Search Results

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.

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.

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 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.

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.

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.

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.

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.

The current transportation fuels have been one of the biggest contributors towards climate change and greenhouse gas emissions. The use of carbon-free fuels has constantly been endorsed through legislations in order to limit the global greenhouse gas emissions. In this regard, ammonia is seen as a potential alternative fuel, because of its carbon-free nature, higher octane number and as hydrogen carrier. Furthermore, many leading maritime companies are doing enormous research and planning projects to utilize ammonia as their future carbon-free fuel by 2050. Flash boiling phenomenon can significantly improve combustion by enhancing the spray breakup process and ammonia possessing low boiling point, has a considerable potential for flash boiling. However, present literature is missing abundant research data on superheated ammonia sprays.

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.

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.

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.

The objective of this paper is to analyse the performance and the combustion of a large-bore single-cylinder medium speed engine running with hydrotreated vegetable oil. This fuel has a paraffinic chemical structure and high Cetane number. These features enable achievement of complete and clean combustion with different engine setups. The main benefits are thus lower soot and nitrogen oxides emissions compared to diesel fuel. The facility used in this study is a research engine, where the conditions upstream the machine, the valve timing and the injection parameters are fully adjustable. In fact, the boundary conditions upstream and downstream the engine are freely controlled by a separated supply air plant and by a throttle valve, located at the end of the exhaust pipe. The injection system is common-rail: rail pressure, injection timing and duration are completely adjustable.

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 present paper focuses on gaining a deeper understanding about the turbulent flow inside an engine cylinder using large eddy simulation. While the main motivation of the current study is to gain a deeper understanding of the flow patterns and especially about the swirl, the background motivation of this study is the development and testing of suitable methods for the large eddy simulation of combustion engines and the validation of the used simulation methodology. In particular, we study the swirl and other flow features generated by the intake jets inside the cylinder. The simulated geometry is the Sisu Diesel 84 engine cylinder where the exhaust valves are closed and the intake valves have constant valve lifts. Furthermore, the piston has been removed so that the flow is able to exit from the opposite end of the cylinder.

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.

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.

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.