Implementing variable valve actuation on a diesel engine at high-speed idle operation for improved aftertreatment warm-up

Abstract

Aftertreatment thermal management is critical for regulating emissions in modern diesel engines. Elevated engine-out temperatures and mass flows are effective at increasing the temperature of an aftertreatment system to enable efficient emission reduction. In this effort, experiments and analysis demonstrated that increasing the idle speed, while maintaining the same idle load, enables improved aftertreatment “warm-up” performance with engine-out NOx and particulate matter levels no higher than a state-of-the-art thermal calibration at conventional idle operation (800 rpm and 1.3 bar brake mean effective pressure). Elevated idle speeds of 1000 and 1200 rpm, compared to conventional idle at 800 rpm, realized 31%–51% increase in exhaust flow and 25 °C–40 °C increase in engine-out temperature, respectively. This study also demonstrated additional engine-out temperature benefits at all three idle speeds considered (800, 1000, and 1200 rpm, without compromising the exhaust flow rates or emissions, by modulating the exhaust valve opening timing. Early exhaust valve opening realizes up to ~51% increase in exhaust flow and 50 °C increase in engine-out temperature relative to conventional idle operation by forcing the engine to work harder via an early blowdown of the exhaust gas. This early blowdown of exhaust gas also reduces the time available for particulate matter oxidization, effectively limiting the ability to elevate engine-out temperatures for the early exhaust valve opening strategy. Alternatively, late exhaust valve opening realizes up to ~51% increase in exhaust flow and 91 °C increase in engine-out temperature relative to conventional idle operation by forcing the engine to work harder to pump in-cylinder gases across a smaller exhaust valve opening. In short, this study demonstrates how increased idle speeds, and exhaust valve opening modulation, individually or combined, can be used to significantly increase the “warm-up” rate of an aftertreatment system.

An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union

“…In very general terms, this is obtained through an overall reduction of the air-to-fuel ratio, as detailed in Shaver et al [72]. CDA in combination with a cylinder cut out and advanced ventilation strategies can increase turbine out exhaust temperature by 50-150 • C achieving, at the same time, about a 6% reduction in fuel consumption when compared to baseline [73]. Additional examples of implementation of the same approach have led, for an X15 6-cylinder Cummins engine with variable geometry turbine (VGT) and highpressure exhaust gas recirculation (EGR), to an increase of 40-100 • C of the turbo-out temperature, with an overall reduction of roughly 20% in fuel consumption together with a simulated reduction of NOx going from 45% to 66% and a 1.5-3.7% decrease in CO 2 depending on the cycle considered (FTP (federal test procedure) or LLC (low load cycle), respectively) [74][75][76].…”

Development of control strategy for fast idling condition of diesel engine based on target torque

“…V represents speed, its unit is m/s, r represents arm of force, its unit is m. Equation ( 17) is obtained from equations ( 12), (15), and (16).…”

“…The exhaust advance angle can realize the emission reduction of pollutants such as NOx and micro particles when the idling speed increases. 15,16 To sum up, the increase of idling speed is conducive to the improving of warm-up speed; there is an optimal warm-up mode which makes the fuel consumption and HC emission of the diesel engine lower during the warm-up period. 17 Therefore, on the basis of previous studies, this article intends to develop the control strategy of fuel injection quality when the engine warms up.…”

Exhaust valve phasing controllers for cold start NOx emissions reduction in heavy duty diesel engines

“…1 Currently, because 80% of emissions are exhausted during the cold start phase of a federal test procedure (FTP), 2 various warm-up solutions are being proposed by manufacturers to speed up temperature increase of the aftertreatment system in a cold start test to comply with stringent emission standard levels. Example strategies include bypassing the exhaust gas recirculation (EGR) cooler to warm up the cylinder inlet charge; 3,4 increasing the EGR flow during the engine idle to reduce the air-fuel ratio and increase exothermic reactions inside the diesel oxidation catalyst (DOC); 5 throttling the intake manifold and cylinder deactivation; 6,7 increasing idle speed; and adding a supplemental air heater upstream of the selective catalytic reaction (SCR) system. 2 Even when the aftertreatment system is warmed up, the diesel engine air path control is critical to reduce the engine out emissions [8][9][10] and maintain the catalytic system temperature and its efficiency.…”