Effects of Benzoylthiourea-Based Ni and Co Complexes on the Combustion Characteristics and Emissions of a Diesel Engine

This study evaluates the effects of novel metal-based fuel additives on the combustion, thermal behavior, and emissions of a common-rail diesel engine. Two transition metal complexes, Bis-[N-(1,1′-biphenyl)-2-chlorobenzoylthioureato]nickel(II) (NiL2) and cobalt(II) (CoL2), were synthesized and utilized as diesel additives for the first time. Experiments were conducted on a 1.5-L, four-cylinder engine at 1750 rpm under three load conditions: 50, 75, and 100 Nm. The results demonstrated that 25 ppm of NiL2 and CoL2 altered the combustion kinetics. At medium loads, the additives increased maximum cylinder pressure by 3% and shortened ignition delay at low loads. Peak heat release and heat transfer rates improved by 4% and 7%, respectively. CoL2 exhibited the most pronounced thermal effect, raising average in-cylinder gas temperatures by up to 4% at high loads. However, despite these thermodynamic changes, the additives did not yield any reductions in NO, HC, or CO emissions; in fact, emission levels were generally similar to or slightly higher than those of neat diesel. These findings suggest that while these specific complexes act as combustion modifiers that enhance in-cylinder thermal parameters, they do not offer significant advantages regarding emissions under the tested configurations.