Engine Operating Physics

Course Content

• Week 1

  Engine thermodynamic operating

  • History.
  • Thermodynamics basic knowledge: first and second principles, engine efficiency limits. Internal energy, enthalpy, entropy. Ideal gas equation. Laplace equation. Thermodynamic cycles, Beau de Rochas cycle.
  • Compressor isentropic efficiency.

• Engine architecture - Performance and efficiency parameters

  • Geometric parameters: bore, stroke, volumetric ratio, timing diagram.
  • Effective mean pressure: MEP, MFP, MIP.
  • Real cycle, differences with theoretical cycle.
  • Global efficiency: analysis using the 4 efficiencies and setting parameter influence.
  • Fuel/air ratio, volumetric efficiency: calculation of the main engine parameters at stabilized rpm.
  • Adaptation to the vehicle: Willans line.

• Week 2

  Engine mechanics

  • Acyclism
  • Determine the movements of stresses due to gas pressure in the parts.
  • Stresses caused by gas pressure and inertia stresses, impact of the conrod spacing on acyclisms.
  • Acyclism consequences and solutions to limit their impact on the powertrain.
  • Balancing
  • Inertia stresses caused by the rotating weight and the alternative weight.
  • Calculation of rotating and alternating inertia forces.
  • Timing: description of the different valve control types, lift law, valve timing.

• Air loop

  • Link between loading and performances. Fluid mechanics.
  • Air loading.
  • Variable timing: presentation of the main technologies and their applications.
  • Turbocharging: operating, technology, mapping, adaptation process.

• Week 3

  Combustion

  • Air and fuel. Heating value. Ignition equation. Stoichiometric quantity. Equivalence ratio. Specific energy of an air/fuel mixture. Application exercise.
  • Gasoline combustion: flame front propagation, influence of turbulence; influence of the burning rate (HLC) and of the combustion timing (CA 50) on the efficiency; exhaust gas composition depending on the equivalence ratio; calculation of specific emissions, abnormal combustions (knock, pre-ignition, rumble).
  • Diesel combustion: self-inflammation delay, pre-mixture and diffusion flames, formation of pollutants (PM, NOx, HC, CO). Common-rail injection systems; swirl number, EGR.

• Fuels

  • Fuels groups: fuel main required properties for engine operating (heat value, volatility), octane and cetane ratings, Diesel fuel resistance to cold, sulfur content, …
  • Manufacturing process of fuels in a refinery.
  • Biofuels: fuels-ethanol mixtures, vegetable oils, fatty acid esters.

• Exhaust gas after-treatment

  • Structure and operating of oxidation catalysts (Diesel) and trifunctional ones (gasoline). Starting, efficiency. Ageing mechanisms. OSC (Oxygen Storage capacity). Oxygen probe. NOx traps, SCR (Selective Reduction Catalyst). Particles filtration.

• Week 4

  Materials - Mechanical strength

  • Metallurgist basic tools: iron/carbon diagram, TTT, CCT. Characteristics of the alloy steels used in the automotive industry: cast irons, steels, alumina. Rough casting manufacturing processes. Surface treatment. Parts mechanical properties: Young’s modulus, minimum yield, shear rating. Analysis of the engine major parts whose material and manufacturing process have to be chosen.

• Part damage modes

  • Thermal, mechanical and tribologic damages. Goodmann diagram. Stribeck curve.

• Vibro-acoustics/NVH

  • Waves and sound: magnitudes defining a wave, propagation mode (air, solids). NVH vocabulary: dB, dBA, harmonics, resonance, …
  • Signal creation and lock-on, analysis and interpretation (sonogram, tracking).
  • Powertrain noises and vibrations. Attenuation, isolation. Vibration impact on the surrounding parts. Line shafting vibration.