Increasing Exhaust Temperature of an Idling Light-Duty Diesel Engine through Post-Injection and Intake Throttling 2018-01-0223
Especially in crowded urban areas, light-duty vehicles often spend a great deal of time operating under idle conditions for which exhaust temperatures may be too low to maintain exhaust catalyst activity. This study investigated two methods of increasing Diesel exhaust temperature of a light-duty Diesel engine under idle conditions: post injection of fuel after TDC and intake throttling. For this particular study, EGR was not used. The engine operating parameters considered included three idle speeds of 800, 1100 and 1200 rpm, with the engine fully warmed up. Two rail pressures of 500 and 800 bar were studied with the injection strategy being the primary variable. The parameters measured included exhaust temperature, exhaust concentrations of NOx and HCs, as well as fuel consumption, IMEP and COV of IMEP. For the baseline idle conditions, manifold-out exhaust temperature was approximately 100 °C-105 °C. It was found that under idle conditions the post-injected fuel had to be injected within 30-45 degrees after TDC for the fuel to contribute to both IMEP and to higher exhaust temperatures. Without throttling, the contribution of the post-injection to increased exhaust temperature was relatively modest, about 20 °C. With heavy throttling it was possible to significantly increase idle exhaust temperature by more than 60 °C. The addition of post-injection in combination with heavy throttling allowed further temperature increases, on the order of 20-30 °C, yielding manifold-out exhaust temperatures above 200 °C. HC emissions, however, roughly doubling over the baseline idle condition. For conditions for which heavy throttling was used, it was interesting to note that the highest exhaust temperatures were found for a post-injection timing of approximately 25o –30oCA aTDC which also corresponded to a minimum in engine-out NOx emissions.