On the possibility to reduce CO2 emissions of heat engines fuelled partially with hydrogen produced by waste heat recovery

When the problems of industrial pollution and global warming are discussed, one of the main concerns is related to the CO2 emission. The fuel prices continuously increase and the depletion of the oil reserves demand solutions for improving internal combustion engines efficiencies. Therefore, the engine research and development activities aiming to reduce the harmful effects on environment are currently divided into two main directions: the alternative fuel usage, and the reduction of fuel consumption by means of different techniques, the waste heat recovery being one of them. In the alternative fuels domain, hydrogen represents a promising candidate due to its combustion characteristics and to its no-carbon based on emissions. As a mean to recover the engines wasted heat, thermoelectricity and Rankine cycles are some possibilities, but due to the higher efficiency of the Rankine cycle in comparison to the current thermoelectric materials intrinsic conversion ratio, Rankine cycle represents a more effective choice. The present paper considers a merge of the two possible solutions: hydrogen on-site, safe and adequate production by means of water electrolysis and its usage as a supplementary fuel, and the recovery of wasted heat by means of a Rankine cycle for power electricity production based on a steam turbine coupled with an electric generator. Simulations of the combined cycles performed with the AVL Boost code emphasize how the combined power and hydrogen production could improve the engines overall efficiency and how their CO2 emissions could be reduced.