Chemical kinetics and CFD analysis of supercharged micro-pilot ignited dual-fuel engine combustion of syngas

- CFD-compatible chemical kinetics was developed for dual-fuel engine combustion.
- Mechanism predicted in-cylinder combustion well for biomass and coke-oven syngas.
- Two expressions of HO2 + OH = H2O + O2 reaction used to simulate biomass-derived syngas.
- For coke-oven syngas rate parameter for H2O2 + H = H2 + HO2 is within uncertainty limits.

A comprehensive chemical kinetics and computational fluid-dynamics (CFD) analysis were performed to evaluate the combustion of syngas derived from biomass and coke-oven solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. The developed syngas chemical kinetics mechanism was validated by comparing ignition delay, in-cylinder pressure, temperature and laminar flame speed predictions against corresponding experimental and simulated data obtained by using the most commonly used chemical kinetics mechanisms developed by other authors. Sensitivity analysis showed that reactivity of syngas mixtures was found to be governed by H2 and CO chemistry for hydrogen concentrations lower than 50% and mostly by H2 chemistry for hydrogen concentrations higher than 50%. In the mechanism validation, particular emphasis is placed on predicting the combustion under high pressure conditions. For high hydrogen concentration in syngas under high pressure, the reactions HO2 + HO2 = H2O2 + O2 and H2O2 + H = H2 + HO2 were found to play important role in in-cylinder combustion and heat production. The rate constants for H2O2 + H = H2 + HO2 reaction showed strong sensitivity to high-pressure ignition times and has considerable uncertainty. Developed mechanism was used in CFD analysis to predict in-cylinder combustion of syngas and results were compared with experimental data. Crank angle-resolved spatial distribution of in-cylinder spray and combustion temperature was obtained. The constructed mechanism showed the closest prediction of combustion for both biomass and coke-oven syngas in a micro-pilot ignited supercharged dual-fuel engine.