Exploring the lean limit operation and fuel consumption improvement of a homogeneous charge pre-chamber torch ignition system in an SI engine fueled with a gasoline-bioethanol blend

The transportation sector faces a big energy challenge as it looks for more advanced technologies and renewable sources, in which pre-chamber ignition systems and bioethanol have gained worldwide recognition. In this manuscript, a homogenous torch ignition (HTI) system was experimentally analyzed in a commercial four-cylinder engine equipped with port-fuel injection and fueled with a gasoline-bioethanol blend with 25% of bioethanol by volume (E25). Tests were performed at a wide range of speeds and loads for stoichiometric and lean mixtures. Through in-cylinder pressure measurement, a combustion analysis was carefully carried out. Results show that the HTI system leads to a much faster combustion rate and low engine cycle-to-cycle variation due to enhanced ignition energy and turbulence levels in the main chamber, and is able to extend the lean combustion limit with acceptable combustion covariance up to lambda = 1.30. Moreover, improved combustion phasing combined with reduced pumping losses and lower heat transfer to the cooling system decreased fuel consumption. BSFC was improved up to 8.4%, 12.1% and 10.2% for engine speeds of 2500, 3500 and 4500 rpm, respectively, for the 3.5 and 4.6 BMEP conditions at lambda = 1.20, while the higher load (5.8 bar BMEP) was improved up to 8.6% at lambda = 1.30. (C) 2020 Elsevier Ltd. All rights reserved.