Analysis of engine characteristics and emissions fueled by in-situ mixing of small amount of hydrogen in CNG

► We investigated the engine characteristics and emissions of a CNG-DI engine. ► Low levels of H2 enrichment (<10%) in CNG, utilizing an in-situ mixing systems. ► A small amount of H2 has improved engine characteristics and emissions at 2000 rpm. ► A small amount of H2 at high engine speed (4000 rpm) could decrease in engine torque. ► The findings in this paper were useful for CNG operation at low engine speeds.