The outputs of the METHACAR project give some fundamental answers to the questions which were the basis for its definition:
1. Natural gas is a fuel with high environmental potential, provided that new solutions are adopted for feeding the gas to the engine and for after-treatment of exhaust gases.
Multi-point sequential gas injection systems directly derived from gasoline solutions have to be used in order to get the required flexibility when controlling A/F ratios during transients.
Dedicated catalysts with high methane oxidation efficiency for effective treatment of exhaust gases are needed if the most stringent emissions standards foreseen for the future have to be reached. Moreover, careful design by means of CAE has to be used when designing the exhaust system, otherwise during the critical light-off phase the temperatures will be unacceptably low.
Close coupling of the catalyst and effective thermal insulation of the exhaust manifold have to be implemented in the design. If this is not possible, the adoption of a starter catalyst will bring the same results but the cost will be increased.
2. Provided the rules of point 1 are followed, EC-EUDC 2005 proposed standards may be reached, although deterioration of the efficiency of the after-treatment system needs to be verified by field test longer than those performed within this project.
3. In order to get the maximum benefit from natural gas, dedicated cars have to be considered since the higher compression ratio possible allows to reach lower fuel consumption (5/7 % if compared with gasoline on an energy basis); CO2 emissions will also be reduced by 20/25 %.
4. In order to cope with the standard automotive safety constraints, the construction of NG dedicated cars equipped with safety monitoring systems appears to be the best available solution.
5. The gas composition has also shown to be a critical issue.
Recent studies have shown that the presence of Sulfur has to be considered extremely critical for the catalyst efficiency over time. Inerts (N2, CO2) are often found with high percentage in some countries NG and this can affect performance and emissions. The recently approved Brite Euram III project "Natural gas Components and Fuels" aims at clarifying these aspects.
6. Hopefully, the evolution of EC emissions standards should exclude methane from HC calculation as it is currently in US.
Compressed natural gas (CNG) vehicles represent the most promising solution to meet future very low ozone level and quite negligible mutagenicity of exhaust together with a substantial improvement of brake thermal efficiency of spark ignition engines. However, the very high environmental performance of natural gas can be guaranteed only if it is used in dedicated vehicles having a sophisticated gas injection system, methane selective catalysts and light fuel tanks of innovative technology. The new demand of dedicated CNG cars has to be supported by a coherent network of research activities:
- computational fluid dynamics modelling of air/gas mixing and combustion process;
- basic modelling and laboratory approach of 3-way selective catalysts;
- integrated design of vehicle and tanks plus CNG storage control;
- study of system reliability and environmental impact assessment.
Knowledge achieved by the development of the above technologies and methodologies will offer the guide-lines for the construction of a prototype CNG car allowing the final technology validation. The consortium comprises a vehicle manufacturer, a gas distribution company, an engine research laboratory, manufacturers of catalysts and composite materials for tanks, plus an university.
Funding SchemeCSC - Cost-sharing contracts
B91 2JW Solihull
00030 Colleferro Stazione Roma
2600 JA Delft