Biodiesel unsaturation and the synergic effects of hydrogen sharing rate on the characteristics of a compression ignition engine in dual-fuel mode

In this study, a comparison of the behavioural characteristics of CI engine operated under single-fuel mode with biodiesel and dual-fuel mode enriched with hydrogen was conducted. The influence of unsaturation degree on the engine behaviour has been assessed and compared between Grapeseed biodiesel (GSBD) and Wheat Germ biodiesel (WGBD) with Coconut biodiesel (CBD) since CBD has a very low level of unsaturation compared to the other two fuels in the single-fuel mode. In addition, this work also investigates the impact of unsaturation on the H2 induction, performance, combustion and emission characteristics of a CI engine in dual-fuel operation. The obtained results showed that with the increasing degree of unsaturation, H2 induction decreases, with CBD tolerating Hydrogen Energy Share (HES) of 13.8 % without knocking, followed by 13.5 % and 12.5 % for GSBD and WGBD, respectively. Comparing the industrial biomass residues alone in dual fuel mode for maximum HES, GSBD-H2 exhibited superior characteristics with 34 % brake thermal efficiency, 0.22 g/kWh of hydrocarbon, 2.3 g/kWh of carbon monoxide and 35.4 % of smoke opacity as against 32.5 %, 0.31 g/kWh, 3.5 g/kWh and 40.3 % for WGBD, respectively. However, the nitric oxide emissions were slightly higher for GSBD compared to WGBD in both single-fuel and dual-fuel modes.