240
Alternative Fuels for Transportation
TABLe 8.3
Comparison of Tail-Pipe Emissions
Typical Bi-Fuel Vehicles Grams Per Kilometer
Emission Type
CNG
Gasoline (Benzene)
Reduction %
Carbon monoxide
99
3.34
–86%
Nonmethane hydrocarbons
0.04
0.23
–83%
Nitrogen oxides
0.09
0.12
–25%
Carbon dioxide
246
311
–21%
bulk quenching. The increase in PM with ethane and propane is primarily
due to increased black carbon emissions. As total PM mass increases with
the heavier hydrocarbons, this result indicates that ethane and propane are
increasing both BC and volatile PM mass emissions.
The emission reduction potential of CNG vehicles is depicted in Table 8.3.
8.7 CNG Advantages
1. Environmental: CNG vehicles produce far less of all regulated
po llutants compared to gasoline or diesel vehicles, including NO x
and particulate matter. Natural gas has a low C/H ratio and hence
lower CO and HC emissions. CNG vehicles produce far less unregulated air toxics and greenhouse gases. Due to proper combustion of
gas–air mixtures, reduced unburned HC emissions will reduce the
environmental pollution of visible photochemical smoke.
2. Energy security: NG usage reduces the consumption of gasoline and
diesel fuel.
3. Operating cost: NG is cheaper at the pump than gasoline and diesel
fuel.
4. Distribution efficiency/safety: Natural gas has a higher ignition
temperature than gasoline or diesel. Natural gas is lighter than air
and hence disperses quickly in the event of leakage of fuel. This is the
safest and most efficient energy distribution system. The explosive
limit of NG–air mixtures is higher than diesel–air mixtures. For continuous flame propagation, NG requires a minimum of 5% by volume
as compared to around merely 2% for propane and 1% for gasoline
vapor. Hence, it is safer than other conventional fuels.
5. Flexibility: CNG vehicles can be produced as dedicated and bi-fuel
versions. Dedicated vehicles are most appropriate where vehicles
tend to operate in an area where NG fueling is available. Bi-fuel
vehicles have both NG and gasoline storage tanks on board, and
Alternative Fuels for Transportation
TABLe 8.3
Comparison of Tail-Pipe Emissions
Typical Bi-Fuel Vehicles Grams Per Kilometer
Emission Type
CNG
Gasoline (Benzene)
Reduction %
Carbon monoxide
99
3.34
–86%
Nonmethane hydrocarbons
0.04
0.23
–83%
Nitrogen oxides
0.09
0.12
–25%
Carbon dioxide
246
311
–21%
bulk quenching. The increase in PM with ethane and propane is primarily
due to increased black carbon emissions. As total PM mass increases with
the heavier hydrocarbons, this result indicates that ethane and propane are
increasing both BC and volatile PM mass emissions.
The emission reduction potential of CNG vehicles is depicted in Table 8.3.
8.7 CNG Advantages
1. Environmental: CNG vehicles produce far less of all regulated
po llutants compared to gasoline or diesel vehicles, including NO x
and particulate matter. Natural gas has a low C/H ratio and hence
lower CO and HC emissions. CNG vehicles produce far less unregulated air toxics and greenhouse gases. Due to proper combustion of
gas–air mixtures, reduced unburned HC emissions will reduce the
environmental pollution of visible photochemical smoke.
2. Energy security: NG usage reduces the consumption of gasoline and
diesel fuel.
3. Operating cost: NG is cheaper at the pump than gasoline and diesel
fuel.
4. Distribution efficiency/safety: Natural gas has a higher ignition
temperature than gasoline or diesel. Natural gas is lighter than air
and hence disperses quickly in the event of leakage of fuel. This is the
safest and most efficient energy distribution system. The explosive
limit of NG–air mixtures is higher than diesel–air mixtures. For continuous flame propagation, NG requires a minimum of 5% by volume
as compared to around merely 2% for propane and 1% for gasoline
vapor. Hence, it is safer than other conventional fuels.
5. Flexibility: CNG vehicles can be produced as dedicated and bi-fuel
versions. Dedicated vehicles are most appropriate where vehicles
tend to operate in an area where NG fueling is available. Bi-fuel
vehicles have both NG and gasoline storage tanks on board, and