A sequential CFD-chemistry investigation of the chemical and dilution effects of hydrogen addition on the combustion of PRF-85 in an HCCI engine

The effects of hydrogen addition on the combustion characteristics of a primary reference fuel PRF-85 in a Homogeneous Charge Compression Ignition engine have been investigated analytically. The numerical modeling was focused on both chemical and dilution effects of hydrogen enrichment. The analysis used a sequential procedure combining a fluid mechanics code (IC Engine coupled with ANSYS FLUENT) to determine temperature and mass distributions as a function of crank angle, assuming motored conditions, and a mutli-zone model (ANSYS Chemkin multi-zone HCCI model) to calculate combustion and engine efficiency using a detailed chemical kinetic mechanism containing 1550 species evolved in 6000 reactions. Analysis was performed using an HCCI engine with a constant speed (1200 rpm) and an intake manifold pressure of 1 bar. The obtained results indicate that hydrogen dilution effect retarded combustion phasing, decreased both combustion duration and specific fuel consumption, and boosted the engine thermal efficiency. Opposite trends were observed for the chemical effect. In all cases, it was found that, whatever the hydrogen percentage in the fuel mixture, the dilution effect was very important as compared to the chemical one, suggesting that combustion characteristics and engine power output variations with hydrogen enrichment were essentially due to the dilution effect.

Automated summary

The study analytically investigated the effects of hydrogen addition on the combustion characteristics of a primary reference fuel in a Homogeneous Charge Compression Ignition engine. The results showed that hydrogen dilution effect had a positive impact on combustion characteristics, leading to higher engine thermal efficiency.