Synergies in renewable fuels and exhaust heat thermochemical recovery in low carbon vehicles

The impact of renewable fuels on exhaust energy recovery using catalytic thermochemical process in modern gasoline direct injection is studied with main aim of reducing vehicle carbon footprints. It is proven that supplying the engine with increased calorific value reformate would be beneficial in terms of CO₂ reduction and fuel economy. In this research, the influence of butanol and ethanol on heat recovery, H₂ production, and reforming efficiency are analytically and experimentally studied under various key parameters, including steam to carbon molar ratio and reactor inlet temperature under lean engine operating condition. Gibbs free energy and chemical equilibrium analyses are implemented to identify the key reaction pathways in reforming of the fuels. At lower exhaust gas temperatures where the reactions are thermodynamically limited the conversion rate is mainly controlled by the steam to carbon molar ratio and reducing fuel flow rate leads to a significant increase in fuel conversion levels. Maximum calorific value was achieved by ethanol reforming at 600 °C. However, at higher temperatures and steam to carbon molar ratios, butanol generally indicates better performance in terms of engine fuel economy, energy replacement by reformate, and CO₂ reduction. These advantages are attributed to higher calorific value and higher reforming process efficiency of butanol compared to ethanol. In contrast, at lower temperatures, ethanol reforming generates more H₂ as a result of highly endothermic nature of butanol steam and dry reforming reactions compared to ethanol with weaker molecular bonds and higher molecular diffusivity rate which leads to efficient use of the catalyst.