Diesel fueled compression ignition engines are widely used in power generation and freighttransport owing to their high fuel conversion efficiency and ability to operate reliably for longperiods of time at high loads. However, such engines generate significant amounts ofcarbon dioxide (CO2), nitrogen oxides (NOx), and particulate matter (PM) emissions. Onesolution to reduce the CO2 and particulate matter emissions of diesel engines whilemaintaining their efficiency and reliability is natural gas (NG)-diesel dual-fuel combustion. Inaddition to methane emissions, the temperatures of the diesel injector tip and exhaust gascan also be concerns for dual-fuel engines at medium and high load operating conditions.In this study, a single cylinder NG-diesel dual-fuel research engine is operated at two highload conditions (75% and 100% load). NG fraction and diesel direct injection (DI) timing aretwo of the simplest control parameters for optimization of diesel engines converted to dualfuel engines. In addition to studying the combined impact of these parameters oncombustion and emissions performance, another unique aspect of this research is themeasurement of the diesel injector tip temperature which can predict potential cokingissues in dual-fuel engines. Results show that increasing NG fraction and advancing dieseldirect injection timing can increase the injector tip temperature. With increasing NGfraction, while the methane emissions increase, the equivalent CO2 emissions(cumulative greenhouse gas effect of CO2 and CH4) of the engine decrease. IncreasingNG fraction also improves the brake thermal efficiency of the engine though NOx emissionsincrease. By optimizing the combustion phasing through control of the DI timing, brakethermal efficiencies of the order of ～42% can be achieved. At high loads, advanced dieselDI timings typically correspond to the higher maximum cylinder pressure, maximumpressure rise rate, brake thermal efficiency and NOx emissions, and lower soot, CO,and CO2-equivalent emissions.
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