Impact of off-road engine electrification through EGR pumping on CO 2,soot,and NO x emissions reductions during steady-state operating conditions

Abstract

Off-road vehicles are emphasizing brake thermal efficiency improvements to meet upcoming diesel emission standards set by the California Air Resources Board (CARB), aiming for enhanced engine and vehicle component efficiency. CARB is implementing regulations demanding a 90% reduction in oxides of nitrogen (NO_x) emissions compared to current EPA Tier 4 standards, extending to off-highway vehicles by 2031. The experimental study described in this paper investigated how high-efficiency turbocharging (HET) and electric 48 V EGR pumping (EGRP) enable improved fuel efficiency in a 13.6 L off-road Diesel engine during steady-state operation. The integration of a 48 V EGR Pump enables the complete use of the high-efficiency turbo, encompassing both fuel reduction and NO_x mitigation, at reduced engine delta pressure (exhaust—intake manifold pressure). Fuel consumption reductions in excess of 8% at low-speed/high-loads, nearly 5% on the torque curve at 1200 rpm, and 1.6%–3.1% in high-speed/high-load scenarios were demonstrated. NO_x levels were generally similar to or lower than the baseline. Soot emissions remained comparable to or lower than the baseline. Open cycle efficiency (OCE) was improved across all points studied. Closed cycle efficiency improved under specific conditions, particularly at low-speed/high-load scenarios for which advanced injection timing could be used as a result of improved EGR flow control with the EGR pump. The OCE improvements were driven by reduced pumping work, with primary attribution to the high-efficiency turbocharger. The EGR pump played a pivotal role in maintaining engine-out NO_x levels, especially under conditions where the conventional high-pressure EGR system would have been limited due to reduced pressure differentials between the intake and exhaust manifold (as a result of the high-efficiency turbocharging).