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Validation of the Ford General Engine SIMulation program (GESIM) with measured firing data from a modified single cylinder Ricardo HYDRA research engine is described. GESIM predictions for peak cylinder pressure and burn duration are compared to test results at idle operating conditions over a wide range of valve overlap. The calibration of GESIM was determined using data from only one representative world-wide operating point and left unchanged for the remainder of the study. Valve overlap was varied by as much as 36° from its base setting. In most cases, agreement between model and data was within the accuracy of the measurements. A cycle simulation computer model provides the researcher with an invaluable tool for acquiring insight into the thermodynamic and fluid mechanical processes occurring in the cylinder of an internal combustion engine.

A model is presented which incorporates the key mechanisms in the formation and reduction of unburned HC emissions from spark ignited engines. The model includes the effects of piston crevice volume, oil layer absorption / desorption, partial burns, and in-cylinder and exhaust port oxidation. The mechanism for the filling and emptying of the piston crevice takes into account the location of the flame front so that the flow of both burned gas and unburned gas is recognized. Oxidation of unburned fuel is calculated with a global, Arrhenius-type equation. A newly developed submodel is included which calculates the amount of unburned fuel to be added to the cylinder as a result of partial burns. At each crankangle, the submodel compares the rate of change of the burned gas volume to the rate of change of the cylinder volume.

Experimental data have been obtained that characterize knock occurrence times and knock intensities in a spark ignition engine operating on indolene and 91 primary reference fuel, as spark timing and inlet temperature were varied. Individual, in-cylinder pressure histories measured under knocking conditions were conditioned and averaged to obtain representative pressure traces. These averaged pressure histories were used as input to a reduced and detailed chemical kinetic model. The time derivative of CO concentration and temperature were correlated with the measured knock intensity and percent cycles knocking. The goal was to evaluate the potential of using homogenous, chemical kinetic models as predictive tools for knock intensity.

An experimental and analytical study was conducted to investigate the effects of load control with port throttling on stability and fuel consumption at idle. With port throttling, the pressure in the intake port increases during the valve-closed period due to flow past the throttle. If the pressure in the port recovers to ambient before the valve overlap period, back flow into the intake system from the cylinder is eliminated. This allows increased valve overlap to be used without increasing the residual mass fraction in the cylinder. Results showed that, with high valve overlap and port throttling, idle stability and fuel consumption can be maintained at values associated with low overlap in a conventionally throttled engine. However, implementation of this concept in production is regarded to require precision-fit and balanced port throttles, an external vacuum pump for vacuum systems support, and revision of the PCV system.

LDA measurements of the flow in a motored engine near TDC of compression have been obtained, along with burnrate data in a firing engine having a near-central spark plug location. Results are reported for two different intake ports and four intake valve lifts varying from 25% to 100% of full lift. Opposite trends of swirl vs valve lift were found for the two ports, and the rms velocity fluctuation was found to be relatively insensitive to changes in valve lift. Regression analysis of the burn duration data was conducted, with swirl ratio and rms as independent variables. The analysis indicated that burn duration decreases with an increase in swirl ratio and/or rms velocity fluctuation. In light of the experimental findings, a new conceptual model is proposed regarding the effect of valve lift on the dissipation of turbulent velocity via changes in the length scale.

An Engine Simulation Model was used to study the effect of in-cylinder swirl level on turbulence intensity and burn rate while holding the inducted kinetic energy constant. Experimental measurements of burn rate for three different swirl levels were obtained and compared with model predictions. The turbulence model used previously did not include wall shear effects and showed little enhancement of turbulence due to swirl, causing small changes in predicted burn rate when the swirl level was changed. An improved turbulence model is proposed which includes production of turbulence due to wall shear effects. Turbulence intensity predictions from the improved model resulted in excellent agreement between the measured and predicted burn rates as swirl level was changed. In addition, the model was used to predict the effect of swirl levels on ISFC. Results showed that ISFC changes were overall small for the range of swirl levels considered.

A computer simulation for the performance of a four-stroke spark-ignition engine is used to assess the effects of in-cylinder flow processes on engine efficiency. The engine simulation model is a thermodynamic model coupled to submodels for the various physical processes of in-cylinder swirl, squish and turbulent velocities, heat transfer and flame propagation. The swirl and turbulence models are based on an integral formulation of the angular momentum equation and a K-ε turbulence model, These models account for the effects of changes in geometry of the intake system and the chamber design on in-cylinder flow processes. The combustion model is an entrainment burn-up model applicable to the mixing controlled region of turbulent flame propagation. The flame is assumed to propagate spherically from one or two spark plug locations. A heat transfer model that is dependent upon the turbulence level is used to compute the heat loss from the unburned and burned gases.

A flow model is presented that predicts the swirl and turbulent velocities in an open chamber, cup-in-piston I.C. engine. The swirl model is based on an integral formulation of the angular momentum equation solved with an assumed tangential velocity profile form, Vθ(r). This enables the swirl model to predict a non-solid body rotation which is a function of the inlet flow, wall shear and squish motion during the engine cycle. The mean flow model is coupled with a global K-ε model which together predict shear stresses, mixing rates and heat transfer coefficients. An integrated form of the K-ε turbulence model is used which includes the compressibility, shear and boundary layer effects. Turbulence generated by the inlet flow is included and assumed to be proportional to the velocity past the intake valve. Also, the production of turbulence due to the boundary layer effects are included.

A PROCO Flow Simulation (PFSIM) model has been developed to calculate the angular velocity (swirl) and radial velocity (squish) as a function of crank angle for the four strokes of the motored engine cycle. In addition, the PFSIM model calculates the time dependent cylinder pressure, temperature and mass. The model accepts the following swirl-related parameters as input: dimensionless angular momentum and mass flow coefficients for a specific intake and exhaust system configuration. These parameters determine the intake-generated swirl which is computed from the angular momentum flux entering the cylinder during the induction process. An angular momentum flux swirl meter was used to obtain the required input data for three different intake port configurations, and calculations of the bulk cylinder flow were carried out with PFSIM for each intake port configuration.

The flow and combustion processes of a three-valve, stratified charge engine with small prechamber are examined for exhaust emissions. The exhaust emissions from a single-cylinder version of this engine are shown to depend on the internal flow processes as well as mixture supply stoichiometry. A theoretically-based simulation model of the engine flow and combustion processes is described. Model predictions are compared with time-resolved prechamber air-fuel ratio measurements made during intake and compression strokes. These comparisons are used to illustrate and describe the complex flow phenomena which take place in this engine. The combustion process is then examined with the aid of calculations using the simulation model. The complexity of the combustion process is illustrated by showing that, in addition to burned gas temperatures, the cylinder and prechamber burned gas air-fuel ratios change with time.