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Real gas effects are studied during the compression stroke of a diesel engine. Several different real gas models are compared to the ideal gas law and to the experimental pressure history. Comparisons are done with both 1-D and CFD simulations, and reasons and answers are found out for the observed differences between simulations and experimental data. The engine compression ratio was measured for accurate model predictions. In addition, a 300bar extreme pressure case is also analyzed with the real gas model since an engine capable for this performance level is currently being built at the Aalto University School of Science and Technology. Real gas effects are even more important in these extreme conditions than in normal operating pressures. Finally, it is shown that the predicted pressure history during an engine compression stroke by a real gas model is more accurately predicted than by the ideal gas law.

Gasoline blending is known to be complicated, because individual gasoline fractions with different octane numbers, Research Octane Number (RON) or Motor Octane Number (MON) do not always blend linearly. Instead, they may blend non-linearly, in a synergistic or antagonistic manner. Even though RON and MON are regulated properties, linear and non-linear octane blending is not a broadly understood topic. The target in the developing process of a modern SI engine is to have 100% combustion efficiency which would lead to the reduction of hydrocarbon and carbon monoxide emissions. Therefore, the properties of gasoline, especially RON and MON, need to be optimized to ensure proper ignition in the engine and prevent harmful autoignition reactions. There are hundreds of hydrocarbons in gasoline which have different octane numbers (ON). The explanations for these variations are the structural differences in hydrocarbon molecules that influence on their reactivity.

The engine fueled with methane/diesel is a promising and highly attractive operation mode due to its high performance-to-cost ratio and clean-burning qualities. However, the combustion process and chemical reactions in dual fuel combustion are highly complex, involving short transient pilot-fuel injection into the premixed gaseous fuel charge, autoignition, and combustion mode transition into premixed flame propagation. The motivation of the current investigation is to gain an insight into the combustion dynamics in dual fuel combustion engine based on chemical radicals and thermal radiation. The chemiluminescence (CL) and natural luminosity (NL) are expected to provide specific characteristics in combustion control and monitoring. To visualize the highly unsteady combustion process in terms of OH*, CH2O* radicals and natural luminous emissions, the band pass filters with 308 nm, 330 nm combined with an image doubler are employed to visualize the OH* and CH2O* CL simultaneously.

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.

The direct injection (DI) natural gas engine is considered as one of the promising technologies to achieve the continuing goals of the higher efficiency and reduced emissions for internal combustion engines. Shock wave phenomena can easily occur near the nozzle exit when high pressure gaseous fuel is injected directly into the engine cylinder. In the present study, high pressure gas issuing from a prototype gas injector was experimentally studied using planar laser-induced fluorescence (PLIF) technique. Acetone was selected as a fuel tracer. The effects of injection pressures on the flow structure and turbulent mixing were investigated based on a series of high resolution images. The jet macroscopic structures, such as jet penetration, cone angle and jet volume, are analyzed under different injection pressures. Results show that barrel shock waves can significantly influence the jet flow structure and turbulent mixing.

The objective of this paper is to analyze the performance and the combustion of a large-bore medium-speed engine running with hydro-treated vegetable oil (HVO) at low engine load. This fuel has a paraffinic chemical structure and high cetane number (CN). The main benefits are thus lower emission compared to diesel fuel and low soot values. The facility used in this study is a research engine, where the conditions before and after the machine, the valve timing and the injection parameters are fully adjustable. Several in-cylinder conditions before the combustion have been tested. The results are promising and show the benefits of HVO compared to diesel fuel. In fact, it has been possible to reduce nitrogen oxides (NOx) emission over 50% running with HVO and opportunely tuned valve timing.

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.

As CO2 emissions from traffic must be reduced and fossil-based traffic fuels need to phase out, bio-based traffic fuels alone cannot meet the future demand due to their restricted availability. Another way to support fossil phase-out is to include synthetic fuels that are produced from circular carbon sources with renewable energy. Several different fuel types have been proposed, while, methanol only requires little processing from raw materials and could be used directly or as a drop-in fuel for some of the current engine fleet. CO2 emissions arising from fuel production are significantly reduced for synthetic renewable methanol compared to the production of fossil gasoline. Methanol has numerous advantages over the currently used fossil fuels with high RON and flame speed in spark-ignition engines as well as high efficiency and low emissions in combustion ignition engines.

The flow through the valves of an engine cylinder head is very complex in nature due to very high gas velocities and strong flow separation. However, it is also the typical situation in almost every engine related flow. In order to gain better understanding of the flow features after the cylinder head, and to gain knowledge of the performance level that can be expected from CFD analysis, flow field measurements and computations were made in an engine rig. Particle image velocimetry (PIV) and paddle wheel measurements have been conducted in a static heavy-duty diesel engine rig to characterize the flow features with different valve lifts and pressure differences. These measurements were compared with CFD predictions of the same engine. The simulations were done with the standard k-ε turbulence model and with the RNG turbulence model using the Star-CD flow solver.

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.

In this work simulation results of a round spray jet are presented using the combination of Large-Eddy Simulation (LES) and Lagrangian Particle Tracking (LPT). The simulation setup serves as a synthetic model of non-atomizing spray particles taken from the Rosin-Rammler size distribution that enter a chamber filled with gas through an inlet hole with diameter D. At the inlet gas velocity and droplet velocities are specified in addition to the initial size distribution of droplets. The Reynolds number as referred to the gas inflow velocity and jet diameter is Re=10000. The setup is advantageous for understanding the details of diesel sprays since it avoids near-nozzle spray modeling and thereof the corresponding error which is especially important in LES. Here, the implicit LES is applied so that the compressible Navier-Stokes equations are solved directly with a numerical algorithm in a fine mesh without a subgrid scale 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.

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.

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.

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.

The objective of this study is to achieve high reduction of NOx emissions in a medium-speed single-cylinder research engine. The main feature of this research engine is that the gas exchange valve timing is completely adjustable with electro-hydraulic actuators. The study is carried out at high engine load and using a very advanced Miller valve timing. Since the engine has no turbocharger, but a separate charge air system, 1-D simulations are carried out to find the engine setup, which would be close to the operating points of a real engine. The obtained NOx reduction is over 40% with no penalty in fuel consumption.

A new variable density / physical property wall function formalism has been developed. The new formalism is designed to extend the validity range of wall functions to cover both the low- and high-Reynolds-number domains so that the restrictions on the non-dimensional near-wall mesh resolution can be avoided. The new formalism also accounts for the temperature gradient induced variations of density, viscosity, heat conductivity and specific heat capacity. The new wall function formalism is constructed in conjunction with a modified low-Reynolds-number turbulence model in order to avoid the conflicting requirements of low- and high-Reynolds-number models on the near wall mesh resolution. The new formulation is validated with test simulations of strongly heated air flows in circular tube against measurements and Direct Numerical Simulation (DNS) results.

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.

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.

The design and testing of the valve train for a new two-stroke diesel engine concept [1,2] is presented. The gas exchange of this process requires extremely fast-acting inlet valves, which constituted a very demanding designing task. A simulation model of the prototype valve train was constructed with commercially available software. The simulation program served as the main tool for optimizing the dynamic behavior of the valve train. The prototype valve train was built according to the simulations and valve acceleration measurements were performed in order to validate the simulation results. The simulations and measurements are presented in detail in this paper.