Lean-burn Gasoline Technology
A promising means to further reduce fuel consumption and emissions, but not without challenges
Modern lean-burn gasoline engines can accomplish higher fuel efficiency along with better torque output in comparison to conventional IC engines. The technology helps drivers save fuel costs in both city and highway conditions as well as emitting fewer CO2 emissions. These engines incorporate a highly efficient mixing process along with specially shaped pistons and intake manifolds. The engines’ inlet ports simulate a technique borrowed from direct injection diesel engines, by being shaped to cause swirl action inside the combustion chamber. This action improves the mixing of fuel and air and enables cleaner burning, delivering unaltered output with reduced pollutants. The operation range of lean-burn engines is beyond stoichiometric air/fuel (A/F) ratio of 16:1, which can go as high as 32:1. The excess oxygen available in lean A/F mixtures ensures complete combustion of the fuel, whilst lowering the formation of CO2 and NOx emissions and decreasing the need for exhaust aftertreatment. Further advancement in gasoline combustion technology has led to reduced engine-out emissions for homogeneous lean operation compared to stratified lean operation. If standards mandate even lower tailpipe emissions (further NOx reduction), the lean-burn engine emission reduction may be further controlled with advanced catalytic converters, engine management systems and precise direct fuel injection systems. Whilst selective catalytic reduction (SCR) aftertreatment systems are an effective means to further reduce NOx emissions, the cost of such systems is prohibitive to implement on mass market gasoline engines at present.