Development of a Reference Dataset to Evaluate PEMS Post-Processing Software

Abstract

Since the implementation of in-use emissions standards, an outcome of the consent decree between heavy-duty diesel engine manufacturers and the Environmental Protection Agency (EPA), there has been an increased interest in the research and development of portable emissions measurement systems (PEMS) that are capable of analyzing exhaust emissions continuously while a vehicle or equipment powered by an internal combustion engine is performing its intended vocation. Ultimately for an engine to pass in-use emissions requirements, the brake specific emissions of regulated pollutants measured over valid Not-to-Exceed (NTE) events must be less than or equal to 1.25 or 1.5 times the engine emission certification standards, based on the engine model year (MY), plus an additional margin known as in-use measurement allowance. The vehicle has to satisfy the in-use emissions standard for 90% of the NTE events provided the brake specific emissions over the rest of the events are less than two times the certification level to comply with in-use emission regulations. As in-use emissions measurement and regulation together form a requirement since 2004 for certification of engines, it is imperative to develop procedures of oversight similar to ones that exist for laboratory-based engine certification. Therefore, a reference data set that incorporates all the in-use emissions regulations used to quantify the measured emissions over an NTE event, including the conditions used to validate an NTE event is developed in the direction of providing a means to validate commercial PEMS data analysis software. A reference data set was designed and used to evaluate the post-processing software of two commercial PEMS devices. A black box testing methodology was implemented to evaluate the performance of the post-processing software. Specifically, the input data set was developed to execute different sections of the program based on logical conditions required to branch into a particular section therefore verifying the truth in executing a logical condition and the interpretation of in-use emissions regulation. Also, the brake specific emissions results to be expected from the given input data set were known a priori to verify the accuracy of the equations used in calculating the final emissions results. The dataset was also used to evaluate PEMS data post-processing software developed at WVU. The test results indicated that definition of NTE emissions performance was not in agreement for the post-processing software evaluated. Being that compliance is required for manufacturers to sell engines without penalty, it is critical that the metric by which compliance is assessed must be accurate and robust. As such, the reference data set developed will serve in identifying interpretation errors of inuse emissions regulations as well as calculation error and reduce the chances of triggering false positives and negatives that could prove costly to engine manufacturers as well as air quality regulating agencies. This reference data set will also serv...

Effects of Boundary Parameters on the Work-Based Window (WBW) and Not-to-Exceed (NTE) In-Use Emissions Quantification Methods

“…Due to observed effects on air quality and human health in the last decades, the levels of emissions standards periodically decreased. This has led to further development in advanced combustion strategies and aftertreatment technologies to reduce NOx and PM emissions without potentially affecting engines efficiency [1].…”

“…The accuracy margin is an additive factor that balances the threshold for reduced accuracy of the emissions measuring device. The estimated value was based on comparisons between the in-use emissions measurement device and the laboratory grade analyzers [1].…”

“…Heavy-duty diesel (HDD) engines produce exhaust emissions that affect the environment and human health. Stricter emissions regulations led engine manufacturers to adopt advanced aftertreatment control and implement engine control strategies that minimize oxides of nitrogen (NOx) and particulate matter (PM) emissions without adversely affecting the engine performance [1]. Several studies found that engines were emitting higher NOx emissions during on-road operation compared to results based on test cell evaluation [2].…”

“…Compared to lab grade flow and emissions measurement devices, a portable emissions measurement systems (PEMS) has a lower measurement accuracy due to the variations in ambient conditions during the in-use emissions test. As a result, a measurement allowance factor is added to balance the influence of inaccuracies that may occur during in-use emissions measurements [1].…”

Development of an Emissions Monitoring Methodology Using On-Board NOx Sensors and Revision to Current In-Use Emissions Regulatory Protocols

“…Since, the promulgation of the in-use emissions standards, USEPA and engine manufacturers have agreed to multiple exclusions to the NTE standard. In addition to the requirement of a minimum of 30 seconds of operation within the NTE region, the current NTE regulatory protocol provides multiple exclusions such as exhaust aftertreatment temperature requirements, intake manifold temperature (IMT) requirements, engine coolant temperature (ECT), altitude restrictions [10]. The exclusion criteria will decide the validity of a 30 second NTE operation to be used for compliance assessment.…”