An Engineering Calculation Method for Multi-Component Stagnant Droplet Evaporation With Finite Diffusivity

A practical engineering calculation method has been formulated for commercial multicomponent fuel stagnant droplet evaporation with variable finite mass and thermal diffusivity. Instead of solving the transient liquid phase mass and heat transfer partial differential equation set, a totally different approach is used. With zero or infinite mass diffusion resistance in liquid phase, it is possible to obtain vapor pressure and vapor molecular mass based on the distillation curve of these turbine fuels. It is determined that Peclet number (Pef) is a suitable parameter to represent the mass diffusion resistance in liquid phase. The vapor pressure and vapor molecular mass at constant finite Pef is expressed as a function of finite Pef, vapor pressure, and molecular mass at zero Pef and infinite Pef. At any time step, with variable finite Pef, the above equation is still valid, and PFsPef=∞, PFsPef=0, MfvPef=∞, MfvPef=0 are calculated from PFsPef≡∞, PFsPef≡0, MfvPef≡∞, MfvPef≡0, thus PFs and Mfv can be determined in a global way which eventually is based on the distillation curve of fuel. The explicit solution of transient heat transfer equation is used to have droplet surface temperature and droplet average temperature as a function of surface Nusselt number and non-dimensional time. The effect of varying com position of multi-component fuel evaporation is taken into account by expressing the properties as a function of molecular mass, acentric factor, critical temperature, and critical pressure. A specific calculation method is developed for liquid fuel diffusion coefficient, also special care is taken to calculate the binary diffusion coefficient of fuel vapor-air in gaseous phase. The effect of Stefan flow and natural convection has been included. The predictions from the present evaporation model for different turbine fuels under very wide temperature ranges have been compared with experimental data with good agreement.

Simplified Models for NOx Production Rates in Lean-Premixed Combustion

Simplified models for predicting the rate of production of NOx in lean-premixed combustion are presented. These models are based on chemical reactor modeling, and are influenced strongly by the nitrous oxide mechanism, which is an important source of NOx in lean-premixed combustion. They include 1) the minimum set of reactions required for predicting the NOx production, and 2) empirical correlations of the NOx production rate as a function of the CO concentration. The later have been developed for use in an NOx post-processor for CFD codes. Also presented are recent laboratory data, which support the chemical rates used in this study.

Development of a Lean-Premixed Two-Stage Annular Combustor for Gas Turbine Engines

The development, from concept to hardware of a lean-premixed two-stage combustor for small gas turbine engines is presented. This Annular Low Emission Combustor (ALEC) is based on a patent of R.J. Mowill. Emission characteristics of several prototypes of this combustor under a variety of conditions are presented. It is shown that ultra-low NOx levels (< 10 ppm) can be reached with satisfactory CO levels (< 50 ppm).

Aerodynamic Behavior of Asymmetric Jets in 3-D Furnaces

The purpose of this paper is to present and evaluate numerical experiments illustrating the flow features in a 3-D furnace utilizing unconventional asymmetrical jet that creates natural recirculation zone. The numerical simulation of this aerodynamic stabilization method have unveiled the three-dimensional nature of the flow pattern which possesses a quite large reverse flow region. The size and strength of the built recirculation zone would be capable of stabilizing the burning of low-quality fuels.

Evaporation Characteristics of Spray in a Lean Premixed-Prevaporization Combustor for a 100 KW Automotive Ceramic Gas Turbine

Spray characteristics of liquid fuel air-assisted atomizers developed for a lean premixed-prevaporization combustor were evaluated under two kinds of conditions: in still air under non-evaporation conditions at atmospheric pressure and in a prevaporization-premixing tube under evaporation conditions with a running gas turbine. The non-evaporated mass fraction of fuel spray was measured using a phase Doppler particle analyzer in the prevaporization-premixing tube, in which the inlet temperature ranged from 873K to 1173K. The evaporation of the fuel spray in the tube is mainly controlled by its atomization and distribution. The NOx emission characteristics measured with a combustor test rig were evaluated with three-dimensional numerical simulations. A low non-evaporated mass fraction of less than 10% was effective in reducing the exhausted NOx from lean premixed-prevaporization combustion to about 1/6 times smaller than that from lean diffusion (spray) combustion. The flow patterns in the combustor are established by a swirl chamber in fuel-air preparation tube, and affect the flame stabilization of lean combustion.

Updating the ANSI Standard on Measurement of Exhaust Emissions

The American National Standards Institute (ANSI) required that the source testing Standard on Measurement of Exhaust Emissions from Stationary Gas Turbine Engines, B133.9, be brought up to date with today’s regulatory requirements and best measurement technology. The criteria for the design of the Standard along with its content and format are discussed. The selection of measurement methods for gaseous components, smoke, and particulates emitted by present day emission controlled industrial gas turbine engines is presented.

Emission and Performance of a Lean-Premixed Gas Fuel Injection System for Aeroderivative Gas Turbine Engines

A dry-low-NOx, high-airflow-capacity fuel injection system for a lean-premixed combustor has been developed for a moderate pressure ratio (20:1) aeroderivative gas turbine engine. Engine requirements for combustor pressure drop, emissions, and operability have been met. Combustion performance was evaluated at high power conditions in a high-pressure, single-nozzle test facility which operates at full baseload conditions. Single digit NOx levels and high combustion efficiency were achieved A wide operability range with no signs of flashback, autoignition, or thermal problems was demonsuated. NOx sensitivities 10 pressure and residence time were found to be small at flame temperatures below 1850 K (2870 F). Above 1850 K some NOx sensitivity to pressure and residence Lime was observed and was associated with the increased role of the thermal NOx production mechanism at elevated flame temperatures.

Effects of Buoyancy on Heat Transfer and Oxygen Consumption in Fuel-Thermal-Stability Studies

A unique methodology is used to investigate the effects of gravity on fuel flowing through the small-bore heated tubes that are often used in the study of fuel-thermal-stability characteristics. The copper block that houses the fuel tube (or test section) is located on a swivel, and experiments are conducted for different tube orientations namely; horizontal, vertical with flow from bottom to top and vice versa. Results obtained for different fuel-flow rates and block temperatures are discussed. An axisymmetric, time-dependent numerical model is used to simulate the flow patterns in the test section. This model solves momentum, energy, species and k-ε turbulence equations. The buoyancy term is included in the axial-momentum equation. Natural flow resulting from buoyancy was found to have a significant effect on heat transfer and oxygen consumption for fuel-flow rates up to 100 cc/min (Reynolds numbers up to 2300). Flow instabilities were observed when the fuel was flowing downward in a vertically mounted test section. The effect of block temperature and flow rate on these instabilities was also studied.

New Catalytic Combustion Technology for Very Low Emissions Gas Turbines

A catalytic combustion system has been developed which feeds full fuel and air to the catalyst but avoids exposure of the catalyst to the high temperatures responsible for deactivation and thermal shock fracture of the supporting substrate. The combustion process is initiated by the catalyst and is completed by homogeneous combustion in the post catalyst region where the highest temperatures are obtained. This has been demonstrated in subscale test rigs at pressures up to 14 atmospheres and temperatures above 1300°C (2370°F). At pressures and gas linear velocities typical of gas turbine combustors, the measured emissions from the catalytic combustion system are NOx < 1 ppm, CO < 2 ppm and UHC < 2 ppm, demonstrating the capability to achieve ultra low NOx and at the same time low CO and UHC.

Solar Turbines Incorporated “Taurus 60” Gas Turbine Development

The Taurus gas turbine was first introduced in 1989 with ratings of 6200 HP for single shaft and 6500 HP for twin shaft configurations. A new design of the single shaft third stage turbine rotor and exhaust diffuser brought its power to 6500 HP in 1991. A program was initiated early in 1992 to identify opportunities to further optimize performance of the Taurus. Thorough investigation of performance sensitivity to thermodynamic cycle parameters has resulted in significant improvement over the original design with no change in firing temperature. Aerodynamic and mechanical design changes were implemented in 1993 which raised Taurus performance to 7000 HP and 32% thermal efficiency. Selection of the final design configuration was the outcome of performance maximization versus cost increase, durability risk and loss of commonality with previous engines. This paper details these changes and the design selection process.