Improving diesel engine efficiency at high speeds and loads through improved breathing via delayed intake valve closure timing

Abstract

Valve train flexibility enables optimization of the cylinder-manifold gas exchange process across an engine's torque/speed operating space. This study focuses on the diesel engine fuel economy improvements possible through delayed intake valve closure timing as a means to improve volumetric efficiency at elevated engine speeds via dynamic charging. It is experimentally and analytically demonstrated that intake valve modulation can be employed at high-speed (2200 r/min) and medium-to-high load conditions (12.7 and 7.6 bar brake mean effective pressure) to increase volumetric efficiency. The resulting increase in inducted charge enables higher exhaust gas recirculation fractions without penalizing the air-tofuel ratio. Higher exhaust gas recirculation fractions allow efficiency improving injection advances without sacrificing NOx. Fuel savings of 1.2% and 1.9% are experimentally demonstrated at 2200 r/min for 12.7 and 7.6 bar brake mean effective pressure operating conditions via this combined strategy of delayed intake valve closure, higher exhaust gas recirculation fractions, and earlier injections.

Utilizing Production Viable Valve Strategies at Elevated Speeds and Loads to Improve Volumetric Efficiency via Intake Valve Modulation

“…IVC modulation is commonly cited as a strategy for altering volumetric efficiency through increased dwell at peak lift of the profile. Previous work by the authors has demonstrated the merit behind improving volumetric efficiency via LIVC dwell profiles as a means to improving fuel efficiency (Vos et al, 2017). The efforts described in this article focus on demonstrating that production viable alternatives to these dwell profiles can achieve a similar impact on volumetric efficiency.…”

“…Approximately 50% of the fuel energy is consumed at elevated speeds near 2,200 RPM and elevated loads of 12.7 bar BMEP and higher. In the previous work, the authors have demonstrated an experimental fuel savings of 1.2% at 2,200 RPM and 12.7 bar BMEP enabled via volumetric efficiency improving LIVC dwell profiles (Vos et al, 2017). However, the efforts described in this article focus on demonstrating similar fuel efficiency enabling volumetric efficiency benefits while utilizing production viable alternatives to these dwell profiles.…”

“…Prior research has focused on understanding the impact that IVC modulation has on the engine gas exchange, particularly, advancing or delaying IVC to modulate volumetric efficiency. Vos et al (2017) FigUre 1 | (a) Example of a dwell profile and a required cam profile for an IVC of 40 CAD after nominal. The dark blue dashed line represents the nominal profile, the red solid line represents the dwell profile, the light blue dot-dash line represents an EIVC profile, and the green dashed line represents a cam profile that is required to achieve the LIVC timing via the dwell shape profile.…”

“…demonstrated experimentally that late IVC realizes a 2-5% increase in volumetric efficiency, enabling a 1.2-1.9% improvement in BSFC at elevated engine speeds for a medium-duty diesel engine. Specifically, volumetric efficiency improvements enabled a decrease in BSFC via exhaust gas recirculation (EGR) and start of injection (SOI) optimization without penalizing BSNOx emissions (Vos et al, 2017). Modiyani et al (2011) showed that both volumetric efficiency and effective compression ratio (ECR) are directly affected by IVC modulation, wherein a one-to-one relationship between volumetric efficiency and ECR occurs.…”

Strategies for using valvetrain flexibility instead of exhaust manifold pressure modulation for diesel engine gas exchange and thermal management control

“…dynamic charging). 15,16 At elevated engine speeds, dynamic charging utilizes the momentum of the gas to load the cylinder with more charge, resulting in more trapped mass, per equation (1). Dynamic charging loses its effect as LIVC timings are delayed significantly beyond bottom dead center (BDC), at which point the upward motion of the piston begins expelling the charge gas out of the cylinder before the intake valve closes, as shown in Figure 5.…”