Burnt fraction sensitivity analysis and 0-D modelling of common rail diesel engine using Wiebe function

The sensitivity of each Wiebe parameter, namely, the efficiency factor (a), form factor (m), crank angle of combustion start (φ0), and combustion crank angle duration (Δφ), is analysed to ensure that these parameters are estimated reasonably and precisely. The sensitivity of each Wiebe parameter is roughly positively associated with the heat release rate normalized by the total fuel energy. The sensitivities of m and φ0 are larger than the sensitivities of a and Δφ. m and φ0 should be estimated carefully, while a and Δφ can be roughly confirmed. All of sensitivities, the signal-to-noise ratio in cylinder pressure and the certainty in the heat release analysis in the middle stage of combustion are larger than in the early and last stages. Therefore, it is reasonable and necessary to ignore the early and last stages of the combustion process during the confirmation of the Wiebe parameters. The estimated value of φ0 using the 50-per cent burnt angle, the angle associated with the maximum value of the sensitivity of φ0 and ignition time are φ0-50, φ0-smax and φignite. The simulation results indicate that, compared with φignite and φ0-50, φ0-smax is the most suitable to be set as φ0 in standard and double Wiebe functions.