Chapter 1 - Gaseous Fuels: Their Physical Properties and Characteristics Flashcards
9 Reasons to use gaseous fuels
Transported easily Stored at low pressures Operate with minimum excess air Heat output adjusted visually Environmentally friendly Easy to ignite Burned in low-cost devices Handling procedures known Safety procedures known and easy to implement
Three main types of gaseous fuels in the USA
NG, LP, Butane
Heat Content definition/units
BTU/ft^3 - Heat/energy contained per cubic foot of gas
Specific Gravity definition/units
Ratio of density of a substance to the density of a standard (for us the standard is air)
What is ultimate CO2?
It is the amount of CO2 produced from perfect combustion for a certain gas
Explain the air/fuel stoichiometric mixture ratio
It is a ratio that shows what the amount of air/fuel would be required for perfect combustion
It is based off of theoretical equations
Define BTU
amount of heat required to raise one pound of water one degree F
Roughly a flame from a kitchen match is the equivalent of 1BTU
Why are BTUs and knowing BTUs important?
It’s a measure of how much heat a gas burner/appliance is producing
Why are combustion limits important?
Tells you the limits by percentage how much air/fuel you need for the fuel to burn
What is self-ignition temperature?
The temperature in which the gas will “Spontaneously combust” solely because of the high temperature it is at
Why is specific gravity an important safety feature?
If the gas is lighter than air if will rise and this is safer than if it sinks and settles on the ground. On the ground there is a higher risk of igniting and causing injury and damage
Explain why flame speed is an important safety and performance parameter
Higher flame speed increases the risk of flashback
Which parameters/properties affect flame speed
Increased mixture temperature and mixture quality increase flame speed.
What is a Therm?
The volume of gas required to deliver 100,000BTUs
Therm of NG (98ft^3) is not the same as a therm of LP (40ft^3) or Butane (31ft^3)
What is an octane number? What’s its significance?
It is a standard measure of an engine or aviation gasoline capability against compression.
Higher the number the more pressure the fuel can tolerate before detonating.
Lower octane number increase the risk of engine knock (or of the air/gas mixture igniting/exploding in an envelope outside of the normal combustion front)
How does carbon content affect heat content?
Higher carbon content, higher heat content
How does carbon content affect ultimate CO2?
Higher carbon content, higher ultimate CO2
How does hydrogen content affect specific heat?
Higher hydrogen content, higher specific heats
What is specific heat?
Amount of heat per unit mass required to raise the temperature by one degree C
Rule of Thumb #1 (related to fuel coming out of a storage tank)
Fuel must undergo a phase change. This requires heat for vaporization of the fuel. Takes between 750-1000 BTUs/hr to vaporize one gallon of liquid propane
Rule of Thumb #2 (related to vaporization of fuel)
one gallon of liquid propane contains 91,599BTUs - will generate 36.3ft^3 of gaseous fuel.
One gallon liquid butane - 102,600BTUs - 31.5ft^3
Define CNG and its importance
Compressed Natural Gas - Desirable to use this in some instances in a gas tank because it is safer than other fuels because of its specific gravity (will rise if not contained)
Fourteen Hundred Gas
F gas, G gas
Mix of Propane and air
F gas - Specific gravity of 1.16
G gas - mix of Butane gas and air - Specific gravity 1.42
LNG
Liquefied Natural Gas
For shipment overseas
