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A CFD model of natural gas engine was established, and working process from intake stroke to combustion stroke was simulated in this paper. Based on the validation of CFD model through experimental method, the combustion characteristics of lean-burn natural gas engine are studied under different ignition timings and different ignition energies. Results indicate that, the in-cylinder indicated mean effective pressure increases with the ignition timing advancing from 22°CA BTDC to 32°CA BTDC at the same load level. Meanwhile, the heat release rate is increased by 23.18J/°CA and its peak phase is advanced by 9°CA. The peak pressure is also increased by 45.95% and its phase is advanced by 4.5°CA. On the other hand, when the ignition energy decreases from 91.97mJ to 33.1mJ at the same load level, the in-cylinder indicated mean effective pressure decreases.

In this paper we have obtained real-time series of in-cylinder pressure by carrying out some experiments and studied the in-cylinder pressure cycle-to-cycle variations in a diesel engine. By using recurrence plot (RP) and recurrence quantification analysis (RQA), we have investigated the dynamical characteristics of combustion in diesel engine through the in-cylinder pressure cycle-to-cycle variations. The results show that the combustion process exhibits many chaotic features and deterministic nature, the qualitative and quantitative change in combustion can be easily related to patterns in recurrence plots (RPs) and RQA, and combustion system is sensitive to initial conditions. The conclusions of our research work may be helpful in developing effective control strategies to improve diesel engine performance.