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In the last ten years, the number of natural gas vehicles worldwide has grown rapidly with the biggest contribution coming from the Asia-Pacific and Latin America regions. As natural gas is the cleanest fossil fuel, the exhaust emissions from natural gas spark ignition vehicles are lower than those of gasoline powered vehicles. Moreover, natural gas is less affected by price fluctuations and its resources are more evenly widespread over the globe than to oil. However, as natural gas vehicles are usually bi-fuel gasoline and natural gas, the excellent knock resistant characteristics of natural gas cannot be completely exploited. This paper shows the results of an experimental activity performed on a passenger car fuelled alternatively by gasoline and compressed natural gas (CNG). The vehicle has been tested on a chassis dynamometer over standard (NEDC) and real driving cycles (Artemis CADC), allowing to investigate a wide range of operating conditions.

The fossil fuel consumption and the related environmental impact are important issues for the world research community: hydrogen seems to be a good alternative to fossil fuels provided that it is produced from renewable energy sources. The aim of the present work is the comparison between natural gas and a hydrogen-natural gas blend (HCNG in the following) in terms of exhaust emissions and fuel consumption. A passenger car has been tested on a chassis dynamometer according to the European emission regulations, without any change on engine calibration (i.e. spark advance). The HCNG blend used during the test has a 12% vol. of hydrogen content. CO emissions showed a reduction of about 19% when HCNG blend is used, while HC emissions remained constant. A 70% increase was observed for NOx emissions with HCNG. A 3% reduction for CO2 emission was observed using HCNG because of the lower carbon content in the blend and the reduced fuel consumption on a mass basis.

Plasma sustained ignition systems are promising alternatives to conventional spark plugs for those applications where the conditions inside the combustion chamber are more severe for spark plug operation, like internal combustion engines with high compression ratio values and with intake charge dilution. This paper shows the results of an experimental activity performed on a spark ignition engine equipped alternatively with a conventional spark plug and a radio frequency sustained plasma ignition system (RFSI). Results showed that RFSI improved engine efficiency, extended the lean limit of combustion and reduced cycle-by-cycle variability, compared with the conventional spark plug at all test conditions. The adoption of the RFSI also had a positive impact on carbon monoxide and unburned hydrocarbon emissions, whereas nitrogen oxide emissions increased due to higher temperatures attained in the combustion chamber.

Internal combustion engine downsizing allows the reduction of fuel consumption, in particular for those applications where the engine operates frequently at part load conditions. This design solution is usually combined with intake charge dilution by means of exhaust gas recirculation, for the purpose of limiting abnormal combustion events, reducing pumping losses and nitrogen oxide formation. While the exhaust gas recirculation is widely used in compression ignition engines, it still causes some technological issues, in particular for spark ignition engines. This paper presents the results of an experimental campaign performed on a spark ignition engine for the investigation of different dilution techniques for low temperature combustion. Nitrogen, carbon dioxide and exhaust gas recirculation have been adopted as diluents, comparing engine performance and pollutant emissions.