Читать книгу Internal Combustion Engines - Allan T. Kirkpatrick - Страница 64

Diesel combustion energy release is characterized by a double peak energy release, resulting from the two types of combustion that occur during the diesel fuel injection process. The first type is premixed combustion resulting from the leading edge of the fuel jet rapidly mixing and then reacting with the cylinder air. The second phase is a diffusion flame in which the remaining injected fuel mixes and reacts with the cylinder air more slowly. The rate of combustion in a diffusion flame is limited by the rate at which the fuel can be mixed with the cylinder air.

A dual Wiebe function (see Figure 2.18), has been used to fit diesel combustion energy release data (Miyamoto et al. 1985). The dual equation, Equation (2.72) with seven parameters is

(2.72)

The subscripts and refer to the premixed and mixing controlled combustion portions, respectively. The parameter is a nondimensional constant, and are the burning durations for each phase, and are the integrated energy release for each phase, and and are the nondimensional shape factors for each phase. The and parameters are determined empirically from engine performance data. The dual Wiebe function is described in more detail and applied to a fuel–air compression ignition cycle in Chapter 4.

Figure 2.18 Dual Wiebe function for diesel energy release. (Adapted from Miyamoto 1985.)