The Study On Characteristics And Dynamics Of Combustion Cycle-to-cycle Variations In A Lean Burn Natural Gas Fueled Engine

It's valuable to study statistic characteristics and dynamic characteristics of cycle-to-cycle combustion variations (CCV) for optimizing emissions and fuel economy in natural gas fueled IC engines, since those investigations can show a lot of fundamental materials for modeling and controlling a natural gas fueled IC engine.The study was carried out in a high-speed, light duty, compressed natural gas fueled engine. A set of multi-channel simultaneous data acquisition and analysis system was developed for statistic characteristics and dynamic features of CCV. By the data acquisition system, multi parameters was recorded fast and consecutively by several thousands cycles.Based on the in-cylinder pressure time series under operating conditions with different ignition timings, equivalent ratios, engine speeds and throttle opening positions, correlations between characteristic parameters of CCV were discussed. The result shows that two couple of paramiters, maximum in-cylinder pressure and its position, maximum in-cylinder pressure and maximum rate of pressure rise, have a good and stable linear correlation under most conditions. The correlation coefficients between indicate mean effective pressure and maximum in-cylinder pressure, indicate mean effective pressure and maximum in-cylinder pressure position, indicate mean effective pressure and maximum rate of pressure rise are strongly influenced by ignition timing, equivalence ratio, engine speed and throttle opening position.The coefficient of variations of indicate mean effective pressure drops firstly and then increases as ignition timing is delayed monotonically. Under the minimum CCV ignition timing conditions, the influence of operating parameters on characteristics of CCV was investigated. According the trends of characteristics of CCV indicated by indicate mean effective pressure and maximum in-cylinder pressure separately, the same trends is founded under small equivalence ratio, high engine speed and small throttle opening conditions.Methods borrowed to the nonlinear dynamical system theory were applied to discovery the dynamics of CCV. Phase spaces were reconstructed from in-cylinder pressure time series and Poincare' sections were calculated in those phase spaces. The features in Poincare' sections show that there are both stochastic characteristics and determinative characteristics in the evolution of consecutively cycles of combustion. Return maps calculated from indicate mean effective pressure series show a transition from stochastic behavior to noisy nonlinear determinism as equivalence ratio decreasing under lean burn conditions, throttle opening lowering under part load conditions and engine speed rising to relatively high speed.