Fuel-efficient thermal management in diesel engines via valvetrain-enabled cylinder ventilation strategies

Abstract

Modern diesel engine aftertreatment systems require elevated temperatures for effective reduction of engine-out emissions. Maintaining elevated aftertreatment temperatures in a fuel-efficient manner is a challenge, especially at low-load engine operation where engine-outlet temperatures are low; therefore, higher engine-outlet temperatures are typically achieved via increased fuel consumption. Previous studies have demonstrated that strategies such as cylinder deactivation (method where there is neither valve motion nor fuel injection in a subset of cylinders, thereby isolating the deactivated cylinders from the gas exchange process) and cylinder cutout (method where there is no fuel injection in a subset of cylinders, implemented with high recirculated gas rates) reduce fuel consumption while elevating engine-outlet temperatures, by reducing the overall airflow through the engine. This article introduces and characterizes “non-fired cylinder ventilation” as alternate means to achieve fuel-efficient aftertreatment thermal management, by reduction of overall airflow through the engine. Fuel injection is deactivated from a subset of cylinders during non-fired cylinder ventilation, and the non-firing cylinders participate in the gas exchange process with the same manifold at a time, thereby reducing the intake-to-exhaust manifold gas exchange through the cylinders. It is demonstrated that non-fired cylinder ventilation shows similar fuel efficiency and thermal management as cylinder deactivation when the valves of the non-firing ventilated cylinders are open by at least 4 mm, due to similar, negligible, gas-exchange losses, while non-fired cylinder ventilation with lower valve lifts enables elevated engine-outlet temperatures with relatively higher fuel consumption than cylinder deactivation. Non-fired cylinder ventilation strategies demonstrate 75 °C higher temperatures at fuel-neutral conditions, and up to 35% fuel savings at similar temperatures, compared to six-cylinder operation.

Cylinder deactivation technique in multi-cylinder engines for fuel consumption reduction

“…It also turns off the fuel injection to the cylinder. Figure 1 shows the schematic of the cylinder deactivation technology for diesel engines [12]. As it is tied to the rotating crankshaft, the piston still goes up and down.…”

Thermal Management Concept for the Exhaust Aftertreatment of Commercial Vehicle Diesel Engines Using Variable Mixtures of Diesel Fuel and Rapeseed Oil

“…However, this measure also requires a substantial technological effort in order to be realized, both in terms of additional engine components and in terms of application effort. In a recent publication, several alternatives to cylinder deactivation for thermal management are studied, in which a part of the cylinders are skipfired without completely deactivating the valve lift of the intake and/or exhaust valves [16]. In these cases, either the opening duration of the valves of the non-fired cylinders was significantly increased, or the valve spread was modified in order to open the valves around bottom dead center.…”

EGR cylinder deactivation strategy to accelerate the warm-up and restart processes in a Diesel engine operating at cold conditions

“…Some of these strategies are the cylinder cutout 13 or the variable valve timing (VVT), 14,15 which can be combined with novel strategies as the cylinder ventilation. 16 Another strategy that offers good results is the cylinder deactivation (CDA). 17,18 This strategy helps to reduce the fuel consumption and increase the exhaust temperature up to 100°C, thus activating the aftertreatment systems in shorter times.…”