This is in contradiction with real behavior of the controllers that usually only allow timed feeding of a fuel batch. The most important point regarding combustion efficiency is the volatile matter release and burning. The rapid release of volatiles means that there is necessity of quite large amount of air to be mixed with the released gas within the hot zone. If the air is not available, then the volatiles do not burn completely and are in form of carbon monoxide and hydrocarbons released to the flue gas without using their energy content. From this point of view a reasonable solution is to introduce the combustion air above the fuel layer to mix well with the released volatiles. However, there still remains the fixed carbon that is in solid form on the grate