Hi,

I see that a lot of people use atmospheric combustion measurements for correlating their CFD codes. What is the main difference with the high pressures and temperatures in engines for example?

Ralf.

There are some issues

- chemical kinetics is getting more complicated. I heard that some people had problems with reaction mechanisms

- the laminar flame speed is influenced by pressure.

- as well as laminar/turbulent flame speed correlation

Energy yielded by the combustion reaction is basically proportional to the difference between the temperature at ignition and the adiabatic flame temperature of the mixture. In other words, it's esentially inversely proportional to the mixture temperature before ignition. As the temperature at ignition rises, the energy released is reduced. So if you calculate the energy evolution inside of a cylinder, you'll find it to be lower than that offered under atmospheric conditions.

High pressure combustion is different to atmospheric combustion and has been the subject of many practical and numerical studies.

It can be summarised.

1. Laminar burning velocity is reduced by pressure but increased by temperature (see explanation given by Richard Wagner). 2. However, as pressure increases the ratio of turbulent to laminar burning velocity increases. Higher ratios have been linked to Lewis number effects (thermo diffusion) however the Lewis number itself is almost independent of pressure. This has led to the adoption of more complex ways to define the thermo diffusive aspects of flames. 3. A satisfactory and well correlated explanation based on fundamental principles is yet to be developed.