In times of climate change, power generation from renewable sources gets more and more important. Seasonal and regional dependent overproduction of wind or solar energy can be stored and distributed via power to gas or power to liquid processes. In order to reconvert the chemically bound energy from these e-fuels into electric power, fuel-flexible internal combustion engines are a promising approach for this reconversion.

This study is a simulative investigation comparing renewable and sustainable fuels used in stationary fuel-flexible high-pressure-dual-fuel (HPDF) four-stroke engine. The HPDF combustion uses a small amount of a self-igniting fuel like Diesel or the e-fuel polyoxymethylene dimethyl ethers (OME3) to ignite the also direct injected flexible main fuel, which is burned in a diffusive combustion regime to gain maximum efficiency. Through the direct injection of the main fuel and the diffusive flame, the combustion is very stable in a wide engine operating range. There is no risk of knocking or backfire, so the compression ratios of these engines can be as high as in common diesel engines which leads to a high degree of efficiency.

The investigations are conducted with a numerical 3D-CFD model, which has already proven its suitability for HPDF combustion for the fuel pairings diesel-CH4, and OME3-CH4 in prior studies. Comparisons with measurements from a fully optically accessible large bore fast speed single cylinder research engine already stated the quality of the model statements for these fuel parings. Therefore, it is to be expected that the results for the herein simulative investigated fuel pairings give a well-founded statement of the trends in pressure traces, heat releases and ignition.

Different fuel combinations in the HPDF combustion are investigated, the pilot fuel varying between diesel and OME, while hydrogen, methane, methanol and ammonia are used as main fuels. In order to establish comparability between the individual fuels and their tendency to soot and formaldehyde formation the in-cylinder conditions at the start of injection as well as the timings and temperatures for the pilot fuel injections for all cases are kept constant for all fuel combinations. For the main fuels the temperatures, pressures and energy flow are constant for comparability. This results in different nozzle diameters of the injector.

The evaluation is focused on the exhaust gases and the possibly required exhaust aftertreatment systems to comply with the current legislation in Europe. A distinction is made between carbon-based fuels and ammonia&hydrogen. For the latter two, the main focus is on NOx formation. This is followed by an analysis with regard to after-treatment methods and controllability in the application of a stationary engine. In the case of carbon-based fuels, the tendency to soot and formaldehyde formation is investigated. Finally, the applicability of the individual fuel combinations is evaluated in a comparative manner and their suitability for stationary use for the re-conversion of chemically stored energy is evaluated.


Numerical Study on Renewable and Sustainable Fuels for HPDF Engines

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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