CNG bus emissions roadmap

In the 1990s, there were several motivations for an increased interest in the use of compressed natural gas (CNG) buses around the globe. However, the imposition of more stringent emission standards for new engines over the last 20 years has stimulated the development of new diesel engine and fuel technologies in the US and the EU, and has made new “advanced” diesels competitive with CNG engines from an emissions standpoint.

In consequence, U.S. and EU interest in CNG buses has waned somewhat; CNG buses currently comprise less than 10% of the total urban bus fleet in industrialized countries. By contrast, the availability and low cost of natural gas, less stringent new engine emissions standards, and fuel sulfur levels higher than required to utilize the most advanced diesel engines, all contribute to a continued high level of interest in CNG vehicles in many developing countries. This report is focused on heavy-duty natural gas engine technologies that can achieve Euro III, IV, V and VI emission compliance levels. An international perspective was intended, but due to lack of sources of technical information from developing countries, most of the report is based on information from the US and Europe.