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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.

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.

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.

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.

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.

The discrete droplet model is widely used to describe two-phase flows such as high-velocity dense sprays. The interaction between the liquid and the gas phase is modeled via appropriate source terms in the gas phase equations. This approach can lead to a strong dependence of the liquid-gas coupling on the spatial resolution of the gas phase. The liquid-gas coupling requires the computation of source terms using the gas phase properties, and, subsequently, these sources are then distributed onto the gas phase mesh. In this study, a Lagrange polynomial interpolation method has been developed to evaluate the source terms and also to distribute these source terms onto the gas mesh. The focus of this investigation has been on the momentum exchange between the two phases. The Lagrange polynomial interpolation and source term distribution methods are evaluated for non-evaporating sprays using KIVA3 as a modeling platform.

Non-evaporating diesel sprays have been simulated utilizing the ETAB and the WAVE atomization and breakup models and have been compared with experimental data. The experimental penetrations and widths were determined from back-lit spray images and the droplet sizes have been measured by means of a Malvern particle sizer. The model evaluation criteria include the spray penetration, the spray width and the local droplet size. The comparisons have been performed for variations of the injection pressure, the gas density and the fuel viscosity. The fuel nozzle exit velocities used in the simulations have been computed with a special code that considers the effect of in-nozzle cavitation. The simulations showed good overall agreement with experimental data. However, the capabilities of the models to predict the droplet size for different fuels could be improved.

Natural gas has been considered as one promising alternative fuel for internal combustion (IC) engines to meet strict engine emission regulations and reduce the dependence on petroleum oil. Although compressed natural gas (CNG) intake manifold injection has been successfully applied into spark ignition (SI) engines in the past decade, natural gas direct injection compression ignition (DICI) engine with new injection system is being pursued to improve engine performance. Gas jet behaves significantly different from liquid fuels, so the better understanding of the effects of gas jet on fuel distribution and mixing process is essential for combustion and emission optimization. The present work is aimed to gain further insight into the characteristics of low pressure gas jet. An experimental gas jet investigation has been successfully conducted using tracer-based planar laser-induced fluorescence (PLIF) technique. For safety reason, nitrogen (N₂) was instead of CNG in this study.

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.

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.

This investigation is a continuation of a previous study by these authors in which a Lagrange polynomial interpolation method was developed to evaluate spray source terms and also to distribute the source terms onto the gas mesh; the method was applied to the liquid-gas momentum exchange. For this investigation, the method has been extended to the mass exchange between the liquid and gas phases due to evaporation. The Lagrange polynomial interpolation and source term distribution methods are applied to the liquid-gas mass and momentum exchange and are evaluated for evaporating sprays using KIVA3 as a modeling platform. These methods are compared with the standard “nearest neighbor” method of KIVA3, and experimental data are used to establish their validity. The evaluation criteria used include the liquid and vapor spray penetration, gas velocities and the computational stability.

Decarbonization of the automotive industry is one of the major challenges in the transportation sector, according to the recently proposed climate neutrality policies, e.g., the EU 'Fit for 55' package. Hydrogen as a carbon-free energy career is a promising alternative fuel to reduce greenhouse gas emissions. The main objective of the present study is to investigate non-reactive hydrogen jet impingement on a piston bowl profile at different injection angles and under the effect of various pressure ratios (PR), where PR is the relative ratio of injection pressure (IP) to chamber pressure (CP). This study helps to gain further insight into the mixture formation in a heavy-duty hydrogen engine, which is critical in predicting combustion efficiency. In the experimental campaign, a typical high-speed z-type Schlieren method is applied for visualizing the jet from the lateral windows of a constant volume chamber, and two custom codes are developed for post-processing the results.

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.

This study presents a novel crank mechanism which enables easy and fast compression ratio adjustment. The novel crank mechanism and piston travel are explained and highlighted. The basic idea is that eccentric gear is installed on a crankshaft web. Eccentric gear is fitted to the big end of the connection rod and eccentricity is controlled by rotating the control gear a discrete amount. Thus the position of eccentricity is varied and controls an effective stroke length. The compression ratio is adjusted to best fit current load demand, either optimizing fuel efficiency or engine power and torque. Adjustments are individual to each cylinder. The system is capable of adjusting from min to max within 10 milliseconds [ms]. Emphasis is on reduction of CO2 emissions and reducing fuel consumption, especially at part load condition. The governing mechanical equations are presented.

The present-day transport sector needs sustainable energy solutions. Substitution of fossil-fuels with fuels produced from biomass is one of the most relevant solutions for the sector. Nevertheless, bringing biofuels into the market is associated with many challenges that policymakers, feedstock suppliers, fuel producers, and engine manufacturers need to overcome. The main objective of this research is an investigation of the impact of alternative fuel properties on light vehicle engine performance and greenhouse gases (GHG). The purpose of the present study is to provide decision-makers with tools that will accelerate the implementation of biofuels into the market. As a result, two models were developed, that represent the impact of fuel properties on engine performance in a uniform and reliable way but also with very high accuracy (coefficients of determination over 0.95) and from the end-user point of view.

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.

Distillation properties of gasoline are regulated to ensure the safe and efficient operation of SI-engines. Blending various gasoline components affects the distillation values in a non-linear fashion, making the prediction of these properties challenging. Furthermore, the rise of renewable components necessitates the development of new property prediction methods. In this work, a variety of Machine Learning models were created to predict the distillation points of gasoline blends based on the blending recipe. As input data, real industrial data from a refinery was used together with data from blends created for R&D purposes. The predicted properties were the evaporated volume at the 70 and 100 °C distillation points (E70 and E100). Altogether four different machine learning models were trained, cross-validated and tested using seven different pre-processing methods. It was found that Support Vector Regression (SVR) was the most effective at predicting the distillation points.

Compressed natural gas direct-injection (CNG-DI) engines based on diesel cycle combustion system with pilot ignition have ability to achieve high thermal efficiency and low emissions. Generally, underexpanded jets can be formed when the high pressure natural gas is injected into the combustion chamber. In such conditions, shock wave phenomena are the typical behaviors of the jet, which can significantly influence the downstream flow structure and turbulent mixing. In the present study, the characteristics of high-pressure transient jets were investigated using planar laser-induced fluorescence (PLIF) of acetone as a fuel tracer. The evolution of the pulsed jet shows that there are three typical jet flow patterns (subsonic, moderately underexpanded, and highly underexpanded) during the injection. The full injection process of high-pressure pulsed jets is well described with the help of these shock wave structures.