Combustion Control System Technology

Nearly every practical combustion system requires some form of control and monitoring equipment for safe and effective operation.  One class of system with a requirement for such equipment is combustion test stands which are used to evaluate the performance of prototype or experimental combustion devices.  An introduction to Combustion Test Stands can be found by following the link at right.

BML's Combustion Control System (CCS) technology has been successfully used for the operation of rocket motor and oxy-fuel combustion test stands.  The system can readily be modified for use with other combustion devices such as industrial flares and burners and gas turbine engines. 

BML offers custom CCS software for test stand operation as well as the following CCS-related services:

• development of complete data acquisition and control system hardware
• installation and interfacing of electronics, sensors and actuators
• hardware-in-the-loop testing of control algorithms
• on-site test support
• user training
• test procedure development and review
• operation of test stand as Test Conductor

1) Automatic Control Functions
BML's CCS software can include a variety of automatic control functions to meet the requirements of a particular combustion test stand.  Existing, test-proven, automatic control functions include:

• Igniter Auto Start
• Main Combustor Auto Start
• Main combustor performance monitor
• User-programmable sequencing of flow valves
• Closed-loop control functions such as run-tank pressure control
• Pre-programmed schedules for proportional flow control valves
• Slaving together of digital control channels
  

The Main Combustor Auto Start function is useful for ensuring a safe and reliable start of the combustion system.  Additional details on this function can be found by following the link at right.

2) Centralized Operator Station
The CCS software enables the implementation of a centralized operator station through a compact and intuitive Graphical User Interface (GUI).  The GUI is designed to reduce the complexity of the information presented to the operator and to improve the operator's awareness of the state of test stand.

An example of this design approach is illustrated by the GUI for a notional water-cooled oxy-fuel combustion system of moderate complexity, shown at right.  Visible in this GUI are:

• Schematic representation of the fuel, oxidizer, nitrogen and water flow paths
• Buttons for manual control of pneumatically actuated  flow valves via relays and solenoid valves
• Buttons for manual control of pumps
• Plots and displays for monitoring system parameters
• Buttons to initiate system auto-start and shutdown
• Indicators presenting the status of the ignition system
• Data recording control switch

Click on the link at right for a full-sized view of the GUI.

3) Remote Operation Capability
Physical separation of test personnel from the test stand is accomplished through the use of two PCs.  One PC, named the Control System PC, runs the CCS software and is typically located in a hardened enclosure or building adjacent to the test stand.  The other PC, the Remote PC, is stationed in the remotely located control room and is used to operate the control system PC via an Ethernet link.

This arrangement has been proven to be effective over distances of up to approximately 1800 ft.  Theoretically, greater separation distances are feasible.

The GUI forms the top level of the Combustion Control System architecture.  As shown in the schematic at right, the GUI interfaces with control functions and other functions such as the data recording function and the instrumentation signal processing function.

The software is interfaced to electrical signals through four types of converters.  These are i) Analog to Digital converters, ii) Digital to Analog converters; iii) Digital input modules; and, iv) Digital output modules.  Typical applications for each hardware interface are provided in the following table.

Amplifiers and relays convert low level signals into higher level signals for either measurement or control purposes.  Amplifiers are typically used to increase the amplitude of low level sensor outputs.  Relays are normally used to provide high current levels to solenoid valves or other actuators.

Test stand sensors can include pressure transducers, thermocouples and load cells.  Actuators may include components such as pneumatically actuated valves, solenoid valves, spark igniters.

The CCS software is written using the LabVIEW programming environment from National Instruments (NI).  A beneficial feature of LabVIEW is the ease with which GUIs and the underlying control software can be created and modified.  As a result, the CCS software can readily be customized to match a particular test stand configuration.

NI and other vendors offer a large number of data acquisition and control hardware products and associated software drivers.  The availability of this hardware and the software drivers reduces the time required to interface the CCS software and hardware.

The CCS software is written in a "State Machine" architecture which enables the code to be written in a logical and easily understood format.  Modifications to the code which may be required over the course of a test campaign, can be implemented in a relatively straightforward manner with the State Machine architecture.  More information on this programming concept can be found in the description of the State Machine Demo in the BML LabVIEW Corner.

The CCS technology is easily scaled for control of large systems.  One implementation of the BML Combustion Control System employed 32 digital control channels and featured the use of two displays.  For this system, one display showed the normal GUI and the other presented real-time plots of user-selectable system parameter,

A free evaluation copy of the GUI software for the notional oxy-fuel system shown above is available upon request by contacting BML.