An optical investigation on the effects of split-injection on hydrogenated catalytic biodiesel/gasoline dual-fuel engine under cold start conditions

•Effects of split-injection on combustion characteristics of RCCI operation under cold start conditions.•HCB with high CN promote stable combustion with premixed gasoline of port injection.•High activity atmosphere created by pilot-injection improves ignition characteristics under cold boundaries.•Best combustion performance can be achieved under S-35/15 condition with a pilot ratio of 30%.