In recent years, the automotive scientific community and vehicle companies have focused considerable research effort on maximizing overall engine efficiency and reducing emissions from internal combustion engines. One of the low temperature combustion concepts, named Reactivity Controlled Compression Ignition (RCCI), has drawn a lot of attention since it could maintain high engine efficiency, lower engine-out emissions, and also effectively control the combustion phasing. The goal of this project is to obtain an in-depth understanding of the dual-fuel RCCI combustion concept. In this project, two alternative fuels (natural gas and methanol) are used as the low-reactivity fuels, which are either port-injected or early direct-injected to form a premixed mixture with air. The high reactivity fuel diesel is direct injected in the cylinder to tune mixture reactivity and control combustion phasing. Experimental investigation of natural gas-Diesel RCCI combustion indicated that high thermal efficiency together with low NOx and soot emissions were obtained. Additionally, direct injection of methanol was studied and compared with port injection of methanol in the attempt to reduce unburned HC and CO emissions from port-injected methanol RCCI combustion. Methanol-Diesel RCCI showed benefit in NOx, soot and CO2 emissions but engine efficiency did not, compared to pure Diesel case. Although these initial experiments using methanol direct injection prototypes didn't reduce emissions of HC and CO compared to port injection of methanol, further optimization of methanol direct injection systems using proper spray targeting and better fuel distribution are expected to improve both fuel economy and emissions.