Using alcohol fuels in dual fuel operation of compression ignition engines: a review

Because of global warming and increasing air pollution, alternative fuels are increasingly being considered for use in internal combustion engines (ICEs). Among the alternatives, alcohol fuels seem very interesting. They can be produced in a renewable way and possess certain advantageous properties that give them the potential to lower pollutants and CO2 emissions from ICEs. Methanol and ethanol are the most researched alcohols today. In fact, in some areas of the world, gasoline is blended with methanol or ethanol for use in spark ignition (SI) engines. These alcohols are ideally suited for SI engines because of their high octane number (low tendency to knock). That makes them, however, not very well suited for compression ignition (CI) engines which require high cetane number fuels. There exist, however, CI engine technologies that burn alcohol fuels. One of these technologies is Dual Fuel (DF) operation. In DF operation, the engine runs effectively on two fuels. There exist several concepts to achieve this. One of these is to inject a mixture of diesel and alcohol fuel directly into the cylinder. Another is to separately inject diesel and alcohol fuel directly into the cylinder. A third concept (so-called fumigation) is to inject the alcohol fuel into the intake and the diesel directly into the cylinder (the homogeneous alcohol-air mixture is then ignited by a pilot injection of diesel). The paper will provide an overview of the literature regarding this fumigation concept. This work has been carried out as a part of the LeanShips project. LeanShips stands for 'Low Energy And Near-to-Zero emission Ships'. It is a Horizon 2020 (H2020) project funded by the European Commission aimed at developing green shipping technologies and bringing these to the market. One of the Work Packages of the LeanShips project, 'Demonstrating the Potential of Methanol as an Alternative Fuel' aims to demonstrate a high-speed heavy-duty marine diesel engine converted to Dual Fuel (DF) operation on methanol (and diesel) while achieving significant reductions of emitted pollutants

Increasing exhaust temperature to enable after-treatment operation on a two-stage turbo-charged medium speed marine diesel engine

Nitrogen-oxides (NOx) are becoming more and more regulated. In heavy duty, medium speed engines these emission limits are also being reduced steadily: Selective catalytic reduction is a proven technology which allows to reduce NOx emission with very high efficiency. However, operating temperature of the catalytic converter has to be maintained within certain limits as conversion efficiency and ammonia slip are very heavily influenced by temperature. In this work the engine calibration and hardware will be modified to allow for a wide engine operating range with Selective catalytic reduction. The studied engine has 4MW nominal power and runs at 750rpm engine speed, fuel consumption during engine tests becomes quite expensive (+- 750kg/h) for a measurement campaign. This is why a simulation model was developed and validated. This model was then used to investigate several strategies to control engine out temperature: different types of wastegates, injection variation and valve timing adjustments. Simulation showed that wastegate application had the best tradeoff between fuel consumption and exhaust temperature. Finally, this configuration was built on the engine test bench and results from both measurements and simulation agreed very well

The temperature dependence of Laminar burning velocities of methanol-syngas-air flames

Using the simplest alcohol – methanol – as a fuel for spark ignition (SI) engines, enables an increase of thermal efficiency compared to gasoline. Additionally, with the enrichment of hydrogen rich gas from methanol reforming (syngas) using exhaust heat, the efficiency can be further improved. The complexity of optimizing such an arrangement asks for numerical support. However, there is no research that publishes the effect of unburned mixture temperature and equivalence ratio on the laminar burning velocity of methanol-syngas blends, which is needed for developing an engine cycle code to simulate methanol fueled SI engines with syngas addition from exhaust gas fuel reforming. The influence of temperature on the laminar burning velocity of methanol-syngas blends is investigated in this study using CHEM1D. The simulation shows that the flame speed increases dramatically with the enrichment of syngas, especially at lean and rich conditions. The effect of syngas ratio on the improvement of burning velocity is less important at higher temperatures, and there is almost no influence at stoichiometry. Some well-known mixing rules are then examined. In general, the Hirasawa mixing rule shows the best fit with the numerical data. For blends with high syngas content, the Le Chatelier’s mixing rule is recommended. The temperature power exponent α is calculated and compared to other correlations. It shows that the published correlations are unable to predict the influence of temperature on laminar burning velocity accurately enough for the combustion of methanol, syngas and their blends in air

Verification of an analytic fit for the vortex core profile in superfluid Fermi gases

A characteristic property of superfluidity and -conductivity is the presence of quantized vortices in rotating systems. To study the BEC-BCS crossover the two most common methods are the Bogoliubov-De Gennes theory and the usage of an effective field theory. In order to simplify the calculations for one vortex, it is often assumed that the hyperbolic tangent yields a good approximation for the vortex structure. The combination of a variational vortex structure, together with cylindrical symmetry yields analytic (or numerically simple) expressions. The focus of this article is to investigate to what extent this analytic fit truly reflects the vortex structure throughout the BEC-BCS crossover at finite temperatures. The vortex structure will be determined using the effective field theory presented in [Eur. Phys. Journal B 88, 122 (2015)] and compared to the variational analytic solution. By doing this it is possible to see where these two structures agree, and where they differ. This comparison results in a range of applicability where the hyperbolic tangent will be a good fit for the vortex structure.Comment: 14 pages, 7 figure

Modeling of a heavy duty diesel engine to ease complex optimization decisions

Engine optimization becomes more difficult every day, more and more limits regarding emissions of noxious components have to be met. Considering heavy duty marine engines such as the 6DZC from ABC there are several important instances: IMO III reduces NOx by 75% from 2021, EPA reduces NOx by 70% from 2016. Therefore very complex systems are implemented, which each have multiple calibration or working parameters. Some are fixed, some can change depending on engine load and speed. An example of a fixed parameter is compression ratio, it can only be changed while building the engine. Other fixed parameters include: choice of injection nozzle (#holes, hole-diameter), bore, stroke, etc. Exhaust gas recirculation (EGR) is a parameter that can be changed continuously during operation of the engine. Typically there are other parameters present: Variable Valve Timing, injection timing, injection duration, injection pressure, secondary injection, wastegate setting(s), etc. Ideally these parameters are configured in a way that the engine emits very little harmful components and fuel consumption is very low. The most straightforward approach would be to test every parameter combination, record emission components and fuel consumption and choose the optimal parameter combination. This has to be repeated for every speed and load of the engine, which results in an engine map. This method becomes more and more expensive, both in time as in fuel consumption because every additional operating parameter increases the amount of tests exponentially. This is why engine simulation becomes inevitable. Accurate engine simulation is able to exclude regions of parameter values that are clearly infeasible and can give a good indication where engine tests are more interesting