Wajid A. Chishty

Emissions Assessment of Alternative Aviation Fuel at Simulated Altitudes

To address the global fuel challenges of energy security, economic sustainability and climate change the stakeholders of aviation industry are actively pursuing the development and qualification of alternative ‘drop-in’ fuels. New standards will be required to regulate the use of these new fuels, which requires not only fuel specification and rig/engine and flight testing but also an emission life cycle impact assessment of these fuels. This paper reports on emission data measured at various simulated altitudes and engine speeds from a jet engine operated on conventional and alternative aviation fuels. The work was conducted as part of on-going efforts by departments within the Government of Canada to systematically assess regulated as well as non-regulated emissions from the use of alternative aviation fuels. The measurements were performed on an instrumented 1000 N-thrust turbojet engine using a baseline conventional Jet A-1 fuel and a semi-synthetic (50/50) blend with Camelina based Hydroprocessed Renewable Jet (JP8-HRJ8) fuel. Emission results reported here include carbon dioxide, carbon monoxide, nitrogen oxides and particulate matter measured at several simulated altitudes and power settings. In order to ensure that the assessments have a common baseline, relevant engine performance and operability data were also recorded.Copyright

Characterization of Emissions From the Use of Alternative Aviation Fuels

Alternative fuels for aviation are now a reality. These fuels not only reduce reliance on conventional petroleum-based fuels as the primary propulsion source, but also offer promise for environmental sustainability. While these alternative fuels meet the aviation fuels standards and their overall properties resemble those of the conventional fuel, they are expected to demonstrate different exhaust emissions characteristics because of the inherent variations in their chemical composition resulting from the variations involved in the processing of these fuels.This paper presents the results of back-to-back comparison of emissions characterization tests that were performed using three alternative aviation fuels in a GE CF-700-2D-2 engine core. The fuels used were an unblended synthetic kerosene fuel with aromatics (SKA), an unblended Fischer Tropsch synthetic paraffinic kerosene (SPK) and a semi-synthetic 50-50 blend of Jet A-1 and hydroprocessed SPK.Results indicate that while there is little dissimilarity in the gaseous emissions profiles from these alternative fuels, there is however a significant difference in the particulate matter emissions from these fuels. These differences are primarily attributed to the variations in the aromatic and hydrogen contents in the fuels with some contributions from the hydrogen-to-carbon ratio of the fuels.Copyright

Altitude Performance of a Turbojet With Alternate Fuels

To enhance energy security and reduce the environmental impact of aviation, alternate fuels derived from various non-petroleum based sources are being developed. Currently alternate fuels are produced to match the properties of existing jet fuels allowing the new fuels to be used in current fleets concurrently with traditional jet fuel. The alternate fuels must, therefore, perform as well as the traditional fuels through the entire operating envelope. This paper provides the results of performance testing in an altitude chamber up to 11,300 m (35,000 feet) with a simulated forward speed up to Mach 0.75. The test engine was an instrumented 1.15 kN thrust turbojet burning conventional Jet A-1 as a baseline; a semi-synthetic blend of camelina based hydro processed renewable jet and JP8; a blend of 50% Fischer-Tropsch synthetic paraffinic kerosene and 50% JP8; and a 100% Fischer-Tropsch synthetic paraffinic kerosene. Both steady state and transient performance are presented. The theoretical effect of the alternate fuels for a simple idealized Brayton cycle is also presented. The work was conducted as part of on-going efforts by departments within the Government of Canada to systematically assess alternative aviation fuels.© 2011 ASME

3-D Simulations of the Bubble Formation From a Submerged Orifice in Liquid Cross-Flow

The results are presented from a 3-D simulation of the bubble formation from a submerged orifice in liquid cross-flow. VOF model is used for the simulations. The VOF equation is solved using an explicit time-marching scheme. A second order upwind differencing scheme is applied for the solution of momentum equation. The pressure-implicit with splitting of operators (PISO) scheme is used for the pressure-velocity-coupling scheme. Pressure is discretized with a PRESTO scheme. The computational domain has the dimensions of 100 mm length, 50 mm width and 16 mm height with an orifice of 0.25 mm radius, placed at the bottom of the channel and 10 cm from the water inlet. The water inlet velocity of 0.05 and 0.136 m/s and air inlet mass flow rate of 10−6 and 10−5 kg/s are considered. The simulation results are compared with the experimentally acquired images of the bubbles in the cross-flow stream using a high speed camera (3000 fps). A good agreement with respect to bubble shape and bubble terminal velocity is observed between the experimental and simulation results for both cases. The 3-D numerical model is compared with the 2-D model in order to highlight and emphasize the need for 3-D model to correctly simulate the dynamics of such flow configurations.© 2009 ASME

Application of Dielectric Barrier Discharge to Improve the Flashback Limit of a Lean Premixed Dump Combustor

In recent years, lean-premixed (LP) combustors have been widely studied due to their potential to reduce NOx emissions in comparison to diffusion type combustors. However, the fact that the fuels and oxidizers are mixed upstream of the combustion zone makes LP type of combustors a candidate for upstream flame propagation (i.e., flashback) in the premixer that is typically not designed to sustain high temperatures. Moreover, there has been a recent demand for fuel-flexible gas turbines that can operate on hydrogen-enriched fuels like Syngas. Combustors originally designed for slower kinetics fuels like natural gas can potentially encounter flashback if operated with faster burning fuels like those containing hydrogen as a constituent. There exists a clear need in fuel-flexible lean-premixed combustors to control flashback that will not only prevent costly component damage but will also enhance the operability margin of engines. A successful attempt has been made to control flashback in an atmospheric LP combustor, burning natural gas-air mixtures, via the application of Dielectric Barrier Discharge (DBD). A low-power DBD actuator was designed, fabricated and integrated into a premixer made out of quartz. The actuator was tuned to produce a low magnitude ionic wind with an intention to modify the velocity profile in the premixer. Flashback conditions were created by decreasing the air flow rate while keeping the fuel flow rate constant. Within this experimental setup, flashback happened in the core flow along the axis of the cylindrical premixer. Results show that the utilization of the DBD delays the occurrence of flashback to higher equivalence ratios. Improvements as high as about 5% of the flashback limit have been obtained without compromising the blowout limit. It is anticipated that this novel application of DBD will lead to future demonstrations of the concept under realistic gas turbine operating conditions.© 2011 ASME

Sea Level Performance of a CF-700 Engine Core With Alternative Fuels

The use of alternative fuels has the potential to enhance energy independence and reduce environmental impact of air travel. It is important to characterize gas turbine operation using such fuels under controlled conditions before implementing them in flight. The performance of a CF-700 engine core was examined in a sea level test facility. The following fuels were tested and will be reported on:1. Jet A-1 – baseline fuel2. 100% unblended Hydroprocessed Esters and Fatty Acids (HEFA) synthetic kerosene fuel with aromatics (SKA)3. 100% unblended Fischer-Tropsch (FT) synthetic paraffinic kerosene (SPK)4. Blended 50% HEFA-SPK and 50% Jet A-1Fuel 2 above is an alternative fuel that can potentially be used without blending with conventional fuel. One purpose of the static engine testing was to determine if this fuel was suitable for use on subsequent test flights in a Dassault Falcon 20 aircraft. Engine performance testing was conducted at various power settings for each fuel. Relevant plots of performance are presented, compared and discussed. Transient tests were also performed including slams and chops. Observations of the effects of the different fuels on the engine fuel system are presented as some alternative fuels have the potential to cause seals to shrink and leaks to occur. The leaks observed are noted as are the steps taken to mitigate the problem.© 2015 ASME

Evaluation of the Impact of Alternative Fuel Use on the Emissions and Performance of a Service-Exposed T56 Engine

Alternative fuel sources are becoming an operational reality; these fuels have the potential to reduce emissions, improve combustion characteristics and to increase fuel supply security. A test with a T56 turboprop engine was performed to demonstrate that a CHEFA/JP8 (Camelina Hydroprocessed Ester and Fatty Acids and standard JP8) fuel blend would meet operational requirements. The primary test objective was to assess whether a fuel change had an immediate impact on the engine condition, performance, emissions or vibration characteristics. This paper presents test results comparing engine performance with JP8 and a 50/50 blend of JP8 and CHEFA. Comparison runs were conducted before and after a 20 hour ground durability test with the CHEFA fuel blend. A nearly time-expired, nacelle-dressed T56 on an outdoor test stand was tested. The engine was equipped with minimally-intrusive non-standard pressure, temperature and emissions monitoring equipment, and a field vibration assessment suite in addition to the standard flight instrumentation. This paper discusses the test plan, data acquisition methods, results and data repeatability. The performance and emissions results are compared to the changes predicted theoretically from the fuel properties. Observations from the borescope inspections before, during and after the 20 hour durability test are also presented. The lessons learned in this test could be applied to future fuel or process-change tests, and the results provide a performance baseline for engine health assessment.© 2012 ASME

The Influence of Channel Orientation and Flow Rates on the Bubble Formation in a Liquid Cross-Flow

For gas turbines burning liquid fuels, improving fuel spray and combustion characteristics are of paramount importance to reduce emission of pollutants, improve combustor efficiency and adapt to a range of alternative fuels. Effervescent atomization technique, which involves the bubbling of an atomizing gas through aerator holes into the liquid fuel stream, has the potential to give the required spray quality for gas turbine combustion. Bubbling of the liquid stream is presently used in a wide range of other applications as well such as spray drying, waste-water treatment, chemical plants, food processing and bio- and nuclear-reactors. In order to optimize control of the required aeration quality and thus the resulting spray quality over a wide range of operating conditions, it is important that the dynamics of bubble formation, detachment and downstream transport are well understood under these circumstances. The paper reports on an experimental study conducted to investigate the dynamics of gas bubbles in terms of bubble detachment frequency when injected from an orifice that is subjected to a liquid cross-flow. The experiments were conducted over a range of gas and liquid flow rates and at various orientations of the liquid channel. Analyses presented here are based on shadowgraph images of two-phase flow, acquired using a high speed camera and a low intensity light source. An image processing algorithm was developed for the detection and characterization of the bubble dynamics. Results show that bubble detachment frequency is a function of both liquid cross-flow rate and the gas-to-liquid flow rate ratio.© 2010 ASME

Limited Qualification Tests of an F404 Engine With Blended Fischer Tropsch SPK and NATO F-34 Fuel

The purpose of this project was to compare the performance and operability of 50% Fischer-Tropsch Synthetic Paraffinic Kerosene (SPK) and 50% NATO F-34 (JP-8) blend and 100% Jet A-1 in a General Electric F404-400 augmented turbofan engine in the configuration currently in use with the Canadian Forces (CF). The paper describes the main test elements to simulate several aspects of CF use of the engine like acceptance testing, post-overhaul tests, performance (steady state and transient), operability, and durability. An abbreviated endurance test is described as is the special condition monitoring instrumentation. In addition, limited combustor and augmentor combustion stability tests were conducted and some results are described. Fuel properties are documented for reference. The linkage with and support of members of The Technical Cooperation Program (TTCP) is highlighted in terms of joint development of the test plans and sharing the results. Discussions of needs for future limited alternative fuel qualification tests are also presented.Copyright

Experimental Characterization of the Damping of Fuel-Air Ratio Fluctuations Using Transfer Function Analysis

This paper presents the theoretical and experimental framework used to characterize the capability of premixers used in Dry Low Emission (DLE) gas turbines to dampen fuel-to-air ratio (FAR) oscillations and thus serve as a passive control device for combustion noise. Based on a convection-diffusion volume model, transfer function analysis in the frequency-domain was used to describe the interaction between convection and turbulent diffusion mechanisms. The study showed that the best achievable damping was obtained when the ratio of convection to turbulent diffusion effects (expressed in terms of Peclet number) was unity. For this particular condition, the spreading of Residence Time Distribution (RTD) is optimal hence decreasing the coherence between incoming and outgoing perturbations. For large Peclet numbers, mixing mechanisms are not sufficient to dampen incoming FAR fluctuations and for very small Peclet numbers FAR perturbations can be communicated almost instantaneously to the premixer outlet, without attenuation.Copyright