Abstract
KEYWORDS - hydrogen, engine, stoichiometric, heat flux, EGR
Due to the low volumetric calorific value of hydrogen-air-mixtures one primary goal of combustion engine engineering is to increase the efficiency of future hydrogen engines. To achieve an optimized efficiency it is very important to gain sufficient knowledge regarding the thermomechanical boundary conditions or the particular engine components. They define the frame within which an engine optimization is possible. Generally one can derive a reasonable good estimate of the heat loss and temperatures of the engine components by various simulation tools. However, to achieve a high reliability of the simulation, one has to adapt the model of heat transfer according to the true boundary conditions of the hydrogen combustion process. Because of the significant differences between hydrogen- and hydrocarbon-combustion regarding their combustions characteristics (i.e., the combustion temperature, the burning velocity and quenching distance), a separate theoretical approach is required.
To develop an optimized heat transfer model, surface temperatures have been determined on a single cylinder research engine. These investigations were done with respect to the influences of the revolution rate, the air-fuel ratio, as well as to other essential engine parameters (i.e., ignition angle, EGR-rate, ...). The measurement points have been chosen in representative sites of the combustion chamber roof, the liner and the piston. To properly map the thermal boundary conditions of the hydrogen combustion chamber, a high resolution regarding the surface temperatures and the heat fluxes is required, both temporally and spatially. Based on the detailed knowledge of the surface-temperature changes the heatflux into the combustion chamber walls can be calculated by means of the so called "surface-temperature method".