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

Abstract

<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>

Development of a fractal engine simulation model in a multidimensional simulation for the cold start process of a gasoline direct injection engine

“…It has been reported that more than 90% of hydrocarbon (HC) emissions originate from the first 2 min of engine operation when the temperature of the catalysts is low. 2 In the cold start process, the very first firing cycle deserves special attention, as most HCs come out during this cycle, and then gradually decrease during subsequent cycles, as shown by prior cycle-resolved cold start experiments 3,4 by our research team. The fuel rail pressure (FRP) is much lower when the engine is first started during the very first firing cycle, and the cold walls in the engine make the fuel film evaporation very slow, resulting in more fuel injected for compensation and leading to more mixture stratification in the cylinder.…”

“…where D is the fractal dimension, which quantitively characterizes the degree of the flame wrinkling; L max is the maximum flame wrinkling scale, which is larger than the integral length scale (L i ), as in equation (3) shown in previous studies, 17,19 or equals the instantaneous flame radius in the early combustion phase when the flame radius is still smaller than L i ; L min is found to be larger than the Kolmogorov length scale (h) in the aforementioned studies, as shown in equation (4).…”

A detailed multidimensional simulation for the cold start process of a gasoline direct injection engine using a fractal engine simulation model

“…All these simulations were carried out using different constant engine speeds. However, as indicated by the cycle-to-cycle experimental measurements in a prior study by our research team, 12 most of the hydrocarbon (HC) emissions originate in the very first firing cycle of the cold start, and then decrease gradually. Therefore, the very first firing cycle should be given special attention.…”

Survey of strategies to reduce cold-start particulate, CO, NOx, and hydrocarbon emissions from direct-injection spark-ignition engines

“…bag 1 emissions from an FTP-75 test). However, the first 20 s have been identified as the most critical in terms of meeting particulate and gaseous emissions regulations, 10 and studies have focused on the development of fast diagnostics to report time-resolved measurements of emissions 29 instead of or in addition to the total accumulated values.…”