Technological and economic concerns correlated to fulfilling future emissions and CO₂ standards require great research efforts to define an alternative solution for low emissions and highly efficient propulsion systems. Alternative fuel formulation could contribute to this aim. Liquefied petroleum gas (LPG) with lower carbon content than other fossil fuels and which is easily vaporized at ambient conditions has the advantage of lowering CO₂ emissions and optimizing the combustion process. Liquefied petroleum gas characteristics and availability makes the fuel a promising alternative for internal combustion engines. The possible combination of using it in high-efficiency compression ignition engines makes it worth analyzing the innovative method of using LPG as a blend component in diesel. Few relevant studies are detectable in literature in this regard. In this study, two blends containing diesel and LPG, in volume ratios 20/80 and 35/65, respectively, were formulated and utilized. Their effects on combustion and emissions performance were assessed by performing proper experimental tests on a modern light-duty single-cylinder engine test rig. Reference operating points at conventional engine calibration settings were examined. A specific exhaust gas recirculation (EGR) parametrization was performed evaluating the LPG blends’ potential in reducing the smoke emissions at standard engine-out NOx levels. The results confirm excellent NOx-smoke trade-off improvements with smoke reductions up to 95% at similar NOx and efficiency. Unburnt emissions slightly increase, and to acceptable levels. Improvements, in terms of indicated specific fuel consumption (ISFC), are detected in the range of 1–3%, as well as the CO₂ decrease proportionally to the mixing ratio.

In this article, a glycerol ethers mixture obtained from etherification of glycerol with tert-butyl alcohol and isobutylene has been used in blend (10% and 20% v/v) within a commercial diesel fuel to feed a single-cylinder research engine derived from a Euro5 compliant four-cylinder engine. The engine has been run in three significant operating points in the New European Driving Cycle emission homologation area. The results have shown the possibility to burn the diesel–glycerol ethers mixture blends without significant impact on combustion characteristics and efficiencies while, due to the oxygen content of the glycerol ethers mixture, important benefits are obtained in terms of NO_x-particulate matter trade-offs at the exhaust. Moreover, tests have been performed on a diesel engine with optical access through the piston bowl. The injection and combustion processes of the pilot have been investigated by means of the simultaneous use of digital imaging in the visible and infrared ranges in order to have more information on the vapour distribution, the fuel motion before the ignition and the location of hot gas.

A major challenge for internal combustion engines (ICEs), and diesel engines, in particular, is the reduction of exhaust emissions, essentially nitrogen oxides (NOx) and particulate matter (PM). In this regard, the potential of LPG-diesel blends was evaluated in this work. The LPG and diesel blends were externally prepared by exploiting their perfect miscibility at high pressures. Two diesel-LPG mixtures with 20% and 35% by mass LPG concentrations were tested. In terms of spatial and temporal evolution, the spray characterization was performed for the two blends and pure diesel fuel through high-speed imaging technique. The combustion behavior, engine performance and exhaust emissions of LPG-diesel blends were evaluated through a test campaign carried out on a single-cylinder diesel engine. Diesel/LPG sprays penetrate less than pure diesel. This behavior results from a lower momentum, surface tension and viscosity, of the blend jets in comparison to diesel which guarantee greater atomization. The addition of LPG to diesel tends to proportionally increase the spray cone angle, due to the stronger turbulent flow interaction caused by, the lower density and low flash-boiling point. Because of improved atomization and mixing during the injection phase, the blends have shown great potential in reducing PM emissions, without affecting engine performance (CO₂ emissions). The addition of LPG resulted in a significant smoke reduction (about 95%) with similar NOx emissions and acceptable THC and CO emissions. Furthermore, the low cetane number (CN) and high low-heating value (LHV) ensuring leaner air-fuel mixture, and improvements in terms of efficiency, particularly for a blend with a higher concentration of LPG.

Blends of propane-diesel fuel can be used in direct injection diesel engines to improve the air-fuel mixing and the premixed combustion phase, and to reduce pollutant emissions. The potential benefits of usinf propane in diesel engines are both environmental and economic; furthermore, its use does not require changes to the compression ratio of conventional diesel engines. The present paper describes an experimental investigation of the injection process for different liquid preformed blends of propane-diesel fuel in an optically accessible Common Rail diesel engine. Slight modifications of the injection system were required in order to operate with a blend of propane-diesel fuel. Pure diesel fuel and two propane-diesel mixtures at different mass ratios were tested (20% and 40% in mass of propane named P20 and P40). First, injection in air at ambient temperature and atmospheric pressure were performed to verify the functionality of the modified Common Rail injection system. Second, injection process was investigated within the engine. In both configurations, images of the injection process were recorded; in particular, the in-cylinder process was visualized through a sapphire window in the piston bowl. The experimental investigation was performed at four engine operating points of the NEDC (New European Driving Cycle). Results show that the penetration of the blend fuel is as long as the diesel one in the first phase of the injection and is shorter than the diesel fuel at the end of the injection. The cone angle of the blend fuel is always higher than diesel because of the sudden evaporation of propane exiting from the nozzle hole. For these reasons, the use of propane-diesel blends in a diesel engine could allow a better homogenization of the air-fuel mixture.

In recent years, several studies on the efficiency of modern diesel engines have focused on the modeling of combustion process in its different phases. Here, analytical equations are used to describe the physical phenomena that occur in the cylinder. The good agreement between the experimental and simulated data could improve the predictive capabilities of the computational code and reduce the cost of experimental activities. For the modeling of a diesel spray, the first step has been to investigate its behavior in a non-combusting environment; in particular, Musculus and Kattke proposed a model for the simulation of the injection of fuel in non-reacting still environment. Starting from that knowledge, the authors apply the injection model to a compression ignition research engine. By means of an optical engine, injection phase has been investigated via 2D digital imaging. The main jet characteristics like penetration and dispersion angle have been measured. The penetration data were compared with those provided by the 1D model with the same in-cylinder conditions. Some differences have been noted. In order to match the experimental data with the predicted ones: dispersion angle, ramp-up of injection rate, and the equivalence ratio curve need to be modified.