Numerical simulation of second generation biodiesel/gasoline reactivity controlled compression ignition(RCCI) combustion mode with dual-direct injection strategy at low loads was carried out based on the fluid simulation software CONVERGE. The combustion characteristics of RCCI with dual-direct injection and RCCI with conventional intake port injection were compared

and the effect of dual fuel injection timings on combustion was discussed. The results show that compared with the conventional intake port gasoline injection RCCI

the dual-direct injection RCCI can effectively control the distribution of in-cylinder gasoline mixture and reduceincomplete combustion. With the delay of start of injection(SOI) of gasoline

stratified combustion weakens

combustion duration shortens

combustion efficiency is reduced

indicated thermal efficiency declines first and then increases and finally decreases again

NOx emissions is reduced and soot emissions increases. With the delay of SOI of the second generation biodiesel

stratified combustion intensifies

combustion duration is prolonged

combustion efficiency increases

indicated thermal efficiency increases first and then decreases

NOx emissions rise and soot emissions fall.