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.