Dynamics of cycle-to-cycle variations in a natural gas direct-injection spark-ignition engine

• Published in: Applied energy 2011-07, Vol.88 (7), p.2324-2334
• Main Authors: Sen, Asok K., Zheng, Jianjun, Huang, Zuohua
• Format: Article
• Language: English
• Subjects: Applied sciences; Combustion; Cycle-to-cycle variations; Direct injection; Direct injection Spark ignition Natural gas Cycle-to-cycle variations Wavelet analysis; Dynamic tests; Dynamics; Energy; Energy. Thermal use of fuels; Engines; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fluctuation; Natural gas; Spark ignition; spark ignition engines; Spectra; Time series; time series analysis; wavelet; Wavelet analysis; Wavelet transforms
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2011.01.009

► Cycle-to-cycle variations (CCV) in a natural gas SI engine are investigated. ► The CCV of the indicated mean effective pressure (IMEP) are analyzed. ► Analysis is based on continuous wavelet transform. ► Effect of compression ratio on the CCV of the IMEP are studied. The dynamics of cycle-to-cycle variations (CCV) was investigated in a natural gas direct-injection spark-ignition engine. The method of continuous wavelet transform was used to analyze the time series of the indicated mean effective pressure (IMEP) and other combustion variables. The dominant oscillatory modes in the CCV were identified, and the engine cycles over which these modes may persist were delineated. Results were obtained for four compression ratios: CR = 8, 10, 12 and 14, at two engine speeds of 1200 and 1800 rpm. The results reveal that the CCV exhibit multiscale dynamics with fluctuations occurring at different timescales. At the engine speed of 1200 rpm, the spectral power of CCV for CR = 12 was found to be significantly reduced at the different timescales compared to the CCV at other values of CR. At the higher engine speed of 1800 rpm, this reduction was less pronounced. In addition, cross wavelet transform was used to explore the relationships between the CCV of IMEP and those of flame development duration, main combustion duration and total combustion duration. Strong interdependence was found to exist between the IMEP and main combustion duration as well as total combustion duration, over a wide range of frequencies and engine cycles.