Knocking behavior and emission characteristics of a port fuel injected hydrogen enriched compressed natural gas fueled spark ignition engine

Highlights: • HCNG is fast emerging to be an alternative to conventional liquid fuels. • Experiments on a port fuel injected engine prototype using HCNG. • HCNG emitted lower CO₂, HC and CO, but higher NO_X. • Lowest knocking intensity exhibited by 30HCNG at all loads. • HCNG particulates have no additional toxicity/ threat to human health. Natural gas has highest hydrogen-to-carbon ratio among hydrocarbon fuels, which helps in reducing greenhouse gas emissions. Blending natural gas with hydrogen decreases emissions even further because of superior combustion characteristics of hydrogen enriched compressed natural gas (HCNG) mixtures. This study focuses on measurement of carbon dioxide, nitrogen oxides, hydrocarbons, carbon monoxide and particulate emissions from HCNG mixtures and compare them with that of baseline compressed natural gas. Hydrogen enriched fuels are prone to higher knocking therefore, experiments were conducted on a single cylinder port fuel injected spark ignition engine prototype using variety of test fuels such as compressed natural gas, 10, 20, 30, 50, 70% HCNG mixtures and hydrogen for in-depth understanding of relative particulates and gaseous emissions, in addition to determining the engine's knocking characteristics. Experimental results showed that hydrogen enrichment of natural gas reduced emissions of carbon dioxide, hydrocarbons, and carbon monoxide however emissions of nitrogen oxides increased. Lowest knock intensity was observed for 30HCNG mixture. HCNG mixtures improved the engine out emissions and reduced the knocking tendency experienced with hydrogen fueling in internal combustion (IC) engines. Hydrogen enrichment of natural gas also reduced the carbon intensity of fuels, which in-turn reduced greenhouse gas emissions.