q , at constant volume; 2 H Q at constant pressure, and at constant volume, in kJ L Q d. the work of the engine per cycle in kJ, and the power per cylinder in kW, when the two-stroke engine operates at 79 rpm The engine is now fitted with a turbocharger and charge cooler. The compressor pressure ratio of the turbocharger is 3.9 and the polytropic efficiency 0.83 PC η = . The effectiveness of the charge cooler ( ) ( ) 1 1 /0 COMP COMP W TT ε =− = . 8 K where the cooling water temperature , the air temperature leaving the compressor and entering the charge cooler is and the temperature of the air leaving the charge cooler and entering the engine cylinder is T . 300 o W T = COMP T Determine: e. the temperature of the air leaving the charge cooler and entering the engine cylinder 1 1 T f. Repeat the tasks a through d for the new situation.
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ps5 - Massachusetts Institute of Technology DEPARTMENT OF...

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