Use of natural gas/hydrogen blends in heavy-duty spark ignition engines: outcomes from an experimental campaign and methodologies for on-board H2 blending ratio determination

• Natural gas/Hydrogen blends for internal combustion engines fuelling. • Experimental activity on a Heavy-Duty SI engine in steady-state operating conditions. • Combustion and emission analysis. • Methodologies for Hydrogen Blending Detection. In the present scenario of global warming and energy transition emergencies, the scientific community is investigating on alternative and cleaner energy sources to reduce the environmental impact of the transportation industry. As a matter of fact, various alternative fuels have been investigated, such as natural gas, bio-methane and, most recently, hydrogen. Among all, hydrogen is one of the most promising fuels for use in internal combustion engines due to its lack of carbon and combustion properties capable of maintaining high engine performance. Hydrogen can be used in its pure form in engines specially designed for the purpose or blended with Compressed Natural Gas (CNG) in conventional engine technologies, with limited mass percentage, to increase combustion efficiency and overall engine performance as well as reducing carbon-based emissions. In this study an experimental campaign has been performed to investigate the impact of natural gas/hydrogen blends on performance and emissions of a spark ignition heavy-duty engine. Experimental tests were conducted on CNG and two natural gas/hydrogen blends, at 15% and 25% of hydrogen in volume. The hydrogen addition was firstly analysed keeping the standard CNG engine calibration and then acting on the spark advance to run at same combustion center timing or nitrogen oxide emissions of the reference CNG case. The testing activity highlighted the need of an ignition timing decreasing to counterbalance the rapid combustion evolution when hydrogen is burned, as well as the expectable nitrogen oxides increment. The optimal parameters setting depends on the hydrogen percentage. Therefore, achieving a flexible fuel supply, with mixtures ranging from a minimum to a maximum hydrogen content, relies on the ability to measure the hydrogen concentration in the cylinders. In this scenario, two methodologies to estimate the hydrogen percentage in CNG/H 2 blends have been proposed. The description of the calculation methods under development and the discussion of the initial results, which have proven to be very promising for the implementation of future on-board procedure, are the focus of this paper.