Fuel-efficient exhaust thermal management using cylinder throttling via intake valve closing timing modulation

Abstract

Most diesel engines meet today’s strict NOx and particulate matter emission regulations using after-treatment systems. A major drawback of these after-treatment systems is that they are efficient in reducing emissions only when their catalyst temperature is within a certain range (typically between 250 °C and 450 °C). At lower engine loads this is a major problem as the exhaust temperatures are usually below 250 °C. The primary objective of this study was to analyze “cylinder throttling” via both delayed and advanced intake valve closure timing. The effect of cylinder throttling on exhaust gas temperatures, fuel consumption, in-cylinder combustion and emissions is outlined. A significant increase in turbine outlet temperature accompanied by a decrease in fuel consumption, NOx, and particulate matter emissions was observed. Both delayed and advanced intake valve closure timings were equally effective. The increase in exhaust gas temperatures was attributed to a drop in air flow through the engine, which resulted from a reduction in the volumetric efficiency via cylinder throttling. The increase in fuel efficiency resulted from a decrease in the pumping work through a reduction in air flow through the engine. Reductions in NOx are attributed to the combined effect of a lower in-cylinder temperature due to a reduction in piston-motion-induced compression and a shift to a more premixed combustion mode. Particulate matter emissions were also reduced as a result of additional premixing. At the 1200 RPM and 2.5 bar brake mean effective pressure (BMEP) operating point, both delayed and advanced intake valve closure timings resulted in a turbine outlet temperature increase from 195 °C to 255 °C accompanied by an increase in brake thermal efficiency of 1.5% (absolute) and a reduction in brake-specific NOx and particulate matter emissions by 40% and 30%, respectively.

Effects of application of variable valve timing on the exhaust gas temperature improvement in a low-loaded diesel engine

“…The engine simulated was experimentally studied earlier and promising results were found for EIVC and LIVC [24]. Maximum valve lifts for intake and exhaust valves were taken as 8.5 mm and 9.9 mm in these experiments.…”

“…The main properties and the operating condition of the engine are shown on Table 1. Engine was previously studied by Garg and experimental results for exhaust gas temperatures at different IVC timings were obtained at l200 RPM engine speed and at constant engine loading (BMEP was kept constant at 2.5 bar) [24]. Those experimental results are utilized in this study in order to validate the simulation and to obtain a reliable model for exhaust temperature analysis at low-loaded cases.…”

“…Variable IVC timing is preferred to be applied in the simulation. Since it is considerably effective at rising the exhaust gas temperatures and the results can be compared with an experimental study utilizing the same technique on a diesel engine [24]. The validated simulation achieved on the study is expected to be helpful to guide further VVT search on aftertreatment improvement.…”

“…It is shown that these additional openings are more effective at increasing the exhaust gas temperatures compared to the case where only LIVC is applied to the system. Garg et al [24] explored the effect of IVC timing modification on turbine-out exhaust gas temperatures of a diesel engine through an experiment. It is shown in the analysis that sweeping IVC timing backward and forward from the nominal timing is definitely beneficial to achieve greater than 250 o C exhaust gas temperature at a low-loaded engine case.…”

Improving Exhaust Temperature Management At Low-loaded Diesel Engine Operations Via Internal Exhaust Gas Recirculation

“…Therefore, it requires fuel consumption penalty (above 5 %) to keep engine load constant [12]. In addition to EEVO, decreasing in-cylinder air induction can also increase exhaust temperatures on diesel engine systems [13][14][15][16]. Those air-flow reducing methods are highly effective, however, they cause a dramatic reduction on volumetric efficiency which can be critical during transientstate operations.…”