INTERNAL COMBUSTION ENGINE PERFORMANCE PARAMETERS

1. ENGINE
PERFORMANCE
PARAMETRS

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)