Variation in Squish Length and Swirl to reach higher levels of EGR in a CNG engine 2019-01-0081
Gaseous methane fuel for internal combustion engines has proven to be a competitive source of propulsion energy for heavy duty truck engines. Using biogas can even reduce the carbon footprint of the truck to near zero-levels, creating a fully environmental friendly transport. Gas engines have already been on the market and proved to be a popular alternative for buses and waste transport. However, for long haulage these engines have not been on par with the equivalent diesel engines. In order to improve the power and efficiency of the EURO VI gas engines running stoichiometric the direct way forward is adding more boost and spark advance in combination with more EGR to mitigate knock. By achieving a higher mixing rate through increased in-cylinder turbulence, the fuel can still be combusted efficiently even though the fraction of inert gases increased. In this report, previous findings from diesel engine simulations are investigated for the applicability on stoichiometric gas combustion. The results from different in-cylinder flow motions are investigated as a variation of swirl levels in the cylinder head and squish lengths in the piston. The testing has been performed on a single cylinder research engine operated in the equivalent multi cylinder engine operating points. The results show that the previous modelling findings are verified on the pre-mixed gas combustion studied. By choosing the levels of swirl and squish, it is possible to increase the combustion speed and the fraction of EGR in the combustion charge, without the latter having a negative impact on the combustion.
Ludvig Adlercreutz, Andreas Cronhjort, Ola Stenlaas
AVL MTC AB, KTH Royal Institute of Technology, Scania CV AB
International Powertrains, Fuels & Lubricants Meeting