PyrInno: Practical results of a small scale burner development

Abstract Modern household heating systems must exhibit a low minimal power, a wide power modulation range and a high power density. The combination of innovative concepts and technologies like the vaporisation on porous media, the preparation of a homogeneous fuel/air mixture supported by Cool Flames [1] and the combustion in inert porous media [2] will help to meet the changed requirements. The intention of the project “PyrInno” is to develop an extremely compact oil heating system which reveals low emissions, a power modulation range from 1 kW to 8 kW and meets the German air pollution guidelines for environmental protection. In this contribution the operating model of this compact premix burner for light fuel oil is presented and experimental results are shown. INTRODUCTION The decreasing heating energy demand due to tightened regulations and better insulation of buildings leads to changed requirements of household heating systems. These must exhibit a lower minimal power, a wide power modulation range and a higher power density than technologies available on the market. The development and combination of innovative concepts and technologies will help to face the changed requirements. Within the frame work of InnoNet funded by the German Federal Ministry of Economics and Technology the project “PyrInno” (project number IN-5068) is conducted with the intention to develop an extremely compact oil heating system. The combination of procedures like the vaporisation on porous media, the preparation of a homogeneous fuel/air mixture supported by Cool Flames [1] and the combustion in inert ceramic porous media [2] is used in order to develop a small scale, low emission premixed burner for light fuel oil. This fully-modulating burner with a power modulation range from 1 kW to 8 kW will meet the German air pollution guidelines for environmental protection. The highly flexible porous burner technology is based on the stabilisation of combustion reactions within an inert open cell ceramic structure and is successfully applied in many different fields of combustion [3, 4, 5]. In comparison to conventional free flame burners the combustion in porous structures offers exceptional advantages, e.g. low emissions, high power modulation range, small scale sizes and high radiation output and is therefore particularly suitable for such a system. For using liquid fuels with the porous medium burner a fuel pretreatment is needed in order to produce a homogeneous, gaseous mixture of air and fuel. This is done by using the Cool Flame phenomena. Cool Flames are capable to produce homogenous fuel/air mixtures from liquid hydrocarbons. The key point is the separation of the vaporising/mixing zone from the combustion zone that follows, to avoid auto ignition of the mixture before reaching the combustion zone. Cool Flame reactions in fuel/air mixtures using light fuel oil start at nearly 320 °C. This auto thermal process has a self-limiting character at a temperature up to 480 °C and is unsusceptible when varying the fuel/air ratio and educt temperature. The slightly exothermic Cool Flame reactions supply the vaporising enthalpy by converting 5 % to 10 % of the fuel energy into heat. In the temperature range between 320 °C and 480 °C Cool Flame reactions with a negative temperature coefficient are dominant. The fuel is delivered to the porous medium in the newly developed vaporiser by a piston pump. The vaporisation process of the fuel oil is supported by recuperated air and Cool Flame reactions, resulting in a very robust operational behaviour over the entire power modulation range. In this paper the compact premix burner system for light fuel oil and the experimental results of field tests are presented. The research and development efforts are still in progress in the framework of a combined research project. InnoNet intends to develop and support innovative, collaborative networks. The network of the PyrInno project includes all different necessary expertise for such a system development like tank and fuel handling experts (Rotex), boiler design (Solvis), electronic controls (ISSENDORFF Mikroelektronik), professional associations and craftspeople (IWO, FVSHK, Hamacher, Volkert and Muhlenberg Haus & Technik), heating components (J. Eberspacher and promeos), Cool Flame process (OWI) and porous burners (LSTM, promeos).