High-Temperature Ignition Kinetics of Gas Turbine Lubricating Oils

Lubricant ignition is a highly undesirable event in any mechanical system, and surprisingly minimal work has been conducted to investigate the auto-ignition properties of gas turbine lubricants. To this end, using a recently established spray injection scheme in a shock tube, two gas turbine lubricants (Mobil DTE 732 and Lubricant A from Cooper et al. 2020) were subjected to high-temperature, post-reflected-shock conditions, and OH* chemiluminescence was monitored at the sidewall location of the shock tube to measure ignition delay time (tign). An extended shock-tube driver and driver-gas tailoring were utilized to observe ignition between 1183 K and 1385 K at near-atmospheric pressures. A two-stage-ignition process was observed for all tests with Mobil DTE 732, and both first and second stage tign are compared. The secondary ignition was found to be more indicative of combustion and was used to compare tign values with lubricant A. Both lubricants exhibit three ignition regimes: a high-temperature, Arrhenius-like regime (>1275 K); an intermediate, negative-temperature-coefficient-like regime (1230-1275 K); and a low-temperature ignition regime (<1230 K). Lubricant A was found to be less reactive in the intermediate-temperature regime, but Mobil DTE 732 was less reactive in the low-temperature regime. As the low-temperature regime is more relevant to gas turbine conditions, Mobil DTE 732 is considered more desirable for system implementation.

Optimization of Power Train Involving Gas Turbine Driven Compressors and Aerial Coolers

Multi-objective optimizations were conducted for a compressor station comprising two dissimilar compressor units driven by two dissimilar gas turbines, two coolers of different size, and two parallel pipeline sections to the next station. Genetic algorithms were used in this optimization along with models describing the performance characteristics of gas turbines, compressors, aerial coolers, and downstream pipeline section. Essential in these models is the heat transfer between the gas and soil as it affects the pressure drop along the pipeline, and hence relates back to the coolers and compressor flow/pressure settings. Further investigative techniques were developed to also minimize NOx and CO2e emissions along with total energy consumption, i.e. fuel (used in the driver gas turbines) and electrical energy (used in the electrical fans of the aerial coolers). Two optimization scenarios were conducted: 1) Two-objective optimization of total energy consumption and NOx emission, and 2) Two-objective optimization of total energy consumption and CO2e emission. The results showed that savings in the energy consumption in the order of 5–6% is achievable with slight adjustment to unit load sharing and coolers by-pass/fan speed selections. It appears that most of the savings (around 70–75%) are derived from optimizing the load sharing between the two parallel compressors, while the balance of the savings is realized from optimizing the aerial coolers settings. In order to optimize operation for minimum NOx emission as well, a shift towards employing more of the aerial coolers is required. Preliminary cost analysis was conducted for valuation of balancing between energy consumption vs. emission loading in terms of both NOx and CO2e.

Application of a One-Dimensional Modular Dynamic Model for Compressor Surge Avoidance

In this paper, a one-dimensional model for the simulation of surge is used to study the dynamic behavior of a compression station. The station consists of a main line where the compressor operates and of a secondary line which allows the recirculation of the working fluid in order to prevent surge occurrence. With respect to the three maneuvers considered (from startup to normal operation, emergency shutdown and operating point variation), a sensitivity analysis is carried out to evaluate the influence of: • working fluid (methane and biogas); • surge margin value; • presence of a suitable PID controller; • presence of a cooler along the main flow line; • compressor driver (gas turbine and electric motor).

Modern developments in hypersonic wind tunnels

The development of new methods of producing hypersonic wind-tunnel flows at increasing velocities during the last few decades is reviewed with attention to airbreathing propulsion, hypervelocity aerodynamics and superorbital aerodynamics. The role of chemical reactions in these flows leads to use of a binary scaling simulation parameter, which can be related to the Reynolds number, and which demands that smaller wind tunnels require higher reservoir pressure levels for simulation of flight phenomena. The use of combustion heated vitiated wind tunnels for propulsive research is discussed, as well as the use of reflected shock tunnels for the same purpose. A flight experiment validating shock-tunnel results is described, and relevant developments in shock tunnel instrumentation are outlined. The use of shock tunnels for hypervelocity testing is reviewed, noting the role of driver gas contamination in determining test time, and presenting examples of air dissociation effects on model flows. Extending the hypervelocity testing range into the superorbital regime with useful test times is seen to be possible by use of expansion tube/tunnels with a free piston driver.