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In this work, surrogate fuels composed of n-decane and alpha-methylnaphthalene (AMNL) with different compositions according to the reference cetane numbers 53, 45, 38, and 23 are investigated. In addition to the two-component mixtures, we examine a three-component mixture composed of n-decane, AMNL, and di-n-butyl ether (DNBE) corresponding to a reference cetane number of 53. Spray characteristics of liquid and fuel vapor phase and the relationship between ignition quality and lift-off length are investigated. The experimental results show, first of all, that for these mixtures, the cetane number is a good indicator for the ignition delay. Diesel and surrogate fuels have different liquid penetration lengths, which depend on the evaporation rate, and hence vapor pressure and boiling point of the fuels.

Ethanol is frequently used as a blending component in standard gasoline, with blend rates up to 10%vol liq . n-Butanol has received recent interest as an alternative fuel instead of ethanol for use in spark ignition engines. Similar to ethanol, n-butanol can be produced via the fermentation of sugars, starches, and lignocelluloses obtained from agricultural feedstock. It is of great interest to modern engine development to understand the effect of ethanol and n-butanol as blending components on the laminar burning velocity of standard gasoline. The laminar burning velocity is one key parameter for the numerical simulation of gasoline engine combustion processes. Tested fuel components are ethanol, n-butanol, and standard marked gasoline without any oxygen content. Fuel blends consist of standard-marked gasoline containing ethanol and butanol. The maximum blend rate of oxygenates is 10%vol liq . Experiments were done at different equivalence ratios between 0.7 and 1.3.

Increasing concern for the environment and the impending scarcity of fossil fuels requires continued development in hydrocarbon combustion science. For compression-ignition engines, adding oxygenated compounds to the fuel can reduce noise, soot formation, and unburned hydrocarbons while simultaneously increasing thermal efficiency. In order to reliably model and design compression-ignition engines to use new fuel blends, accurate spray characteristic data is required. In this study, the spray characteristics of various blends of the oxygenated compound di-n-butyl ether (DNBE) with standard EN590 Diesel fuel are presented, including spray cone angle and spray penetration length for both liquid and gas phases. The experiments were conducted in a spray chamber at ambient conditions of 50 bar and 800 K, simulating TDC conditions in a Diesel engine. Injection pressures were varied from 700-1600 bar.

Fuels containing oxygenates have become more and more important for spark ignition engines in recent years. Oxygenates are either used as an octane booster or as a biofuel component for fulfilling legislative regulations. Ethanol has been well established for blend rates up to 10%volliq. On the other hand butanol has been introduced as an alternative biofuel component. The effect of the laminar burning velocity of different fuel components on modern engine development is investigated by conducting experiments under high initial pressure and temperature. Initial conditions in this work are a pressure of p = 10 bar and a temperature of T = 373 K. Experiments were done at different fuel - air ratios between 0.8 and 1.3. Test fuels were the pure fuel components iso-octane, ethanol and n-butanol. Different chemical kinetic mechanisms for iso-octane, ethanol and n-butanol from literature are used to calculate laminar burning velocities.

Oxygenates, such as methanol or ethanol, are frequently used as blending components in standard gasoline. One oxygenate, dimethyl ether (DME), is also used as a fuel component in some regions of the world, for example in Asia. In addition, patent reviews show the potential of DME as a blending component in liquefied petroleum gas (LPG) or mixed with propane. The laminar burning velocity is one key parameter for the numerical simulation of gasoline engine combustion processes. Therefore, it is of great interest for modern engine development to understand the effect of oxygenates on the laminar burning velocity. The experimental results have been conducted under engine-like conditions with elevated initial pressures of up to 20 bar and initial temperatures of 373 K. Experiments were done at equivalence ratios between 0.8 and 1.3. The experimental setup consists of a spherical closed pressurized combustion vessel with optical access.

The laminar burning velocity is one key parameter for the numerical simulation of gasoline engine combustion processes. In order to understand the effect of the laminar burning velocity of different fuel components on modern engine development it is of great interest to conduct experiments under high initial pressure and temperature. Initial conditions in this publication are a pressure of p = 10bar and a temperature of T = 373K. Special focus has been laid on the common C1 and C2 alcohols, methanol and ethanol, which are frequently used for blending components in standard gasoline. The experimental setup consists of a spherical closed pressurized combustion vessel with optical access. Schlieren measurements coupled with a high speed camera are used for image acquisition to track the expanding flame front. Finally, a post processing tool is used to extrapolate the measurements to zero stretch. Experiments were done at different fuel-air ratios between Φ = 0.8 and up to Φ = 1.2.

Recently, fuels containing ethanol have become more and more important for spark ignition engines. Fuels with up to 10 vol.-% ethanol can be used in most spark ignition engines without technical modification. These fuels have been introduced in many countries already. Alternatively, for fuels with higher amounts of ethanol so called flex fuel vehicles (FFV) exist. One of the most important quantities characterizing a fuel is the laminar burning velocity. To account for the new fuels with respect to engine design, reliable data need to be existent. Especially for engine simulations, various combustion models have been introduced which rely on the laminar burning velocity as the physical quantity describing the progress of chemical reactions, diffusion, and heat conduction. However, there is very few data available in the literature for fuels containing ethanol, especially at high pressures.

Engine noise pollution is as harmful as other forms of pollution to human health. Apart from the health effects, noise also has an adverse effect on the engine structure, thus requiring a sturdier construction to maintain long engine life. In a conventional direct injection diesel engine the fuel ignites spontaneously shortly after the beginning of injection. The Combustion process causes fluctuations in heat release and therefore, fluctuations in combustion chamber pressure. Combustion generated noise can be lowered by lowering the fluctuations in heat release or pressure. Which can be achieved by separating the fuel evaporation and fuel-air mixing from start of ignition in space and in time. The noise is mainly affected by the early part of the combustion process due to higher rates of heat release. Combustion noise generation in the early stage of combustion is not yet entirely understood.

Diesel engine modeling by means of CFD (computational fluid dynamics) has become a more and more important tool in the development process for new engine design. An adequate and reliable Diesel engine model relies on many features. Beside the combustion and spray modeling, the question what model fuel should be used is discussed and in the past, a mixture of n-decane and α-methylnaphthalene, denoted as IDEA fuel, was found to be a good surrogate fuel for Diesel for the conventional Diesel combustion mode. New combustion designs such as PCCI (premixed charged compression ignition) are a possible solution for the strict upcoming emission limits. Due to a shift to lower temperatures and better homogenization, less NOx and soot is formed. To model these combustion designs, a re-evaluation of the model fuel that is to be used is required when the benefit of a detailed chemical reaction mechanism is favored in the combustion modeling.

Combustion and pollutant formation in a new recently introduced Common-Rail DI Diesel engine concept with roof-shaped combustion chamber and tumble charge motion are numerically investigated using the Representative Interactive Flamelet concept (RIF). A reference case with a cup shaped piston bowl for full load operating conditions is considered in detail. In addition to the reference case, three more cases are investigated with a variation of start of injection (SOI). A surrogate fuel consisting of n-decane (70% liquid volume fraction) and α-methylnaphthalene (30% liquid volume fraction) is used in the simulation. The underlying complete reaction mechanism comprises 506 elementary reactions and 118 chemical species. Special emphasis is put on pollutant formation, in particular on the formation of NOx, where a new technique based on a three-dimensional transport equation within the flamelet framework is applied.

Early injection strategies in the case of part-load conditions are offering the possibility to enhance mixing and evaporation. Due to the early injection, ignition and evaporation are separated in time and space for that less rich pockets from where soot is formed are occurring. For reducing NOx, cooled EGR is a method to dilute the intake charge. The combustion is shifted to lower temperatures and less NOx is formed. More, the cooling of the intake charge and the higher heat capacity enhance the evaporation time for that ignition starts at later times and combustion is retarded. For the simulation of such engine cases using high rates of EGR with an early fuel injection, a CFD (Computational Fluid Dynamics) code is coupled interactively with the flamelet model that will be applied here as combustion model. That approach, known as RIF (Representative Interactive Flamelet) model, requires a re-evaluation of the chemical reaction mechanism.

The non-premixed turbulent combustion and emission formation in a modern DI diesel engine relies mostly on the mixture formation process induced by the diesel fuel spray. Therefore the numerical simulation of this process has to incorporate accurate spray modeling which captures the physics of the spray formation, propagation and vaporization. A widely used framework for spray modeling is the Discrete Droplet Model (DDM) which also is applied in the present work. In the DDM framework, separate submodels account for droplet breakup, droplet-droplet interaction and evaporation. Due to the empirical nature of these submodels (particularly droplet breakup and collision) necessitated by an incomplete representation of the physics, and by the inability to isolate each process under diesel engine relevant conditions, some of the constants controlling the outcomes of these submodels require calibration.

Correct prediction of mixture formation in fuel sprays is a prerequisite in the framework of 3D CFD engine simulations using a reliable combustion model. To understand the process of fuel evaporation and mixture formation in dense atomized sprays a simultaneous Mie/Shadow imaging technique and a 1D-linear Raman scattering technique are applied to investigate spray formation of high pressure direct injection. Mixture composition is one of the most important parameters in fuel sprays and is difficult to measure because liquid and vapor phases appear simultaneously. Ethanol is used as a model fuel since the phase-dependent spectral shift of the OH stretching vibration allows the Raman signal separation of liquid and vapor phase. The investigations are carried out in a high temperature high pressure injection chamber, where pressures and temperatures can be set up to 5MPa and 800 K.

Soot formation in DI diesel engines is caused by the in-homogeneous mixture of evaporated diesel fuel and air. Locally fuel-rich regions are the origin of soot formation. Even though the higher temperatures during the combustion process assist the oxidation process, the formation of NOx pollutants increases with increasing temperature, which is known as soot-NOx trade-off. One measure to reduce both soot and NOx emissions uses an emulsified fuel where the fuel is replaced by an emulsion of diesel-water in order to homogenise the mixture formation process. The influence of such an emulsion on the pollutant formation was numerically examined using the CFD code KIVA-3V for the flow and the Representative Interactive Flamelet model (RIF) for the combustion modelling and combustion turbulence interaction respectively. The diesel fuel was replaced by a surrogate fuel consisting of 70% n-decane and 30% α-methylnaphthalene.

Quenching of premixed flames at cold walls is investigated to study the importance of the model fuel choice for combustion modeling. Detailed chemical mechanisms for two different fuels, namely the low-molecular-weight fuel methane, and the more complex fuel iso-octane are employed. For both fuels the response of the flame to the very rapid heat loss at the cold wall is studied. The most important and significant difference between methane and iso-octane for this problem is the postquench oxidation of unburned hydrocarbons. Methane shows fast oxidation of unburned fuel and intermediate hydrocarbons whereas postquench oxidation for iso-octane is slow especially for the intermediate hydrocarbons. Furthermore, the Soret effect which is usually considered to be of minor importance appears to be important in modeling the rate limiting diffusion process. This is caused by different directions of the thermal diffusive transport for certain species.

Combustion and pollutant formation in a DI-Diesel engine are numerically investigated using the Eulerian Particle Flamelet Model (EPFM). A baseline case for part load operating conditions is considered as well as an EGR variation. The surrogate fuel consisting of n-decane (70% liquid volume fraction) and α-methylnaphthalene (30% liquid volume fraction) is used in the simulation. Results are compared to experimental data that has been obtained using real diesel fuel. The effect of multiple flamelets on the simulation of the auto-ignition process and the pollutant formation is discussed and a converging behavior of the model with respect to the number of flamelets is found. The effect of homogenization of the three-dimensional mixture field is investigated and it has been included in the formulation of the scalar dissipation rate.

Auto-ignition in Diesel engines, occurring essentially under non-premixed and partially premixed conditions, is considerably different to homogeneous ignition. In order to study the relevant chemistry--mixing interactions, it is assumed that the ignition of Diesel fuel can be described by using the single component model fuel n-heptane. Starting from a detailed chemical reaction scheme with about 1000 elementary reactions among 168 chemical components, a skeletal mechanism consisting of 98 reactions and 40 components is derived, which is still capable of describing the auto-ignition process under Diesel engine conditions and concentrations of NO, relevant intermediate components. Introducing steady state assumptions for intermediate species which are consumed rapidly leads to a reduced 14-step mechanism. The mechanism is validated with auto-ignition delay times from shock tube experiments by Adomeit for different temperatures, pressures, and equivalence ratios.