Effect of natural gas injection timing on combustion performance & methane slip emission of diesel - NG dual fuel engine: An experimental study

Development of marine engine technology is driven increasingly by strict emissions regulations. Dual fuel technology which uses natural gas as supporting fuel is a smart solution due to it is cleaner, cheaper and can reduces dependency on fossil fuel oil. However the phenomenon of methane slip is the biggest challenges on applications of diesel - natural gas dual fuel engine. A large amount of fuel with poor oxygen especially when engine on low load condition make some parts of methane were unburned, these uncompleted combustion raises methane slip. Meanwhile crevice or dead volume in the cylinder make gas trapped and come out as exhaust gas without participating on combustion. It is evident that being the same greenhouse gases the effect of methane slip is more dangerous than CO₂ causing global warming and climate change. This research was carried out experimentally to find out how the natural gas injection time affected on the combustion performance and methane slip. On this study, three variation pulse width as injection timing of natural gas 260° BTDC, 230° BTDC and 214° BTDC were investigated to single cylinder diesel engine on constant speed 2000 rpm. The pressure of gas injection was taken fixed 3 bar, while the pilot injection timing was constant at 18 BTDC. From 30 cycles analyzed at each injection time, a significant relationship was found between optimizing the gas injection time and the gas duration to the methane slip value. Backing the injection time towards the closing of the intake valve with the right injection duration can reduce the value of methane slip. Although the 260° BTDC injection time in this research is optimal compared to the others due to the CNG wasted due to the duration of the injection that passes through the intake valve.