Cycle-Resolved Cold Start Emissions Characteristics of a 2 liter GDI Engine for the First Several Combustion Cycles 2020-01-0312
There is keen interest in understanding the origins of engine-out unburned hydrocarbons emitted during SI engine cold start. This is especially true for the first few firing cycles, which can contribute disproportionately to the total emissions measured over standard drive cycles such as the US Federal Test Procedure (FTP). In this study introduces a new methodology for capturing and quantifying unburned hydrocarbon emissions, CO, and CO2 on a cycle-by-cycle basis during an engine cold start. The method was demonstrated by applying it to a 2 liter GTDI engine for cold start conditions at ambient temperatures of approximately 22oC. The entirety of the engine exhaust gas was captured for a predetermined number of firing cycles. By capturing the exhaust of different numbers of firing cycles, from one to five for example, the emissions contribution of each successive cycle was determined on an ensemble average basis. The development of custom engine control software allowed predetermined cycle-by-cycle control of individual cylinder fuel injection and spark settings.
A dual injection strategy was studied with both an early and a late injection as used in the serial production engine. The effect of spark timing was examined; this included an early spark timing that gave stable relatively high peak cylinder pressures and a transition to a late spark timing strategy (after TDC) that is commonly used to increase exhaust temperatures for the purpose of early catalyst light-off.
Emitted masses of HCs (on a C3 propane basis), CO and CO2 were measured for each successive cycle. It was found that the first two firing cycle out of five contributed the most unburned hydrocarbon and CO mass, with emissions decreasing rapidly for later cycles. These ranged from approximately 25 mg/cylinder per cycle for HCs (treated as C1 H1.87) for the first two firing cycles to less than 5 mg/cylinder per cycle for the fifth firing cycle. The change in CO mass per cycle was relatively small over the first five cycles, however CO2 mass increased significantly as the HC mass fell.
Jinghu Hu, Matthew Hall, Ron Matthews, Peter Moilanen, Steven Wooldridge, Jianwen Yi
University of Texas, Ford Motor Company