Klaus Lucka

Mixture preparation by cool flames for diesel-reforming technologies

Abstract The separation of the evaporation from the high-temperature reaction zone is crucial for the reforming process. Unfavorable mixtures of liquid fuels, water and air lead to degradation by local hot spots in the sensitive catalysts and formation of unwanted by-products in the reformer. Furthermore, the evaporator has to work with dynamic changes in the heat transfer, residence times and educt compositions. By using exothermal pre-reactions in the form of cool flames it is possible to realize a complete and residue-free evaporation of liquid hydrocarbon mixtures. The conditions whether cool flames can be stabilised or not is related to the heat release of the pre-reactions in comparison to the heat losses of the system. Examinations were conducted in a flow reactor at atmospheric pressure and changing residence times to investigate the conditions under which stable cool flame operation is possible and auto-ignition or quenching occurs. An energy balance of the evaporator should deliver the values of heat release by cool flames in comparison to the heat losses of the system. The cool flame evaporation is applied in the design of several diesel-reforming processes (thermal and catalytic partial oxidation, autothermal reforming) with different demands in the heat management and operation range (air ratio λ , steam-to-carbon ratio, SCR). The results are discussed at the end of this paper.

Diesel Steam Reforming for PEM Fuel Cells

Different applications for the decentralized stationary or mobile power supply require the usage of liquid hydrocarbons such as fuel oil, diesel, or gas oil in fuel cell systems. Reducing the sulfur content of conventional liquid fuels such as diesel or gasoline below 10 ppm, the usage of these fuels in fuel cell applications becomes increasingly promising. The first process step represents thereby the reforming, which can be carried out in different ways. One of the commonly favored gas process technologies is the steam reforming process, which is state of the art for natural gas applications. Using a proton exchange membrane (PEM) fuel cell requires a complex gas cleanup system. Using a pressurized steam reforming process offers a significant reduction of the whole system size by efficiently compressing the liquid educts. Complete PEM systems with steam reformers tend to have a higher efficiency than, for example, systems using the autothermal reforming process. Advanced diesel steam reformers for industrialization still have to be developed and improved. The Oel-Warme-lnstitut gGmbH has successfully carried out research on steam reforming with variations of important parameters using a sulfur free reference fuel and desulfurized diesel. During the experiments, several parameters such as steam to carbon ratio, reformer inlet temperatures, catalysts, and fuels were varied. While running the process, a continuous product gas measurement was taken. The reformer is equipped with several thermocouples. Three of them are moveable to measure the temperature profile of the catalyst. The experiments show that product gas concentrations reach a nearly equilibrium concentration with reformer inlet temperatures ϑ >700°C of a reference fuel/steam mixture. Hydrogen concentrations over 70% were feasible. Constant inlet temperatures of ϑ=850°C and a variation of the steam to carbon ratio only have a noticeable effect on the water gas shift equilibrium. After all experiments, carbon deposits were found in the steam reformer system and under some circumstances on the catalysts. Experiments with operating times of more than 20 h were performed at a steam to carbon ratio of 4.5. The application of continuously desulfurized diesel fuel indicates a degradation of the catalyst after a few hours. For the overall system design of PEM fuel cell applications, an operation mode at a reduced steam to carbon ratio bas to be developed [DOL: 10.1115/15/1.2784313] carbon ratio has to be developed.

Microbial challenges for domestic heating oil storage tanks

Microbial growth on hydrocarbons is common in nature and used in bioremediation of contaminated sites, whereas in fuel storage tanks this phenomenon can affect the stability of the fuel and the tank. The impact of microbial growth and produced metabolites on materials, which are used in the construction of storage tanks, were analyzed. In contrast to metal tank components, polymeric materials did not affect or were influenced by microorganisms. Zinc was highly corroded by microbial growth, most likely due to the formation of organic acids that were produced during microbial growth on hydrocarbons. A contaminated water phase in a storage tank of a heating system was simulated with a self‐constructed pump test bench. Microbial growth began in the water phase of the storage tank and microbes were distributed throughout the tank system, through water‐in‐oil microemulsions. No microbial growth was observed in oil that was previously contaminated, indicating that essential nutrients had been depleted. The identification and removal of these essential nutrients from fuels could minimize or prevent microbial contamination. The results are discussed with regard to developing recommendations for the design and operation of domestic heating oil storage tanks to lower the risk of technical failure due to microbial contamination.

Potenzial der Kalte-Flammen-Technologie zur Darstellung der vorgemischten, homogenen Verbrennung in einem Dieselmotor

Die IAV GmbH entwickelt im Rahmen des Projekts Advanced Diesel Combustion System (ADCS) das Dieselbrennverfahren weiter. Ziel ist die innermotorische Senkung der Emissionen und eine Verbesserung des Gerauschs bei konstantem Kraftstoffverbrauch. In Kooperation mit dem Oel-Warme-Institut (OWI) wurde eine Potenzialuntersuchung zur externen Vormischung von Dieselkraftstoff und Luft durchgefuhrt.

Internal Diesel Injector Deposits: Investigations with the Non-Engine Test “ENIAK”

Alongside the well-known injector deposits on the nozzle tips and inside the spray holes, the so-called „external diesel injector deposits“ (EDID), deposits within the injector, so-called „internal diesel injector deposits“ (IDID) have been reported worldwide since 2008 [1-8]. At the same time, the developments in diesel engine technology mainly aimed at fast reacting highly sophisticated injectors in conjunction with steadily increasing injection pressures. This combination enables combustion shaping by multiple injections. Each increase in injection pressure is accompanied by ever smaller clearings within the injector. This ongoing trend continues towards higher injection pressures, smaller clearings and more sophisticated injectors. Such highly sophisticated injectors are assumed to be less resistant against IDID compared to “older” ones [3, 4, 8-13]. At the same time, the fuel temperature increases steadily. The return flow from the injectors can reach temperatures of 150 °C [14] or even 190 °C at 250 MPa [15]. An increased fuel temperature on the other hand leads to an increased IDID formation tendency [1, 11-13, 16-17].

Potential of cool flame technology to realize premixed, homogeneous combustion in a diesel engine

To advance the diesel combustion process, a Cool Flame Vaporizer produced at OWI (Oel-Warme-Institut) was modified for use on a passenger car diesel engine. For test bench experiments IAV GmbH adapted the vaporizer to a single-cylinder test engine for external mixture preparation. The engine was run with the vaporizer in different operating states and the results were compared with conventional DI diesel combustion as well as DI premixed combustion with early homogenization (PCCI).

Flüssige Brennstoffe im Kommen

Alle modernen Verbrennungsverfahren haben ein gemeinsames Konstruktionsmerkmal: Eine ausgeklugelte Technik bereitet aus dem gasformigen, flussigen oder festen Brennstoff und der Luft ein zundfahiges Gemisch. Die Gemischbildung stellt ein entscheidendes Kriterium fur die Qualitat der Verbrennung dar. Bei Inhomogenitaten, gleich welcher Art, bilden sich verstarkt Schadstoffe. So treten bei Mangel an Sauerstoff im Abgas mehr unverbrannte Kohlenwasser-stoffe und Rus auf. Zugleich steigt die Verbrennungstemperatur, aus dem Luftstickstoff und dem Sauerstoff entstehen zusatzlich schadliche Stickoxide.