Effect of Compression Ratio Change on Emission Characteristics of HCNG Engine

This study focused on a heavy-duty natural gas engine fuelled with HCNG (CNG: 70 vol%, hydrogen: 30 vol%) and CNG. To study the emission characteristics of an HCNG engine with high compression ratio, the exhaust gas of CNG and HCNG fuel were analyzed in relation to the change in the compression ratio at the half load condition. The results showed that the thermal efficiency improved with an increase in the compression ratio. Consequently, CO2 emission decreased. CO emission increased with inefficient oxidation due to the low exhaust gas temperature. NOx emission with high compression ratio was increased at the same excess air ratio condition. However, NOx emission was not affected by a compression ratio exceeding = 1.9 because of the same MBT timing. λ