Increasing concern over climate change on planetary scale and urban pollution on a local spatial dimension are the pressing needs which invite to reduce greenhouse gas emissions in transportation as well as pollutant emissions. Both goals have prompted governments, industry stakeholders, and researchers to pursue innovative pathways toward sustainability in the on-the-road transportation sector trying to interpret this concept on the three requested dimensions, social, economic and environmental. Within this framework, hydrogen–methane mixtures have emerged as a promising alternative fuel solution which in someways match the three expectations.
Hydrogen is characterized by carbon-free combustion, while methane is a comparatively clean and widely available fossil fuel. When blended, these two fuels can lower overall emissions relative to the use of pure methane, while still being compatible with existing internal combustion engines. This compatibility makes the adoption of such blends both economically viable and technically achievable in the short to medium term, also increasing the market demand for hydrogen, reducing its cost. The social dimension of this choice is also saved, re-focusing the attention on the reciprocating internal combustion engines which represent a great part of the industrial economy.
This study describes the methodology adopted to assess the emissions performance of a hydrogen-methane-fueled (HCNG) bus for on-road emission testing. Two experimental campaigns were carried out: the first using conventional methane, and the second employing an HCNG blend composed of 15% hydrogen and 85% methane by volume. Tests were conducted along two routes, representing urban and extra-urban driving conditions, with different drivers and traffic conditions.
The experimental results enabled a direct comparison between the two fuels. In both driving scenarios, a slight decrease in CO₂ emissions was observed when using the HCNG blend, corresponding to a reduction in fuel consumption. More significant decreases were recorded for pollutants such as CO, HC, and PN, whereas NOx emissions showed a modest increase of only a few percentage points. The analysis indicates that the HCNG blend enhances vehicle responsiveness compared to conventional methane and represents a step ahead in public urban transportation like the one from diesel fuel to methane.