A Novel Technique for Measuring Cycle-Resolved Cold Start Emissions Applied to a Gasoline Turbocharged Direct Injection Engine

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). This study reports on the development of a novel methodology for capturing and quantifying unburned hydrocarbon emissions (HC), CO, and CO₂ on a cycle-by-cycle basis during an engine cold start. The method was demonstrated by applying it to a 4 cylinder 2 liter GTDI (Gasoline Turbocharged Direct Injection) engine for cold start conditions at an ambient temperature of 22°C. For this technique, 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 event-by event control of individual cylinder fuel injection and spark settings. A dual injection strategy was studied with both an early and a late injection. 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 for later cycles. Measured cycle-resolved HC mass decreased monotonically from approximately 35 mg for the first firing cycle to less than 5 mg for the 5th cycle, an inordinately high value potentially due to misfires at the first two firing events. Cycle-resolved CO masses were on the order of approximately 15 mg per cycle. An advantage of the technique is that is not subject to some of the possible sampling issues that may be encountered with the use of a modal approach (i.e., fast FID + mass flow estimation) and allows the cycle-resolved quantification of CO and CO₂ mass quantities in addition to HC mass.