Investigation of the effect of reformer gas on PRFs HCCI combustion based on exergy analysis

Lack of a direct method to control combustion timing is one of the main disadvantages of homogeneous charge compression ignition (HCCI) engines. Fuel blending, in which two fuels with different auto-ignition characteristics are blended, can be used to control combustion timing. Utilizing different additives is another method for HCCI combustion control. The aim of this research is investigation on the effect of reformer gas addition on the availability terms in HCCI engines fueled with primary reference fuels (PRFs). A multi zone model (MZM) coupled with a semi detailed chemical kinetics mechanism is used for calculation of different terms of exergy analysis. Heat and mass transfer between zones and convective heat transfer between in-cylinder charge and combustion chamber walls are considered in MZM. The chemical kinetics mechanism contains 101 reactions and 594 species. Blended fuels of iso-octane and n-heptane, PRF, with different octane numbers are used as engine main fuel. Reformer gas is used as additive to the main fuel and the study is carried out with different percentages of reformer gas ranging from 0 to 30 percent. Results show that irreversibility and exergy loss due to convective heat transfer are reduced by RG addition for all compositions of the main fuel. Peak value of work availability occurs when low values of reformer gas are added to PRFs with different octane numbers. For PRFs 100, 80 and 40, it occurs when 5% of RG is added to the main fuel. For PRF 60, it occurs when 10% RG is added and for PRFs 0 and 20, it occurs when no amount of RG is added. Exergy loss due to conduction and mass transfer is negligible for different percentages of RG.