Teilprojekt A01 Stephan

Teilprojekt A01 Stephan

Experimental investigation of film evaporation of multicomponent fluid with affinity for deposition building

Motivation

Energy carriers such as gasoline or diesel fuel are complex multi component fluids based on hydrocarbons. During combustion, unburned hydrocarbons can condense on combustion chamber walls. Under certain process conditions, they will then form deposits on the wall. Some evaporation processes in process engineering or, for example, urea injection in a flue show fundamentally similar phenomena. These deposits disturb the process in a number of ways. They affect the heat transfer at the wall or clog the fuel injector nozzle. The latter will lead to altered spray characteristics. Deposits have also been shown to significantly lower the efficiency of energy conversion while increasing pollutant emissions. So far, extensive studies revealed the significance of certain influencing factors on deposit formation in combustion chambers, notably the wall temperature. Detailed insights on the underlying mechanisms and their interactions, however, are still missing.

Objectives

The focus of this subproject is on fundamental, experimental studies on evaporation and deposit formation of fuel (conventional or alternative), substitute fuel and urea solutions, using two generic experimental setups. Thereby a contribution to the fundamental understanding of the complex interactions between wetting properties, multi-phase heat and mass transfer and chemical-physical processes of deposit formation shall be made. The mainly qualitative findings of the first funding period will be expanded and quantified by a systematic parametic variation regarding test fluids (for example E-Fuels), wall material and wall surface as well as process parameters (pressure, temperature, retention time, flow velocity, gas atmosphere…).

Previous Findings

During the first funding period, the deposit forming tendencies of fuels and urea solutions was studied, using two newly built experimental setups. The Screening setup allows the investigation of deposit formation of single drops on a heated surface. The Flow Channel is used to study deposit formation on a shear driven fluid film. Regarding fuels, the content of aromatic hydrocarbons was found to be the main cause of deposit formation. The latter was significantly affected by wall temperature and retention time. Film and deposit formation under practical conditions was generically simulated in the flow channel.

Approach

The Screening Setup is built around a test chamber containing a heatable substrate holder.

By using heating cartridges, a substrate temperature of up to 300 °C can be reached. A flow of fresh air, controlled by a mass flow meter, secures an oxidative atmosphere within the chamber. The injector is situated above the substrate and test fluid drops are applied to the substrate by gravity. The usage of a syringe pump allows high-precision fluid application of low volumes and varying drop frequency. Multiple thermocouples measure the temperature at the substrate bottom, the chamber wall and the gas atmosphere. An optical system consisting of a monochrome camera, a light source and a diffusor allows for the in situ observation of drop evaporation and deposit formation.

Process diagram of the screening setup
Process diagram of the screening setup

The Flow Channel possesses a rectangular (50x30 mm) geometry and contains a heatable airflow, which is induced by either a compressor or a vacuum pump. Using a bypass channel and multiple control valves, the flow can be set to a desired velocity. A pre and main filter precipitate evaporated test fluid. The test chamber, which is built in a modular way, is located in the rear part of the rig. There, the test fluid can be applied to a foil heater using a syringe pump and is driven along the foil by shear forces of the airflow. A high-speed infrared camera below the heater captures the wall temperature profile. A monochrome camera above the heater records the dynamics of the fluid film. Additionally, multiple thermocouples, optical accesses and sensors for mass flow and total pressure are integrated into the rig.

Process diagram of the flow channel
Process diagram of the flow channel

Cooperation

Experimental data are provided to B01 (Gambaryan-Roisman) to validate numerical models and simulation. The formed deposits are examined via a 3D confocal microscope as well as via REM, EDXS and, if necessary, TEM. They can then be compared to the engine-produced deposits of C02 (Kubach/Koch) and the deposits of the exhaust gas system of C04 (Deutschmann). An optical access to the flow channel allows TDLAS measurements in cooperation with A05 (Wagner).

Selected Publications

  • Bender, A., Hänichen, P., Gambaryan-Roisman, T., Stephan, P.: Modeling crystallization and heat transfer in an evaporating urea water drop. Proc. Int. Heat Transfer Conference, Kyoto, Japan, August 10-15 (2018) (accepted).
  • Hänichen, P., van Eyk, M., Stephan, P.: Experimental investigations of fuel film evaporation with deposit formation. Int. J. Heat Fluid Flow 70, 125–130 (2018).
  • Hänichen, P., Stephan, P.: Experimental Investigations of Film Evaporation of Methylnaphthalene with Deposit Formation. 9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics (2017).