Date of Award
Master of Science (MS)
Rapid compression machines (RCM) are laboratory devices used to measure gas-phase fuel reactivity at conditions relevant to combustion engines. Test mixtures are generally prepared by rapidly compressing a gas phase fuel+oxidizer+diluent mixture to high pressure and temperature (e.g., 10-50 bar, 650-1000 K). It is extremely challenging to utilize diesel-relevant liquid fuels in these devices due to their involatility. One proposed method involves the delivery of an aerosol of suspended fuel droplets (∼ 0.1 mLfuel/Lgas at stoichiometric fuel loading) to the machine. The compression stroke of the RCM subsequently heats the gas phase of the aerosol thereby achieving vaporization of the fuel. The properties of the aerosol delivered to the RCM such as the droplet size distribution (DSD) are critical to ensuring successful execution of the experiments. For instance, the fuel droplets must be smaller than a critical threshold (e.g., d0 ∼ 6 - 10 μm to ensure timely fuel evaporation and gas-phase mixing; in addition, the droplets must resist gravitational forces that could cause them to fall out of suspension. Low aerosol velocities are required in order to minimize fluid motion and thus heat loss from the compressed reacting gases during the RCM experiment. An aerosol model has been developed in this thesis project in order to understand the aerosol dynamics during the generation and machine delivery processes. Issues such as droplet impingement, coagulation, evaporation and settling can be investigated with the model, and thus the configuration (i.e., intake valve geometry, mixing chamber design, etc.) and operational characteristics (i.e., gas flow rates, fuel loading, etc.) of the aerosol RCM can be understood/improved/optimized. The system model is validated against gravimetric measurements using a mock up of a proposed delivery system. ‘Operating maps’ are generated for n-dodecane and n-hexadecane in oxygen + diluent mixtures covering a range of fuel loadings and delivery flow rates.