This work investigates the effect of blending biodiesel with diesel on the combustion of an isolated fuel droplet. Biodiesel blends substituting diesel oil in different concentrations on volumetric basis, in addition to neat diesel and biodiesel, were studied. High-speed Schlieren and backlighting imaging techniques have been used to track droplet combustion. The results showed that partial substitution of diesel oil by biodiesel at the test conditions led to increasing secondary atomization from the droplet, compared to neat diesel or biodiesel fuel droplets. This in turn enhances evaporation, mixing, and then combustion. Additionally, the results showed that biodiesel has a higher burning rate compared to diesel, and that increasing biodiesel in the blend increases the burning rate of the blend. Nucleation has also been traced to take place inside the droplets of the blends. Moreover, flame size (height and width) has been reduced by increasing biodiesel concentration in the blend.

The consumption of fossil fuels is increasing as people become more reliant on them. It is consequently vital to discover more environmentally friendly and sustainable alternative energy sources. Because of its considerable potential to reduce greenhouse gas emissions and its renewable nature, biodiesel derived from WCO has gained attention as a feasible alternative. Enhancing product quality and guaranteeing consistent economic growth are substantial challenges. This investigation aims to assess the feasibility of utilizing WCO as a renewable resource to produce biodiesel. In particular, the investigation investigates the feasibility of obtaining cost-effective and high-quality biodiesel results. To optimize outcomes, this investigation implements a transesterification approach that employs calcium oxide catalysts. Biodiesel's economic value and environmental benefits are assessed through the Life Cycle Cost Assessment (LCCA) assessment method. WCO biodiesel exhibits a high conversion rate and favorable physicochemical properties, as indicated by the results. Therefore, WCO biodiesel can meet the worldwide demand for fuel. The results show that WCO biodiesel has favorable physicochemical properties and a high conversion rate. As a result, WCO biodiesel can meet global fuel demand. It has the potential to generate many benefits for the environment, but there are problems with the collection and processing of WCO. However, WCO collection and processing issues still exist. Biodiesel derived from WCO reduces harmful pollutants, improves public health and air purity, according to engine performance tests.

The hydrogen diffusion flame is commonly described as difficult to see in the visible range. However, even in controlled laboratory conditions with careful imaging, the flame appears reddish. Previous research has reported a variety of colours generated from hydrogen flames. Some researchers believe that the visible colour is due to sodium in airborne dust. Other studies suggest the flame colour is caused by the vibration–rotation band of water vapour. In addition, $\mathrm{H}-\mathsf{\alpha }$ emits radiance in the visible range; therefore, the visible colour of the hydrogen flame could be contributed from the $\mathrm{H}-\mathsf{\alpha }$ emission. Nevertheless, a definitive conclusion to explain the visible reddish colour of the hydrogen flame is lacking. This paper reports precisely instrumented spectroscopic imaging tests, calibration, and data processing in order to resolve the spectral lines in the red colour zone (580–700 nm). This study used a spectrograph and a DSLR camera to capture the spectrum of hydrogen diffusion flames under different co-flow conditions. The values of emission lines in this range were compared with the databases provided by HITRAN molecular spectroscopy and the National Institute of Standards and Technology (NIST). The results of this study show that $\mathrm{H}-\mathsf{\alpha }$ emission is highly likely to appear in a hydrogen diffusion flame, which contradicts the previous hypothesis. This work may provide new insight into hydrogen-based combustion.

The development of a novel on-demand droplet generator is reported in this paper based on off-the-shelf electromechanical components. With the ability to produce a broad range of droplet sizes, this device was designed to have minimum components without compromising reliability. The generator performance was assessed by producing water droplets for fire dynamics and suppression studies. Droplet formation at the tip of the nozzle was visualized using high-speed imaging. Stable and unstable regions can be identified easily through the images. Interchangeable nozzles can be used, allowing different droplet sizes. The setting parameters of the device allow accurate control of droplet size and initial speed. The device controls the liquid pressure actively and precisely. The active control of pressure and the ability to have specific droplet ejection parameters ensured the repeatability of droplet conditions. Characterization of the device is presented along with the calibration data, which can be collected in an efficient methodology. These data enable the selection of droplet size and speed when required. This system could easily be implemented in other research areas. Hence, the intention is to share and highlight the generator features for its use in a range of other scientific applications.