Design

1
Design Selection of Systems for Best Heat
Release

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Supply of Sufficient Oxygen for Digestion
.. Sizing of Hard Ware As per the Need. To
Understand the Complex Relation between Fuel
Combustion Mode.
2
Space for innovation - infinite in pollutants

• Pollutants are a non-equilibrium effect
• Burn Fuel O2 N2 H2O CO2 N2 CO
  UHC NO
• On A Faster Expansion CO UHC NO frozen at
  high level
• With slow expansion, no heat loss CO UHC NO
  H2O CO2 N2
• But how to slow the expansion and eliminate heat
  loss?
• Worst problems cold start, transients, old or
  out-of-tune vehicles .
• 90 of pollution generated by 10 of vehicles
  !!!!

3
Space for innovation - very little in power

• IC engines are air processors
• Fuel takes up little space
• Air flow power
• Limitation on air flow due to
• Choked flow past intake valves
• Friction loss, mechanical strength - limits RPM
• Slow burn

4
The Ideal Artifical Horse

• 1824 Sadi Carnot, who founded the science of
  thermodynamics, identified several fundamental
  ideas that would be incorporated in later
  internal combustion engines
• 1. He noted that air compressed by a ratio of 15
  to 1 would be hot enough (200C) to ignite dry
  wood.
• 2. He recommended compressing the air before
  combustion. Fuel could then be added by "an
  easily invented injector".
• 3. Carnot realized that the cylinder walls would
  require cooling to permit continuous operation.
  Later, Diesel thought he could avoid this, but
  found out the hard way.
• 4. He noted that usable heat would be available
  in the exhaust, and recommended passing it under
  a water boiler.

5
Area of Power Cycle Vs Supply of Air
17 Extra
80 Extra
20 Less
26 Less
6
Heat Release Rate
What is the optimal air/fuel ratio?
7
Industrial Experience SI Engines
8
Generalized Theory of Extent of Reaction Possible
P1,T1
P2,T2
P3,T3
Entropy of Universe
Extent of Reaction
9
EQUILIBRIUM

• An isolated mixture with conservative amounts of
  substance ni tends to reach an equilibrium state
  defined by its entropy S(U,V,ni) being a maximum.
• In absence of external fields, that the
  temperature T?U/?S, pressure pT?S/?V, and
  chemical potential for each conservative species
  ?i-T?S/?ni, are uniform at equilibrium in
  absence of external forces.

10
Universal Law for Completion of Reaction
End of Reaction for an adiabatic system
For every fuel, a designer should know all
possible reactants !!! Some products will
influence the efficiency of reaction. Few other
may not influence the efficiency of reaction but
severely affect the environment. The optimal
parameters for efficient reaction may not be
optimal for safe reaction !!
11
Hydro carbon Chemistry Classification of Crude
Oils

• Paraffin based crudes (a waxy residue)
• Asphalt based crudes (an asphalt type residue)
• Mixed type-based crudes
  ( a combination residue)
• Components of Crude Oils.
• Paraffins (CnH(2n2))
• Olefins
• Aromatics
• Ultimate Analysis
• C 84 -- 87 H 11 -- 16 O 0.3 -- 1.8
  N 0.1 -- 1.5 S 0.1 -- 3

12
Fuel Model

• Ultimate Analysis Gravimetric
• C 84 -- 87 H 11 -- 16 O 0.3 -- 1.8
  N 0.1 -- 1.5 S 0.1 -- 3
• Percentage of carbon x --- Number of moles, X
  x/12
• Percentage of hydrogen y --- Number of atomic
  moles, Y y/1
• Percentage of oxygen k --- Number of atomic
  moles, K k/16
• Percentage of sulfur z Number of atomic moles,
  Z z/32
• Equivalent chemical formula CXHYSZOK
• Equivalent Molecular weight 100 gms.
• Liquid and gaseous fuels generally have very
  little sulfur, oxygen and moisture.
• Generally popular chemical formulae CXHY

13
Fuel Model

• Ultimate Analysis of fuel Gravimetric
• C 84 -- 87 H 11 -- 16 O 0.3 -- 1.8
  N 0.1 -- 1.5 S 0.1 -- 3
• Percentage of carbon x --- Number of moles, X
  x/12
• Percentage of hydrogen y --- Number of atomic
  moles, Y y/1
• Percentage of oxygen k --- Number of atomic
  moles, K k/16
• Percentage of sulfur z Number of atomic moles,
  Z z/32
• Equivalent chemical formula CXHYSZOK
• Equivalent Molecular weight 100 gms.
• Liquid and gaseous fuels generally have very
  little sulfur, oxygen and moisture.
• Generally popular chemical formulae CXHY

14
Ideal combustion

• CXHY 4.773 (XY/4) AIR ? P CO2 Q H2O R N2

Molecular weight of fuel
Homogeneous Mixture model for Air
Molecular weight of Air
Air-fuel Ratio
15
Equivalence Ratio

• The equivalence ratio of a system is defined as
  the ratio as the ratio of the actual fuel/air
  ratio to the stoichiometric ratio.
• Mathematically