6.1 CNG and LPG vehicles
Compressed natural gas is basically methane (CH4). Liquefied petroleum gas consists of a mixture of propane (C3H8) and butane (C4H10). Both or these have a higher ratio of hydrogen to carbon than petrol or diesel fuel. As shown in Table 4, these fuels have a slightly lower CO2 emission factor than conventional DERV or petrol.
| Fuel | LHV CO2 emission factor /g CO2 MJ−1 |
|---|---|
| DERV (no blended biofuel) | 74 |
| Petrol (no blended biofuel) | 70 |
| LPG | 64 |
| CNG | 57 |
CNG and LPG are cleaner burning than petrol or diesel and produce lower emissions of particulates. As such, these fuels have been promoted in cities with serious air-pollution problems, such as Buenos Aires in Argentina and New Delhi in India.
Overall, although CNG and LPG can improve urban air quality, they cannot drastically reduce transport’s carbon intensity simply because they are derived from fossil fuels.