Reverse breathing in diesel engines for aftertreatment thermal management

Abstract

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.

Internal exhaust gas recirculation via reinduction and negative valve overlap for fuel-efficient aftertreatment thermal management at curb idle in a diesel engine

“…The contributing factors to brake thermal efficiency (BTE) are open cycle efficiency (OCE), closed cycle efficiency (CCE) and mechanical efficiency (ME). The three efficiencies contribute to the brake thermal efficiency (BTE) as shown in equation (11). Additional details can be found in Stanton.…”

“…Recent results from literature demonstrate that low-airflow strategies – including cylinder deactivation (CDA), 8 intake valve modulation, 9 cylinder cut-out, 10 and internal EGR via reverse-breathing and intake re-breathing 11 can be used to maintain desirable ATS temperatures in a fuel-efficient manner at idle. This is achieved by maintaining engine-outlet temperatures elevated enough to delay cool-down of a warmed-up ATS, while maintaining NO X emissions lower than the conventional thermal management operation.…”

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

“…Previous studies by several of the authors, and others, have demonstrated the ability to raise exhaust temperatures for more efficient aftertreatment thermal management (TM) by utilizing various strategies such as maximally closing a variable geometry turbine (VGT), cylinder deactivation (CDA), intake valve modulation, and exhaust valve modulation. 2,10–17…”