Effects of Injection Pressure, Intake throttling, and Cylinder Deactivation on Fuel Consumption and Emissions for a Light Duty Diesel Engine at Idle Conditions 2020-01-0303
The continuing growth of urban population centers has led to increased traffic congestion for which vehicles can spend considerable periods at low speed/low load and idle conditions. For light-duty Diesel vehicles, these low load conditions are characterized by low engine exhaust temperatures (~100oC). Exhaust temperatures can be too low to maintain the activity of the catalytic exhaust aftertreatment devices (usually need >~200oC) which can lead to high emissions that contribute to deteriorating urban air quality.
This study is a follow on to two previous studies on the effects of throttling, post-injection, and cylinder deactivation (CDA) on light-duty Diesel engine exhaust temperatures and emissions. The focus of the present study is on fuel consumption and emissions with and without cylinder deactivation and the sensitivity to or effects of fuel rail pressure, along with observations of apparent idle engine friction.
The baseline injection strategy was adapted from a 2014 Chevrolet Cruze having an engine similar to the light-duty 2.0 liter GM engine used for this study. All measurements were made under idle conditions and with the engine speed of 850 rpm maintained by adjusting the duration of the main injection.
With and without cylinder deactivation, and also for deactivated fueling to two of four cylinders, the engine was throttled between MAP values from approximately 50-101 kPa. For the cases with cylinder deactivation (CDA) of two cylinders, the effect of injection pressure was investigated, with rail pressures between 300 and 550 bar. The parameters measured included exhaust temperature, exhaust concentrations of NOx, HC, CO, and CO2, as well as, fuel consumption net IMEP, gross IMEP, pumping IMEP, and COV of net IMEP. The cylinder pressure in one of the deactivated cylinders was also measured, providing insight into possible contributions to pumping IMEP and effects of blowby.
Deactivated fueling showed a modest improvement in fuel consumption, between 4-16% less than with 4 active cylinders, while CDA achieved a 33% fuel consumption improvement at idle for WOT and about 40% at some throttled cases where pumping losses were greater.
Deactivated fueling and CDA resulted in higher NOx emissions concentrations relative to standard operation on all four cylinders; this was attributed to higher in-cylinder temperatures. The heat release rate (HRR) was found to increase with heavier throttling up to 65 kPa MAP, then started to fall, trending the same behavior as NOx with MAP. For CDA, an increase in HC concentrations of about 150% was found for the heaviest throttled case, while the increase was about 180% for the all four cylinders active case.
The effects of rail pressure on engine performance and emissions were studied for the CDA case. Net IMEP trended higher with increasing rail pressure. The HRR for different rail pressures was studied. Energy release was retarded for lower injection pressures. Furthermore, fuel consumption increased with lower rail pressure, consistent with the late energy release that occurred with lower rail pressures. For the conditions examined, the optimal operating condition with regard to fuel consumption was at WOT and 550 bar rail pressure.
Exhaust temperature, as measured at the exhaust port, increased by 20oC with cylinder deactivation and increased by an additional 25oC with the deactivated fueling method. Reducing MAP caused the exhausted temperature to increase by as much as 80oC with all four cylinders active and 95oC for CDA and for deactivated fueling.
Meng Lyu, Yousif Alsulaiman, Corey Tambasco, Matthew Hall, Ron Matthews