Utilization of green fuels as a complement in natural gas used in internal combustion engines: A study on the gas properties and reduction in emissions

The reduction of carbon dioxide (CO2) emissions is a pressing concern globally, with the energy, industrial, and transport sectors being the primary contributors due to their reliance on fossil fuels. A viable solution is the adoption of carbon-free fuels, such as hydrogen (H2) and ammonia (NH3), produced using renewable energy sources. However, a direct transition from fossil fuels to these alternatives is not easily feasible due to infrastructure and technological limitations. A first step involves blending small amounts of H2 or NH3 into natural gas (NG) to decrease CO2 emissions. This approach enables the gradual development of infrastructure for renewable fuels and the adaptation of applications that utilize these fuels. Furthermore, gas consumers can continue to utilize NG, which is currently the least polluting fossil fuel, while slowly transitioning to H2-NG and NH3-NG blends for their applications. This transitional strategy allows for a smoother shift towards green fuels, targeting for a low-carbon future.
This research aims to investigate the maximum amount of H2 or NH3 that can be blended with NG of varying compositions while adhering to natural gas quality standards. Previous studies have focused on the effects of hydrogen and ammonia on pure methane, but natural gas is typically a mixture of hydrocarbons and inert gases. Therefore, it is crucial to examine how different NG compositions are affected by H2 and NH3 addition and the resulting reduction in CO2 equivalent (CO2eq) emissions. The primary focus is on internal combustion engines, with the goal of informing engine manufacturers and owners that even a small proportion of H2 or NH3 can reduce CO2eq emissions without significantly impacting engine performance or the need to do major changes on existing engine configuration.
To meet natural gas quality requirements, the results indicate that the maximum amount of hydrogen can be injected into NG with a high methane content and a small amount of ethane, while NG with a high amount of heavier hydrocarbons and lower methane content can accept the highest level of ammonia. Blending natural gas with hydrogen or ammonia reduces CO2eq emissions by up to 2% or 4%, respectively, when following both Euromot and EASEE-gas standards. When adhering solely to Euromot's guidelines, a 5% decrease in CO2eq emissions can be achieved with a H2-NG blend with 16% H2. In contrast, conforming to EASEE-gas's Common Business Practices allows for an 8% reduction in CO2eq emissions with an NH3-NG mixture containing 19% ammonia.
An experimental test demonstrated that a 12 MW spark-ignited engine could operate at 100% load using a fuel consisting of a H2-NG blend with 25 mol-% hydrogen. Although the engine performed well, it did not meet Euromot requirements. Therefore, it is worth thinking that Euromot limitations could be revised to include a clause accepting a methane number under 70 if the NG consists of up to 25% H2. Additionally, the absence of specifications for the maximum allowed ammonia content in natural gas warrants consideration for updates to the standards set by both Euromot and EASEE-gas. The research contributes to the ongoing efforts to achieve carbon neutrality and underscores the importance of revising existing standards to accommodate the use of alternative fuels.