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An experimental methodology was developed and applied to optimize the EcoBoost turbo-charged direct injection engine cold start. Specific focus was on minimizing hydrocarbon and NOx emissions and IMEP variation for the catalyst heating portion of the engine start. The methodology uses steady state single cylinder engine testing with conditioned fluids to screen main factors affecting the emissions and stability responses. The main factors include injector spray pattern design, piston crown design, injection timing, fuel rail pressure, valve timing, and port heat flow. Following the steady state testing, a transient single cylinder engine test was conducted at the optimized conditions to verify emissions and engine stability. This step typically produces results more closely correlated to actual engine starts when compared with the steady state single cylinder engine testing due to better approximation of the engine thermal conditions.

Tumble flow has been recognized as an important and positive enhancement of combustion for SI engines. Tumble flow modeling with quasi-dimensional models is difficult because of the transient nature of tumble vortex, compared with swirl flows. Although multi-dimensional models have obtained plenty of attention recently in engine research, quasi-dimensional SI engine models will continue to dominate industrial applications in the near future. In the present research, a bulk flow model has been developed for tumble flows based on angular momentum conservation. Its effect on turbulence was then modeled using a Two-Equation Model (k-ε Model). A methodology has also been developed to use particle tracking velocimetry (PTV) measurement to calibrate the quasi-dimensional bulk flow model at engine BDC to model tumble vortex and tumble-generated turbulence. The Entrainment Combustion Model was used for combustion modeling.

We have developed a new wall wetting model to predict the transient Air/Fuel ratio excursion in a port fuel injected (PFI) engine due to changes in air or fuel flow. The quasi-dimensional model accounts for fuel films both in the port as well as in the cylinder of a PFI engine and includes the effects of back-flow on the port fuel films to redistribute and vaporize the fuel. A multi-component fuel model is included in the simulation; it gives realistic fuel behavior and allows the effects of different fuel distillation curves to be studied. The multi-component fuel model calculates the changing composition of the fuel puddles in the port and cylinder during the cycle. The inclusion of an in-cylinder fuel film allows the model to be used for cold start conditions down to 290 K. The model uses the Reynold's analogy to calculate the fuel vaporization process and uses a boundary layer calculation to solve for the liquid film flow.

In premixed turbulent combustion models, two mechanisms have been used to explain the increase in the flame speed due to the turbulence. The newer explanation considers the full range of turbulence scales which wrinkle the flame front so as to increase the flame front area and, thus, the flame propagation speed. The fractal combustion model is an example of this concept. The older mechanism assumes that turbulence enables the penetration of unburned mixtures across the flame front via entrainment into the burned mixture zone. The entrainment combustion or eddy burning model is an example of this mechanism. The results of experimental studies of combustion regimes and the flame structures in SI engines has confirmed that most combustion takes place at the wrinkled flame front with additional combustion taking place in the form of flame fingers or peninsulas.

Lean mixture combustion might be an important feature in the next generation of SI engines, while diluents (internal and external EGR) have already played a key role in the reductions of emissions and fuel consumption. Lean burn modeling is even more important for engine modeling tools which are sometimes used for new engine development. The effect of flame strain on flame speed is believed to be significant, especially under lean mixture conditions. Current quasi-dimensional engine models usually do not include flame strain effects and tend to predict burn rate which is too high under lean burn conditions. An attempt was made to model flame strain effects in quasi-dimensional SI engine models. The Ford model GESIM (stands for General Engine SIMulation) was used as the platform. A new strain rate model was developed with the Lewis number effect included.

Experimental measurements of burn rates have been carried out in a single cylinder homogeneous charge engine. Three different combustion chambers were investigated (75 % and 60 % squish bowl-in-piston chambers and a disk chamber) using a cylinder head with a swirl producing intake port and near central spark location. Data were obtained with each combustion chamber as a function of spark timing, EGR, and load at 1500 RPM. The combustion rate is strongly influenced by chamber shape. The 10-90 % burn durations of the 75 % and 60 % squish chambers are respectively about 40 % and 60 % that of the disk chamber. Chamber configuration had less effect on 0-10 % burn duration. The disk had about 25 % longer 0-10 % burn time than the bowl-in-piston chambers. Modifications to the GESIM model enabled good overall agreement between predictions and experimental data, a rather severe test of the model because the coupling of fluid mechanics, combustion and chamber geometry must be properly modeled.