Measurement of Road Grade for In-use Emissions Testing Assessment

The United States Environmental Protection Agency (EPA) has implemented regulations over the last four decades on emissions from on- and off-road heavy-duty engines as they contribute a significant portion to mobile source emissions. These regulations compelled manufacturers to develop more advanced techniques for engine combustion and emissions formation control and measurement of those emissions. While engine dynamometers, chassis dynamometers, and in-use emissions measurements using portable emissions measurement systems (PEMS) have been used for emissions measurement, grade effects on inventory loading are not well defined. A method to accurately measure road grade for emissions modeling is needed.;This study was conducted to examine continuous, real-time, in-situ methods to measure or infer road grade for vehicle power estimations and the resulting emissions generated. The study examined utilization of direct global position system (GPS) data and inference of altitude change through barometric pressure changes using absolute and differential pressure transducers. Studies were conducted to evaluate the accuracy and repeatability of the road grade determination through controlled laboratory experiments and road driving over a defined 4.25 km route with an altitude change of approximately 80 meters through city and suburban driving conditions.;The results from laboratory experiments showed select absolute pressure sensors had the lowest variability with a standard deviation of 0.7 meters for repeated measurements, while other absolute and differential pressure sensors had a standard deviation between 1.3 and 11 meters for repeated measurements.;The data from 32 repeat road tests were collected to examine the variation of altitude determination at discrete locations along the route for each sensor. GPSSite altitude obtained from latitude and longitude had the best repeatability and reproducibility with maximum and average COV being 0.50% and 0.12%, respectively. The absolute pressure sensor with the best repeatability and reproducibility had a maximum and average COV being 0.89% and 0.47%, respectively. The grade obtained from these sensors varied from +15% to -20%. Although altitude obtained from GPS latitude and longitude had the lowest variability, it had the largest variations in the grade determination. Therefore, inference of grade from absolute pressure was considered as the best approach.