Effects of injection pressure, post injection, cylinder deactivation and intake throttling on fuel consumption and emissions for a light duty diesel engine at idle condition

Due to their high efficiency and power, the transportation sector relies heavily on diesel engines. However, diesel engines face many challenges regarding their hazardous emissions and the different regulations for fuel economy which get more stringent over time. One of the main concerns is engine idling where the engine is consuming fuel and emitting pollutants without any utilized power output. In this study, the effects of cylinder deactivation accompanied by throttling and post injection on fuel consumption and emissions were investigated for a 4 cylinder diesel engine at idle conditions. Three different engine operating methods were used. In the 1st method, the engine operated on 4 cylinders, while in the 2nd method; fueling was deactivated for 2 cylinders without valve deactivation. In the last operating method, full cylinder valve deactivation was applied to 2 cylinders. Furthermore, the effects of rail pressure on emissions, IMEP and fuel consumption were investigated. Method 2 with deactivated fueling achieved a minor fuel savings compared to the 4 cylinders operation, between 4-16% depending on the throttling level where more fuel savings were accomplished at higher throttle positions. Method 3 with full cylinder deactivation resulted in 33% fuel savings at WOT compared to Method 1 and 40% at the heaviest throttling level. Pumping losses and fuel consumption were found to increase with throttling, while the net IMEP decreased with heavier throttle conditions. Both CO₂ and hydrocarbons increased with throttling, while NO [subscript x] emissions increased with throttling until 65 kPa of manifold absolute pressure and then started to fall at lower MAP values. These trends correlated with the heat release rate results. Also, fuel consumption and net IMEP increased with a decrease in rail pressure, where the peak heat release rate was more retarded for the lower injection pressure. Finally, the effects of different operating methods and intake throttling on exhaust temperature was analyzed. The temperatures were measured at the exhaust port exits, and for Method 2 prior to any mixing with air from the non-fired cylinders. At wide open throttle (WOT), Method 3 achieved a 20°C increase in exhaust temperature compared to Method 1, and Method 2 resulted in an additional increase of 25°C. Exhaust temperature increased with throttling for all methods, where it rose by 80°C with maximum throttling in Method 1 and 95°C for Methods 2 and 3.