Impact of hydrogen substitution for stable lean operation on spark ignition engines fueled by compressed natural gas

Abstract

Compressed Natural Gas (CNG) appears as a midterm solution to conventional fuels, such as gasoline and diesel. The low carbon content and the possibility of being obtained from renewable sources (animal or agriculture waste, landfills, waste of the industry food or aquatic biomass) make CNG an attractive option to reduce Greenhouse Gases (GHG) emission. Applying lean combustion strategies on CNG improves efficiency levels while reducing pollutant emissions. In these conditions, heat transfer losses are reduced, and the thermal efficiency increased, especially at partial loads where increasing air dilution is one of the main strategies to reduce pumping losses. Hydrogen (H2) addition helps to enhance combustion in these diluted conditions and to reduce the combustion instability. This combustion concept has been widely studied over the last years, however further research is still needed. This investigation focuses on how hydrogen substitution affects the performance and emissions (both CO2 and pollutant) of a port fuel injection (PFI) spark ignition (SI) engine fueled by CNG. Thus, the main objective of this investigation is to contribute to the existent knowledge about dual-fuel combustion strategies based on CNG and H2 blends. Results demonstrated that hydrogen substitution helps to reduce the CO2 emissions by two ways: improving the engine efficiency and substituting part of the main carbon-based fuel. Despite of this advantage, NOx emissions are not reduced, and they will require after-treatment systems to deal with current pollutant regulations.