Lambda load control in spark ignition engines, a new application of prechamber ignition systems

Abstract

Energy shortages based on current global demand requires the technological solutions to increase fuel conversion efficiency in internal combustion engines. In this context, lean combustion is a relevant technique for increasing thermal efficiency and reducing pumping losses. Another strategy to reduce engine pumping losses is operating without restrictions imposed by the throttle valve, as in wide open throttle (WOT) conditions, when load is regulated by fuel injection. This technique, already used in diesel engines, is not currently used in Otto cycle engines due to limitations of operating outside fuel stoichiometry. However, lean operation is increasingly feasible with the development of technologies such as the prechamber ignition system (PCIS), which provides high ignition energy and mixture turbulence, improving combustion. The present work compares the effects of mixture enleanment in an Otto ethanol multicylinder engine using a prototype PCIS with the original ignition system running stoichiometrically. The results indicate that the use of PCIS enables the engine load control by variations of lambda, extending the lean limit to λ = 1.35 and λ = 1.6 with the homogeneous and stratified systems respectively. The use of PCIS in SI engines could increase the efficiency of stationary generator sets and hybrid vehicles, also reducing NOx, CO and CO2 engine-out emissions at partial loads.