FTIR Gas Analyzer Performance Evaluation / Qualification for Automotive Testing
The scope of this document focuses on the tests required by EPA to validate the performance of the FTIR system following the section in the Code of Federal Regulations Part 1065 (40CFR1U.1065 and hereafter referred to as “EPA Part 1065”) on the guidelines and performance criteria for various regulated gases. This document focuses on the use of continuous emissions sampling for both Engine and Vehicle testing. Future addenda will be needed to cover bag and other sampling techniques.
Gas components that do not currently have performance criteria but may soon be regulated are noted and EPA suggestions as to what should be required are applied. This will help ensure that the FTIR will be recognized as a valid and alternative tool for engine exhaust emissions testing. Components in engine exhaust that are specifically called out in this document include: carbon monoxide (CO), carbon dioxide (CO2), oxides of nitrogen (NO, NO2 and N2O), ammonia (NH3), methane (CH4), and formaldehyde (H2CO). Others may be added as needed by following this standard operating procedure and determining the certification requirements from EPA or other governing bodies as required.
This SAE standard references the specific sections in the EPA Part 1065 certification test requirements (current as of April 23, 2014) for all of the steps required to provide proof of performance. The document provides the user a guideline for the FTIR gas analyzer as applied to engine or vehicle emissions testing. This document is applicable to a wide range of fuels including, but not limited to, diesel, gasoline, natural gas, liquid petroleum gas (LPG), blends, bio-fuel and bio-fuel blends.
While this document specifically references 191 °C as the temperature used for performance validation, this may not always be the case. The temperature specification applies specifically to the raw gaseous emissions that have not been diluted. If the analysis is to be performed upon a diluted gas stream where the emission gas is at a lower temperature then the analyzer can also be run at a lower temperature provided that the components of interest do not condense or react prior to reaching the analyzer.
Over the past several decades, manufacturers have made great strides in reducing emissions and improving fuel efficiency of the modern internal combustion engine. Integral to these improvements has been the use of various emissions monitoring equipment to test, verify and certify the improvements. As industry compliance standards become ever more stringent, the need for new capabilities has forced automotive emissions engineers to utilize alternate technologies for monitoring gaseous emissions. The Fourier Transform Infrared (FTIR) gas analyzer is one example of a technology that shows much promise in meeting the needs of the modern emissions engineer. As use of FTIR analyzers become more wide-spread in both R&D and Certification, there is a growing need for an SAE standard to provide recommended practices and minimum performance standards for the analyzer in various automotive related applications.
This document is to be used as a guideline for the use of Fourier Transform Infrared (FTIR) spectrometry in engine exhaust certification testing as well as engine and vehicle development activities. The goal is to create a test protocol that follows the concepts and procedures as laid out in EPA document 40 CFR Part 1065 for Engine emissions testing but applied to a multi-component FTIR analyzer. This document contains instructions on how to perform and certify the various stages of the verification testing as well as what needs to be done after major maintenance and other interruptions as defined by Part 1065. By using this procedure one can verify the ability of the FTIR and sampling system to measure multiple gases in the presence of interfering constituents such as high concentration components like water and carbon dioxide. The FTIR system chosen for this application should have the necessary sensitivity and linearity across the full range of concentration values for each of the selected exhaust species that will be seen for each particular engine test encountered. The full range is defined by the specific EPA standard for the test or the end user requirements whichever is greater.
Since the FTIR can monitor multiple components simultaneously, self-validating procedures as described below are implemented and utilized to initially validate the technology as well as provide routine tests that ensure compliance after implementation of the integrated system. Because all the infrared (IR) active exhaust components are measured at the same time without any chemical reaction any potential interference observed can normally be reduced or eliminated by modifying the analytical method resident in the software and / or by reducing the internal pressure of the gas cell. If interference is noted during the verification process, all the data collected can be reprocessed against an updated method (provided the overall system pressure and temperature remains the same) to demonstrate that the interference has been reduced or eliminated to acceptable levels.
Once the FTIR validation has been completed, there will be sufficient data to support the use of FTIR in order to meet the existing 1065 analyzer performance requirements.
Note that it is the responsibility of the user to ensure that the equipment used for certification testing is approved by the appropriate certification authorities.