A novel algorithm is proposed for the automatic segmentation of diesel spray images and the calculation of their macroscopic parameters. The algorithm automatically detects each spray present in an image, and therefore it is able to work with diesel injectors with a different number of nozzle holes without any modification. The main characteristic of the algorithm is that it splits each spray into three different regions and then segments each one with an individually calculated binarization threshold. Each threshold level is calculated from the analysis of a representative luminosity profile of each region. This approach makes it robust to irregular light distribution along a single spray and between different sprays of an image. Once the sprays are segmented, the macroscopic parameters of each one are calculated. The algorithm is tested with two sets of diesel spray images taken under normal and irregular illumination setups.

Knock remains one of the main limitations for increasing the efficiency in spark-ignition engines. The use of certain alcohol–gasoline blends is an effective way to either mitigate or eliminate knock, allowing the use of higher compression ratios, therefore increasing the efficiency of spark-ignition engines. Methanol and ethanol are alcohols commonly employed for reducing knock, due to their higher octane number and vaporization heat value. Major attention is being paid recently to butanol and its blends with gasoline since they present similar characteristics to gasoline; however, it was found to be the least knock resistant among the three fuels. In the present work, a comparison between the knock performance of methanol–gasoline, ethanol–gasoline and butanol–gasoline blends is carried out, by volume concentrations up to 20 v/v%. This comparison is made in terms of knock intensity and knock probability. Tests are performed in a single-cylinder, variable-compression ratio, Cooperative Fuel Research engine equipped with port fuel injection system, facilitating the comparison against future results obtained by similar experimental facilities. Results obtained allow to reach meaningful conclusions about the capacity of each blend to mitigate knock.

An experimental study was performed to explore the influence of dwell time on the hydraulic interactions between injection events using pilot injection strategy, split injection strategy, post injection strategy and a solenoid diesel injector. To do so, a sweep of dwell time from 0.55 up to 2 ms using all multiple injection strategies and levels of rail pressure, of 80, 100 and 120 MPa, and single level of back pressure, of 5 MPa, was performed. The hydraulic interactions between injection events were characterized through the second injection hydraulic delay and second injection mass in an injection discharge curve indicator equipped with all the components required for its operation and control. In order to define the operating conditions of the multiple injection strategies, to ensure the same injected fuel mass in all cases, the characteristic curves of injection rate for the solenoid diesel injector studied were obtained. The second injection hydraulic delay increases with dwell time values in the range of 0.55–0.9 ms for all multiple injection strategies and levels of rail pressure tested. Conversely, the second injection hydraulic delay decreases with dwell time values higher than 0.9 ms. Moreover, the second hydraulic delay depends mainly on the dwell time and not on the injected fuel mass during the first injection event. The second injection mass increases with dwell values less than 0.6 ms. By contrast, the second injection mass is not significantly affected by that of the first injection at a dwell time higher than 0.6 ms.

There is a significant interest to evaluate alternative injection strategies in order to improve the performance of biofuels and its blends in internal combustion engines as a way to decarbonize the transport sector, particularly in high potence demand niche. Biodiesel is the renewable analogue for petroleum diesel but the performance assessment of its blends from related to their spray macroscopical properties is scarce in the literature. This article evaluates the effect of Waste Cooking Oil Biodiesel (WCO) produced at semi-industrial scale in blends (B05, B10, B20) with commercial Ultra Low Sulphur Diesel (ULSD) on the fuel spray macroscopic properties such as penetration, angle, and area when a split injection strategy is used in a constant volume chamber under non-reactive and evaporative conditions using an injection and back pressure of 120 MPa and 5 MPa, respectively. These results were analysed in conjunction with relevant physicochemical properties of the fuels to identify the optimum diesel-WCO biodiesel blend, that could be implemented in a conventional diesel engine. It was observed that the increase of density and viscosity directly influences spray tip penetration, whereas surface tension affects spray angle. The values of spray penetration and spray area of all fuels during the second injection were higher than those of the first injection. Accordingly, the first injection event provokes an improvement mixing process of the second injection event in all cases. The values of spray penetration and area corresponding to B10 and B20 were higher than those of B5 and ULSD in both injection events at all times. Therefore, the split injection could be an effective strategy to improve the mixing process of biodiesel blends as well as the efficiency and emission performance in conventional diesel engines.