Unstable oil markets combined with the alarming statistics of continuously growing emission problems causes anxiety among many nations. The greatest dilemma lies in the answer about how to rationally overcome the dependency of fossil based energy sources. The truth seems to be found on utilizing renewable energy generating low emissions. Methane is suggested as one of the worthwhile solutions for substituting crude-oil based fuels. Methane as a fuel combined with modern engine technology seems to open possibilities solving the above mentioned problems. Charge air mixed methane combined with a compression ignition engine utilizing a small diesel pilot injection seems to form a profitable compromise between good engine efficiency and low emission outcome. Problems concerning dual-fuel technology profitableness seems to be related to fully control the combustion in relation to lean conditions. Lean operating conditions solves the problems concerning pumping losses, but brings challenges in controlling the slow heat release of the premixed methane. A study concerning lean condition dual-fuel combustion was executed. In the research, a single cylinder ‘free parameter’ diesel engine was adapted for dual-fuel (diesel-methane) usage. A parameter research related to lambda window widening possibilities was carried out. The main variables studied were diesel pilot injection parameters (timing and pressure) and the relation between combustion characteristics and charge air temperature. Diesel pilot injection parameter optimization seems to affect less on combustion quality compared to the benefits from increasing the charge mass reactivity through preheating the charge air. Improvements in combustion quality were noted in all lean condition tests in the diesel substitution rate scale 0 – 70%. However, significant variation in combustion characteristics were noted through the whole substitution rate range. Remarkable accomplishments in combustion behavior were experienced in the misfire boundary conditions in a form of premixed mixture ignition in the end gas region (PREMIER).