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In the present study, a new approach for modelling emissions of coke particles or cenospheres from large diesel engines using HFO (Heavy fuel oil) was studied. The model used is based on a multicomponent droplet mass transfer and properties model that uses a continuous thermodynamics approach to model the complex composition of the HFO fuel and the resulting evaporation behavior of the fuel droplets. Cenospheres are modelled as the residue left in the fuel droplets towards the end of the simulation. The mass-transfer and fuel properties models were implemented into a cylinder section model based on the Wärtsilä W20 engine in the CFD-code Star CD v.4.24. Different submodels and corresponding parameters were tuned to match experimental data of cylinder pressures available from Wärtsilä for the studied cases. The results obtained from the present model were compared to experimental results found in the literature.

Dual fuel (DF) combustion technology as a feasible approach controlling engine-out emissions facilitates the concept of fuel flexibility in diesel engines. The abundance of natural gas (90-95% methane) and its relatively low-price and the clean-burning characteristic has attracted the interest of engine manufacturers. Moreover, with the low C/H ratio and very low soot producing tendency of methane combined with high engine efficiency makes it a viable primary fuel for diesel engines. However, the fundamental knowledge on in-cylinder combustion phenomena still remains limited and needs to be studied for further advances in the research on DF technology. The objective of this study is to investigate the ignition delay with the effect of, 1) methane equivalence ratio, 2) intake air temperature and 3) pilot ratio on the diesel-methane DF-combustion. Combustion phenomenon was visualized in a single cylinder heavy-duty diesel engine modified for DF operations with an optical access.

Measurements have been done in order to obtain information concerning the effect of EGR for the smoke and NOx emissions of a heavy-duty diesel engine. Measured smoke number and NOx emissions are explained using detailed chemical kinetic calculations and CFD simulations. The local conditions in the research engine are analyzed by creating equivalence ratio - temperature (Phi-T) maps and analyzing the CFD results within these maps. The study uses different amounts of EGR and the standard EN590 diesel fuel. The detailed chemical kinetic calculations take into account the different EGR rates. The CFD calculations are made with a flamelet-based combustion model together with detailed chemistry. The results are compared to a previous study where a hybrid local flame area evolution model combined with an eddy breakup - type model was used in the CFD simulations.

Soot modeling has become increasingly important as diesel engine manufacturers are faced with constantly tightening soot emission limits. As such the accuracy of the soot models used is more and more important but at the same time 3-D CFD engine studies require models that are computationally not too demanding. In this study, soot Phi-T maps created with detailed chemistry code have been used to develop a soot model for engineering purposes. The proposed soot model was first validated against detailed chemistry results in premixed laminar environment. As turbulence in engines is of major importance, it was taken into account in the soot oxidation part of the model with the laminar and turbulent characteristic time- type of approach. Finally, the model was tested in a large bore Diesel engine with varying loads. Within the steps described above, the proposed model was also compared with the well-known Hiroyasu-Magnussen soot model.

The study aims at providing more accurate initial conditions for turbulence prior to combustion with the help of a four valve, large bore diesel engine CFD model. Combustion simulations are typically done with a sector mesh and initial turbulence in these simulations is usually taken from relatively inaccurate correlations. This study also aims at developing a more accurate initial turbulence correlation for combustion simulations. A one-dimensional model was first used to provide boundary conditions as well as the initial flow conditions at the beginning of the simulation. Steady state and transient boundary conditions were studied. Also, the standard κ - ε and RNG/κ - ε turbulence models were compared. From the averaged values of turbulence kinetic energy and its dissipation rate over the cylinder volume, a re-tuned correlation for defining the initial turbulent conditions at bottom dead center (BDC) prior to the compression stroke is proposed.

Three-dimensional diesel engine combustion simulations with single-step chemistry have been compared with two-step and three-step chemistry by means of the Laminar and Turbulent Characteristic Time Combustion model using the Star-CD program. The second reaction describes the oxidation of CO and the third reaction describes the combustion of H2. The comparisons have been performed for two heavy-duty diesel engines. The two-step chemistry was investigated for a purely kinetically controlled, for a mixing limited and for a combination of kinetically and mixing limited oxidation. For the latter case, two different descriptions of the laminar reaction rates were also tested. The best agreement with the experimental cylinder pressure has been achieved with the three-step mechanism but the differences with respect to the two-step and single-step reactions were small.

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.

The development of new high power diesel engines is continually going for increased mean effective pressures and consequently increased thermal loads on combustion chamber walls close to the limits of endurance. Therefore accurate CFD simulation of conjugate heat transfer on the walls becomes a very important part of the development. In this study the heat transfer and temperature on piston surface was studied using conjugate heat transfer model along with a variety of near wall treatments for turbulence. New wall functions that account for variable density were implemented and tested against standard wall functions and against the hybrid near wall treatment readily available in a CFD software Star-CD.

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.

This study is presenting a comparative spray study of modern large bore medium speed diesel engine common rail injectors. One subject of paper is to focus on nozzles with same nominal flow rate, but different machining. The other subject is penetration velocity measurements, which have a new approach when trying to understand the early phase of transient spray. A new method to use velocimetry for spray tip penetration measurements is here introduced. The length where spray penetration velocity is changed is found. This length seems to have clear connection to volume fraction of droplets at gas. These measurements also give a tool to divide the development of spray into acceleration region and deceleration region, which is one approach to spray penetration. The measurements were performed with backlight imaging in pressurized injection test rig at non-evaporative conditions. Gas density and injection pressure were matched to normal diesel engine operational conditions.

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.

Dual-fuel technology is suggested as a solution for effectively utilizing alternative fuel types in the near future. Charge air mixed methane combined with a compression ignition engine utilizing a small diesel pilot injection seems to form a worthwhile compromise between good engine efficiency and low emission outcome. Problems concerning dual-fuel technology profitableness seems to be related to fully control the combustion in relation to lean conditions. Lean operating conditions solves the problems concerning pumping losses, but brings challenges in controlling the slow heat release of the premixed methane-air mixture. In the present work, a single cylinder ‘free parameter’ diesel engine was adapted for dual-fuel (diesel-methane) usage. A parameter study related to lambda window widening possibilities was carried out.

Marine transportation sector is highly dependent on fossil-based energy carriers. Decarbonization of shipping can be accomplished by implementing biobunkers into an existing maritime fuel supply chain. However, there are many compatibility issues when blending new biocomponents with their fossil-based counterparts. Thus, it is of high importance to predict the effect of fuel properties on marine engine performance, especially for new fuel blends. In the given work, possible future solutions concentrated on liquid fuels are taken into account. Under consideration are such fuels as biodiesel (FAME), hydrotreated vegetable oil (HVO), straight vegetable oil (SVO), pyrolysis oil, biocrude, and methanol. Knowledge about the behavior of new fuel in an existing engine is notably important for decision makers and fuel producers. Hence, the main goal of the present work is to create a model, which can predict the engine performance from the end-user perspective.

Two different medium-speed diesel engine cylinder head designs have been studied. The focus of the study has been the effect of intake channel design in the in-cylinder flow. The study has been carried out by CFD. The first cylinder head is a standard Wärtsilä 20 cylinder head and the second one is a specially designed head for a single cylinder research engine, called Extreme Value Engine (EVE). The CFD boundary conditions have been simulated by the help of a 1-d simulation code. In the full load cases the maximum cylinder pressure was 300 bar. Simulations have been done at lower load level too. One simulation with the new cylinder head was carried out with one intake valve closed in order to get an idea of the swirl to be generated by this approach. In the study the in-cylinder flow field, the cylinder charge and turbulence kinetic energy have been examined.

Several high-speed diesel engine test runs were carried out during 2010 in Aalto University using a single-cylinder research engine. The main focus was on miller cycle and exhaust gas recirculation (EGR) tests using hydrotreated vegetable oil (HVO) as fuel. But also reference tests were run using both HVO and regular EN590 diesel in normal engine configuration and running parameters. The miller tests included a sweep of three different intake valve closing timings and also a sweep with advanced start of injection. The results showed a reduction in both nitrous oxides (NOx) and smoke emissions. EGR tests showed a significant decrease in NOx emissions as was expected. The lower smoke emissions of HVO compared to EN590 enable higher EGR percentages with similar PM emission and hence bigger NOx emission reduction.

Direct injection of natural gas in engines is considered a promising approach toward reducing engine out emissions and fuel consumption. As a consequence, new gas injection strategies have to be developed for easing direct injection of natural gas and its mixing processes with the surrounding air. In this study, the behavior of a hollow cone gas jet generated by a piezoelectric injector was experimentally investigated by means of tracer-based planar laser-induced fluorescence (PLIF). Pressurized acetone-doped nitrogen was injected in a constant pressure and temperature measurement chamber with optical access. The jet was imaged at different timings after start of injection and its time evolution was analyzed as a function of injection pressure and needle lift.

Renewable diesel-type fuels and their compatibility with a single-cylinder medium-speed research diesel engine were studied. The report consists of a literature study on the fuels, introduction of the simulation model designed and simulations made, and of the results and summary sections. The fuels studied were traditional biodiesel (fatty acid methyl ester, FAME), hydrotreated vegetable oil (HVO), Fischer-Tropsch (FT) diesel fuels and dimethyl ether (DME). According to the simulations, the behaviors of different renewable diesel fuels in the fuel injection system are quite similar to one another, with the greatest deviations found with DME. The main differences in the physical properties are fuel densities and viscosities and especially with DME compressibility, which have some predictable effect. The chemical properties of the fuels are more critical for a common rail fuel injection system.

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.

Over the past few years, the growing concerns about global warming and efforts to reduce engine-out emissions have made the dual-fuel (DF) engines more popular in marine and power industries. The use of natural gas as an alternative fuel in DF engines has both the environmental and economic advantages over the conventional diesel combustion. However, the misfire phenomenon at lean conditions limits the operating range of DF combustion and causes emissions of unburned hydrocarbon (UHC) and unburned methane (methane-slip) in the environment. The greenhouse effect of methane is considered 28 times greater than CO2 over a 100-year perspective, which raises concerns for the governments and marine engine manufacturers. In efforts to reduce the UHC and methane-slip from DF engines, this study discusses ethane enrichment of diesel-methane DF combustion in a full-metal single-cylinder research engine under lean condition (λGFB = ~2.0) while keeping the total-fuel energy rather constant.

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.