Combustion speed in ICE: thermodynamic model for combustion speed, expansion speed, data base.

An analysis of the turbulent premixed combustion speed in an internal combustion engine using natural gas, hydrogen and intermediate mixtures as fuels is carried out, with different air-fuel ratio and engine speeds. The turbulent combustion speed has been calculated by means of a two-zone diagnosis thermodynamic model combined with a geometric model using a spherical flame front hypothesis. 48 operating conditions have been analysed. At each test point, the pressure record of 200 cycles has been processed to calculate the mean turbulent combustion speed for each flame front radius. An expression of turbulent combustion speed has been established as a function of the turbulence intensity and laminar combustion speed ratio; integral spatial scale and laminar combustion thickness ratio taking into account the instabilities on the flame front. The conclusion of this initial study is that the position of the flame front has a great influence in the expression for calculate the combustion speed. A unified valid correlation for all positions of the flame front has been obtained by adding one correction term based on the expansion speed as a turbulence source. This unified correlation is then valid for all experimental conditions of fuel types, air-fuel ratios, engine speeds, and flame front position. The correlation can be used in quasi-dimensional predictive models to determine the heat released in an ICE