1984-02-01

The Effect of Intake Valve Lift on Turbulence Intensity and Burnrate in S.I. Engines-Model Versus Experiment 840030

An Engine Simulation Model was used to study the effect of changing the maximum intake valve lift to control in-cylinder turbulence intensity and burn rate. Experimental measurements of burn rate for two different valve lift profiles were obtained and compared with predictions. The standard K-ε turbulence model was found to be inadequate for predicting the proper behavior of turbulence level during compression and expansion. Further investigation showed that the dissipation of turbulence calculated by the standard K-ε model was inadequate, thus causing the turbulence levels and burn rates to be approximately independent of the intake valve lift.
A new turbulent dissipation model is proposed which uses the eddy angular momentum to scale the dissipation constant. Turbulent intensity predictions from this model resulted in acceptable agreement between the measured and predicted burn rates as the intake valve lift was changed. The effect of throttling the engine using intake valve lift was investigated and predictions made of turbulence intensity, burn rate, combustion efficiency and brake specific fuel consumption (BSFC) as a function of air-fuel ratio and load. Results showed a significant reduction in BSFC at 13 BMEP, 1500 RPM when conventional throttling was compared with intake valve throttling at equal burn rates. In addition, the effect of B/S ratio on turbulence intensity, burn rate and ISFC was investigated and results showed the independent effects of engine geometry and turbulence on burn rate when the engine was stroked holding the cylinder bore constant.

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