Extreme lean gasoline technology – best efficiency and lowest emission powertrains

Development of mobile propulsion technology is driven by fuel consumption and exhaust emission reduction. New gasoline powertrains currently developed at FEV address both these major trends using extreme lean combustion systems to combine best efficiency with lowest emission levels. This paper elaborates on the technology potentials and development methodologies used to handle challenges associated with gasoline lean burn.One focus lies on the definition of a central DI combustion system, which is capable for stable operation at rel. AFR of >1.9 and an outstanding thermal efficiency by charge motion and combustion chamber optimization based on FEV’s CMD approach. A further focus is put on the analysis of suitable boosting systems and stoichiometric- lean switching strategies, which is obtained here by a combined TC and e-charger system in combination with a two-step variable valve lift system. The performance of such system investigated in detail by gas exchange simulation including a comprehensive lean combustion model capable to predict cyclic combustion stability. Finally, the CO₂ and fuel consumption reduction of an extreme lean GDI engine concept is compared to an equivalent stoichiometric engine.