INTERNAL COMBUSTION ENGINE PERFORMANCE PARAMETERS
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The document discusses key performance parameters of engines including thermal efficiencies, power outputs, specific fuel consumption, air-fuel ratios, and volumetric efficiency. It defines indicated thermal efficiency as the ratio of indicated power to fuel energy, and brake thermal efficiency as the ratio of brake power to fuel energy. Mechanical efficiency is the ratio of brake power to indicated power. Volumetric efficiency is the ratio of actual to theoretical air intake. Mean effective pressures and specific power input are also discussed.
INTERNAL COMBUSTION ENGINE PERFORMANCE PARAMETERS
- 2. Energy Flow in engine
- 3. IndicatedThermal Efficiency ■ ƞ𝒊𝒕𝒉 = 𝑰𝒏𝒅𝒊𝒂𝒄𝒕𝒆𝒅 𝑷𝒐𝒘𝒆𝒓 (𝑲𝑾) 𝑬𝒏𝒆𝒓𝒈𝒚 𝒐𝒇 𝒇𝒖𝒆𝒍 𝒑𝒆𝒓 𝒔𝒆𝒄𝒐𝒏𝒅 ■ Indicated Power (IP) – power produced in cylinder ■ IP (KW) = 𝑷 𝒊𝒎𝒆𝒑×𝑳×𝑨×𝒏×𝒌 𝟔𝟎×𝟏𝟎𝟎𝟎 n = 𝑵 𝟐 k= no. of cylinders ■ 𝑬𝒏𝒆𝒓𝒈𝒚 𝒐𝒇 𝒇𝒖𝒆𝒍 𝒑𝒆𝒓 𝒔𝒆𝒄𝒐𝒏𝒅 = 𝒎 × 𝑪𝒂𝒍𝒐𝒓𝒊𝒇𝒊𝒄 𝒗𝒂𝒍𝒖𝒆 𝒐𝒇 𝒇𝒖𝒆𝒍 𝒊𝒏 𝑲𝑱/𝑲𝒈
- 4. BrakeThermal Efficiency ■ ƞ𝑖𝑡ℎ = 𝑩𝒓𝒂𝒌𝒆 𝑷𝒐𝒘𝒆𝒓 (𝑲𝑾) 𝑬𝒏𝒆𝒓𝒈𝒚 𝒐𝒇 𝒇𝒖𝒆𝒍 𝒑𝒆𝒓 𝒔𝒆𝒄𝒐𝒏𝒅 ■ Brake Power (BP) - power available at crankshaft ■ IP (KW) = 𝑃 𝑏𝑚𝑒𝑝×𝐿×𝐴×𝑛×𝑘 60×1000 n = 𝑁 2 k= no. of cylinders ■ BP (KW) = 2𝜋𝑁𝑇 60×1000 ■ 𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝑓𝑢𝑒𝑙 𝑝𝑒𝑟 𝑠𝑒𝑐𝑜𝑛𝑑 = 𝑚 × 𝐶𝑎𝑙𝑜𝑟𝑖𝑓𝑖𝑐 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑓𝑢𝑒𝑙 𝑖𝑛 𝐾𝐽/𝐾𝑔
- 5. Mechanical efficiency ■ƞ 𝑚𝑒𝑐ℎ = 𝑩𝒓𝒂𝒌𝒆 𝑷𝒐𝒘𝒆𝒓 (𝑲𝑾) 𝑰𝒏𝒅𝒊𝒄𝒂𝒕𝒆𝒅 𝑷𝒐𝒘𝒆𝒓 (𝑲𝑾) = ■ Friction Power (FP) = Indicated power – Brake power
- 6. Volumetric Efficiency ■ ƞ 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 = 𝐴𝑐𝑡𝑢𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑎𝑖𝑟 𝑖𝑛𝑡𝑜 𝑖𝑛𝑡𝑎𝑘𝑒 𝑠𝑦𝑠𝑡𝑒𝑚 𝑉𝑜𝑙𝑢𝑚𝑒 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑑 ×( 𝑁 2 ) ■ 𝐴𝑐𝑡𝑢𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑎𝑖𝑟 𝑖𝑛𝑡𝑜 𝑖𝑛𝑡𝑎𝑘𝑒 𝑠𝑦𝑠𝑡𝑒𝑚 = 𝑚 ρ ■ 𝑚 = mass flow rate in kg/sec ■ ρ = Density of air
- 7. Mean effective pressure ■ Average pressure inside cylinder based on measured or calculated power output. ■ Imep – indicated mean effective pressure ■ Bmep – brake mean effective pressure ■ Used for comparing different engines
- 8. Mean speed of piston ■ 𝑉𝑝 = Piston Speed (m/sec) ■ 𝑉𝑝 = 2× 𝐿 × 𝑁 ■ L= Length of stroke ■ N= revolution per second ■ 8 to 15 m/sec
- 9. Specific power input ■ SPI = 𝐵𝑟𝑎𝑘𝑒 𝑃𝑜𝑤𝑒𝑟 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑃𝐼𝑠𝑡𝑜𝑛 ■ SPI = constant× 𝑏𝑚𝑒𝑝 × 𝑉𝑃 ■ Effect of bmep and piston speed
- 10. Specific fuel consumption ■ Fuel characteristics of engine – KG/KWH ■ Sfc = 𝑭𝒖𝒆𝒍 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒑𝒆𝒓 𝒖𝒏𝒊𝒕 𝒕𝒊𝒎𝒆 𝑷𝒐𝒘𝒆𝒓 = 𝒌𝒈/𝒉𝒓 𝑲𝑾 = 𝒌𝒈 𝑲𝑾𝑯 ■ Depending upon power ■ Bsfc – brake specific fuel consumption ■ Isfc – Indicated specific fuel consumption ■ It is inversely proportional to thermal efficiency
- 11. Air- fuel ratio ■ Chemical correct or Stoichiometric air fuel ratio (15:1) ■ Just enough air for complete combustion of fuel ■ Equivalence ratio = φ = 𝐴𝑐𝑡𝑢𝑎𝑙 𝑎𝑖𝑟 𝑓𝑢𝑒𝑙 𝑟𝑎𝑡𝑖𝑜 𝑆𝑡𝑖𝑜𝑐ℎ𝑖𝑜𝑚𝑒𝑡𝑟𝑖𝑐 𝑎𝑖𝑟 𝑓𝑢𝑒𝑙 𝑟𝑎𝑡𝑖𝑜 ■ φ < 1 --- Lean mixture ■ φ > 1 --- Rich mixture ■ SI (Petrol) - 11:1 to 20:1 ■ CI (Diesel) - 18:1 to 80:1
- 12. Calorific value ■ Thermal energy released per unit quantity of fuel. ■ HCV-Water vapors present are condensed ■ LCV- Water vapors present are not condensed
- 13. Inlet value Mach index ■ 𝑢𝑖 = 𝐴 𝑝×𝑉𝑝 𝐶 𝑖 ×𝐴 𝑖 𝑢 𝑖 𝛼 = Z = 𝐴 𝑝×𝑉𝑝 𝐶 𝑖 ×𝐴 𝑖 × 𝛼 ■ 𝑢𝑖 = gas velocity at inlet value at smallest flow area ■ 𝐴 𝑝 = Area of Piston ■ 𝑉𝑝 =Velocity of piston ■ 𝐶𝑖 = Inlet value flow coefficient ■ 𝐴𝑖 = Nominal intake value opening area ■ 𝛼 = sonic velocity ■ Z = Mach number
- 14. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 Volumetricefficiency InletValue Mach Number (Z)