Experimental Investigation of Orifice Design Effects on a Methane Fuelled Prechamber Gas Engine for Automotive Applications

Due to its molecular structure, methane provides several advantages as fuel for internal combustion engines. To cope with nitrogen oxide emissions high levels of excess air are beneficial, which on the other hand deteriorates the flammability and combustion duration of the mixture. One approach to meet these challenges and ensure a stable combustion process are fuelled prechambers. The flow and combustion processes within these prechambers are highly influenced by the position, orientation, number and overall cross-sectional area of the orifices connecting the prechamber and the main combustion chamber. In the present study, a water-cooled single cylinder test engine with a displacement volume of 0.5 l is equipped with a methane-fuelled prechamber. To evaluate influences of the aforementioned orifices several prechambers with variations of the orientation and number of nozzles are used under different operating conditions of engine speed and load. The orifices and therefore the intermediate products of the combustion emanating the prechamber are either aimed towards the squish area of the main chamber or perpendicular to the piston surface. With a constant diameter of the orifices the overall flow area varies proportional to the number of nozzles. Thereby, the impact of timing and duration of the methane injection into the different prechambers, the extension of the lean misfire limit and a variation of the ignition timing are investigated. To rate the overall combustion process the exhaust emissions of unburnt hydrocarbons and nitrogen oxides are examined. Considering the reference point the combustion duration was reduced between 30 and 45 percent compared to conventional spark plug operation using prechambers, whereby the combination of number and orientation of orifices plays an important role.