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

Paper #:
  • 2017-24-0096

  • 2017-09-04
Due to its molecular structure, methane provides several advantages as fuel for internal combustion engines. First, owing to the single carbon atom per molecule, a formation of particular matter becomes drastically more unlikely and second the carbon to hydrogen ratio of methane reduces the amount of carbon dioxide by 20 % at the same energy output. To cope with nitrogen oxide emissions a high level of excess air is 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 fuel scavenged 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-scavenged 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. 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. Moreover, nozzles designed to produce higher levels of turbulence within the prechamber show a much higher impact of the injection as other symmetric models. To rate the overall combustion process the exhaust emissions of unburnt hydrocarbons, nitrogen oxides and formaldehyde are examined.
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