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005 basic properties of fuels

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005 basic properties of fuels

  1. 1. LECTURE UNIT NO. 5BASIC PROPERTIES OF FUEL A. Mass density of fuel - at standard temperature (60°F or 15.6°C) - at temperature to other than the standard B. Heating or Calorific Value - Higher Heating Value (HHV) - Lower Heating Value (LHV)A. Mass Density of FuelAt standard temperature (60°F or 15.6°C) ρ = 62.4 lbm/ft3 (English Units) ρ = 1000 kg/m3 (SI Units)Specific Gravity (SG) of fuel can be determined if: a. The °BAUME is given (For English or SI Units) b. The °API (American Petroleum Institute) is givenAt any given temperature toWhere: (For English Units) SGF(corrected @ to) = SGF (@ 60°F) 1 – 0.0004 (to – 60°) (For SI Units) SGF(corrected @ to) = SGF (@ 15.6°C) 1 – 0.0007 (to – 15.6°)B. Heating or Calorific ValuesHigher Heating Value (HHV) or Gross Calorific Value (GCV) - used in External Combustion Power Plant ECPPASME Formula HHV = 41130 + (139.6 * °API), kJ/kgBureau of Standards formula HHV = 51716 – 8793.8 (SGF(@ 15.6°C)) 2, kJ/kg Note: 1 kJ/kg = 0.239 kcal/kg = 0.429 Btu/lbLower Heating Value (LHV) or Net Calorific Value (NCV) - used in Internal Combustion Power Plant ICPP or Diesel Electric Power Plant DEPP LHV = HHV – heat energy required to vaporize the moisture in the products of combustion LHV = HHV - qv
  2. 2. Where: qv = mw hfg , kJ/kgFAnd from the combustion of: H2 + O2 H2O 1mol H2 + ½ mol O2 1 mol H2O (1)(2) kg H2 + (½)(32) kg O2 (1)(9) kg H2OSuch that: mw = 9 (% GH2), kgH2O / kgF Where: % GH2 in fuel will be given in percent by weight (ultimate analysis) % GH2 = 26 – (15 * SGF (@15.6°C)), unit in percent Also, for Internal Combustion Engines (ASME Power Test Code) the latent heat of vaporization of 1 kg (1 lb) of water at a combustion base temperature of 25°C (77°F) hfg = 2442 kJ/kgH2O using steam tableSubstituting: qv = 9 (% GH2) (2442), kJ/kgFTherefore: LHV = HHV – 21980 (% GH2), kJ/kgTYPICAL HEAT BALANCE IN A DIESEL ELECTRIC POWER PLANTIllustration: 1. Percent Cooling Loss . . Solving for the mass of Jacket or Cooling Water . mj = 0.2548 __BP__ , kg/s (tb – ta) Use: %Qj = 32% if not given . mj = ρW Vj . Let ρW = 1000 kg/m3 if not given
  3. 3. 2. Percent Exhaust Loss . . Let: Cpg = 1.0062 kJ/kg-K if not givenTherefore: EC = eB + %Qj + %QE + FRULPROBLEMS: 1. A single acting, four-cylinder, 4-stroke cycle diesel-engine with a bore x stroke of 22 x 28 cm, operating at 300 rpm, consumes 8.2 kg/h of fuel whose heating value is 44000 kJ/kg. The Indicated mean effective pressure is 480 kPa. The load on the brake arm, which is 0.95 m is 113 kg. a. What is the brake thermal efficiency b. What is the mechanical efficiency 2. A single cylinder, single acting, 305 mm x 460 mm, four stroke diesel engine was tested for one hour and the following data were determined: Fuel used -------------------------------------- 7.5 kg Total revolutions ----------------------------- 12120 rpm Jacket water ----------------------------------- 680 kg Rise of temperature of jacket water -------- 28 ºC Area of the indicator Card ----------------------------------- 5.5 sq. cm Length -------------------------------- 7 cm Scale of indicator Spring -------------------------------- 80 MPa / m Torque due to brake load ------------------- 120 kg-m Heating value of fuel ------------------------ 44200 kJ/kg Find: a. Indicated power, Brake power and Mechanical Efficiency b. The percentage of total heat absorbed by the jacket water 3. A 6 cylinder, 4 stroke diesel engine with 75 mm bore and 90 mm stoke when tested in the lab running at 2000 rpm. The brake torque was 16 kg-m when all cylinders were firing but 12.5 kg-m when one of the cylinders was cut off. The engine consumed 12.5 kg/h of fuel with a heating value of 45,120 kJ/kg and 137 kg of air at 15.6 ºC per hour. Determine the following: a. Brake power b. Indicated power c. Mechanical efficiency d. Indicated thermal efficiency e. Indicated mean effective pressure f. Volumetric efficiency of air 4. A six cylinder, four stroke diesel engine with 76mm bore x 89 mm stroke was run in the laboratory at 200 rpm, when it was found that the engine torque was 153.5 N-m with all cylinders firing but 123 N-m when one cylinder was out. The engine consumed 12,2 kg of fuel per hour with a heating value of 54,120 kJ/kg and 252,2 kg of air at 15.6 per hour. Determine the indicated power. a. 32.1 kW c. 23.3 kW b. 38.4 kW d. 48.3 kW 5. A single-acting, four cylinder, 4-stroke cycle diesel engine with a bore to stroke of 21.59 x 27.94 cm, operating at 275 rpm, consumes 8.189 kg/hr of fuel whose heating value is 43,961.4 kJ/kg. The indicated mean effective pressure is 475.7 kPa. The load on the brake arm, which is 93.98 cm is 113.4 kg. What is the brake arm mean effective pressure in kPa? a. 415.20 c. 319.95 b. 24.17 d. 645.53 6. A diesel electric plant in one of the remote provinces in the South utilized diesel fuel with a API of 28º at 15.6 ºC. The plant consumes 680 liters of diesel fuel at 26.6 ºC in 24 hours, while the power generated for the same period amounts to 1980 kW-hrs. Determine a. Density of fuel at 26.6 ºC, kg/l b. Higher heating value, J/g c. Overall thermal efficiency of the plant
  4. 4. 7. A diesel electric plant supplies energy for Meralco. During a 24 hour period, the plant consumed 200 gallons of fuel at 28ºC and produced 3930 kw-hr. Industrial fuel used is 28 ºAPI and was purchased at P5.50 per liter at 15.6ºC. What should be the cost of fuel to produce one kw-hr. a. P1.05 c. P1.069 b. P1.10 d. P1.008. A 2000 kW diesel engine unit uses 1bbl oil per 525 kW-hr produced. Oil is 25 ºAPI. Efficiency of generator is 93%, mechanical efficiency of engine is 80%. What is the thermal efficiency of the engine based on indicated power (%) a. 31.69 c. 39.6 b. 29.47 d. 35.69. A supercharged six-cylinder four-stoke cycle diesel engine of 10.48 cm bore and 12.7 stroke has a compression ratio of 15. When it is tested on a dynamometer with a 53.34 cm arm at 2500 rpm, the scale reads 81.65 kg, 2.86 kg of fuel of 45,822.20 kJ/kg heating value are burned during a 6 min test, and air metered to the cylinders at the rate of 0.182 kg/sec. Find the brake thermal efficiency. a. 0.327 c. 0.307 b. 0.367 d. 0.357

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