Comparative Analysis of Different Methodologies to Calculate Lambda (λ) Based on Extensive And systemic Experimentation on a Hydrogen Internal Combustion Engine

Hydrogen Internal Combustion Engines (H₂-ICEs) are subject to increased attention thanks to their extremely low criteria pollutant emission and near-zero CO₂ tailpipe emissions. However, to further minimize exhaust emissions and increase the efficiency of a H₂-ICE, it is important to carefully control the relative air-fuel ratio of operation, i.e. Lambda (λ), which will lead in turn to an optimal combustion process. The precise λ control mainly relies upon the methodology to calculate λ on board of the engine, where the availability of reliable sensors specifically-developed for hydrogen combustion is currently limited. In this article, a comparative analysis of different methodologies for the calculation of λ is performed, comparing four methodologies: exhaust gas analysis through a Spindt-Brettschneider approach (λ_EMI), raw Universal Exhaust Gas Oxygen (λ_R-UEGO), processed Universal Exhaust Gas Oxygen (λ_P-UEGO) and speed-density (λ_SD) outputs. The experimental data used to compare the four methodologies were acquired through detailed and systematic experimentation on a fully-instrumented single-cylinder H₂-ICE. Results show that the λ_P-UEGO is the closest one to the reference Spindt-Brettschneider analysis λ_EMI and the most robust to ample variations in the nominal λ values. The sensor’s raw UEGO output λ_R-UEGO is instead affected by the sensor calibration which is usually performed across a range of carbon-based fuels, a procedure that introduces a bias. The results can be used for the selection of the correct methodology to calculate λ in a H₂-ICE and to choose optimal sensors for mobile applications.