Heat Recuperation from Internal Combustion Engines by Fuel Reforming: Kinetics-Based Analysis

Abstract

In an effort to estimate the feasibility of heat recuperation from an internal combustion engine (ICE) by steam reforming (SR) or by decomposition of the fuel, we study here the required size of a reformer heat exchanger in order to power a 3.7 kW engine. To that end, we experimentally test the heat transfer in a structured commercial reactor with ∼0.39 m² of heat transfer area in an ∼1 L unit. We then simulate the required length for evaporation and reforming of several fuels, using published kinetics with a highly active catalyst, under a fixed exhaust temperature of 973 K, and study the effect of pressure and steam-to-fuel ratio. Both co- and counter-current schemes are considered. Methanol decomposition is probably the best solution from the energy point of view. However, it is known to lead to deactivation. Methanol SR (with S/M = 1) requires about 2 L of reformer-HE and seems to be a reasonable solution, yielding a chemical energy gain of ∼16%, a value close to the asymptotic thermodynamic value. Moreover, the presence of CO₂ in the reformate is known to mitigate to NO_x emissions down to zero-impact levels. Ethanol SR (with S/E = 1 or 3) yields poor results since CH₄ is an intermediate, which requires high temperatures for reforming; operating ESR requires exhaust temperatures of ∼1250 °K or higher. While such high temperatures may be attained and may yield an energetic gain of more than 20%, it will require modification of the process. Methylal SR (S/MA = 1) yields good results as well.