Effect of spark characteristics on the performance of an IC engine using gasoline and propane: An experimental and theoretical study.

摘要

This thesis describes a combined experimental and theoretical study on the effects of using different spark characteristics under marginal combustion conditions in a spark ignition (SI) engine. Steady state tests were conducted for both gasoline and propane at two operating speed/load points representing urban and highway driving. The engine was run using a stoichiometric fuel/air ratio and different exhaust gas recirculation (EGR) rates for mixture dilution. Three basic types of spark waveforms were investigated: sustained constant current, inductive-like and multiple striking, all at several different energy levels. Heat release analysis of the measured pressure traces was carried out in order to resolve the effects of the spark characteristics on the 10% mass fraction burned.; Three dimensional computations of ignition and combustion were performed using a modified version of KIVA-3V(TM). A finite element mesh was built for the engine used in the experimental study. In-cylinder processes were modeled starting from the induction stroke to predict the conditions at ignition. A spark ignition model was developed to simulate the actual spark energy deposition rates occurring in a running engine. Good agreement between the predicted and measured pressure data was obtained. A parametric study was then conducted to determine the potential of spark delivered energy in improving ignition under various levels of EGR and different flow conditions.; The experimental results for both test conditions and both fuels with 0% EGR showed no apparent effect for the different sparks studied. However, when increasing the mixture dilution, increasing the energy level had a favorable impact on the amount of cyclic variation up to a certain point, beyond which further energy addition did not seem to have a significant further impact. The operation with gasoline showed slower early flame propagation which could be attributed to the non-uniformity of the mixture.; The trends predicted by the model were in good agreement with those found from the measured data. The rate of energy deposition was shown by the model to be the dominant parameter in assessing the impact of different spark types. It also predicted that spark characteristics can significantly affect the success or failure of ignition as well as the subsequent combustion under heavy EGR dilution, higher flow velocities and turbulence intensities at the spark region. Under those adverse conditions, sparks characterized by higher immediate post breakdown power for short durations were shown to have greater impact than lower-power sparks delivering the same total energy over longer durations. The results also suggested that, for the multiple-strike type spark, lower re-strike frequencies could achieve better ignition.; The results of this study imply that suitable spark characteristics could significantly improve cyclic variability and produce better engine performance by improving the cycles that are harder to ignite.