• Internal Combustion = Convert chemical energy to heat energy by burning fuel with air internally
• Boyle's law: P 𝜶 1/V
• Charle's law: V𝜶T
• Combined gas law: PV/T = constant
• Eqn. of continuity (Mass flow) (Alien vs Predator) AV⍴ = Mass flow = constant
• Bernoulli's: Ps + Pdyn = constant
  

• Mechanism for Heat Transfer: Conduction, Convection (via circulation of a fluid), Radiation (via EM waves)
• Newton's laws
• F (Thrust) = m*a (Newton's 2nd)
• Momentum = m*v
• Work (Joules) = F*d
• Power (Watt) = Rate of doing work = W/t
• Torque = F*dist (and depends on angle applied)
• Efficiency = a measure of output c/f input

4 stroke cycle (Otto Cycle) - ICPE

• Induction > Compression > Power > Exhaust
• Top dead centre (TDC), Bottom Dead Centre (BDC)
• Stroke = TDC - BDC (180deg crank rotation)
• Power stroke only one that generates power!
• 2 revs of crank needed for 4 stroke
• Typical Firing seq: 1 -3-4-2

Types

• Rotary: Fixed crankshaft with cylinders rotating around it
• Radial: Fixed cylinders with central rotating crankshaft
• In Line: cylinders in line,⬇️frontal area, cooling problem ∴usually only 4 or 6
• Inverted In Line: Clearance over eng. for good viz. Risk of hydraulicing.
• Horizontally opposed most common - cylin & piston horizontal either side of central crankshaft
  Good viz, smaller than in-line (can fit into nacelle = less drag), No hydraulicing, more even cooling
• V: ⬆️cylinders without ⬆️engine length

Components

• Piston: Crown > Compression Ring (cast iron. Carbon in it = self-lube) > Oil control ring (even spread oil in cylin. > Skirt ( joined to con-rod small end by Gudgeon pin)
  

• Connecting Rod
  

  • Small end joined to piston via Gudgeon pin
  • Big End (2 halves) joined to crankshaft big end bearing/journal
    

• Crankshaft: Steel (case = iron), main journal (oil ways), BE journals. Throw = BE to crankshaft. Throw = 1/2 stroke
  

• Cylinder head + cylin. Barrel. Head has more cooling fins cos of combustion
  

  • Cam shaft: EXAM: Rotates at 1/2 speed of crankshaft. Driven by crankshaft. Controls poppet valves open/close

• Ports: Inlet bigger than exhaust
• Valves (Poppet): Inlet bigger than exhaust
• Valve Gear: Cam lobe > hydr. tappet > push rod >rocker arm > clearance > valve (via stem)
  

  Springs rtns valve to open. Springs wound different direction to stop valve rotating

• Sodium filled exhaust valves for cooling

Calcs

• Swept volume = how much charge can be displaced
• Clearance volume = vol. between TDC and top of cylinder (where piston can’t go)
• $Compression \;Ratio = \frac{Swept\;Volume\;+\; Clearance \;Volume}{Clearance\; Volume}$

• Work = Force * Dist.
• Power (HP) = Work / Time (rate of Work)
• 1hp = 330lbs coal pulled 100ft in 1 min = 33000 lb ft/min
• Friction (Prony) brake - measure hp (tries stop eng from turning)
  

• \( Brake\;HP\;(actual\;HP) = \frac{Force\;*\;Moment\;arm\;*\;2pi\;*RPM}{33000} \)
• \( Brake\;HP\;(actual\;HP) = Torque\;*\;RPM \)
  

• \( Indicated\;HP = \frac{PLANE}{33000} \)
  

  • P = Indicated Mean Effective Pressure (mean press. put on piston in power stroke)
  • L = Length of stroke
  • A = Area of piston crown
  • N = Number of POWER strokes per min
  • E = Number of cylinders
    .
  • P * A = Force
  • L = Distance
  • N * E = rate
    

• BHP = IHP (theoretical HP) - FHP (friction HP)

Factors Affecting Power Output - DME

• Density - affected by Press, Temp, humidity
• Mixture Ratio - becomes richer as density ⬇️correct manually
• Exhaust Back Press. - as press. ⬇️ with alt., scavenging ⬆️ cos less work to get exhaust out
  

⬆️ Volumetric Efficiency - Practical cycle

• Ineffective crank angle - Close to TDC & BDC v. lil linear movement of piston even though angular rotation speed of crankshaft unchanged
  

• Practical 4-stroke cycle - counter Ineffective crank angle
  

  • Inlet Lead and Lag
  • Ignition Advanced
  • Exhaust Lead & Lag
  • Valve Overlap
    .

• SFC ( Lb (or Kg) / BHP/ Hour )
  

  • The mass of fuel used per unit HP produced per unit time