<div class="section abstract"><div class="htmlview paragraph">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 CO<sub>2</sub> 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 C<sub>3</sub> propane basis), CO and CO<sub>2</sub> 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 CO<sub>2</sub> mass quantities in addition to HC mass.</div></div>
<div class="section abstract"><div class="htmlview paragraph">A series of cold start experiments using a 2.0 liter gasoline turbocharged direct injection (GTDI) engine with custom controls and calibration were carried out using gasoline and iso-pentane fuels, to obtain the cold start emissions profiles for the first 5 firing cycles at an ambient temperature of 22°C. The exhaust gases, both emitted during the cold start firing and emitted during the cranking process right after the firing, were captured, and unburned hydrocarbon emissions (HC), CO, and CO<sub>2</sub> on a cycle-by-cycle basis during an engine cold start were analyzed and quantified. The HCs emitted during gasoline-fueled cold starts was found to reduce significantly as the engine cycle increased, while CO and CO<sub>2</sub> emissions were found to stay consistent for each cycle. Crankcase ventilation into the intake manifold through the positive-crankcase ventilation (PCV) valve system was found to have little effect on the emissions results. Cold start experiments fueled by highly volatile iso-pentane saw an overwhelming majority of the injected carbon captured in the exhaust gases, while a significant portion of the injected carbon during the gasoline-fueled cold starts was not captured. The comparative results not only validated the experimental methods, but also demonstrated that a significant fraction of the injected gasoline failed to evaporate during cold starts. During the first 5 firing cycles, 22% to 34% of the injected fuel mass was estimated to remain in the liquid phase and escaped capture. Because fuel could be carried over from one cycle to the next, in some cases, the actual unevaporated gasoline portion in a given cold start cycle could be even higher than that measured.</div></div>
A parametric study was carried out for the first firing cycle of a 4-cylinder, 2.0-liter, turbocharged gasoline direct injection (GDI) engine. The primary goal was to see how changes in the fuel injection parameters would affect the GDI engine combustion and emissions for the first four combustion events that constitute the first firing cycle. Experimental studies were carried out with a custom-designed powertrain control system to measure the HC emissions and pressure development for the first firing cycle. The quantitative experimental results were accompanied by simulations of the detailed temporal and spatial fuel concentration profiles using Converge CFD engine simulation software. An alternative calculation method was used to calculate the average combustion equivalence ratio for each of the four cylinders. This method showed that the majority of the cold start HC emissions during the first firing cycle was unburned gasoline and its possible decomposition products, which did not contribute significantly to the combustion and heat release. For the same amount of fuel injected into a cylinder, increased fuel rail pressure resulted in better evaporation and combustion, while slightly increasing the HC emissions during the cold start process. A multiple injection strategy was studied that split the fuel delivery between the intake stroke and the compression stroke with either one or two injections in each of those strokes (two or four injections total). The quadruple injection strategy led to better first cycle combustion, with higher engine IMEP and lower HC emissions. This resulted from a richer fuel mixture in the region near the spark plug due to better fuel evaporation and a better spatial fuel distribution. While increasing fuel rail pressure with either injection strategy failed to significantly lower the HC emissions given the same amount of injected fuel mass, higher rail pressure with the quadruple injection strategy resulted in higher IMEP for the same amount of injected fuel; this may provide the possibility to reduce the total fuel injection mass which may have benefits for both fuel consumption and emissions.
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