Conversion to hydrogen of automobile internal combustion engines powered by fuels of petroleum origin is the most important direction for solving environmental, energy and climate problems of modern civilization.
A number of researchers, based on experimental studies, note the presence of a phenomenon of a significant increase in heat losses in hydrogen engines compared to gasoline engines. This phenomenon is explained by an increase in temperature and speed of movement of the working fluid. In this paper, it is shown that the main reason for the increase in thermal losses is the ability of the hydrogen flame to penetrate into the narrow gap between the piston and the engine sleeve. This problem has not been discussed in engine theory before.
D mathematical modeling of flame penetration and extinguishing processes in the specified gap of a hydrogen engine (D/S=86/86 mm/mm, Ne=60 kW, n=5500 min-1) was carried out. Critical gap sizes for various fuels have been established, heat transfer coefficients in the gap have been determined, and a significant difference has been found between the thermal states of the piston for cases of flame penetration and extinguishing in the gap. When a hydrogen-air flame penetrates into the gap, the maximum value of the instantaneous heat transfer coefficient to the piston firing belt reaches 6158 W/(m2K). At the same time, the local temperature of the piston in the area of the upper compression ring increases from 269 °C to 316 °C compared to the case of flame extinguishing.
Direct measurements of the unsteady heat flow in the gap on the piston surface confirm the true reason for the increase in heat losses. By changing the excess air coefficient, it is possible to extinguish the flame into the gap and reduce heat losses.