Community Research and Development Information Service - CORDIS

FP7

LeVeR Report Summary

Project ID: 296671
Funded under: FP7-JTI
Country: United Kingdom

Final Report Summary - LEVER (Lean Burn Control System Verification Rig)

Executive Summary:
Lean Burn technologies need to be implemented on future gas turbines. Such technologies are considered necessary in order to meet the future emissions requirements and maintain a competitive advantage in the market place.

Lean Burn fuel systems require improved verification rigs to deal with their inherent complexity and unique modes of operation relative to existing “rich burn” fuel systems. To develop these improvements in rig capability, Rolls-Royce Controls and Data Services Limited (CDS) has designed and built a Lean Burn Verification Rig (LeVeR).

LeVeR initially used an EEC to control the hydro-mechanical systems. However the system was developed to alternatively use a bespoke test box in conjunction with the Hydro-Mechanical Rig (HMR) computers to provide a more flexible engineering solution.

The Advanced Generic Test Rig (AGTR) uses an Electronic Engine Controller (EEC) and Remote Data Concentrator (RDC) and provides an electrical simulation for the environment in which these units are designed to operate.

LeVeR builds upon the AGTR configuration by adding fuel system components i.e. hydro-mechanical unit (HMU), fuel pumps, hydro-mechanical staging unit (HSU), scheduling valves etc, in other words accurately modelling the core of the gas turbine engine and therefore providing a route to verify and de-risk hardware and performance before running on a gas turbine engine.

To date, rigs simulate core engine pressure by using a restrictor in the fuel delivery pipe. This is adequate for modelling the continuous fuel flow of rich-burn architecture engines.
Lean burn systems however require far higher air to fuel ratios for lean combustion whilst still maintaining combustion stability. This is achieved by using staged combustion, where the high air to fuel required for lean combustion is delivered in mains burners, but combustion stability is achieved by also using pilot burners. Consequently fuel flow delivery varies significantly between pilots and mains burners and a simple restrictor cannot accurately simulate engine pressure with these varying flows. The rig must therefore be able to reproduce the engine pressures seen during steady state and transient manoeuvres to provide accurate modelling.
The verification of Lean Burn systems requires a real engine pressurise simulation to establish the behaviour and effects on the system when valves, actuators and fuel pipes operate in this environment. The development and demonstration of this real engine pressure or ‘P30’ system is a fundamental requirement of the LeVeR project.
Where feasible the rig will model abnormal transient behaviours, such as engine surges. Test bed and EEC logged data has been gathered from engine development programmes to capture the characteristics for the P30 values ideally required do produce a real time engine model (RTEM).

Project Context and Objectives:
A summary description of the project context and the main objectives are as follows

1.2 P30 pressure vessel

Many of the current systems used on rigs rely upon the P30 pressure (P30, pressure at the exit of the engine high pressure compressor) being generated by a restrictor in the fuel delivery pipe. As these systems model the continuous flow of rich burn architectures, this approach is both simple and sufficiently accurate for this purpose.

Lean burn systems however require far higher air to fuel ratios for lean combustion whilst still maintaining combustion stability. This is achieved by using staged combustion, where the high air to fuel required for lean combustion is delivered in mains burners, but combustion stability is achieved by also using pilot burners. Consequently fuel flow delivery varies significantly between pilots and mains burners and a simple restrictor cannot accurately simulate engine pressure with these varying flows.

Varying fuel flow to the pilot and main burners is provided by a separate staging unit. The verification of Lean Burn systems requires accurate and representative engine core pressures to establish the behaviour and effects on the system when valves, actuators and fuel pipes are pressurised with a “real” P30. The development and demonstration of this P30 system is a pivotal part of the LeVeR project.

The P30 pressure should faithfully track typical values found during engine steady state and transient manoeuvres. Where feasible the rig will model abnormal transient behaviours, such as engine surges. Test bed and EEC logged data has been gathered from engine development programmes to capture the characteristics for the P30 values ideally required do produce a real time engine model (RTEM).

Typically the RTEM determines the rig value for P30. An RTEM based calculation should be performed on LeVeR and used to control the pressure within the pressure vessel.
Also in order to maintain representative flow numbers in the system, the correct number of fuel injectors (for the Trent 1000 engine being modelled) have been fitted.

1.3 Empty volumes

The operation of the fuel staging unit and the fuel scheduling valves will introduce fuel spikes and dips into the system. The most significant perturbations will also be introduced when transitioning from pilot only operation to pilot and mains operation, as fuel volumes in the mains may have purged (partially or fully) and will subsequently require priming.

The LeVeR does not have the capability to externally introduce fuel dips or spikes. The fuel dips and spikes that are measured are as a result of the fuel metering and staging processes themselves. However it is required to introduce empty volumes that represent partially or fully purged injector pipe volumes downstream of the scheduling valves.

When the mains are turned off, it is expected that fuel between the check valve and the spray nozzle will drain out. Not all of the injectors will drain as it depends upon their physical location in the combustion chamber. For this reason the LeVeR is required to have control over these volumes.

When the mains are turned back on, the initial flow of fuel into the empty volume behind the check valve will just be driving against air that is at P30 pressure. It is only when this volume is filled that the HP fuel delivery system will see an increase in effort to overcome the restriction presented by the spray nozzle. It is this initial priming stage that is investigated and monitored on LeVeR, as there are effects upon not only the mains delivery but also the flows in the pilot delivery system. The behaviour of the initial priming is also affected by P30. This is another reason why a representative P30 system is required.

Typical fuel volumes are less than 10 cubic centimetres. This in itself presents challenges. The purging system employed by LeVeR has as “clean flow” as possible. This means that the pipe work between the check valve and the spray nozzle is as representative of real injector as possible so as not to introduce unrepresentative flow characteristics. It has been very important to produce a process of priming the empty volume that closely resembles what happens in a real engine injector.

1.4 Fuel scheduling valves and injectors

The engine injectors have the fuel scheduling valves fitted directly upon them in pairs, one pilot and one mains. They are all part of the completed assembly that also includes the fuel tube ending in the spray nozzle. The arrangement required to implement the empty volumes is likely to mean that the engine injector’s fuel scheduling valves will not be suitable. Therefore custom-made individual fuel scheduling valves were manufactured for LeVeR. These valves are functionally identical to the engine standard but allow for fitting to the LeVeR.
By having individual valves made it was far easier to build the LeVeR skid. For example the interfaces with pipe work and the empty volume system was simplified and less restrictive from a design perspective. It is also far easier to simulate mechanical fault insertion testing. For example, a valve stuck open fault may be simulated by removing the individual fuel scheduling valve in question and replacing it with a simple straight through pipe that has the same flow number.

1.5 Fuel staging unit

The LeVeR requires a staging unit. The flow into the mains injectors needs to be switched in a representative manner to verify the flow into the empty fuel volumes and then the combustion chamber. It is the transient flow characteristics/profile that need to be verified as part of any lean burn project. An Advanced Low Emissions Combustion System (ALECSys) staging unit was used as it represents the most modern Staging Unit design and has representative electrical and mechanical characteristics.

1.6 Test box

It was initially thought that the current generic test box could be used for LeVeR control. However it soon became apparent that a new design of test box was required to:
• Realise the increase in I/O required for LeVeR
• Enable the test box to be linked to the AGTR
• Meet the latest regulatory standards for the new CDS test facilities
• Allow the Matrix Laboratory simulation software (MATLAB) / Simulation & model based design (Simulink) EEC source models to be directly run in the test box
• Enhance the data logging capabilities
• Enable the control software to operate at similar timings to that of a real EEC.

1.7 LeVeR control computers

A CDS Birmingham hydro-mechanical rig is allocated for use by LeVeR. When using a test box three computers currently control this rig:
• PXI Controller PC – control of the HMR plant and services. For example control of motor, valves, heating, cooling and monitoring.
• Test Box PC – Implements the closed loop LabVIEW software and interface with the test box.
• DEWSOFT PC – The capture, analysis, recording and display of the HMR plant and rig instrumentation

It was necessary to carry out enhancements to these computers to enable LeVeR functionality. The additions required to the following functionality:
• Integration of the RTEM
• MATLAB/SIMULINK integration with the test box control
• Extra high speed data acquisition and processing

It also may prove beneficial to run the RTEM in a separate additional PC.

1.8 Donor fuel system

The most suitable candidate for the donor fuel system is a Trent 1000 pack A LP and HP fuel pump in conjunction with the Trent 1000 pack A HMU.

1.9 Rig instrumentation and data acquisition

Pressure tappings have been installed in every fuel line.
The duration of the fuel dips and spikes that need to be verified currently have requirements down to 2 ms. The pressure transducers used have a bandwidth of 5 kHz thus enabling measurements at 0.2 ms intervals. This gives a good measurement capability against current requirements whilst also allowing for future growth.
Turbine flow meters are used for accurate steady state flow measurements in the Pilot 1, Pilot 2 and Mains fuel delivery pipes. However fuel spikes and dips can only be measured using the pressure transducers.

The rig data acquisition system captures the required data at a bandwidth that allows the requirements to be verified. Also pivotal to the verification process is the ability for all the pertinent data to be captured on a common time base on the one computer that allows storage, replay and analysis.

Project Results:
A description of the main R & T results are summarised as follows:-

Results have been limited on running on the rig due to nitrogen absorption into the fuel within the rig as defined by the Ostwald coefficient, the ratio of the volume of gas to the volume of liquid at a temperature and a partial gas pressure. This has resulted in the decay of the modelled engine P30 pressure, limiting experiments to a few seconds duration. The use of other inert gases are under investigation.

However testing has been completed to verify performance of:
• The operation of the Hydro-Mechanical Staging Unit (HSU)
• Full engine fuel system operation i.e. combined operation of fuel pump, engine Hydro-Mechanical Fuel Unit (HMU) and HSU
• Pilots & Mains fuel flow operation.
• Flow scheduling valve operation (FSV)
• Pilots & Mains burner simulator operation

Results from this testing have identified characteristics of the system which have been fed back and are to be used to define engine operation for both ground & flight test.

Potential Impact:
Specific Technology
Lean Burn technologies need to be applied to future gas turbines to support existing and emerging legislation at a national and international level. Such technologies are considered necessary in order to meet the future requirements to enable aviation transport to be environmentally acceptable and sustainable whilst also maintaining a competitive advantage in the market place.
Lean Burn fuel systems are far more complex than existing rich burn systems and therefore require improved verification rigs to deal with their inherent complexity and unique modes of operation. These complex systems need to be fully understood and tested prior to installing on expensive engine assets, whether run statically on a ground test engine or on a flying test bed engine. To develop these improvements in rig capability, CDS has designed and built a Lean Burn Verification Rig (LeVeR). LeVeR also facilitates this understanding by having levels of instrumentation that would not be possible in the harsh combustion environment of a gas turbine engine. This approach is considerably cost efficient for testing of such systems in terms of roughly a factor of 15 for infrastructure costs and a factor of 40 in terms of annual estimated operating costs.
LeVeR initially used an EEC to control the hydro-mechanical systems. However the system was developed to alternatively use a bespoke test box in conjunction with the HMR computers to provide a more flexible engineering solution.

Complexity

This is the most significantly complex rig project ever designed by CDS who procured a number of fuel test facilities.

The benefits have been a key challenge both to CDS and its partner SCITEK but the learning has been invaluable for future systems

People

Over 25 people have been involved in the project from CDS and SCITEK and the information within CDS, R-R & CLEANSKY forums have developed very positive feedback as the concept of the rig will go onto to test future lean burn systems that are being considered / developed for the next generation of platforms.

In terms of IPR protection as no one has this level of test capability in the world and it could be a disadvantage to R-R if other engine competitors knew what and how we were delivering this capability. Therefore formal dissemination has not occurred.

The skills developed by the people involved have also been enhanced and developed for future successive projects and products.

Environment

As discussed already the ability to test lean burn systems will contribute to the overall benefit that the Cleansky forum is seeking with reduction emissions and noise.

List of Websites:
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Related information

Contact

Gregory Wells, (Business Development Manager)
Tel.: +44 121 607 3652
E-mail
Record Number: 187072 / Last updated on: 2016-07-19
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