The chemical dynamics of hydrogen/hydrogen peroxide blends diluted with steam at compression ignition relevant conditions

Abstract

In the current work, the use of hydrogen peroxide as an additive to hydrogen/air mixtures is proposed and explored computationally, in conditions relevant to compression ignition engines. The hydrogen/hydrogen peroxide blends are supplemented with steam for NOx emissions reduction purposes.The objective of the current work is to explore fundamental aspects of the proposed technology, with an emphasis on identifying the key chemical pathways that control the ignition delay time and NOx emissions, using mathematical tools from the computational singular perturbation (CSP) approach.The proposed technology demonstrates a noteworthy potential for use in CI engines, since a 10% (per fuel volume) addition of hydrogen peroxide decreases the ignition delay time to 1 ms, while the mass fraction of NO in equilibrium drops by 100%. Reactions H + O2 → OH + O and H + O2 (+M) → HO2 (+M) play key roles in the acceleration of the ignition delay time, while the thermal and the NNH mechanisms are identified as the dominant pathways for the production of NO. A further 12% addition of steam (per mixture’s volume) induces a two orders of magnitude drop to NO emissions and slightly increases the ignition delay time by 8%. Finally, at sufficiently high steam addition conditions (in the region of 30% and above by mixture’s volume), the system exhibits two stage ignition (mainly owed to reaction HO2 + OH → H2O + O2), a phenomenon that is unique, considering that the initial mixture includes solely hydrogen-based chemical species.