Toward Sustainable Heavy-Duty Transport: Evaluating Charge Dilution and Advanced Corona Ignition System Effects on SI Natural Gas Engine Efficiency and Combustion Characteristics

Reducing greenhouse gas (GHG) emissions in the transportation sector is a significant challenge. A multi-technology approach is the most practical and sustainable solution for minimizing the environmental impact of road transport. Alternative gaseous fuels derivable from bio sources have the potential to significantly cut equivalent carbon dioxide (CO₂eq) emissions from a Well-to-Wheel (WtW) perspective, and the development of technologies that allow to improve the efficiency of natural gas-powered Heavy Duty (HD) Spark Ignition (SI) engines is of strategic importance. In such applications, charge dilution strategies might have the potential to increase engine efficiency at a relatively low implementation cost. Diluting the in-cylinder charge can reduce fuel consumption by decreasing wall and pumping losses, and increasing the Heat Capacity Ratio (γ). The coupling with innovative technologies aimed at enhancing ignition energy, influencing combustion development, could be a promising scientific path for achieving more significant results. This work presents an experimental study conducted on a modern natural gas HD SI Single Cylinder Engine (SCE) to analyze the efficiency and emission benefits achievable through charge dilution. Additionally, a characterization of the prototypal 2^nd generation Advanced Corona Ignition System (ACIS gen2) was conducted for a preliminary assessment of its potential in gaseous fuel context, and to investigate the effects of its higher ignition energy on combustion features under both diluted and non-diluted charge conditions. The steady-state tests have been carried out across the low/medium load and speed range of the engine map, replicating the most common operating conditions for on-road use cases. The results highlight that charge dilution positively impacts the thermodynamic efficiency of gas HD SI engines within specific limits, lowering the Indicated Specific Fuel Consumption (ISFC) by up to 10%. The ACIS gen2 reduced the combustion duration, particularly impacting the early stages, producing an additional improvement in the ISFC of 1% to 2% in stoichiometric conditions; and suggested further potential that could be obtained by optimizing the entire system. Both technologies show that their use could be beneficial in hydrogen applications.