Academic Company Events NI Developer Zone Support Solutions Products & Services Contact NI MyNI

Customer Solutions

Continuous Monitoring of Internal-Combustion Engines Using LabVIEW

Author(s):

Greg Beshouri, Advanced Engine Technologies Corp; Alden Cramer, Advanced Engine Technologies Corp

Industry:

Oil and Gas/ Refining/ Chemicals

Product:

Data Acquisition, LabVIEW

The Challenge:

Continuously monitoring the performance of large internal-combustion engines at gas transmission pipeline compressor stations.

The Solution:

Developing a PC-based system using a DAQ board and serial port interfaces controlled by LabVIEW.


Introduction
Since 1995, vendors have sold fiber-optic pressure sensors (FOPSs) for continuously measuring combustion pressure in large bore internal-combustion engines in the 2,000 to 25,000 brake horsepower range. These sensors provide the natural gas transmission industry a unique opportunity to significantly enhance on-line monitoring and diagnostics of their gas-powered compressor engines. Moreover, when we integrate FOPS data with engine operational data, we greatly enhance closed-loop engine control and emissions monitoring.
Integration of engine combustion pressure data into overall engine monitoring and control systems, however, presents several challenging tasks.

Pressure data from each cylinder must be continuously acquired at a rate of 2 kHz, phase referenced to top dead center (TDC), and then reduced to extract key pressure values. Results must then be transmitted to the engine distributed-process controller and/or the client’s data highway using a serial communications protocol such as Modbus. Finally, the combustion pressure data must be made available at the engine catwalk for "real-time" combustion pressure analysis and diagnostics.

System Development
Advanced Engine Technologies Corporation (AETC) teamed with a major natural gas pipeline company to develop and operate a "Beta" Continuous Pressure Monitor/Fast Balance system for application at a compressor station with three engines. This development required:

  • Implementation of a 32-channel data acquisition system using the National Instruments AT-MIO-64E-3 board
  • Development of LabVIEW applications for system configuration, transducer calibration, and data reduction
  • Development and implementation of digital communication protocols for data exchange with the client data highway, individual distributed-process controllers, and the operator interface
  • Development of a LabVIEW graphical user interface


Because the client could offer AETC only four months to design, develop, test, and implement the system, we chose to leverage off our experience with National Instruments data acquisition (DAQ) hardware and LabVIEW. We completed the final system on time and within budget.

Hardware
We installed a total of 23 FOPSs on all the power cylinders of the three engines. These unique sensors are immune to electrical noise and can transmit data over great distances. The fiber-optic cables ran between the engine room and the test trailer where the signal conditioning and data acquisition system were located.
We equipped each engine with a magnetic pick-up mounted at the flywheel to sense the passage of a pin or bolt corresponding to TDC of Cylinder 1. The magnetic pick-up from each engine was connected directly to the DAQ board.

For the Continuous Pressure Monitor (CPM) system, we chose the AT-MIO-64E-3 multifunction DAQ board, based on the price and high channel count. We installed it in an ISA slot in the docking-station of a Compaq 486 laptop running Windows 95. The client had specified the laptop/docking-station configuration to meet the requirements of the mobile test trailer.The CPM acquired data from the sensors, reduced it, and transmitted it to the station data highway via RS-232. We also made the data available to connection points in the engine room via RS-485, for transfer to the portable Fast Balance (FB) computer. A National Instruments AT-485 2-port board was used to eliminate the need for RS-232 to RS-485 conversion.
We used a ruggedized handheld Texas Micro Hardbody 486 as the FB computer, which needed to be portable so the operator could view the effects of mechanical adjustments directly.

Software
Continuous Pressure Monitor
Although we based the CPM application on robust field test software developed by AETC, we found it lacking for continuous monitoring because it was written for triggered data acquisition. In shifting from triggered to continuous data acquisition, we knew that simply acquiring data and then reducing and transmitting the data would result in poor performance.As recommended in an article in LabVIEW Technical Resource, we used the Wait for Occurrence function to free up the CPU for data reduction and transmission. It worked surprisingly well, even on the 66 MHz 486 laptop!

Our previous work with FOPS engine analysis greatly simplified the data reduction task. We had developed FOPS data reduction programs for selecting specific points in the combustion cycle.
The points of interest were defined as:

  • Peak Pressure
  • Location of Peak Pressure re TDC
  • Standard Deviation of Peak Pressure
  • Pressure at 10 deg before TDC
  • Pressure at 180 deg before TDC


For the data transmission program, we reused code from previous projects with a wide variety of engine controllers using the Modbus protocol. We used existing LabVIEW subroutines to write data from the CPM to the Bristol 3330 Data Concentrator as a Modbus master. We used the same LabVIEW subroutines to write the data to the FB computer via RS-485.

Fast Balance
To achieve the FB goal of providing the operator an intuitive, simple interface, we manipulated standard LabVIEW controls and indicators for the desired look and feel. A bar graph shows directly which cylinder is running high or low from the average. As one user commented, "It’s simple. Big red bars are bad." We also display numerical values for each cylinder and engine operating parameters from the data highway. The alarms will flash red when the delta value for any cylinder crosses the selected limit line. This feature alerts the operator to a misfire, even when viewing the Peak Pressure display.

Benefits of CPM/FB
The CPM/FB system has accumulated 5,000 hours of continuous operation. Preliminary results indicate the system offers two primary savings over weekly manual balance checks:


1. It eliminates unnecessary testing when the engine is running properly.
2. It flags potentially degenerative conditions immediately so the plant can take corrective action.

Based on the Item 1 alone, the CPM/FB cost could probably be amortized in five years. But also, in engine applications where emissions must be logged and reported, we can use the combustion pressure data acquired by the CPM/FB to calculate engine emissions extremely accurately at a fraction of the cost of traditional exhaust gas analyzers.

For more information, contact:

 Alden Cramer or Greg Beshouri

Advanced Engine Technologies Corp.

2100 Embarcadero, Suite 201

Berkeley, CA, 94710

Tel: (510) 437-8990

Fax: (510) 437-1249

E-mail alden@aetco.com

View the PDF
361030a2.pdf

View the entire user solution in Adobe Acrobat PDF format.