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In the recent years, the interest in heavy-duty engines fueled with Compressed Natural Gas (CNG) is increasing due to the necessity to comply with the stringent CO2 limitation imposed by national and international regulations. Indeed, the reduced number of carbon atoms of the NG molecule allows to reduce the CO2 emissions compared to a conventional fuel. The possibility to produce synthetic methane from renewable energy sources, or bio-methane from agricultural biomass and/or animal waste, contributes to support the switch from conventional liquid fuels to CNG. To drive the engine development and reduce the time-to-market, the employment of numerical analysis is mandatory. This requires a continuous improvement of the simulation models toward real predictive analyses able to reduce the experimental R&D efforts. In this framework, 1D numerical codes are fundamental tools for system design, energy management optimization, and so on.

In the arduous aim to reduce petroleum fuel consumption and toxic emissions, gaseous fuels can represent an alternative solution for heavy duty applications with respect to conventional liquid fuels. At the same time, the imposition of more stringent emission regulations in the transport sector, is a crucial aspect to be taken into account during the development of future gas engines. Aim of the present paper was to characterize a heavy duty spark ignition engine, under development for Euro VI compliance, with a particular focus on exhaust particulate emissions. In this sense, the engine was installed on a dynamic test bench, accurately instrumented to analyze combustion evolution, performance and exhaust pollutant emissions, along the World Harmonized Transient Cycle (WHTC).

The paper reports an experimental study on the effect of compression ratio variation on the performance and pollutant emissions of a single-cylinder light-duty research diesel engine operating in DF mode. The architecture of the combustion system as well as the injection system represents the state-of-the-art of the automotive diesel technology. Two pistons with different bowl volume were selected for the experimental campaign, corresponding to two CR values: 16.5 and 14.5. The designs of the piston bowls were carefully performed with the 3D simulation in order to maintain the same air flow structure at the piston top dead center, thus keeping the same in-cylinder flow characteristics versus CR. The engine tests choice was performed to be representative of actual working conditions of an automotive light-duty diesel engine.