Impact of lean-burn control technology on the fuel economy and NOx emission of gasoline engines

Lean-burn engines operate at a very lean air-to-fuel (A/F) ratio under light-load and part-load regions. Because of better combustion in the lean mixture, fuel economy enhancement is the major merit. Lean-burn technologies also give rise to high engine performance and low emission levels (hydrocarbons and carbon monoxide). In the full-load region, the engine operates in the stoichiometric or rich mode. The drawback of the lean-burn engine is its higher nitrogen oxide (NOx) emission level. The three-way catalyst acts as a suitable device near stoichiometry; however, it is inefficient when the A/F ratio is far from stoichiometry. Hence, advanced catalysts are needed to carry out the NOx storage (oxidation) and purge (reduction) operations. This article is concerned with the lean-burn control applications on gasoline engines, which can also be expanded to other types of engine. Case studies on port fuel injection (PFI) and gasoline direct-injection (GDI) engines have been conducted from different points of view. The experimental investigation on a quasi-homogeneous lean-burn PFI engine has been studied from a fuel economy and NOx reduction viewpoint. The modelling and control approaches are also presented for GDI engines to achieve ultra-lean mixtures for fuel economy enhancement and NOx emission reduction.