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Presented here is experimental and theoretical work on phase transitions and separation time scales for CO2–crude oil mixtures with CO2content ranging from pure to 79 mol %. The experimental work was performed using the wheel flow loop located at the SINTEF Multiphase Flow Laboratory. Under constant volume conditions, phase transition temperature and pressures were determined, as well as the volume fractions of the respective phases. The results indicated good agreement between the experimentally determined phase transitions and the phase diagrams predicted by the thermodynamic model. It was shown that the measured torque was sufficient to determine the pressure–temperature conditions of the phase transitions. Furthermore, separation times were measured for both oil-in-CO2and CO2-in-oil in a range of conditions for the respective fluid systems. Results showed that the separation times were considerably shorter for the CO2continuous fluid system compared to oil continuous. Moreover, a comparison of Weber numbers for the various test conditions indicated that the drop sizes influence the overall separation time, which is affected by settling and coalescence processes. Finally, this study showed that the wheel flow loop is well suited for the study of CO2-rich systems for determination of volume fractions of phases, phase transitions, and transport and separation.

This paper explores a methodology for estimating the minimum time duration of experiments focused on wax deposition studies to be carried out for a passive manifold subsea cooler prototype geometry, upon relevant conditions for offshore oil & gas applications. The methodology encompasses 1D thermohydraulic numerical simulations of a CO2-rich dense-gas and waxy oil mixture flowing, as well as a mass transfer approach for the wax deposition. The idea is to obtain the minimum measurable impact of wax deposits on the pressure drop and temperature at the locations in which corresponding sensors shall be installed. The results applied to 10 different operational conditions for the cooler prototype are presented and thoroughly discussed, together with the phenomenology of the wax deposition and its relationship with the test conditions (operating pressure, liquid content and gas flow rates) and other important flow parameters, such as the mixture temperature, the occurrence of condensation, the pressure profile, among others. The main conclusions and possible next steps for this work are then outlined.

The rate of heat released during the combustion in Diesel engines is important for many reasons, including performance evaluation, pollutant formation, and control. Combustion in Diesel engines can be generally divided into three phases: pre-mixed, diffusive or mixed-controlled, and late combustion. The objective of this paper is to estimate the rate of heat released by the fuel in a marine Diesel engine, in order to identify the pre-mixed and diffusive phases, using the Sampling Importance Resampling (SIR) Bayesian Particle Filter. Experimental pressure data obtained from a piezoelectric sensor, installed in a research marine diesel engine (MAN Innovator 4c), was used to feed the observation model in such Bayesian approach. The evolution model for the pressure was formulated in terms of a set of ordinary differential equations, coming from the First Law of Thermodynamics, together with a random walk model for the unknown state variable. The proposed approach was able to identify the pre-mixed and diffusive combustion phases, for different engine loads. Results were compared with a simple inversion procedure, showing a good agreement. The combustion ignition delay was also calculated, showing its variation with the engine load.