Design & Selection of Systems for Best Heat Release

P M V SubbaraoProfessor

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….

Space for innovation - infinite in pollutantsSpace for innovation - infinite in pollutants

• Pollutants are a non-equilibriumnon-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 !!!!

Space for innovation - very little in powerSpace 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

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 (200°C) 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.

Area of Power Cycle Vs Supply of Air

17% Extra

80% Extra

20% Less26% Less

Heat Release Rate

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What is the optimal air/fuel ratio?

Industrial Experience : SI Engines

Generalized Theory of Extent of Reaction Possible

Extent of Reaction

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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 p=TS/V, and chemical potential for each conservative species i=-TS/ni, are uniform at equilibrium in absence of external forces.

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Universal Law for Completion of Reaction

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 !!

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End of Reaction for an adiabatic system:

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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(2n+2))

• Olefins

• Aromatics

• Ultimate Analysis

• C : 84 -- 87% ; H : 11 -- 16% ; O : 0.3 -- 1.8% ; N : 0.1 -- 1.5% ; S : 0.1 -- 3%

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

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

Ideal combustion

CXHY + 4.773 (X+Y/4) AIR → P CO2 +Q H2O + R N2

Molecular weight of fuel : YXM fuel 008.1011.12

Homogeneous Mixture model for Air:

22 773.3 1 Air of 773.4 NofkmolesOofkmolekmoles

Molecular weight of Air : 96.28773.4

16.28773.332

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Air-fuel Ratio:1

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96.28773.4

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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

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