Combustion Physics

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22 févr. 2014 (il y a 3 années et 3 mois)

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Combustion Physics

Nathan Paul 2/16/2012

Physics 575

Energy Consumption


~75% of non
-
renewable energy
consumption is accounted for by
combustion methods.




Within the renewable energy
sector, ~50% is also accounted for
by combustion.





U.S. Energy Information Administration / Annual Energy Review
2010. Pg. 290.
http://www.eia.gov/totalenergy/data/annual/pdf/aer.pdf

1 Municipal solid waste from biogenic sources, landfill gas, sludge waste,
agricultural byproducts,

and other biomass.

2 Fuel ethanol (minus denaturant) and biodiesel consumption, plus losses
and co
-
products

from the production of fuel ethanol and biodiesel.

Combustion Processes:

Furnaces

Industrial Furnaces

Power Plants

Other Types

Explosions


Jet Engines


Rocket Engines


Disco Inferno

Burn, Baby. Burn.

Internal Combustion Engines

What is Combustion?


Reaction That Converts ‘Fuel’ and Oxidant to
Bi
-
Products, Water and Energy.



Example Methane:



INTERNAL ENERGIES AND ENTHALPIES
OF IDEAL GASES

Hess’ Law:

If a reaction at constant
pressure or constant volume is
carried out in stages, the sum
of the amounts of heat
evolved in the separate stages
is equal to the total when the
reaction occurs directly

OR

The heat liberated by a
reaction is independent of the
path of the reaction between
the initial and final states.

Petroleum Combustion Process

In Cylinder Pressure

Lean and Rich


Lean Air to Fuel Ratio:




Rich Air to Fuel Ratio:



Flame Propagation

Flame Propagation


Temperature and Turbulence highly influence the
flame speed.







Transient events and localized combustion reduce
efficiency and create pollutants.

Turbulence

The
turbulent flow
distorts the flame so
that the surface area is
increased
;


The
turbulence may
increase the transport
of heat and active
species
;


The
turbulence may
mix the burned and
unburned gases more
rapidly

Diesel (CI) Cycle

Otto (SI) Cycle

Emissions


Unburned Hydrocarbons


Too Lean; Too Rich; Too Cold; Wall Deposits;
Misfires; Fuel Quality


Carbon Monoxide


Low Gas Temps; Low Oxidants; Short Burn Time


Nitrous Oxides


High Temp Regions;


Particulate Matter


Over fueling; Poor
C
ombustion; Fuel
Q
uality

CO
2

Emissions

Transportation CO2

Diesel Emission Regulations

Other Possibilities?


Bio
-
Fuels




Hydrogen




HCCI


Bio
-
Fuels

Energy and Emissions

Hydrogen

Enthalpy of Combustion for Hydrogen:


2
H
2
(g) + O
2
(g) → 2
H
2
O(l
) + 572

kJ (286

kJ/
mol
)


No CO2 Emissions; Some
NOx

Emisions


Homogeneous Charge Compression
Ignition (HCCI)

PROS:


In
diesel
engines,
soot
is formed in the fuel
rich
regions and
NOx

in
the hot stoichiometric
regions. It
is difficult to
reduce both
NOx

and
soot simultaneously.


The benefit with HCCI
compared to the Spark
Ignition (SI
) engine is
the much higher part
load efficiency.

Cons:


Difficult to control the
ignition timing over a
wide load and speed
range


Higher emission of
unburned
hydrocarbons.

Side Note: Importance of Efficiency

LED
vs

Traditional
Lighting

Zero
-
Energy Buildings

Smart Grid

Efficiency of a SI Engine