Exhaust Rebreathing Strategy to Improve Low Load Operation Applied on a Heavy-Duty Gasoline Compression Ignition Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">This study investigates the effect of exhaust rebreathe (RB) on the low-load regime of a Gasoline Compression Ignition (GCI) heavy-duty engine. For this engine, a custom-designed cam profile with a second exhaust event occurring during the intake stroke was tested under different experimental load and speed conditions. First, the study focuses on the of rebreathe on combustion and gas exchange processes in the low load range of 240-300 kPa BMEP at three key speeds: 820, 1200, and 1600 rpm. Then, a general analysis of the thermal management of this technology is assessed in the low-load map, evaluating the impact on turbine outlet temperature and after-treatment performance related to the conversion rates for NOx and total hydrocarbons (THC). The detailed analysis revealed an increase of around 9% in the trapped residuals for the RB operation, translating to an in-cylinder temperature increase and raising the exhaust temperature up to 50°C. By trapping more residuals in the cylinders, the gas exchange process is different for RB, resulting in fresh charge air reduction, which translates into less pumping and exhaust losses in the energy balance. RB operation also positively impacted combustion stability on extreme zero torque conditions, increasing combustion efficiency at the conditions tested. Overall, it was observed that RB resulted in 30-50°C higher turbine outlet temperature, which reduced the lowest BMEP with 90% SCR NOx conversion efficiencies by up to 200 kPa.</div></div>