Investigation on nonlinear dynamic characteristics of combustion instability in the lean-burn premixed natural gas engine

In this paper, the nonlinear dynamic characteristics of combustion instability in the natural gas engine were investigated. The experiments covered the whole excess air ratio (λ) in range from 1 to 1.6 and spark advance angle (SAA) in range from 10°CA to 50°CA before top dead center (TDC). And the real-time series of in-cylinder pressure in combustion process were acquired through a piezoelectric transducer. A couple of new coordinates were proposed for the 0-1 test method. Then the characteristics of the experimentally obtained real-time series of in-cylinder pressure in combustion process were analyzed by using the 0-1 test, the largest Lyapunov exponent (LLE) and the phase space reconstruction methods. The effects of SAA and λ on the complexity of combustion instability of the natural gas engine were tested qualitatively and quantitatively. The results show that all the average asymptotic growth rate Kc are approximately equal to 1 and all the LLE are positive. This indicates the combustion process involves some chaotic characteristics. All the attractors are limited to the finite range of phase space and all the attractors have twist and folded geometry structure. This indicates the combustion process has some irregular deterministic components. Both Kc and LLE have higher values, also the attractor is more complex and looser under higher λ and too large or too small SAA conditions. One can conclude that the chaotic behavior is stronger and the combustion process is more complex and sensitive to small variations of initial condition under higher λ and too large or too small SAA conditions.