Experimental assessment of compressed natural gas and Hydrogen spray characteristics using Schlieren Imaging

CNG is one of the most promising alternative fuels and the cleanest for spark-ignited (SI) engines. Its high-octane rating allows a high compression ratio, leading to improved thermal efficiency and less emissions. However, CNG suffers from lower flame speed. Hydrogen-enriched CNG mixture, also known as Hythane considered being promising for SI engine application. This study uses the Schlieren imaging technique to characterise the macroscopic spray characteristics of compressed natural gas (CNG) and Hydrogen simulating PFI engine-like conditions. A comparative analysis of the tests is presented for high-volume flow rate gaseous injectors for Hydrogen and CNG. A different injection pressure in the 2-6 bar range was considered under constant temperature. An apparent trend of increasing jet penetration with fuel injection pressure (FIP) for both hydrogen and methane, however the jet width variation pattern for both fuels. As for the jet of pure H2, the images showed that the jet spreads faster than pure CNG, and the jet has also exhibited a larger cone angle due to the lower density of hydrogen relative to CNG.