The effect of iron-doped cerium oxide (FeCeO₂) nanoparticles as a fuel additive was experimentally investigated with waste cooking oil methyl ester (WCOME) in a four-stroke, single cylinder, direct injection diesel engine. The study aimed at the reduction of harmful emissions of diesel engines including oxides of nitrogen (NO_x) and soot. Two types of nanoparticles were used: cerium oxide doped with 10% iron and cerium oxide doped with 20% iron, to further investigate the influence of the doping level on the nanoparticle activity. The nanoparticles were dispersed in the tested fuels at a dosage of 90 ppm with the aid of an ultrasonic homogenizer. Tests were conducted at a constant engine speed of 2000 rpm and varying loads (from 0 to 12 N.m) with neat diesel (D100) and biodiesel–diesel blends of 30% WCOME and 70% diesel by volume (B30). The engine combustion, performance, and emission characteristics for the fuel blends with nanoparticles were compared with neat diesel as the base fuel. The test results showed improvement in the peak cylinder pressure by approximately 3.5% with addition of nanoparticles to the fuel. A reduction in NO_x emissions by up to 15.7% were recorded, while there was no noticeable change in unburned hydrocarbon (HC) emissions. Carbon monoxide (CO) emission was reduced by up to 24.6% for B30 and 15.4% for B30 with nano-additives. Better engine performance was recorded for B30 with 20% FeCeO₂ as compared to 10% FeCeO₂, in regard to cylinder pressure and emissions. The brake specific fuel consumption was lower for the fuel blend of B30 with 10% FeCeO₂ nanoparticles, in low-to-medium loads and comparable to D100 at high loads. Hence, a higher brake thermal efficiency was recorded for the blend in low-to-medium loads compared to D100.

Iron-doped titanium dioxide nanoparticles, with Fe/Ti atomic ratios from 0% to 10%, were synthesized by flame spray pyrolysis (FSP), employing a single-step method. Ferrocene, being nontoxic and readily soluble in liquid hydrocarbons, was used as the iron source, while titanium tetraisopropoxide (TTIP) was used as the precursor for TiO₂. The general particle characterization and phase description were examined using ICP-OES, XRD, BET, and Raman spectroscopy, whereas the XPS technique was used to study the surface chemistry of the synthesized particles. For particle morphology, HRTEM with EELS and EDS analyses were used. Optical and magnetic properties were examined using UV–vis and SQUID, respectively. Iron doping to TiO₂ nanoparticles promoted rutile phase formation, which was minor in the pure TiO₂ particles. Iron-doped nanoparticles exhibited a uniform iron distribution within the particles. XPS and UV–vis results revealed that Fe²⁺ was dominant for lower iron content and Fe³⁺ was common for higher iron content and the iron-containing particles had a contracted band gap of ~1 eV lower than pure TiO₂ particles with higher visible light absorption. SQUID results showed that doping TiO₂ with Fe changed the material to be paramagnetic. The generated nanoparticles showed a catalytic effect for dye-degradation under visible light.

This study examines the thermo-hydraulic performance of a heat exchanger tube equipped with special fixed ring inserts and twisted tape elements, using a hybrid nanofluid composed of Al₂O₃-CuO/water. Simulations are carried out under turbulent flow conditions, covering Reynolds numbers from 6000 to 14,000. The impact of varying twisted tape torsion ratios (TR = 5, 10, and 15) and hybrid nanofluid volume concentrations (ϕ = 0.3%, 0.6%, and 0.9%) is systematically evaluated. A validated CFD model in ANSYS Fluent demonstrates strong agreement with benchmark data. The results show that, at Re = 14,000, inserting a twisted tape (TR = 5) into a plain tube boosts the Nusselt number (Nu) by 36.28% and the convective heat-transfer coefficient (h) by 36.3% compared to pure water. The tape promotes turbulence and disrupts the thermal boundary layer, enhancing convective heat transfer. However, these gains incur an 8.0% pressure-drop penalty (ΔP). Furthermore, the study highlights the critical role of nanofluid concentration in optimizing heat-exchanger performance. At a 0.9% volume fraction of Al₂O₃–CuO/water nanofluid added to the twisted-tape (TR = 5) configuration, the Nusselt number climbs an additional 3.2%, while the convective heat‐transfer coefficient rises by 18.2%. This nanofluid boost comes with a modest 6.1% pressure-drop penalty (ΔP increases from 284.8 to 302.2 Pa) yet drives the thermal performance factor (TPF) from 1.38 to 3.29. These findings provide a comprehensive understanding of how synergistic passive heat transfer methods and nanofluids can be strategically utilized to enhance the efficiency of industrial heat exchangers.