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Technical Paper

Interaction of Multiple Fuel Sprays in a Heavy-Duty Diesel Engine

This paper aims to study numerically the influence of the number of fuel sprays in a single-cylinder diesel engine on mixing and combustion. The CFD simulations are carried out for a heavy-duty diesel engine with an 8 hole injector in the standard configuration. The fuel spray mass-flow rate was obtained from 1D-simulations and has been adjusted according to the number of nozzle holes to keep the total injected fuel mass constant. Two cases concerning the modified mass-flow rate are studied. In the first case the injection time was decreased whereas in the second case the nozzle hole diameter was decreased. In both cases the amount of nozzle holes (i.e. fuel sprays) was increased in several steps to 18 holes. Quantitative analyses were performed for the local air-fuel ratio, homogeneity of mixture distribution, heat release rate and the resulting in-cylinder pressure.
Technical Paper

Experimental Study of Spray Characteristics between Hydrotreated Vegetable Oil (HVO) and Crude Oil Based EN 590 Diesel Fuel

The aim of current study was to compare the global fuel spray characteristics between renewable hydrotreated vegetable oil (HVO) and crude oil-based EN 590 diesel fuel. According to previous studies, the use of HVO enables reductions in carbon monoxide (CO), total hydrocarbon (THC), nitrogen oxide (NOx) and particle matter (PM) emissions without any changes to the engine or its controls. Fuel injection strategies and global fuel spray characteristics affect on engine combustion and exhaust gas emissions. Due to different physical properties of two different fuels, fuel spray characteristics differ. Fuel spray studies were performed with backlight imaging using a pressurized test chamber imitating real engine conditions at the end of compression stroke. However, the measurements were made in non-evaporative conditions. Various injection parameters such as injection pressures and orifice diameter were tested.
Technical Paper

Improving the Accuracy of 1-D Fuel Injection Modeling

In this study, one-dimensional fluid dynamics simulation software was utilized in producing common rail diesel fuel injection for varying injection parameters with enhanced accuracy. Injection modeling refinement is motivated by improved comprehension of the effects of various physical phenomena within the injector. In addition, refined injection results yield boundary conditions for three-dimensional CFD simulations. The criteria for successful simulation results were evaluated upon experimental test run data that have been reliably obtained, primarily total injected mass per cycle. A common rail diesel fuel delivery system and its core mechanics were presented. System factors most critical to fuel delivery were focalized. Models of two solenoid-type common rail injectors of different physical sizes and applications were enhanced.
Technical Paper

Comparing Breakup Models in a Novel High Injection Pressure SCR System using Polyhedral Meshing

A novel high pressure SCR spray system is investigated both experimentally and numerically. RANS simulations are performed using Star-CD and polyhedral meshing. This is one of the first studies to compare droplet breakup models and AdBlue injection with high injection pressure (Pinj=200 bar). The breakup models compared are the Reitz-Diwakar (RD), the Kelvin-Helmholtz and Rayleigh-Taylor (KHRT), and the Enhanced Taylor Analogy Breakup (ETAB) model. The models are compared with standard model parameters typically used in diesel fuel injection studies to assess their performance without any significant parameter tuning. Experimental evidence from similar systems seems to be scarce on high pressure AdBlue (or water) sprays using plain hole nozzles. Due to this, it is difficult to estimate a realistic droplet size distribution accurately. Thereby, there is potential for new experimental data to be made with high pressure AdBlue or water sprays.
Technical Paper

Liquid Spray Data from an Optical Medium-Speed Diesel Engine and Its Comparison with CFD

Experimental spray tip penetrations obtained from a large-bore medium-speed optical diesel engine were compared to CFD simulations. The optical spray results are unique as they are obtained from a running large-bore (200mm) diesel engine. The experimental spray tip penetration measurements were obtained during the early spray development period when the spray evaporation had not yet reached the quasi steady-state phase. The CFD simulations were conducted in both static chamber environment and in engine conditions. The fuel injection boundary conditions were obtained from 1-D simulations. Within the error margins associated with the experimental and computational data, relatively good accuracy was obtained between measured and simulated spray tip penetration. It was also observed that it is very important to have accurate fuel injection mass flow rate data. This was observed after a sensitivity analysis was made for the injection duration and fuel mass quantity.
Journal Article

Hydrotreated Vegetable Oil (HVO) as a Renewable Diesel Fuel: Trade-off between NOx, Particulate Emission, and Fuel Consumption of a Heavy Duty Engine

Hydrotreating of vegetable oils or animal fats is an alternative process to esterification for producing biobased diesel fuels. Hydrotreated products are also called renewable diesel fuels. Hydrotreated vegetable oils (HVO) do not have the detrimental effects of ester-type biodiesel fuels, like increased NOx emission, deposit formation, storage stability problems, more rapid aging of engine oil or poor cold properties. HVOs are straight chain paraffinic hydrocarbons that are free of aromatics, oxygen and sulfur and have high cetane numbers. In this paper, NOx - particulate emission trade-off and NOx - fuel consumption trade-off are studied using different fuel injection timings in a turbocharged charge air cooled common rail heavy duty diesel engine. Tested fuels were sulfur free diesel fuel, neat HVO, and a 30% HVO + 70% diesel fuel blend. The study shows that there is potential for optimizing engine settings together with enhanced fuel composition.
Technical Paper

Optical In-Cylinder Measurements of a Large-Bore Medium-Speed Diesel Engine

The objective of this study was to build up an optical access into a large bore medium-speed research engine and carry out the first fuel spray Particle Image Velocimetry (PIV) measurements in the running large bore medium-speed engine in high pressure environment. The aim was also to measure spray penetration with same optical access and apparatus. The measurements were performed in a single-cylinder large bore medium-speed research engine, the Extreme Value Engine (EVE) with optical access into the combustion chamber. The authors are not aware of any other studies on optical spray measurements in large bore medium-speed diesel engines. Successful optical measurements of the fuel spray penetration and the velocity fields were carried out. This confirms that the exceptional component design and laser sheet alignment used in this study proved to be valid for optical fuel spray measurements in large-bore medium-speed diesel engines.
Technical Paper

Particle Image Velocimetry Measurements of a Diesel Spray

The current study was focused on flow field measurements of diesel sprays. The global fuel spray characteristics, such as spray penetration, have also been measured. Particle Image Velocimetry (PIV) was utilized for flow field measurements and the global spray characteristics were recorded with high-speed back light photographing. The flow field was scanned to get an idea of the compatibility of PIV technique applied to dense and high velocity sprays. It is well proven that the PIV technique can be utilized at areas of low number density of droplets, but the center of the spray is way beyond the ideal PIV measurement conditions. The depth at which accurate flow field information can be gathered was paid attention to.
Technical Paper

Computational Considerations of Fuel Spray Mixing in an HCCI Operated Optical Diesel Engine

Fuel spray mixing has been analyzed numerically in a single-cylinder optical research engine with a flat piston top. In the study, a narrow spray angle has been used to align the sprays towards the piston top. Fuel spray mass flow rate has been simulated with 1-D code in order to have reliable boundary condition for the CFD simulations. Different start of fuel injections were tested as well as three charge air pressures and two initial mixture temperatures. Quantitative analysis was performed for the evaporation rates, mixture homogeneity at top dead center, and for the local air-fuel ratios. One of the observations of this study was that there exists an optimum start of fuel injection when the rate of spray evaporation and the mixture homogeneity are considered.
Technical Paper

Cylinder Charge, Initial Flow Field and Fuel Injection Boundary Condition in the Multidimensional Modeling of Combustion in Compression Ignition Engines

Cylinder charge, cylinder flow field and fuel injection play the dominant roles in controlling combustion in compression ignition engines. Respective computational cylinder charge, initial flow field and fuel injection boundary affect combustion simulation and the quality of emission prediction. In this study the means of generating the initial values and boundary data are presented and the effect of different methods is discussed. This study deals with three different compression ignition engines with cylinder diameters of 111, 200 and 460 mm. The initial cylinder charge has been carefully analyzed through gas exchange pressure recordings and corresponding 1-dimensional simulation. The swirl generated by intake ports in a high-speed engine is simulated and measured. The combustion simulation using a whole cylinder model was compared with a sector model simulation result.
Technical Paper

Diesel Spray Simulation and KH-RT Wave Model

This study presents diesel spray breakup regimes and the wave model basic theory from literature. The RD wave model and the KH-RT wave model are explained. The implementation of the KH-RT wave model in a commercial CFD code is briefly presented. This study relies on experimental data from non-evaporating sprays that have earlier been measured at Helsinki University of Technology. The simulated fuel spray in a medium-speed diesel engine had a satisfactory match with the experimental data. The KH-RT wave model resulted in a much faster drop breakup than with the RD wave model. This resulted in a thin spray core with the KH-RT model. The fuel viscosity effect on drop sizes was well predicted by the KH-RT wave model.