Approximately 40% of typical heavy-duty vehicle operation occurs at loaded idle during which time conventional diesel engines are unable to maintain aftertreatment component temperatures in a fuel-efficient manner. Fuel economy and thermal management at this condition can be improved via reverse breathing, a novel method in which exhaust gases are recirculated, as needed, from exhaust to intake manifold via one or more cylinders. Resultant airflow reductions increase exhaust gas temperatures and decrease exhaust flow rates, both of which are beneficial for maintaining desirable aftertreatment component temperatures while consuming less fuel via reduced pumping work. Several strategies for implementation of reverse breathing are described in detail and are compared to cylinder deactivation and internal exhaust gas recirculation operation. Experimental data demonstrate 26% fuel consumption savings compared to conventional stay-warm operation, 60 °C improvement in turbine outlet temperature and 28% reduction in exhaust flow compared to conventional best fuel consumption operation at the loaded idle condition (800 r/min, 1.3 bar brake mean effective pressure). The incorporation of reverse breathing to more efficiently maintain desired aftertreatment temperatures during idle conditions is experimentally demonstrated to result in fuel savings of 2% over the heavy-duty federal test procedure drive cycle compared with conventional operation.

Cylinder deactivation is an efficient strategy for diesel engine exhaust aftertreatment thermal management. Temperatures in excess of 200 °C are necessary for peak NO x conversion efficiency of the aftertreatment system. However, during non-fired engine operation, known as motoring, conventional diesel engines pump low-temperature air through the aftertreatment system. One strategy to mitigate this is to deactivate valve motion during engine motoring. There is a specific condition where care must be taken to avoid compressor surge during the onset of valve deactivated motoring when following high load operation. This study proposes and validates an algorithm which (1) predicts the intake manifold pressure increase instigated while transitioning into cylinder deactivation during motoring, (2) estimates future mass air flow, and (3) avoids compressor surge by implementing staged cylinder deactivation during the onset of engine motoring operation.